10273

STUB1

STIP1 homology and U-box containing protein 1, E3 ubiquitin protein ligase;STUB1;STIP1 homology and U-box containing protein 1, E3 ubiquitin protein ligase

CLL-associated antigen KW-8|E3 ubiquitin-protein ligase CHIP|antigen NY-CO-7|carboxy terminus of Hsp70-interacting protein|heat shock protein A binding protein 2 (c-terminal)|serologically defined colon cancer antigen 7

16p13.3

protein-coding

The carboxyl terminus of heat shock cognate 70 interacting protein (CHIP) is an E3 ubiquitin ligase, which can promote ubiquitylation and degradation of many tumor-related proteins. However, the expression of CHIP in human gastric cancer has not been investigated. In this study, the mRNA and protein levels of CHIP expression in 53 cases of gastric cancer and matched normal tissues were determined by quantitative real-time PCR, western blotting and immunohistochemistry. We showed that CHIP was registered from basal to middle portions of normal gastric mucosa. CHIP expression was notably decreased or lost in human gastric cancer samples compared with the matched normal non-cancer samples. The correlations between CHIP downregulation and the clinicopathological characteristics were also evaluated. The expression of CHIP was significantly lower in the gastric cancer samples compared to the matched normal samples at both mRNA and protein levels (P<0.05 and P<0.05, respectively). More importantly, the downregulation of CHIP was correlated with TNM stage (P=0.048) and lymph node metastasis (P=0.010) at the mRNA levels. In addition, the downregulation of CHIP was correlated with lymph node metastasis (P=0.021) and tumor differentiation (P=0.009) at the protein levels. Taken together, at both mRNA and protein levels, the decreased expression of CHIP was correlated with lymph node metastasis. Furthermore, our study suggests that a negative correlation exists between CHIP expression and tumor malignancy in human gastric cancer.

CHIP is a U-box-type ubiquitin ligase that induces ubiquitylation and degradation of its substrates, which include several oncogenic proteins. The relationship between CHIP and tumour progression, however, has not been elucidated. Here, we show that CHIP suppresses tumour progression in human breast cancer by inhibiting oncogenic pathways. CHIP levels were negatively correlated with the malignancy of human breast tumour tissues. In a nude mouse xenograft model, tumour growth and metastasis were significantly inhibited by CHIP expression. In contrast, knockdown of CHIP (shCHIP) in breast cancer cells resulted in rapid tumour growth and metastastic phenotypes in mice. In cell-based experiments, anchorage-independent growth and invasiveness of shCHIP cells was significantly elevated due to increased expression of Bcl2, Akt1, Smad and Twist. Proteomic analysis identified the transcriptional co-activator SRC-3 (refs 13, 14, 15, 16, 17, 18, 19) as a direct target for ubiquitylation and degradation by CHIP. Knocking down SRC-3 in shCHIP cells reduced the expression of Smad and Twist, and suppressed tumour metastasis in vivo. Conversely, SRC-3 co-expression prevented CHIP-induced suppression of metastasis formation. These observations demonstrate that CHIP inhibits anchorage-independent cell growth and metastatic potential by degrading oncogenic proteins including SRC-3.