p53, p63, p73 and the mitochondrial apoptosis signaling pathway in human hepatocellular carcinoma (HCC)

In addition to their functions as nuclear transcription factors p53 and its family members can act in the cytosol and mitochondria to promote apoptosis through transcription-independent mechanisms, including direct protein-protein interactions (PPI) with various members of the Bcl–2 family. Targeting transcription-independent p53 family-mediated cell death may provide a promising strategy for p53-based cancer therapy.To study PPI in a liver cell-based model we adapted LUMIERtechnology (Luminescence-based Mammalian IntERactome mapping, in liver cells. LUMIER is based on the co-purification of two tagged proteins from transiently transfected cells using GATEWAY-compatible ORF clones. We maps protein-protein interaction networks in Hep3B cells (human liver carcinoma, deficient in p53 [p53 -/-]) and applied it to the p53-, p63- and p73- pathway. For our studies, a set of relevant proteins from extrinsic and intrinsic apoptosis signaling pathways, cell cycle and proliferation control was selected for PPI analysis using the Ingenuity Pathway Analysis System and the BIOGRID database. We identified several new interactions of the p53-family with Bcl–2 family members. We demonstrated that Bcl-xl does not only interact with p53 but also with p63 and p73. Furthermore, we found novel PPIs of p63 and Bak–1 as a pro-apoptotic Bcl–2 family member and p63 and Mcl–1 as an anti-apoptotic Bcl–2 family member. In addition we could show a novel PPI between p73 and Mcl–1. Positive interactions have been verified by co-immunoprecipitation and are further characterized functionally. Such interactions of the p53 family members with members of the Bcl–2 family may lead to MOMP, Mitochondrial Outer Membrane Permeabilization and induce mitochondrial apoptosis. Our data show that the p53 family might induce apoptosis through translocation to the mitochondria and direct interaction with members of the Bcl–2 family.

Bcl-2 - HCC - p53-family