Box 3-independent Signaling Mechanisms Are Involved in Leukemia Inhibitory Factor Receptor α- and gp130-mediated Stimulation of Mitogen-activated Protein Kinase
EVIDENCE FOR PARTICIPATION OF MULTIPLE SIGNALING PATHWAYS WHICH CONVERGE AT Ras*
Abstract
Chimeric receptors containing the entire or various cytoplasmic domains of either gp130 or leukemia inhibitory factor receptor α (LIFR) were used to identify signaling molecules and regions of these polypeptides required for the stimulation of mitogen-activated protein kinase (MAPK). Coexpression of dominant-negative Jak2 inhibited chimeric receptor-stimulated MAPK activity by ∼70%, while expression of dominant-negative Ras completely blocked MAPK activation by either receptor polypeptide. Deletion analysis identified a 24-amino acid region of gp130 that was necessary for maximal stimulation of MAPK, and contained box 3 (positions 120–129) and a consensus tyrosine binding motif (Tyr-118) for the protein-tyrosine phosphatase, SHP2. Expression of receptors lacking this region or of chimeric gp130(Y118F) point mutants inhibited MAPK activity by ∼55%, suggesting that Tyr-118, but not box 3, was required during activation of MAPK by gp130. Similarly, expression of chimeric LIFR constructs lacking box 3 maximally stimulated MAPK activity, while those lacking Tyr-115, a putative SHP2 binding site, inhibited stimulation of MAPK by this polypeptide. Our results demonstrate that gp130 and LIFR stimulate MAPK activity through box 3-independent mechanisms involving: (i) effects at Tyr-118 and Tyr-115, respectively, for maximal stimulation of MAPK activity and (ii) a Jak/Tyk-dependent pathway that, together with Tyr-118- or Tyr-115-generated signals, converges at the level of Ras during activation of MAPK by cytokine.
Footnotes
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↵* This work was supported by National Institutes of Health Training Grants GM07750 (to W. P. S) and GM07018 (to J. L. B.), by National Institutes of Health Grant NS30410 (to N. M. N), and by a grant from the Muscular Dystrophy Assocation (to N. M. N.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: University of Washington, Dept. of Pharmacology, Box 357750, Seattle, WA 98195-7750. Tel.: 206-543-9457; Fax: 206-616-4230; E-mail: nathanson{at}u.washington.edu.
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↵1 The abbreviations used are: LIF, leukemia inhibitory factor; DMEM, Dulbecco’s modified Eagle’s medium; EGF, epidermal growth factor; ERK, extracellular signal-regulated kinase; FBS, fetal bovine serum; G-CSF, granulocyte-colony-stimulating factor; G-CSFR, G-CSF receptor; HA, hemagglutinin epitope YPYDVPDYA; IRS-1, insulin receptor substrate-1; LIFR, low affinity LIF receptor α subunit; MAPK, mitogen-activated protein kinase; MBP, myelin basic protein; STAT, signal transducer and activator of transcription proteins.
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↵2 W. P. Schiemann and N. M. Nathanson, unpublished data.
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↵3 W. P. Schiemann and N. M. Nathanson, submitted for publication.
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- Received April 23, 1997.
