Ubiquitin-specific protease 44 inhibits cell growth by suppressing AKT signaling in non-small cell lung cancer.

Ubiquitin-specific protease 44 (USP44) has been reported as a tumor suppressor or promoter in some tumors, but its function in non-small cell lung cancer (NSCLC) is still unclear. In this study, USP44 was found significantly downregulated in both of NSCLC tissues and cell lines, and low expression of USP44 predicted a poor prognosis for NSCLC patients. Overexpression of USP44 markedly downregulated the expression levels of Cyclin D1 and CDK4, but upregulated p53 expression, as a result of which, suppressing the cell growth of NSCLC cells. Further studies indicated that overexpression of USP44 significantly inhibited the phosphorylation of AKT, and its down-stream signals, including mTOR and P70S6K. Moreover, overexpression of USP44 increased PTEN protein but not its mRNA levels, which suggested that USP44 inhibited AKT signaling by stabilizing PTEN in NSCLC cells. In conclusion, we demonstrated that USP44 showed prior evidence of a tumor suppressive function in NSCLC cells, and inhibited NSCLC cell growth by suppressing AKT signaling, suggesting that USP44 could be as a novel target for NSCLC therapy.