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Deubiquitinase ubiquitin‐specific protease 9X regulates the stability and function of E3 ubiquitin ligase ring finger protein 115 in breast cancer cells

2019; Wiley; Volume: 110; Issue: 4 Linguagem: Inglês

10.1111/cas.13953

1349-7006

Qin Lu, Dayun Lu, Zhi‐Ming Shao, Da‐Qiang Li,

Genetics and Neurodevelopmental Disorders

The E3 ubiquitin ligase ring finger protein 115 ( RNF 115) is overexpressed in more than half of human breast tumors and is implicated in the pathogenesis and progression of breast cancer. However, the mechanism behind RNF 115 overexpression in breast tumors remains largely unknown. Here we report that ubiquitin‐specific protease 9X ( USP 9X), a substrate‐specific deubiquitinating enzyme, stabilizes RNF 115 and thereby regulates its biological functions in breast cancer cells. Immunoprecipitation and GST pull‐down assays showed that USP 9X interacted with RNF 115. Depletion of RNF 115 by si RNA s or overexpression of RNF 115 did not significantly affect USP 9X expression. In contrast, knockdown of USP 9X in breast cancer cells by si RNA s reduced RNF 115 protein abundance, which was partially restored following treatment with proteasome inhibitor MG ‐132. Moreover, depletion of USP 9X reduced the half‐life of RNF 115 and increased its ubiquitination. Conversely, overexpression of USP 9X resulted in an accumulation of RNF 115 protein, accompanied by a decrease in its ubiquitination. RNF 115 mRNA levels were unaffected by overexpression or knockdown of USP 9X. Furthermore, USP 9X protein expression levels correlated positively with RNF 115 in breast cancer cell lines and breast tumor samples. Importantly, reintroduction of RNF 115 in USP 9X‐depleted cells partially rescued the reduced proliferation, migration, and invasion of breast cancer cells by USP 9X knockdown. Collectively, these findings indicate that USP 9X is a stabilizer of RNF 115 protein and that the USP 9X‐ RNF 115 signaling axis is implicated in the breast cancer malignant phenotype.