Prolactin (PRL) ()is a multifunctional pituitary hormone involved in the control of a wide variety of physiological processes in vertebrates, including lactation, reproduction, immune responses, and osmoregulation, as well as cell proliferation(1, 2, 3) . The PRL receptor (PRL-R) belongs to the cytokine-growth factor receptor superfamily that includes receptors for growth hormone, erythropoietin, numerous hematopoietic interleukins (IL)-2, IL-3, IL-4, IL-5, IL-6,IL-7, IL-9, granulocyte colony-stimulating factor, granulomacrophage colony-stimulating factor, and ciliary neurotrophic factor(4, 5) . This family of receptors possesses common structural motifs, both external (two disulfide loops and the WSXWS homology box) and internal (proline-rich homology box 1). Recent studies have been marked by considerable progress in understanding the mechanisms of intracellular signaling for the different members of this family, particularly for PRL-R. Most of the data were obtained in the PRL-dependent rat T lymphoma cell line Nb2. It has been shown by several groups that, following binding of PRL to the PRL-R in these cells, dimerization of the receptor occurs (6, 7) prior to phosphorylation of an associated tyrosine kinase (JAK2). This represents the first event in the process of PRL-R signal transduction(8, 9) . Other studies demonstrated that PRL stimulation of Nb2 cells induced a concentration- and time-dependent activation of another protein tyrosine kinase, p59, from the Src protein tyrosine kinase family (10) . On the other hand, more and more studies demonstrate an important role of ion channels in receptor signal transduction(11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22) . Several different mechanisms have been proposed for channel involvement in signal transduction: direct agonist effect on the channel(15, 16) , second messenger participation in channel modulation(17, 18, 19) , and regulation by kinases and phosphatases through channel phosphorylation/dephosphorylation processes(11, 20, 21, 22) . Moreover channel regulation by phosphorylation has been shown to play a key role in physiological processes such as proliferation and transformation (23, 24, 25) . Nothing, however, is known about the putative role of channel phosphorylation in cytokine-growth factor receptor superfamily signal transduction and, in particular, in PRL-R signal transduction.

The signal transduction mechanism for the full-length PRL receptor has been studied using a CHO line stably transfected with the cDNA of the long form of rabbit mammary PRL-R(26) . These CHO-transfected cells responded to PRL by stimulating the cotransfected milk protein gene promoter(27) , proving that such cells are fully capable of transmitting the PRL signal and that PRL-R is functional. In a series of studies using patch clamp and microfluorimetric techniques, we analyzed the first steps of the PRL-R signal transduction pathway: an increase in intracellular Ca(28, 29) and direct stimulation of calcium- and voltage-activated potassium channels (K) by PRL(29) . These observations suggested the existence of a regulatory complex involving a protein kinase tightly associated with K channels and PRL-R. Furthermore, by immunoblotting studies we presented evidence for the tyrosine phosphorylation of this type of PRL-R, the association of JAK2 tyrosine kinase with the receptor, as well as changes in tyrosine phosphorylation of a number of cytoplasmic proteins(30) .

In this article, we report on the very first steps in PRL-R signal transduction at the plasma membrane level: we demonstrate an endogenous large conductance K channel as the primary ionic event triggered by PRL. These K channels are constitutively regulated through tyrosine phosphorylation/dephosphorylation. We also show that JAK2 tyrosine kinase, associated with PRL-R, is implicated in the stimulation of K channels by PRL.

EXPERIMENTAL PROCEDURES

Cell Cultures

Electrophysiological Recordings

Data and Statistical Analysis

Single channel data analysis was performed after elimination of capacity transients and leak current by subtraction of record averages without channel activity from each current record. The openings and closings of the channel were detected using a criterion of a 50% excursion between fully open and fully closed states to determine the occurrence of an opening or closing event such as crossings of the line at a half-distance between zero current level and a level corresponding to the average open channel amplitude. In this way, real current records were put into ideal form by setting all intermediate amplitudes to the level of zero current line or to the level of the average open channel amplitude. The open probability (P) was calculated as the open time integral divided by the number of channels in the patch and the duration of the data segment analyzed. The number of channels was estimated by examining the record for multiple openings under conditions of high open probability (P > 0.75).

Results are expressed as means ± S.D. where appropriate. Each experiment was repeated several times. Student's t test was used for statistical comparison among means and differences with p < 0.05 were considered significant.

Recording Solutions

Western Transfer

Membrane Stripping and Rehybridization

Chemicals

RESULTS

As was demonstrated by our previous studies(35) , a 210-picosiemens K conductance, dependent on voltage and intracellular Ca, was revealed by patch-clamp experiments in CHO cells. To check whether the K channels could be phosphorylated, we studied the effect of ATP, which serves as a substrate for protein kinase, on the activity of the K channels in CHO cells. Experiments using Mg-ATP (10-100 µM), applied to the cytoplasmic side of the membrane, showed an increase in the open probability of the channel, proving that a protein kinase is tightly associated with it. Fig. 1shows the very low K channel open probability values in the absence of ATP in the internal solution and the much higher values in the presence of ATP. The open probability values in the absence of ATP were so low that it was impossible to carry out the statistical analysis required to establish the effect of PRL on K channel activity under these conditions. In whole cell experiments without ATP in the patch pipette, no effect of PRL on K total current was observed. ATP hydrolysis was required for channel modulation, because the nonhydrolyzable ATP analog, AMPPNP, was ineffective (not shown). As, on the one hand, tyrosine kinase was found to be a primary target of PRL in PRL-R signal transduction(8, 9) and, on the other hand, the K channels stimulated by PRL were found to be associated with protein kinase, we assumed the existence of a PRL-R-K channel-tyrosine kinase regulatory complex. To investigate whether the K channels stimulated by PRL may be modulated by an endogenous tyrosine kinase, we examined the effects of different tyrosine kinase inhibitors on K channel activity, using both whole cell and cell-free modes of the patch-clamp technique. In these studies we used two types of experiments differing in the duration of drug application

Figure 1: The time course of the activity of the Ca-activated K channel obtained from excised (outside-out) patch recordings in the absence () or presence () of 100 µM ATP in the patch pipette at a membrane potential of +10 mV and 0.2 µM internal-free Ca. Representative experiments for such experimental conditions are shown.

Short Application of the Drug for Periods Varying from 15 s to Several Minutes

Bath application (3 min) of the protein tyrosine kinase inhibitor genistein (36, 37) caused a progressive reduction in the K current (Fig. 2A). Further application of PRL was ineffective. Genistein concentrations lower than 50 µM were ineffective under these experimental conditions (n = 6). After genistein was washed out, K currents gradually recovered, indicating that the depression was reversible. Genistin, an analog of genistein that lacks protein tyrosine kinase inhibitory activity(36) , had no effect on K current (n = 4; Fig. 9A). We also tested two structurally distinct protein tyrosine kinase inhibitors: herbimycin A (9, 38) and lavendustin A(36, 39) . Herbimycin A (1.5 µM) and lavendustin A (10 µM) depressed K currents to 57 ± 8% (n = 8) and to 54 ± 5% (n = 6) of control, respectively. Fig. 2B shows an example of K current inhibition induced by 3-min application of 10 µM lavendustin A and current-voltage relationships for this effect, where current amplitudes were plotted at different test potentials. K currents were evoked by 160-ms test pulses from a holding potential of -40 to +10 mV.

Figure 2: The effects of tyrosine kinase inhibitors on K current in CHO-E32 cells. A illustrates an example of the effect of 50 µM genistein on K current recorded before genistein application (), 8 min after the application (), and after washout (). The membrane was depolarized from V = -40 to +20 mV at 160-ms intervals. B illustrates an example of the effect of 10 µM of lavendustin A on K current recorded using a similar protocol to the experiment in A. For both inhibitors the original current traces are presented in the top panels and current-voltage (I-V) relationships in the lower panels. Calibration: 30 ms, 100 pA. C illustrates the effects of 6-h treatment of CHO E32 cells with varying concentrations of protein kinase inhibitors (, genistein; , lavendustin A, , herbimycin A) on normalized peak K currents. Results shown (mean ± S.E.) are representative of at least three separate, independent experiments.

Figure 9: Summary histograms of K channel modulation in CHO-E32 cells. A illustrates the histogram showing the effects of the various drugs studied on normalized peak currents obtained by whole cell experiments. B illustrates the histogram showing the effects of these drugs on the ratio of the channel open probability (P) obtained by single channel recordings.

Preincubation of All Cells by Addition of the Drug to the Bath Solution for a Time Varying from 30 min to Several Hours

Cell-free experiments demonstrated that the effects of PRL and protein tyrosine kinase inhibitors were not mediated by intracellular processes, as they could be also observed in detached patches. Fig. 3shows K channel activity stimulation by PRL and its inhibition by genistein (n = 7/9 patches). PRL (5 nM) caused an increase in the open probability of the channels (Fig. 3B), displaying the half-maximum increase in the open probability within 3.6 ± 1.3 min. The open probability of the channel after the addition of PRL was not constant, but oscillated between lower and higher open probability values (Fig. 3B). Subsequent addition of 100 µM genistein inhibited this K channel activity almost completely within 7 ± 2 min (Fig. 3B). The amplitude histograms (Fig. 3C) for K channels in control (mean = 8.48 ± 0.12 pA) and in the presence of PRL (mean = 8.34 ± 0.18 pA) demonstrate that PRL does not activate additional conductances. Moreover, prolactin did not stimulate K channel activity in the presence of 30 nM CTX, a K channel inhibitor in CHO cells(20) , indicating that PRL activated the CTX-sensitive K channels and no other type of outward channels (not shown). As in whole cell experiments, genistin was ineffective (Fig. 9B). Application of 1.5 µM herbimycin A also decreased channel open probability without affecting single-channel conductance (n = 4/5 patches, Fig. 4). The subsequent addition of PRL was ineffective.

Figure 3: Modulation of K single channel activity by PRL and its inhibition by genistein. A illustrates representative recordings of single K currents in a cell-free patch in the outside-out configuration. K channel activity in this patch was obtained with 0.1 µM internal-free Ca at a membrane potential of +40 mV. Recordings are shown for the control solution, 6 min after application of 5 nM PRL, and 2 and 8 min after the subsequent application of 100 µM of genistein, respectively. The time course of the open probability of the K channels in the control and in the presence of PRL and genistein is demonstrated in B. C illustrates the amplitude histograms for single K channel conductance for control and in the presence of 5 nM PRL.

Figure 4: The effect of herbimycin A on K channel activity. Representative records of single K currents in excised (outside-out) membrane patch (top). K channel activity in this patch was obtained with 0.5 µM internal-free Ca at a membrane potential of +20 mV. Records are shown for the control solution, 10 min after 1.5 µM herbimycin application and 3 min after the subsequent addition of 5 nM PRL. The open probability of the K channel versus time is presented in the lower panel.

As protein tyrosine kinase inhibitors in high concentrations are known to be able to inhibit not only protein tyrosine kinase but also protein kinase C and protein kinase A kinases in some cell types(36) , we checked the putative involvement of protein kinase C and protein kinase A in the mechanisms studied. We tested both activators and inhibitors of protein kinase C and protein kinase A (10-8 M phorbol 12-myristate 13-acetate application, as protein kinase C activator; 10-6 M phorbol 12-myristate 13-acetate 24-h incubation, as protein kinase C inhibitor; 250 µM phloretin, as protein kinase C inhibitor; 2 µM forskolin and 1 mM 8-bromo-cAMP, as protein kinase A activators) on K channel activity and on the stimulated effect of PRL. None of these drugs had any effect. A protein kinase C biochemical assay (40) was also carried out. 50-100 µM genistein had no effect in these studies.

The possibility that these channels may be regulated by protein tyrosine phosphatase as well as by protein tyrosine kinase was investigated by application of the protein tyrosine phosphatase inhibitor, sodium orthovanadate(41) , to the cytoplasmic side of the cell-free patch. Orthovanadate (1 mM) increased the open probability of the channels in a time-dependent manner (Fig. 5). On average, activity increased by 198 ± 27% within 5 min (n = 6/9 patches). Fig. 5B shows the duration histograms for the channel prior to application of orthovanadate, then 2 and 8 min afterwards, respectively. In the presence of orthovanadate, channel openings were longer, as indicated by an increase in the relative number of events and the time constant to for the open state.

Figure 5: The effect of orthovanadate on K channel activity. A illustrates representative records of single K currents in excised (inside-out) membrane patches. K channel activity in this patch was obtained with 0.2 µM internal-free Ca at a membrane potential of +40 mV. Records are shown for the control solution, and 2 and 8 min after 1 mM orthovanadate application, respectively. B illustrates the corresponding open time distributions with single exponential fit. Time constants: t = 1.9 ms (n = 604) for control, t = 2.3 ms (n = 668) after 2 min, and t = 6.8 ms (n = 1023) after 8 min of orthovanadate addition, respectively.

The preceding results strongly support the conclusion that the functioning of PRL-stimulated K channels is modulated by protein tyrosine kinases and protein tyrosine phosphatases and thus regulated by constitutive tyrosine phosphorylation/dephosphorylation. It has already been shown that tyrosine-phosphorylated PRL-R is associated with JAK2 kinase(30) . Additional immunoblotting experiments were carried out to find out if this association was constitutive. Solubilized proteins from E32 cells incubated with or without 500 ng/ml of prolactin were immunoprecipitated with anti-PRL-R antibody 46 and analyzed for the presence of JAK2 in the complex. As shown in Fig. 6A, a protein of 130 kDa was detected in the blot hybridized with anti-JAK2, corresponding to JAK2 kinase. This protein was revealed in the presence or absence of stimulation by ovine PRL, showing that this protein is constitutively associated with the PRL receptor. A rehybridization of the same blot with S46 shows the presence of the same amount of receptor in each line. In Fig. 6B, we demonstrate the specificity of the recognition of JAK2 by the antibody. Cell extracts were immunoprecipitated with anti-JAK2 antibody or anti-PRL-R antibody and subjected to SDS-PAGE and Western blotting. Each blot was incubated either with anti-JAK2 antibody or with anti-JAK2 antibody preincubated with a peptide corresponding to the amino acid residues 758-776 of murine JAK2 (JAK2 immunizing peptide). In JAK2 immunoprecipitates we observed that a protein of 130 kDa was specifically displaced by the presence of the peptide. Nonspecific bands were always present following incubation in the presence of the peptide. The same finding was observed in 46 immunoprecipitates. The 130-kDa band was not revealed in the presence of the peptide. Therefore, the 130-kDa protein revealed on the blot is the tyrosine kinase JAK2, and this kinase is constitutively associated with the prolactin receptor. To investigate whether K channels are also constitutively associated with JAK2 kinase we studied the effect of the anti-JAK2 kinase antibody on the of the K channel activity. Anti-JAK2 antibody (diluted 1:1000 from the indicated antibody) was introduced into the internal solution of the patch pipette. In whole cell experiments, the amplitude of the K current gradually decreased following rupture of the seal. In control conditions of whole cell experiments, the K current was stable under internal perfusion. No decrease in current (or ``run-down'') was observed during recordings lasting 20 min or more. Fig. 7shows the time dependence of the decrease in K current caused by anti-JAK2 antibody. Within approximately 10 min the current was almost completely inhibited (n = 5). Subsequent application of PRL was ineffective (Fig. 7). Anti-JAK2 antibody applied to the cytoplasmic side of the membrane in inside-out studies decreased the open probability of the channel to 73 ± 18% (n = 4/4 patches) of control (Fig. 8). Subsequent application of PRL did not stimulate channel activity (Fig. 8). When anti-JAK2 antibody was preincubated with a peptide corresponding to the amino acid residues 758-776 of murine JAK2 (JAK2 immunizing peptide) and this mixture applied to the cytoplasmic side of the membrane, the decrease in K current in the whole cell experiments (Fig. 7) and in the open probability of the channel in inside-out experiments (Fig. 8) were not observed. As the anti-JAK2 antibody was obtained from Upstate Biotechnology, Inc. in rabbit serum, we checked the effect of non-immune rabbit serum on K conductance as a control. Rabbit serum at the same dilution (1:1000) was ineffective in both whole cell and inside-out experiments (not shown). An immune serum antibody (anti-rat PRL antibody) was used as an additional control. At the same dilution it was also ineffective.

Figure 6: Association of JAK2 with the prolactin receptor in CHO cells. A illustrates JAK2 constitutive association with the PRL receptor. E32 cells were left untreated or treated with PRL (500 ng/ml), solubilized, and immunoprecipitated with prolactin receptor antiserum 46. All samples were analyzed by SDS-PAGE under reducing conditions, followed by immunoblotting with anti-PRL-R antibody 46 or anti-JAK2 antibody (Upstate Biotechnology, Inc.). Molecular weight standards are indicated on the left. B illustrates the blockage of anti-JAK2 reactivity with JAK2 peptide. E32 cell lysates were immunoprecipitated with anti-JAK2 antibody or anti-PRL-R antibody 46 and the immunoprecipitates were processed for Western blotting. Blots were probed with anti-JAK2 antibody or with anti-JAK2 antibody + peptide (corresponding to the amino acid acid residues 758-776 of murine JAK2).

Figure 7: Time course of the inhibition of the K current by anti-JAK2 antibody. Top, current traces obtained after seal rupture in the presence of anti-JAK2 antibody in the patch pipette. Currents were evoked by 160-ms test pulses from holding potential of -60 mV to +50 mV test potential. Lower panel, the respective plot of normalized current (I/I) with anti-JAK2 antibody or with anti-JAK2 antibody+ peptide versus time.

Figure 8: Effect of anti-JAK2 antibody on K channel activity. Representative records of single K currents from excised (inside-out) membrane patch (top). K channel activity in this patch was obtained with 0.2 µM internal-free Ca at a membrane potential of +50 mV. Records are shown for control solution, 2 min after anti-JAK2-antibody application, following the subsequent addition of PRL and during recovery. The open probability of the K channel versus time is presented in the lower panel.

Fig. 9presents a summary of the effects of all the drugs studied on normalized peak currents, obtained by whole cell experiments (Fig. 9A) and normalized P, obtained by excised patch experiments (Fig. 9B).

DISCUSSION

We conclude from these findings that the activation of K channels by PRL in CHO cells, transfected with cDNA of the long form of PRL-R, is the primary ionic event in PRL-R signal transduction. K channels are constitutively regulated through tyrosine phosphorylation/dephosphorylation. Stimulation of the channels by PRL possibly occurs through phosphorylation of protein tyrosine residues of the channel or of one or more associated proteins. The observation that K channel stimulation by PRL does not occur in the presence of anti-JAK2 kinase antibody suggests that at least one of the kinases involved in the channel stimulation by PRL may be JAK2 tyrosine kinase.

Although the association of PRL-R with JAK2(8, 9, 30) , JAK1(42) , or Fyn (10) tyrosine kinases has already been clearly demonstrated, the cascade of ionic events induced by PRL and the nature of ion channels involved has not yet been studied. Our earlier studies have characterized a membrane hyperpolarization, caused by K channel stimulation, and Ca influx among the first detectable responses to PRL-R activation(29) . The underlying mechanisms are, however, not very clearly understood. In the present study, we applied the patch-clamp recording technique in order to unravel the mechanism of K channel activation by PRL and to identify the nature of the associated protein kinase.

In our experiments ATP (10-100 µM) increased the open probability of the K channel, therefore showing that a protein kinase is involved in the regulation of channel activity. Moreover PRL was unable to stimulate this activity when ATP was absent from the internal solution, demonstrating that kinase phosphorylation is needed for channel stimulation by PRL. Thus, we concluded that protein kinase is closely associated with K channel and PRL-R in a regulatory complex.

It was recently demonstrated that in murine fibroblast cell lines, transfected with Ras or Raf plasmids, the K, CTX-sensitive channel is up-regulated by oncogenic p21 and that this regulation appears to be due to raf kinase-dependent induction of channel expression(43) . The application of either epidermal growth factor or platelet-derived growth factor to nontransfected cells caused a time-dependent induction of K channels, obviously, through activation of endogenous cellular p21. Epidermal growth factor induction of the K channel was blocked by the tyrosine kinase inhibitors lavendustin A (1 µM) or genistein (50 µM). However, application of genistein to cells transfected by oncogenic ras had no effect on K current density, indicating that genistein had no direct inhibitory effect on the K channel. These results suggest that ras regulates the K channels through serine/threonine kinase and not through protein tyrosine kinase. Our experiments using tyrosine kinase inhibitors show a distinct mechanism of K channel regulation in CHO cells transfected with cDNA of the long form of PRL-R: the direct regulation of K channels by tyrosine kinase (as this activity was inhibited directly in whole cell and single channel experiments by three distinct tyrosine kinase inhibitors) and modulation of this activity by PRL (as PRL was no longer able to stimulate K channel activity when the cells were treated with protein tyrosine kinase inhibitors). Experiments using protein kinase C and protein kinase A activators and inhibitors showed that these kinases are not involved in the channel regulation mechanisms.

For epidermal growth factor receptor, which has intrinsic tyrosine kinase(44) , the first event is activation of voltage-independent Ca channels defined as direct receptor-operated channels (12) . This in turn causes the activation of Ca-dependent K channels, sensitive to charybdotoxin(12, 13) , resulting in delayed membrane hyperpolarization and leading to the activation of a second class of hyperpolarization-sensitive Ca channels(14) . We did not observe the Ca conductance activation prior to K channel stimulation(29) . Conversely, our results demonstrate that the first ionic event in PRL-R signal transduction is K channel activation, since this activation is observed in excised patches. Based on the observed inhibitory effects of protein tyrosine kinase inhibitors on the activity of PRL-stimulated K channels, we propose that tyrosine kinase is involved in the positive regulation of these channels. The direct tyrosine phosphorylation of the delayed rectifier K channel has also been proposed for the m1 muscarinic acetylcholine receptor(11) . This tyrosine kinase regulation is obviously an essential link in PRL signal transduction as it was recently found that the tyrosine kinase inhibitor herbimycin A was able to block a substantial portion of the prolactin signal to the milk protein gene promoter, -lactoglobulin (30) . In Nb2 cells it was shown that herbimycin A could also abolish the JAK2 kinase and receptor phosphorylation(9) .

In our study the effects of PRL and protein tyrosine kinase inhibitors were observed in excised-patch experiments, indicating that the effects are not controlled by cellular metabolism, but are direct and that protein tyrosine kinase remains closely associated with K channel activity. In this context it was of interest to check the effect of anti-JAK2 antibody on K channel activity. The effectiveness of using antibodies in patch-clamp experiments was previously shown by Schweizer et al.(45) . When anti-JAK2 antibody was introduced into the patch pipette in whole cell experiments, the K conductance was almost completely inhibited within an average of 15 min, and PRL was no longer able to stimulate K conductance. Anti-JAK2 antibody also decreased the open probability of K channels when it was applied to the cytoplasmic side of the membrane in the inside-out patch mode. In immunoblotting experiments JAK2 kinase was revealed in the presence or absence of stimulation by PRL, showing that it is constitutively associated with the PRL-R. On the other hand, electrophysiological studies using anti-JAK2 antibody showed that this kinase is also constitutively associated with the K channel. The results with JAK2 immunizing peptide, demonstrating the suppression of the effects observed using anti-JAK2 antibody alone in both electrophysiological and immunoblotting studies, show that the effects of the anti-JAK2 antibody are specific. The ability of the constitutively active kinases to stimulate cellular responses has previously been shown for MAP and phosphatidylinositol 3-kinase(46) . On the other hand, there is growing evidence for the existence of a protein tyrosine kinase activation mechanism that functions indirectly by second messengers. For example, in the brain, membrane depolarization, which causes an increase in intracellular Ca levels, increases protein tyrosine kinase (47) and protein mitogen-activated protein kinase (48) activity. Extracellular signals (in our case PRL) appear to stimulate the activity of protein tyrosine kinase, but it may also be regulated by other factors (e.g. membrane potential and intracellular Ca). This constitutive activity of JAK2 kinase is the reason for K channel inhibition by the anti-JAK2 antibody in the absence of PRL stimulation. Therefore, our results demonstrate the functional involvement of JAK2 kinase in constitutive K channel activity and the stimulation of these channels by PRL. However, it was shown by immunoblotting experiments that genistein (100-500 µM) was not able to inhibit the JAK2 kinase phosphorylation induced by growth hormone but it blocked the tyrosyl phosphorylation of other proteins (intermediary tyrosine kinases)(49, 50) . This fact may be explained by the various examples of interactions at the level of the same protein; many phosphoproteins are phosphorylated at the same or at distinct residues by more than one protein kinase: in the case of tyrosine hydroxylase, the nicotinic acetylcholine receptor, synapsin 1, or Ca channel of the L type(47) . This multisite protein phosphorylation appears to be the rule rather than the exception(47) . Therefore, we cannot completely exclude the possible involvement of other tyrosine kinases in K channel functions.

The fact that the channel was activated by the protein tyrosine phosphatase inhibitor orthovanadate in excised patches suggests that the channel can be modulated in opposite directions by protein tyrosine kinase and protein tyrosine phosphatase. This modulation may be due to phosphorylation/dephosphorylation of the channels themselves or of regulatory protein(s) associated with these channels and the PRL receptor. The protein tyrosine phosphatase endogenous to CHO cells was observed in most excised patches and thus may be a member of the transmembrane class of protein tyrosine phosphatase (51, 52) or of the cytoplasmic protein tyrosine phosphatase which possess an SH2 domain or another means of association with membrane-bound proteins(53, 54) . These studies suggest that tyrosine phosphorylation/dephosphorylation systems can modify K channels rapidly, producing flexible changes in PRL-R signaling. Similar types of complexes that contain regulatory protein kinases and phosphatases have previously been shown for a variety of different ion channels(20, 21, 22, 55, 56, 57) and for K channels in particular(20, 21, 56, 57) . But the participation of such protein tyrosine kinase modulation of K channels in PRL signal transduction has never been shown. To our knowledge this study provides the first example of the regulation of K channels by PRL and protein tyrosine kinase in cell-free preparations. Our study is in accordance with a hypothesis previously proposed (57) about such submembrane complexing of ion channel proteins with modulatory enzymes like kinases and phosphatases as a common means by which cells achieve highly localized regulation of ion channel function by otherwise ubiquitous biochemical processes. Of particular interest is the finding that the modulation described here is due to a constitutive JAK2 tyrosine kinase activity. These results take on added significance because the PRL receptors were expressed in a heterologous system. However, remarkably, the endogenous JAK2 tyrosine kinase and endogenous K channels in the host cell associate closely with heterologously expressed PRL-R and this complex retains its ability to be stimulated by PRL in a detached membrane patch.

As, on the one hand, PRL is known to stimulate the process of proliferation (58, 59, 60, 61) and, on the other hand, K channels have also been shown to be involved in the control of cell proliferation(25, 43, 62) , the mechanism of PRL stimulation of K channels through tyrosine phosphorylation, presented in this work, could provide a clue to understanding the regulation of cell proliferation by PRL.

FOOTNOTES

*

This work was supported by grants from INSERM(N 930704), Association pour la Recherche sur le Cancer (ARC, France) and Association pour la Recherche sur les Tumeurs de la Prostate (ARTP, France). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked ``advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§

To whom all correspondence should be addressed: Laboratoire de Neurophysiologie, CNRS URA 1200, Université de Bordeaux II, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France. Tel.: 33-57-57-15-51; Fax: 33-56-90-14-21.

()

The abbreviations used are: PRL, prolactin; PRL-R, prolactin receptor; IL, interleukin; CHO, Chinese hamster ovary; TTX, tetrodotoxin; CTX, charybdotoxin; AMPPNP, 5`-adenylyl-,-imidodiphosphate.

ACKNOWLEDGEMENTS

REFERENCES

1. Nicoll, C. S. (1980) Fed. Proc. 39,2563-2566 [Medline] [Order article via Infotrieve]
2. Russel, D. H. (1989) Trends Pharmacol. Sci. 10,40-44 [CrossRef][Medline] [Order article via Infotrieve]
3. Kelly, P. A., Djiane, J., Postel-Vinay, M. C., and Edery, M. (1991) Endocr. Rev. 12,235-251 [Abstract/Free Full Text]
4. Bazan, J. F. (1990) Proc. Natl. Acad. Sci. U. S. A. 87,6934-6938 [Abstract/Free Full Text]
5. Cosman, D. (1993) Cytokine 5,95-106 [CrossRef][Medline] [Order article via Infotrieve]
6. Djiane, J., Dusanter-Fourt, I., Katoh, M., and Kelly, P. A. (1985) J. Biol. Chem. 260,11430-11435 [Abstract/Free Full Text]
7. Fuh, G., Colosi, P., Wood, W. I., and Wells, J. A. (1993) J. Biol. Chem. 268,5376-5381 [Abstract/Free Full Text]
8. Rui, M., Kirken, R. A., and Farrar, W. L. (1994) J. Biol. Chem. 269,5364-5368 [Abstract/Free Full Text]
9. Lebrun, J. J., Ali, S., Sofer, L., Ullrich, A., and Kelly, P. (1994) J. Biol. Chem. 269,14021-14026 [Abstract/Free Full Text]
10. Clevenger, C. V., and Medaglia, M. V. (1994) Mol. Endocrinol. 8,674-681 [Abstract/Free Full Text]
11. Huang, X.-Y., Morielli, A. D., and Peralta, E. G. (1993) Cell 75,1145-1156 [CrossRef][Medline] [Order article via Infotrieve]
12. Peppelenbosch, M. P., Tertoolen, L. G. J., and De Laat, S. W. (1991) J. Biol. Chem. 266,19938-19944 [Abstract/Free Full Text]
13. Magni, M., Meldolesi, J., and Pandiella, A. (1991) J. Biol. Chem. 266,6329-6335 [Abstract/Free Full Text]
14. Peppelenbosch, M. P., Tertoolen, L. G. J., Hertog, J., and De Laat, S. W. (1992) Cell 162,295-303
15. Matsunaga, H., Ling, B. N., and Eaton, D. C. (1994) Am. J. Physiol. 267,C456-C465
16. Bormann, J. (1988) TrendsNeurosci. 11,112-116
17. Penner, R., Matthews, G., and Neher, E. (1988) Nature 334,499-504 [CrossRef][Medline] [Order article via Infotrieve]
18. Graier, W. F., Kukovetz, W. R., and Groschner, K. (1993) Biochem. J. 291,263-267
19. Ono, K., Tsujimoto, G., Sakamoto, A., Eto, K., Masaki, T., Ozaki, Y., and Satako, M. (1994) Nature 370,294-297
20. White, R. E., Schonbrunn, A., and Armstrong, D. L. (1991) Nature 351,570-573 [CrossRef][Medline] [Order article via Infotrieve]
21. White, R. E., Lee, A. B., Shcherbatko, A. D., Lincoln, T. M., Schonbrunn, A., and Armstrong, D. L. (1993) Nature 361,263-266 [CrossRef][Medline] [Order article via Infotrieve]
22. Wilson, G. F., and Kaczmarek, L. K. (1993) Nature 366,433-438 [CrossRef][Medline] [Order article via Infotrieve]
23. Collin, C., Papagorge, A. G., Lowy, D. R., and Alkon, D. L. (1990) Science 250,1743-1745 [Abstract/Free Full Text]
24. Repp, H., Draheim, J., Ruland, J., Seidel, G., Beise, J., Preser, P., and Dreyer, F. (1993) Proc. Natl. Acad. Sci. U. S. A. 90,3703-3707
25. Nilius, B., and Wohlrab, W. (1992) J. Physiol. (Lond.) 445,3537-3548
26. Edery, M., Jolicoeur, C., Levi, M. C., Dusanter-Fourt, I., Petridou, B., Boutin, J., Lesueur, L., Kelly, P., and Djiane, J. (1989) Proc. Natl. Acad. Sci. U. S. A. 86,2112-2116 [Abstract/Free Full Text]
27. Bignon, C., Daniel, N., and Djiane, J. (1993) BioTechniques 15,243-245 [Medline] [Order article via Infotrieve]
28. Vacher, P., Tran Van Chuoi, M., Paly, J., Djiane, J., and Dufy, B. (1994) Endocrinology 134,1213-1218 [Abstract/Free Full Text]
29. Prevarskaya, N., Skryma, R., Vacher, P., Daniel, N., Bignon, C., Djiane, J., and Dufy, B. (1994) Am. J. Physiol. 267,C554-C562
30. Waters, M. J., Daniel, N., Bignon, C., and Djiane, J. (1995) J. Biol. Chem. 270,5136-5143 [Abstract/Free Full Text]
31. Lesueur, L., Edery, M., Paly, J., Clark, J., Kelly, P., and Djiane, J. (1990) Mol. Cell. Endocrinol. 71,7-12
32. Lesueur, L., Edery, M., Ali, S., Paly, J., Kelly, P., and Djiane, J. (1991) Proc. Natl. Acad. Sci. U. S. A. 88,824-828 [Abstract/Free Full Text]
33. Gasser, F., Mulsant, P., and Gillois, M. (1985) InVitro Cell. & Dev. Biol. 21,588-592
34. Abercrombie, R. F., Mazukawa, L. H., Sjodin, A., and Livengood, D. (1981) J. Gen. Physiol. 78,413-428 [Abstract/Free Full Text]
35. Skryma, R., Prevarskaya, N., Vacher, P., and Dufy, B. (1994) Am. J. Physiol. 267,C544-C553
36. O'Dell, T. J., Kandel, E. R., and Grant, S. G. (1991) Nature 353,558-560 [CrossRef][Medline] [Order article via Infotrieve]
37. Akijama, T., Ishida, J., Nakagawa, S., Ogawara, H., Watanabe, S., Itoh, N., Shibuya, M., and Fukami, Y. (1987) J. Biol. Chem. 262,5592-5595 [Abstract/Free Full Text]
38. Obinata, A. (1991) Exp. Cell. Res. 193,36-39 [CrossRef][Medline] [Order article via Infotrieve]
39. Onoda, T. (1989) J. Nat. Prod. (Lloydia) 52,1252-11257 [CrossRef][Medline] [Order article via Infotrieve]
40. Parant, M. R., and Vial, J. (1990) Anal. Biochem. 184,283-290 [CrossRef][Medline] [Order article via Infotrieve]
41. Swarup, G., Cohen, S., and Garbers, D. L. (1982) Biochem. Biophys. Res. Commun. 107,1104-1109 [CrossRef][Medline] [Order article via Infotrieve]
42. Dusanter-Fourt, I., Muller, O., Ziemiecki, A., Mayeux, P., Drucker, B., Djiane, J., Wilks, A., Harpur, A. G., Fischer, S., and Gisselbrecht, S. (1994) EMBO J. 13,2583-2591 [Medline] [Order article via Infotrieve]
43. Huang, Y., and Rane, S. G. (1994) J. Biol. Chem. 269,31183-31189 [Abstract/Free Full Text]
44. Ullrich, A., Coussens, L., Hayflick, J. S., Dull, T. J., Gray, A., Tam, A. W., Lee, J., Yarden, Y., Libermann, T. A., Schlessinger, J., Downward, J., Mayes, E. L. V., Whittle, N., Waterfield, M. D., and Seeburg, P. H. (1984) Nature 309,418-425 [CrossRef][Medline] [Order article via Infotrieve]
45. Schweizer, F. E., Schafer, T., Tapparelli, C., Grob, M., Karli, U. O., Heumann, R., Thoenen, H., Bookman, R. J., and Burger, M. M. (1989) Nature 339,709-712 [CrossRef][Medline] [Order article via Infotrieve]
46. Hu, Q., Klippel, A., Muslin, A. J., Fantl, W. J., and Williams, L. T. (1995) Science 268,100-102 [Abstract/Free Full Text]
47. Nester, E. J., and Greengard, P. (1993) in Basic Neurochemistry (Siegel, G. J., Agraneff, B. W., Albers, R. W., and Molinoff, P. B., eds) Vol. 22, pp. 449-474, Raven Press Ltd., New York _
48. Rosen, L. B., Ginty, D. D., Weber, M. J., and Grenberg, M. E. (1994) Neuron 12,1207-1221 [CrossRef][Medline] [Order article via Infotrieve]
49. VanderKuur, J. A., Wang, X., Zhang, L., Campbell, G. S., Allevato, G., Billestrup, N., Norstedt, G., and Carter-Su, C. (1994) J. Biol. Chem. 34,21709-21717
50. Campbell, G. S., Christian, L. J., and Carter-Su, C. (1993) J. Biol. Chem. 268,7427-7434 [Abstract/Free Full Text]
51. Charbonneau, H., Tonks, N. K., Walsh, K. A., and Fischer, E. H. (1988) Proc. Natl. Acad. Sci. U. S. A. 85,7182-7186 [Abstract/Free Full Text]
52. Alexander, D. R. (1990) New Biol. 2,1049-1062 [Medline] [Order article via Infotrieve]
53. Shen, S. H., Bastien, L., Posner, B. I., and Chretien, P. (1990) Nature 352,736-739
54. Yang, O., and Tonks, N. K. (1991) Proc. Natl. Acad. Sci. U. S. A. 88,5949-5953 [Abstract/Free Full Text]
55. Wang, Y. T., and Salter, M. W. (1994) Nature 369,233-235 [CrossRef][Medline] [Order article via Infotrieve]
56. Chung, S., Reinhart, P., Martin, B. L., Brantigan, D., and Levitan, J. (1991) Science 253,560-562 [Abstract/Free Full Text]
57. Esquerra, M., Wang, J., Foster, C. D., Adelman, J. P., North, R. A., and Levitan, J. B. (1994) Nature 369,563-565 [CrossRef][Medline] [Order article via Infotrieve]
58. Syms, A. J., Harper, M. E., and Griffiths, K. (1985) Prostate 6,145-153 [Medline] [Order article via Infotrieve]
59. Romero, L., Munoz, C., Lopez, A., and Vilches, J. (1993) Prostate 22,1-10 [Medline] [Order article via Infotrieve]
60. Rui, H., Lebrun, J. J., Kirken, R. A., Kelly, P. A., and Farrar, W. L. (1994) Endocrinology 135,1299-1306 [Abstract]
61. Wang, Y. F, and Walker, A. M. (1993) Endocrinology 133,2156-2160 [Abstract/Free Full Text]
62. Price, M., Lee, S. C., and Deutsch, C. (1989) Proc. Natl. Acad. Sci. U. S. A. 86,10171-10175 [Abstract/Free Full Text]

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