Receptor-Associated Constitutive Protein Tyrosine Phosphatase Activity Controls the Kinase Function of JAK1

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 94; no. 16; pp. 8563 - 8568
• Main Authors: Haque, S. Jaharul, Wu, Qian, Kammer, Winfried, Friedrich, Karlheinz, Smith, Jonathan M., Kerr, Ian M., Stark, George R., Bryan R. G. Williams
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 05-08-1997; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences of the USA
• Subjects: 3T3 cells; Amino Acid Sequence; Animals; Antigens, CD - metabolism; Biological Sciences; Biology; Cell Line; Cell lines; Cells; Cellular biology; COS cells; Cytokine receptors; Cytokines; DNA-Binding Proteins - metabolism; Down-Regulation; Humans; Insulin; Janus Kinase 1; Molecular Sequence Data; Phosphorylation; Protein Tyrosine Phosphatases - metabolism; Protein-Tyrosine Kinases - metabolism; Proteins; Receptors; Receptors, Interleukin - metabolism; Receptors, Interleukin-4; Signal Transduction; STAT1 Transcription Factor; STAT3 Transcription Factor; STAT6 Transcription Factor; Trans-Activators - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.16.8563

Exposure of cells to protein tyrosine phosphatase (PTP) inhibitors causes an increase in the phosphotyrosine content of many cellular proteins. However, the level at which the primary signaling event is affected is still unclear. We show that Jaks are activated by tyrosine phosphorylation in cells that are briefly exposed to the PTP inhibitor pervanadate (PV), resulting in tyrosine phosphorylation and functional activation of Stat6 (in addition to other Stats). Mutant cell lines that lack Jak1 activity fail to support PV-mediated [or interleukin 4 (IL-4)-dependent] activation of Stat6 but can be rescued by complementation with functional Jak1. The docking sites for both Jak1 and Stat6 reside in the cytoplasmic domain of the IL-4 receptor α -chain (IL-4Rα ). The glioblastoma-derived cell lines T98G, GRE, and M007, which do not express the IL-4Rα chain, fail to support Stat6 activation in response to either IL-4 or PV. Complementation of T98G cells with the IL-4Rα restores both PV-mediated and IL-4-dependent Stat6 activation. Murine L929 cells, which do not express the γ common chain of the IL-4 receptor, support PV-mediated but not IL-4-dependent Stat6 activation. Thus, Stat6 activation by PV is an IL-4Rα -mediated, Jak1-dependent event that is independent of receptor dimerization. We propose that receptor-associated constitutive PTP activity functions to down-regulate persistent, receptor-linked kinase activity. Inhibition or deletion of PTP activity results in constitutive activation of cytokine signaling pathways.