Heat Shock Protein 12A Is a Novel PCNA-binding Protein and Promotes Hepatocellular Carcinoma Growth.

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death. Proliferating cell nuclear antigen (PCNA) plays a pivotal role in cancer development and progression. However, the long-term dismal prognosis of HCC mandates more investigation to identify novel regulators in HCC pathogenesis. Heat-shock protein A12A (HSPA12A) encodes a novel member of the HSP70 family. Here, we report that HCC cells showed increased HSPA12A expression, and overexpression of HSPA12A promoted HCC growth and angiogenesis in mice. Gain- and loss-of-functional studies demonstrated that the proliferation of HCC HepG2 cells, as well as beta-catenin expression and nuclear translocation, was promoted by HSPA12A overexpression, but in turn suppressed by HSPA12A knockdown. HSPA12A did not impact PCNA expression; however, mass spectrometry and co-immunoprecipitation immunoblotting analysis revealed that HSPA12A directly binds to PCNA and promotes its trimerization, which is an essential functional conformation of PCNA for carcinogenesis. Importantly, PCNA inhibition by PCNA-I1 reversed the HSPA12A-mediated HepG2 cell differentiation. These findings indicate that HSPA12A is a novel regulator of HCC cell proliferation and tumor growth through binding to PCNA for its trimerization. HSPA12A inhibition might represent a viable strategy for the management of HCC in humans.