CACYBP Enhances Cytoplasmic Retention of P27^Kip1 to Promote Hepatocellular Carcinoma Progression in the Absence of RNF41 Mediated Degradation

Abstract

Calcyclin-binding protein (CACYBP) is a multi-ligand protein implicated in the progression of various human cancers. However, its function in hepatocellular carcinoma (HCC) remains unknown.Methods: The expression of CACYBP and RNF41 (RING finger protein 41) in HCC cancer and adjacent non-tumor tissues was detected by immunohistochemistry. CCK-8 assays, colony formation assays, flow cytometry detection and xenograft models were used to evaluate the impact of CACYBP expression on HCC cell growth, apoptosis and cell cycle regulation. Immunoprecipitation and ubiquitination assays were performed to determine how RNF41 regulates CACYBP. The regulatory mechanism of RNF41-CACYBP signaling axis on P27Kip1 was investigated by western blotting and immunofluorescence.Results: CACYBP was highly expressed and associated with poor prognosis in HCC. CACYBP expression was required for HCC cell growth in vitro and in vivo. Moreover, we identified RNF41 as a specific binding partner of CACYBP at exogenous and endogenous levels. RNF41 recruited CACYBP by its C-terminal substrate binding domain, subsequently ubiquitinating CACYBP and promoting its degradation in both proteasome- and lysosome-dependent pathways. In HCC tissues, RNF41 expression was reduced and conferred a negative correlation with CACYBP expression. Mechanistically, CACYBP overexpression stimulated the Ser10, Thr157 and Thr198 phosphorylation of P27Kip1 and its cytoplasmic retention, and RNF41 co-expression attenuated this phenomenon. CACYBP depletion led to decreased levels of cyclin D1, cyclin A2, CDK2 and CDK4, causing a typical cell cycle arrest at G1/S phase and increasing apoptosis in HCC cells. P27Kip1-S10D but not P27Kip1-S10A reconstitution rescued partially the cell cycle function and apoptotic feature after CACYBP depletion.Conclusion: Our findings provide novel insights into the functional role and regulatory mechanism of CACYBP in HCC.

Identification of a prognostic and therapeutic immune signature associated with hepatocellular carcinoma

“…CACYBP is up-regulated in HCC compared to normal liver tissues and is related to poor prognosis in HCC patients. It contributes to the development and progression of HCC and may serve as a promising therapeutic and prognostic biomarker [ 42 ]. RAET1E belongs to a ligand family for NKG2D in humans and can produce a soluble, 35-kDa protein (named RAET1E2) in tumor cells.…”

An immune-related gene signature for predicting survival and immunotherapy efficacy in hepatocellular carcinoma

“…Among them, NDRG1 has been reported to be an essential molecule in controlling the metastasis and recurrence of HCC [44]. In addition, the deletion of CACYBP has also been reported to increase apoptosis of HCC cells [45], while the variants of OSGIN1 could reduce apoptosis and are associated with shorter survival [46]. Besides, knockdown and overexpression assays have demonstrated that PSMD14 could promote migration and invasion of HCC cells in vitro, and facilitate tumor growth and metastasis in vivo [47].…”

A Novel Signature Based on mTORC1 Pathway in Hepatocellular Carcinoma

“…Lee's et al study [ 21 ] found that HSPD1 was downregulated during early apoptosis of the hepatoma cell mediated by Paeoniae Radix. In terms of CACYBP , it has been verified that CACYBP can promote hepatocellular carcinoma progression in the absence of RNF41 -mediated degradation [ 22 ]. Moreover, a study [ 23 ] found that PNP /fludarabine suicide gene system induced HCC cell apoptosis and inhibited the growth of HCC cells.…”