Abstract Background SRC homology 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2), acting as a central node of many signaling pathways, has an emerging role in many diseases, including cancer. Transforming growth factor β (TGF-β) affects a wide spectrum of biological processes, including cell proliferation, apoptosis, differentiation and migration, during embryonic development and oncogenesis. TGF-β regulates cell proliferation in a cell-context-dependent manner; loss of TGF-β-mediated growth inhibition is a major characteristic of cancer cells. SHP2 regulates canonical and non-canonical TGF-β signaling in cancer cells and fibroblasts, however, the mechanism by which TGF-β activates SHP2 and the role of SHP2 in TGF-β-mediated growth inhibition has remained unclear. Methods The phosphorylation and activation of SHP2 was assessed after TGF-β stimulation of normal and breast cancer cells. The interaction between SHP2 and SRC was determined by co-immunoprecipitation (co-IP) assay. Pharmacological inhibition and gRNA-mediated knockout were applied to assess the role of SHP2 in TGF-β signaling, and RNA-sequencing to identify gene expression patterns in SHP2 knockout cells treated with TGF-β. Functional studies were performed using breast cancer cells to validate the role of SHP2 in TGF-β -mediated growth inhibition. Results We report that TGF-β activated SHP2 by promoting its tyrosine phosphorylation by SRC. SHP2 depletion in breast cancer cells reduced ubiquitination and degradation of TβRI by impeding the interaction between TβRI and SMAD7, which is a negative regulator of TβRI. Pharmacological or genetic inhibition of SHP2 facilitated TGF-β-induced SMAD2 phosphorylation and transcriptional responses. Consequently, inhibition of SHP2 profoundly enhanced TGF-β-induced cell growth arrest and senescence, including promotion of TGF-β-induced expression of the cell cycle inhibitor p15 at both gene and protein level. Conclusions Our findings uncover a mechanism by which SHP2 is activated by TGF-β in a SRC-dependent manner, and functions in a negative feedback mechanism to regulate TGF-β signaling.
Zhao et al. (Fri,) studied this question.