Phospholipase Cγ1 negatively regulates growth hormone signalling by forming a ternary complex with Jak2 and protein tyrosine phosphatase-1B

Growth hormone binds to its membrane receptor (GHR), whereby it regulates many cellular functions, including proliferation, differentiation and chemotaxis. However, although the activation of growth hormone-mediated signalling is well understood, the precise mechanism responsible for its regulation has not been elucidated. Here, we demonstrate that phospholipase C gamma 1 (PLC gamma 1) modulates the action of growth hormone-mediated signalling by interacting with tyrosine kinase Jak2 (janus kinase 2) in a growth hormone-dependent manner. In the absence of PLC gamma 1 (PLC gamma 1(-/-)), growth hormone-induced JAK2 and STAT5 phosphorylation significantly increased in mouse embryonic fibroblasts (MEFs). Furthermore, the re-expression of PLC gamma 1 reduced growth hormone-induced Jak2 activation. Growth hormone-induced Jak2 phosphorylation was enhanced by siRNA-specific knockdown of PLC gamma 1. Interestingly, PLC gamma 1 physically linked Jak2 and protein tyrosine phosphatase-1B (PTP-1B) by binding to both using different domains, and this process was implicated in the modulation of cytokine signalling through Jak2. In addition, in PLC gamma 1(-/-) MEFs, growth hormone-dependent c-Fos activation was upregulated and growth hormone-induced proliferation was potentiated. These results suggest that PLC gamma 1 has a key function in the regulation of growth hormone-mediated signalling by negatively regulating Jak2 activation.