Abstract
AbstractStability and membrane localization of Transforming growth factor-β (TGF-β) type I receptor (TβRI) is essential for controlling TGF-β signaling. TβRI is targeted for ubiquitination-mediated degradation by Smad7/Smurf2 complex. However, it is unclear whether polyubiquitin modified TβRI can be reversed. Here we performed a genome-wide gain of function screen and identified ubiquitin-specific protease (USP) 4 as a strong inducer of TGF-β signaling. Putative oncogenic USP4 was found to interact with TβRI as deubiquitinating enzyme thus maintains TβR1 levels at the plasma membrane. Depletion of USP4 mitigates TGF-β-induced breast cancer cell migration, epithelial to mesenchymal transition and metastasis. Importantly, Akt/Protein kinase B (PKB), which has been associated with poor prognosis in breast cancer, associates with and phosphorylates USP4. Akt mediated phosphorylation relocates USP4 to cytoplasm and membrane and is required for maintaining its protein stability. Moreover, Akt-induced breast cancer cell migration was inhibited by USP4 depletion and TβRI kinase inhibition. Our results identified USP4 as an important determinant for crosstalk between TGF-β and Akt, which provides new opportunities for cancer treatment.
Highlights
Stability and membrane localization of Transforming growth factor-β (TGF-β) type I receptor (TβRI) is essential for controlling TGF-β signaling[1, 2]
Ectopic expression of USP4, but not its CS inactive mutant, potentiated these TGF-β-induced changes in expression (Fig.3b). Consistent with these results, USP4 knockdown attenuated TGF-β-induced migration of MDA-MB231 cells (Fig. 3c). These results suggest that USP4 regulates TGF-β-induced epithelial to mesenchymal transition (EMT) and migration of breast cancer cells in vitro
We examined the effect of USP4 misexpression in breast cancer cells in vivo by using zebrafish embryo xenograft model where mammalian tumor cells are injected into the zebrafish embryonic blood circulation (Fig. 3d)
Summary
Stability and membrane localization of Transforming growth factor-β (TGF-β) type I receptor (TβRI) is essential for controlling TGF-β signaling[1, 2]. Akt-induced breast cancer cell migration was inhibited by USP4 depletion and TβRI kinase inhibition. Knock-down with two independent shRNAs that selectively target USP4, demonstrated that endogenous USP4 expression is required for maximal TGF-β-induced transcriptional response in HEK293T cells (Fig. 1c).
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