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Signal Transduction by the Chemokine Receptor CXCR3

ACTIVATION OF Ras/ERK, Src, AND PHOSPHATIDYLINOSITOL 3-KINASE/Akt CONTROLS CELL MIGRATION AND PROLIFERATION IN HUMAN VASCULAR PERICYTES*
Open AccessPublished:March 30, 2001DOI:https://doi.org/10.1074/jbc.M010303200
      Hepatic stellate cells (HSC) and glomerular mesangial cells (MC) are tissue-specific pericytes involved in tissue repair, a process that is regulated by members of the chemokine family. In this study, we explored the signal transduction pathways activated by the chemokine receptor CXCR3 in vascular pericytes. In HSC, interaction of CXCR3 with its ligands resulted in increased chemotaxis and activation of the Ras/ERK cascade. Activation of CXCR3 also stimulated Src phosphorylation and kinase activity and increased the activity of phosphatidylinositol 3-kinase and its downstream pathway, Akt. The increase in ERK activity was inhibited by genistein and PP1, but not by wortmannin, indicating that Src activation is necessary for the activation of the Ras/ERK pathway by CXCR3. Inhibition of ERK activation resulted in a decreased chemotactic and mitogenic effect of CXCR3 ligands. In MC, which respond to CXCR3 ligands with increased DNA synthesis, CXCR3 activation resulted in a biphasic stimulation of ERK activation, a pattern similar to the one observed in HSC exposed to platelet-derived growth factor, indicating that this type of response is related to the stimulation of cell proliferation. These data characterize CXCR3 signaling in pericytes and clarify the relevance of downstream pathways in the modulation of different biologic responses.
      HSC
      hepatic stellate cells
      EGF
      epidermal growth factor
      ERK
      extracellular signal-regulated kinase
      GPCR
      G protein-coupled receptors
      GST-RBD
      glutathione S-transferase-Ras-binding domain
      IP-10
      interferon-inducible protein-10
      MAPK
      mitogen-activated protein kinase
      MEK
      MAPK/ERK kinase
      MC
      glomerular mesangial cells
      Mig
      monokine activated by interferon-γ
      PDGF
      platelet-derived growth factor
      PI3K
      phosphatidylinositol 3-kinase
      PAGE
      polyacrylamide gel electrophoresis
      In different tissues, the wound healing response shares many similarities, involving the recruitment of inflammatory cells and the deposition of extracellular matrix, to fill the gap created by the dying cells. The concurrent presence of inflammation and extracellular matrix deposition is a characteristic of chronic tissue injury, where the persistence of a wound healing response may lead to permanent scarring and end-stage organ failure, such as in the case of glomerulosclerosis in the kidney, cirrhosis of the liver, atherosclerosis, or pulmonary fibrosis (
      • Collins T.
      ). The pivotal role played by vascular pericytes of different tissues in the process of wound healing has been clearly recognized in recent years. These cells become activated in the presence of damage to the specific tissue, proliferate, migrate, and acquire a myofibroblast-like phenotype, resulting in the production of extracellular matrix as part of the healing process. Hepatic stellate cells (HSC)1 and renal glomerular mesangial cells (MC) represent tissue-specific pericytes, which are deeply involved in the development of the wound healing response and in the pathogenesis of tissue fibrosis in the setting of a chronic damage (
      • Abboud H.E.
      ,
      • Friedman S.L.
      ). Understanding the biology of these cells may help to devise novel strategies for the treatment of chronic liver and kidney diseases.
      The chemokine system has received considerable attention for its involvement in a number of biologic processes. Although members of this family have been initially recognized for their ability to recruit leukocytes to sites of injury, more recent investigation has shown that this system participates in the regulation of a wide number of conditions, including physiologic leukocyte homeostasis, development, angiogenesis, cancer, and the response to infection (
      • Luster A.D.
      ,
      • Rossi D.
      • Zlotnik A.
      ). Activation of the chemokine system has been reported in the presence of chronic inflammation and fibrosis, two processes that are part of the wound healing response (
      • Romagnani P.
      • Beltrame C.
      • Annunziato F.
      • Lasagni L.
      • Luconi M.
      • Galli G.
      • Cosmi L.
      • Maggi E.
      • Salvadori M.
      • Pupilli C.
      • Serio M.
      ,
      • Marra F.
      • DeFranco R.
      • Grappone C.
      • Milani S.
      • Pastacaldi S.
      • Pinzani M.
      • Romanelli R.G.
      • Laffi G.
      • Gentilini P.
      ). In addition, several studies have shown that the pericytes responsible for tissue fibrosis may both express chemokines and be targets of the action of chemokines (
      • Gharaee-Kermani M.
      • Denholm E.M.
      • Phan S.H.
      ,
      • Wang X.
      • Yue T.L.
      • Ohlstein E.H.
      • Sung C.P.
      • Feuerstein G.Z.
      ,
      • Schecter A.D.
      • Rollins B.J.
      • Zhang Y.J.
      • Charo I.F.
      • Fallon J.T.
      • Rossikhina M.
      • Giesen P.L.
      • Nemerson Y.
      • Taubman M.B.
      ,
      • Marra F.
      • Romanelli R.G.
      • Giannini C.
      • Failli P.
      • Pastacaldi S.
      • Arrighi M.C.
      • Pinzani M.
      • Laffi G.
      • Montalto P.
      • Gentilini P.
      ). In fact, pericytes express chemokine receptors, which, upon activation, elicit biologic actions that favor the wound healing process, including proliferation, migration, and extracellular matrix synthesis (
      • Romagnani P.
      • Beltrame C.
      • Annunziato F.
      • Lasagni L.
      • Luconi M.
      • Galli G.
      • Cosmi L.
      • Maggi E.
      • Salvadori M.
      • Pupilli C.
      • Serio M.
      ,
      • Banas B.
      • Luckow B.
      • Moller M.
      • Klier C.
      • Nelson P.J.
      • Schadde E.
      • Brigl M.
      • Halevy D.
      • Holthofer H.
      • Reinhart B.
      • Schlondorff D.
      ,
      • Schecter A.D.
      • Calderon T.M.
      • Berman A.B.
      • McManus C.M.
      • Fallon J.T.
      • Rossikhina M.
      • Zhao W.
      • Christ G.
      • Berman J.W.
      • Taubman M.B.
      ).
      The chemokine receptor CXCR3 is bound with high affinity by the chemokines interferon-inducible protein-10 (IP-10), monokine activated by interferon-γ (Mig), and interferon-inducible T cell α chemoattractant (
      • Piali L.
      • Weber C.
      • LaRosa G.
      • Mackay C.R.
      • Springer T.A.
      • Clark-Lewis I.
      • Moser B.
      ,
      • Cole K.E.
      • Strick C.A.
      • Paradis T.J.
      • Ogborne K.T.
      • Loetscher M.
      • Gladue R.P.
      • Lin W.
      • Boyd J.G.
      • Moser B.
      • Wood D.E.
      • Sahagan B.G.
      • Neote K.
      ). CXCR3 has been identified on several cells of hematopoietic lineage, including T and B lymphocytes, and natural killer cells (
      • Luster A.D.
      ,
      • Loetscher M.
      • Gerber B.
      • Loetscher P.
      • Jones S.A.
      • Piali L.
      • Clark-Lewis I.
      • Baggiolini M.
      • Moser B.
      ). In addition, expression of CXCR3 has been indicated as a marker of polarization of the T helper subset of T cells toward a Th1 phenotype (
      • Bonecchi R.
      • Bianchi G.
      • Bordignon P.P.
      • D'Ambrosio D.
      • Lang R.
      • Borsatti A.
      • Sozzani S.
      • Allavena P.
      • Gray P.A.
      • Mantovani A.
      • Sinigaglia F.
      ). We have recently reported that CXCR3 is expressed by human MC in culture, where CXCR3 agonists induce an increase in cell proliferation, and the expression of CXCR3 on MC is up-regulated in conditions of chronic glomerular damage, indicating a possible involvement in wound healing and repair (
      • Romagnani P.
      • Beltrame C.
      • Annunziato F.
      • Lasagni L.
      • Luconi M.
      • Galli G.
      • Cosmi L.
      • Maggi E.
      • Salvadori M.
      • Pupilli C.
      • Serio M.
      ). Despite the relevance of this system in a number of pathophysiologic conditions, little information is available on the signal transduction pathways activated by CXCR3 and their possible correlation with the biologic actions elicited by its agonists. In this study we have characterized CXCR3's signaling in HSC and in MC, as paradigm of vascular pericytes belonging to different tissues. We report that CXCR3 activates multiple signaling pathways, including the Ras/ERK pathway, Src, and the PI3K/Akt pathway, which correlate with the ability to induce biologic actions in target cells.

      DISCUSSION

      The biology of chemokines and their receptors has received considerable attention over the past few years. Dissecting the molecular events triggered by activation of chemokine receptors may help to understand the basis for different pathologic processes and to devise better therapeutic strategies. CXCR3 and its ligands have been linked to different processes, including atherosclerosis, glomerular diseases, and recruitment of T lymphocytes to sites of inflammation (
      • Romagnani P.
      • Beltrame C.
      • Annunziato F.
      • Lasagni L.
      • Luconi M.
      • Galli G.
      • Cosmi L.
      • Maggi E.
      • Salvadori M.
      • Pupilli C.
      • Serio M.
      ,
      • Wang X.
      • Yue T.L.
      • Ohlstein E.H.
      • Sung C.P.
      • Feuerstein G.Z.
      ,
      • Shields P.L.
      • Morland C.M.
      • Salmon M.
      • Qin S.
      • Hubscher S.G.
      • Adams D.H.
      ). Accordingly, CXCR3 has been found to be expressed on different cell types, such as T cells, B cells, natural killer cells, and vascular pericytes, including MC (
      • Luster A.D.
      ,
      • Romagnani P.
      • Beltrame C.
      • Annunziato F.
      • Lasagni L.
      • Luconi M.
      • Galli G.
      • Cosmi L.
      • Maggi E.
      • Salvadori M.
      • Pupilli C.
      • Serio M.
      ,
      • Piali L.
      • Weber C.
      • LaRosa G.
      • Mackay C.R.
      • Springer T.A.
      • Clark-Lewis I.
      • Moser B.
      ). In the present study we have characterized the intracellular signaling downstream of CXCR3 in HSC and MC, tissue-specific pericytes which constitutively express CXCR3 and are involved in tissue repair similarly to pericytes of other tissues. Using this approach, we report that CXCR3 ligands activate Ras/ERK, Src, and the PI3K/Akt pathway, thereby regulating critical cellular functions such as cell proliferation and migration. Activation of ERK has been observed in response to a wide number of agonists in different cell types, and chemokine receptors other than CXCR3 have recently been associated with activation of this pathway (
      • Venkatakrishnan G.
      • Salgia R.
      • Groopman J.
      ,
      • Tilton B.
      • Ho L.
      • Oberlin E.
      • Loetscher P.
      • Baleux F.
      • Clark-Lewis I.
      • Thelen M.
      ). In this study, we provide evidence that CXCR3 activates all the components of the ERK cascade, including Ras, Raf-1, and MEK, and that activation of ERK plays an important role in the modulation of the biologic actions by CXCR3. Interestingly, CXCR3 ligands have previously been shown to inhibit ERK activation by granulocyte-macrophage colony-stimulating factor and Steel factor in hematopoietic MO7e cells (
      • Aronica S.M.
      • Gingras A.C.
      • Sonenberg N.
      • Cooper S.
      • Hague N.
      • Broxmeyer H.E.
      ). In addition, exposure of activated T lymphocytes to IP-10 induces only a very early and transient activation of ERK or Akt (
      • Tilton B.
      • Ho L.
      • Oberlin E.
      • Loetscher P.
      • Baleux F.
      • Clark-Lewis I.
      • Thelen M.
      ). These findings indicate that cell specificity is critical and that cross-talk among various receptors for soluble mediators may result in different patterns of signaling response.
      Data from the present study also indicate that CXCR3 activates other signaling pathways with cross-talk with the Ras/ERK cascade. PI3K is a critical enzyme for multiple cellular functions and may be activated by several pathways, depending on the isoform involved and the regulatory molecule implicated (
      • Wymann M.P.
      • Pirola L.
      ). Following phosphotyrosine immunoprecipitation, we have found that PI3K activity is clearly increased in cells exposed to IP-10. These findings identify an additional target of CXCR3 signaling and underscore the possible importance of tyrosine phosphorylation for CXCR3-mediated downstream events. We extended these findings by testing the involvement of Akt, a kinase that is activated downstream of PI3K, with the participation of other signaling molecules such as PDK-1 (
      • Datta S.R.
      • Brunet A.
      • Greenberg M.E.
      ). A transient increase in Akt phosphorylation and kinase activity was induced by IP-10, thus confirming that the PI3K/Akt axis is a target of CXCR3 signaling. The involvement of tyrosine phosphorylation in CXCR3 signaling also prompted us to investigate whether CXCR3 ligands activate the nonreceptor tyrosine kinase Src, because this molecule has been shown to be the target of several GPCRs, including chemokine receptors (
      • Venkatakrishnan G.
      • Salgia R.
      • Groopman J.
      ). Remarkably, Src enzymatic activity and phosphorylation on activation-specific residues were transiently induced by IP-10, thus identifying an additional element of the signaling cascade activated by CXCR3. Moreover, ERK, Src, and PI3K may exhibit cross-talk in different ways, because Src has been shown to effectively activate the ERK cascade via Ras and PI3K may be either upstream of the Ras/ERK pathway or an effector of Ras (
      • Rodriguez-Viciana P.
      • Warne P.H.
      • Dhand R.
      • Vanhaesebroeck B.
      • Gout I.
      • Fry M.J.
      • Waterfield M.D.
      • Downward J.
      ,
      • Hu Q.
      • Klippel A.
      • Muslin A.J.
      • Fantl W.J.
      • Williams L.T.
      ). Experiments using pharmacologic inhibitors of specific signaling pathways allowed us to establish that PI3K is not involved in the activation of the ERK cascade by CXCR3, because wortmannin had no effects on ERK phosphorylation. However, the observation that a tyrosine kinase inhibitor blocks ERK activation induced by IP-10 indicated that Src is likely implicated in the activation of this pathway. We confirmed this hypothesis by testing the effects of PP1, a specific inhibitor of protein tyrosine kinases of the Src superfamily (
      • Hanke J.H.
      • Gardner J.P.
      • Dow R.L.
      • Changelian P.S.
      • Brissette W.H.
      • Weringer E.J.
      • Pollok B.A.
      • Connelly P.A.
      ). PP1 completely blocked the effects of IP-10 on ERK phosphorylation, thus indicating that Src kinase activity is necessary for the activation of this pathway by CXCR3. Receptor tyrosine kinases, in particular the EGF receptor, have been indicated as alternative effectors of ERK activation by GPCR, and may cooperate with Src to induce ERK activation (
      • Venkatakrishnan G.
      • Salgia R.
      • Groopman J.
      ,
      • Daub H.
      • Weiss F.U.
      • Wallasch C.
      • Ullrich A.
      ,
      • Cunnick J.M.
      • Dorsey J.F.
      • Standley T.
      • Turkson J.
      • Kraker A.J.
      • Fry D.W.
      • Jove R.
      • Wu J.
      ). However, in HSC or MC exposed to IP-10, no increase in EGF receptor tyrosine phosphorylation could be observed, and a specific inhibitor of the EGF receptor tyrosine kinase activity did not modify ERK activation. Taken together, these findings are compatible with the hypothesis that activation of CXCR3 results in Src activation, which in turn leads to recruitment of Ras and activation of the ERK cascade. In parallel, activation of PI3K and Akt is also achieved, although the relation between this pathway and activation of Src remains to be established. This proposed picture is in agreement with data reported on the intracellular signaling activated by other GPCR, showing that activation of Src and Src-like kinases is responsible for the activation of Ras (
      • Gutkind J.S.
      ).
      Migration and proliferation of vascular pericytes are critical biologic actions for wound healing and repair in different tissues. Despite the fact that stimulation of cell migration is a known action of chemokine receptors, the fact that cells of nonhematopoietic lineage, such as vascular pericytes, also exhibit increased chemotaxis when exposed to CXCR3 ligands adds further evidence for a role of this receptor in the regulation of tissue repair after wounding. Moreover, data from this study indicate that activation of both ERK and PI3K contributes to the chemotactic effect of CXCR3. In fact, an inhibitor of MEK reduced, although not completely, CXCR3-dependent chemotaxis, and the effects of PI3K inhibitors were even more marked. Similar observations were previously obtained in PDGF-stimulated HSC or MC, where ERK inhibition was always less effective than inhibitors of PI3K, which reduced cell migration by 70–85% at concentrations similar to the ones used in this study (
      • Marra F.
      • Arrighi M.C.
      • Fazi M.
      • Caligiuri A.
      • Pinzani M.
      • Romanelli R.G.
      • Efsen E.
      • Laffi G.
      • Gentilini P.
      ,
      • Ghosh Choudhury G.
      • Karamitsos C.
      • Hernandez J.
      • Gentilini A.
      • Bardgette J.
      • Abboud H.E.
      ,
      • Marra F.
      • Gentilini A.
      • Pinzani M.
      • Ghosh Choudhury G.
      • Parola M.
      • Herbst H.
      • Dianzani M.U.
      • Laffi G.
      • Abboud H.E.
      • Gentilini P.
      ). Interestingly, CXCR3 ligands were unable to induce cell proliferation in HSC, despite the fact that these molecules activate ERK and PI3K. On the other hand, different time kinetics of ERK activation were observed in MC, which proliferate in response to CXCR3 ligands, with the presence of a late peak, appearing 15–24 h following stimulation. Remarkably, a biphasic activation of ERK had been previously reported in cells synchronized in the M phase and subsequently released, compatible with the presence of peaks of ERK activation in the G1 and G2/M phases, respectively (
      • Tamemoto H.
      • Kadowaki T.
      • Tobe K.
      • Ueki K.
      • Izumi T.
      • Chatani Y.
      • Kohno M.
      • Kasuga M.
      • Yazaki Y.
      • Akanuma Y.
      ). Along these lines, interfering with ERK activation has been recently shown to cause a delay of cycling cells to progress through G2 (
      • Wright J.H.
      • Munar E.
      • Jameson D.R.
      • Andreassen P.R.
      • Margolis R.L.
      • Seger R.
      • Krebs E.G.
      ). These data indicate that, upon stimulation with CXCR3 ligands, cells that progress through the cell cycle, such as MC, show a second peak of ERK activation, whereas the response of those that do not proliferate is characterized by a single, early peak. This interpretation is supported by the observation that, when HSC were incubated with PDGF, a known mitogen for these cells, a similar pattern of ERK activation was observed. The different spectrum of biologic actions elicited by CXCR3 ligands in HSC or MC also indicates that pericytes of different tissues maintain specific features that allow them to respond more appropriately to the local events associated with injury. Along these lines, in conditions associated with proliferation of MC in vivo, polarization of immune response toward a Th1 phenotype has been reported, compatible with a role of IP-10 in MC proliferation in this setting (
      • Romagnani P.
      • Beltrame C.
      • Annunziato F.
      • Lasagni L.
      • Luconi M.
      • Galli G.
      • Cosmi L.
      • Maggi E.
      • Salvadori M.
      • Pupilli C.
      • Serio M.
      ,
      • Holdsworth S.R.
      • Kitching A.R.
      • Tipping P.G.
      ). The relevance of cell specificity for the effects of CXCR3 ligands is underscored by our recent observation of the presence of functional CXCR3 receptors on microvascular endothelial cells (
      • Romagnani P.
      • Annunziato F.
      • Lasagni L.
      • Lazzeri E.
      • Beltrame C.
      • Francalanci M.
      • Uguccioni M.
      • Galli G.
      • Cosmi L.
      • Maurenzig L.
      • Baggiolini M.
      • Maggi E.
      • Romagnani S.
      • Serio M.
      ). In this cell type, exposure to IP-10 or Mig leads to inhibition of cell migration and proliferation, which results in a block of angiogenesis, in keeping with the reported antineoplastic effect of CXCR3 ligands. Information on CXCR3 signaling in these cells is likely to provide further information on the relation between signaling events and the biologic actions linked to activation of this receptor.
      In conclusion, the present study provides the first characterization of the signaling pathways activated by CXCR3 in a model system of vascular pericytes, such as HSC and MC, involved in wound healing and repair. Activation of CXCR3 signaling is associated with activation of ERK, Src, and PI3K/Akt and results in stimulation of cell proliferation and migration. Interestingly, these pathways have also been shown to mediate cell survival signals and the possibility that chemokines activating CXCR3 regulate pericyte apoptosis will deserve further investigation. The identification of the activity and signaling of CXCR3 in the wound healing process may help to develop future strategies for the treatment of conditions associated with excessive fibrogenesis in conditions of chronic injury.

      Acknowledgments

      We are indebted to Dr. Johannes L. Bos (University Medical Center Utrecht, The Netherlands) for kindly providing the GST-RBD construct, to Dr. Hanna E. Abboud (UTHSC San Antonio, TX) for providing one of the mesangial cell lines used in this study, and to Dr. Sergio Romagnani (University of Florence, Italy) for critical reading of the manuscript. The skillful technical assistance of Wanda Delogu and Nadia Navari is gratefully acknowledged.

      REFERENCES

        • Collins T.
        Robbin's Pathological Basis of Disease. 6th Ed. W. B. Saunders, Philadelphia1999: 50-88
        • Abboud H.E.
        Annu. Rev. Physiol. 1995; 57: 297-309
        • Friedman S.L.
        J. Biol. Chem. 2000; 275: 2247-2250
        • Luster A.D.
        N. Engl. J. Med. 1998; 338: 436-445
        • Rossi D.
        • Zlotnik A.
        Annu. Rev. Immunol. 2000; 18: 217-242
        • Romagnani P.
        • Beltrame C.
        • Annunziato F.
        • Lasagni L.
        • Luconi M.
        • Galli G.
        • Cosmi L.
        • Maggi E.
        • Salvadori M.
        • Pupilli C.
        • Serio M.
        J. Am. Soc. Nephrol. 1999; 10: 2518-2526
        • Marra F.
        • DeFranco R.
        • Grappone C.
        • Milani S.
        • Pastacaldi S.
        • Pinzani M.
        • Romanelli R.G.
        • Laffi G.
        • Gentilini P.
        Am. J. Pathol. 1998; 152: 423-430
        • Gharaee-Kermani M.
        • Denholm E.M.
        • Phan S.H.
        J. Biol. Chem. 1996; 271: 17779-17784
        • Wang X.
        • Yue T.L.
        • Ohlstein E.H.
        • Sung C.P.
        • Feuerstein G.Z.
        J. Biol. Chem. 1996; 271: 24286-24293
        • Schecter A.D.
        • Rollins B.J.
        • Zhang Y.J.
        • Charo I.F.
        • Fallon J.T.
        • Rossikhina M.
        • Giesen P.L.
        • Nemerson Y.
        • Taubman M.B.
        J. Biol. Chem. 1997; 272: 28568-28573
        • Marra F.
        • Romanelli R.G.
        • Giannini C.
        • Failli P.
        • Pastacaldi S.
        • Arrighi M.C.
        • Pinzani M.
        • Laffi G.
        • Montalto P.
        • Gentilini P.
        Hepatology. 1999; 29: 140-148
        • Banas B.
        • Luckow B.
        • Moller M.
        • Klier C.
        • Nelson P.J.
        • Schadde E.
        • Brigl M.
        • Halevy D.
        • Holthofer H.
        • Reinhart B.
        • Schlondorff D.
        J. Am. Soc. Nephrol. 1999; 10: 2314-2322
        • Schecter A.D.
        • Calderon T.M.
        • Berman A.B.
        • McManus C.M.
        • Fallon J.T.
        • Rossikhina M.
        • Zhao W.
        • Christ G.
        • Berman J.W.
        • Taubman M.B.
        J. Biol. Chem. 2000; 275: 5466-5471
        • Piali L.
        • Weber C.
        • LaRosa G.
        • Mackay C.R.
        • Springer T.A.
        • Clark-Lewis I.
        • Moser B.
        Eur. J. Immunol. 1998; 28: 961-972
        • Cole K.E.
        • Strick C.A.
        • Paradis T.J.
        • Ogborne K.T.
        • Loetscher M.
        • Gladue R.P.
        • Lin W.
        • Boyd J.G.
        • Moser B.
        • Wood D.E.
        • Sahagan B.G.
        • Neote K.
        J. Exp. Med. 1998; 187: 2009-2021
        • Loetscher M.
        • Gerber B.
        • Loetscher P.
        • Jones S.A.
        • Piali L.
        • Clark-Lewis I.
        • Baggiolini M.
        • Moser B.
        J. Exp. Med. 1996; 184: 963-969
        • Bonecchi R.
        • Bianchi G.
        • Bordignon P.P.
        • D'Ambrosio D.
        • Lang R.
        • Borsatti A.
        • Sozzani S.
        • Allavena P.
        • Gray P.A.
        • Mantovani A.
        • Sinigaglia F.
        J. Exp. Med. 1998; 187: 129-134
        • Casini A.
        • Pinzani M.
        • Milani S.
        • Grappone C.
        • Galli G.
        • Jezequel A.M.
        • Schuppan D.
        • Rotella C.M.
        • Surrenti C.
        Gastroenterology. 1993; 105: 245-253
        • Pupilli C.
        • Lasagni L.
        • Romagnani P.
        • Bellini F.
        • Mannelli M.
        • Misciglia N.
        • Mavilia C.
        • Vellei U.
        • Villari D.
        • Serio M.
        J. Am. Soc. Nephrol. 1999; 10: 245-255
        • Pinzani M.
        • Gesualdo L.
        • Sabbah G.M.
        • Abboud H.E.
        J. Clin. Invest. 1989; 84: 1786-1793
        • Marra F.
        • Efsen E.
        • Romanelli R.G.
        • Caligiuri A.
        • Pastacaldi S.
        • Batignani G.
        • Bonacchi A.
        • Caporale R.
        • Laffi G.
        • Pinzani M.
        • Gentilini P.
        Gastroenterology. 2000; 119: 466-478
        • Choudhury G.G.
        • Wang L.M.
        • Pierce J.
        • Harvey S.A.
        • Sakaguchi A.Y.
        J. Biol. Chem. 1991; 266: 8068-8072
        • Marra F.
        • Choudhury G.G.
        • Abboud H.E.
        J. Clin. Invest. 1996; 98: 1218-1230
        • deRooij J.
        • Bos J.L.
        Oncogene. 1997; 14: 623-625
        • Ishida M.
        • Marrero M.B.
        • Schieffer B.
        • Ishida T.
        • Bernstein K.E.
        • Berk B.C.
        Circ. Res. 1995; 77: 1053-1059
        • Robino G.
        • Parola M.
        • Marra F.
        • Caligiuri A.
        • DeFranco R.M.
        • Zamara E.
        • Bellomo G.
        • Gentilini P.
        • Pinzani M.
        • Dianzani M.U.
        J. Biol. Chem. 2000; 275: 40561-40567
        • Venkatakrishnan G.
        • Salgia R.
        • Groopman J.
        J. Biol. Chem. 2000; 275: 6868-6875
        • Treisman R.
        Curr. Opin. Cell Biol. 1996; 8: 205-215
        • Dikic I.
        • Tokiwa G.
        • Lev S.
        • Courtneidge S.A.
        • Schlessinger J.
        Nature. 1996; 383: 547-550
        • Datta S.R.
        • Brunet A.
        • Greenberg M.E.
        Genes Dev. 1999; 13: 2905-2927
        • Romashkova J.A.
        • Makarov S.S.
        Nature. 1999; 401: 86-90
        • Luttrell L.M.
        • Hawes B.E.
        • van Biesen T.
        • Luttrell D.K.
        • Lansing T.J.
        • Lefkowitz R.J.
        J. Biol. Chem. 1996; 271: 19443-19450
        • Hawes B.E.
        • Luttrell L.M.
        • van Biesen T.
        • Lefkowitz R.J.
        J. Biol. Chem. 1996; 271: 12133-12136
        • Gutkind J.S.
        J. Biol. Chem. 1998; 273: 1839-1842
        • Hanke J.H.
        • Gardner J.P.
        • Dow R.L.
        • Changelian P.S.
        • Brissette W.H.
        • Weringer E.J.
        • Pollok B.A.
        • Connelly P.A.
        J. Biol. Chem. 1996; 271: 695-701
        • Daub H.
        • Weiss F.U.
        • Wallasch C.
        • Ullrich A.
        Nature. 1996; 379: 557-560
        • Cunnick J.M.
        • Dorsey J.F.
        • Standley T.
        • Turkson J.
        • Kraker A.J.
        • Fry D.W.
        • Jove R.
        • Wu J.
        J. Biol. Chem. 1998; 273: 14468-14475
        • Levitzki A.
        • Gazit A.
        Science. 1995; 267: 1782-1788
        • Marra F.
        • Arrighi M.C.
        • Fazi M.
        • Caligiuri A.
        • Pinzani M.
        • Romanelli R.G.
        • Efsen E.
        • Laffi G.
        • Gentilini P.
        Hepatology. 1999; 30: 951-958
        • Shields P.L.
        • Morland C.M.
        • Salmon M.
        • Qin S.
        • Hubscher S.G.
        • Adams D.H.
        J. Immunol. 1999; 163: 6236-6243
        • Tilton B.
        • Ho L.
        • Oberlin E.
        • Loetscher P.
        • Baleux F.
        • Clark-Lewis I.
        • Thelen M.
        J. Exp. Med. 2000; 192: 313-324
        • Aronica S.M.
        • Gingras A.C.
        • Sonenberg N.
        • Cooper S.
        • Hague N.
        • Broxmeyer H.E.
        Blood. 1997; 89: 3582-3595
        • Wymann M.P.
        • Pirola L.
        Biochim. Biophys. Acta. 1998; 1436: 127-150
        • Rodriguez-Viciana P.
        • Warne P.H.
        • Dhand R.
        • Vanhaesebroeck B.
        • Gout I.
        • Fry M.J.
        • Waterfield M.D.
        • Downward J.
        Nature. 1994; 370: 527-532
        • Hu Q.
        • Klippel A.
        • Muslin A.J.
        • Fantl W.J.
        • Williams L.T.
        Science. 1995; 268: 100-102
        • Ghosh Choudhury G.
        • Karamitsos C.
        • Hernandez J.
        • Gentilini A.
        • Bardgette J.
        • Abboud H.E.
        Am. J. Physiol. 1997; 273: F931-F938
        • Marra F.
        • Gentilini A.
        • Pinzani M.
        • Ghosh Choudhury G.
        • Parola M.
        • Herbst H.
        • Dianzani M.U.
        • Laffi G.
        • Abboud H.E.
        • Gentilini P.
        Gastroenterology. 1997; 112: 1297-1306
        • Tamemoto H.
        • Kadowaki T.
        • Tobe K.
        • Ueki K.
        • Izumi T.
        • Chatani Y.
        • Kohno M.
        • Kasuga M.
        • Yazaki Y.
        • Akanuma Y.
        J. Biol. Chem. 1992; 267: 20293-20297
        • Wright J.H.
        • Munar E.
        • Jameson D.R.
        • Andreassen P.R.
        • Margolis R.L.
        • Seger R.
        • Krebs E.G.
        Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 11335-11340
        • Holdsworth S.R.
        • Kitching A.R.
        • Tipping P.G.
        Kidney Int. 1999; 55: 1198-1216
        • Romagnani P.
        • Annunziato F.
        • Lasagni L.
        • Lazzeri E.
        • Beltrame C.
        • Francalanci M.
        • Uguccioni M.
        • Galli G.
        • Cosmi L.
        • Maurenzig L.
        • Baggiolini M.
        • Maggi E.
        • Romagnani S.
        • Serio M.
        J. Clin. Invest. 2001; 107: 53-63