P53(Cp44), an Endogenous Human p53 Fragment Generated via M-Calpain-Mediated Cleavage Beyond Degradation

Endogenous fragments of p53 identified recently in human cytomegalovirus (HCMV)-infected human lung fibroblasts, specifically a ~44-kDa N- terminal fragment referred to as p53(Cp44), have been shown to be generated via m-calpain cleavage. p53(Cp44) appeared to be tightly associated with a chromatin-rich fraction, and was stabilized by the proteasome inhibitor MG132, particularly in mock-infected cells. The N- terminal p53 fragments were also present in three human dermal fibroblast cell lines tested, including fibroblasts isolated from post-burn hypertrophic scar. Understanding the biological functions of these fragments in the regulation of physiological and pathological processes, and the mechanisms regulating their generation and degradation, may shed light on currently unrecognized aspects of p53 regulation and function, and may provide a pathway for drug discovery.