Monomeric but not trimeric clathrin heavy chain regulates p53-mediated transcription

Tumor suppressor p53 protein is the transcription factor responsible for various genes including DNA repair, growth arrest, apoptosis and antiangiogenesis. Recently, we showed that clathrin heavy chain (CHC), which was originally identified as a cytosolic protein regulating endocytosis, is present in nuclei and functions as a coactivator for p53. Here, we determined the detailed p53-binding site of CHC and a CHC deletion mutant containing this region (CHC833-1406) behaved as a monomer in cells. Monomeric CHC833-1406 still had a higher ability to transactivate p53 than wild-type CHC although this CHC mutant no longer had endocytic function. Moreover, similar to wild-type CHC, monomeric CHC enhances p53-mediated transcription through the recruitment of histone acetyltransferase p300. Immunofluorescent microscopic analysis exhibited that CHC833-1406 is predominantly localized in nuclei, suggesting that there may be a certain regulatory domain for nuclear export in the C-terminus of CHC. Thus, the trimerization domain of CHC is not necessary for the transactivation of p53 target genes and these data provide further evidence that nuclear CHC plays a role distinct from clathrin-mediated endocytosis.