Independent roles of SOCS-3 and SHP-2 in the regulation of neuronal gene expression by leukemia inhibitory factor.
The neurokine leukemia inhibitory factor (LIF) initiates signaling through heterodimerization of the low affinity LIF receptor (LIFR) and gp130. Tyrosine 759 of gp130 is required for the negative regulation of LIF-mediated signaling by both the protein tyrosine phosphatase SHP-2 and the suppressor of cytokine signaling-3 (SOCS-3). We find that SOCS-3 is expressed in the neuronal cell lines SN56 and IMR32 and negatively regulates LIF-stimulated neuronal gene expression. Studies using antisense oligonucleotides targeted to SHP-2 or SOCS-3 indicate that either protein can negatively regulate LIF-stimulated neuronal gene expression independently of the other. Mutagenesis of the cytoplasmic domain of gp130 demonstrates that the four signal transducer and activators of transcription (STAT) binding sites within gp130 are necessary for the induction of vasoactive intestinal peptide (VIP) and choline acetyltransferase (ChAT) reporter genes, with the sites surrounding tyrosines 905 and 915 (Y905 and Y915) being most important in gp130-mediated reporter gene expression. While there are four STAT binding sites within gp130, only those surrounding Y905 and Y915 can mediate STAT1 activation; these results indicate that STAT1 may be essential for normal gp130-stimulated VIP and ChAT expression. Additionally, the negative regulation of signaling mediated by Y759 of gp130 is dependent upon intact STAT sites within the receptor. This indicates that STAT signaling is necessary for LIF- and CNTF-stimulated VIP and ChAT expression and Y759 of gp130 mediates the activities of SHP-2 and SOCS-3, which act to negatively regulate STAT activity.