Abstract
Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that stimulates the hypothalamo-pituitary-adrenal (HPA) axis through JAK-STAT activation. We show here that LIF-induced JAK2 and STAT3 tyrosine phosphorylation is transient, disappearing within 20 and 40 minutes, respectively. LIF activates the SH2 domain-containing tyrosine phosphatase, SHP-1, with maximal stimulation observed at 30 minutes. SHP-1 is constitutively associated with JAK2, and LIF induces recruitment of phosphorylated STAT3 to this complex. Overexpression of wild-type or dominant negative forms of SHP-1 shows decreased or increased LIF-induced proopiomelanocortin (POMC) promoter activity, respectively. LIF-induced JAK2 and STAT3 dephosphorylation is delayed until after 60 minutes in cells that overexpress the mutant SHP-1. In addition, SOCS-3, a negative regulator of LIF signaling, binds to JAK2 after 60 minutes of LIF stimulation, after which the complex is degraded by the proteasome. SOCS-3 overexpression blocks LIF-induced JAK2 tyrosine phosphorylation, confirming a role for SOCS-3 in deactivating JAK2 by direct association. Using SOCS-3 fusion proteins, we also define regions of the SOCS-3 protein that are critical for inhibition of LIF-induced POMC promoter activity. Corticotrophic signaling by LIF is thus subject to 2 forms of negative autoregulation: dephosphorylation of JAK2 and STAT3 by the SHP-1 tyrosine phosphatase, and SOCS-3-dependent inactivation of JAK2.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Catalysis
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Cell Line
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DNA-Binding Proteins / metabolism
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Down-Regulation
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Growth Inhibitors / pharmacology*
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Interleukin-6*
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Intracellular Signaling Peptides and Proteins
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Janus Kinase 2
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Leukemia Inhibitory Factor
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Lymphokines / pharmacology*
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Mice
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Models, Biological
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Phosphorylation
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Pituitary Gland / metabolism*
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Pro-Opiomelanocortin / metabolism*
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Protein Tyrosine Phosphatase, Non-Receptor Type 11
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Protein Tyrosine Phosphatase, Non-Receptor Type 6
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Protein Tyrosine Phosphatases / metabolism
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Protein Tyrosine Phosphatases / physiology*
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Protein-Tyrosine Kinases / metabolism
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Proteins / physiology*
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Proto-Oncogene Proteins*
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Repressor Proteins*
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SH2 Domain-Containing Protein Tyrosine Phosphatases
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STAT3 Transcription Factor
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Signal Transduction
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Suppressor of Cytokine Signaling 3 Protein
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Suppressor of Cytokine Signaling Proteins
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Time Factors
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Trans-Activators / metabolism
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Transcription Factors*
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Transfection
Substances
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DNA-Binding Proteins
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Growth Inhibitors
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Interleukin-6
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Intracellular Signaling Peptides and Proteins
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Leukemia Inhibitory Factor
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Lif protein, mouse
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Lymphokines
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Proteins
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Proto-Oncogene Proteins
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Repressor Proteins
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STAT3 Transcription Factor
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Socs3 protein, mouse
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Stat3 protein, mouse
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Suppressor of Cytokine Signaling 3 Protein
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Suppressor of Cytokine Signaling Proteins
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Trans-Activators
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Transcription Factors
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Pro-Opiomelanocortin
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Protein-Tyrosine Kinases
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Jak2 protein, mouse
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Janus Kinase 2
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Protein Tyrosine Phosphatase, Non-Receptor Type 11
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Protein Tyrosine Phosphatase, Non-Receptor Type 6
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Protein Tyrosine Phosphatases
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Ptpn11 protein, mouse
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Ptpn6 protein, mouse
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SH2 Domain-Containing Protein Tyrosine Phosphatases