Amphiphysin IIb-1, a novel splicing variant of amphiphysin II, regulates p73 beta function through protein-protein interactions

p73 is a nuclear protein that is similar in structure and function to p53. Notably, the C-terminal region of p73 has a regulatory function, through in teractions with a positive or negative regulator. In this study, we use the yeast two-hybrid technique to identify a novel p73 beta binding protein, d esignated amphiphysin IIb-1. Amphiphysin IIb-1 is one of the splicing varia nts of amphiphysin II, and has a shorter protein product than amphiphysin I Ib, which has been previously reported. We confirmed that amphiphysin IIb-1 binds full-length p73 beta, both in vitro and in vivo. This association is mediated via the SH3 domain of amphiphysin IIb-1 and C-terminal amino acid s 321-376 of p73 beta. Double immunofluorescence patterns revealed that p73 beta is relocalized to the cytoplasm in the presence of amphiphysin IIb-1. Overexpression of amphiphysin IIb-1 was found to significantly inhibit the transcriptional activity of p73 beta in a dose-dependent manner. In additi on, the cell death function of p73 beta was inhibited by amphiphysin IIb-1. These findings offer a new insight into the regulation mechanism of p73 be ta, and suggest that amphiphysin IIb-1 modulates p73 beta function by direc t binding.