Differential protein expression, DNA binding and interaction with SV40 large tumour antigen implicate the p63-family of proteins in replicative senescence

Abstract

P53 activity plays a key role in mammalian cells when they undergo replicative senescence at their Hay¯ick limit. To determine whether p63 proteins, members of the family of p53-related genes, are also involved in this process, we examined their expression in serially passaged rat embryo ®broblasts. Upon senescence, two truncated DNp63 proteins decreased in abundance whereas two TAp63 isoforms accumulated. 2-D gel analysis showed that the DNp63 proteins underwent post-translational modi®cations in both proliferating and senescent cells. Direct binding of DNp63 proteins to a p53 consensus motif was greater in proliferating cells than senescent cells. In contrast p63a isoforms bound to DNA in a p53 dependent manner and this was higher in senescent cells than proliferating cells. An interaction of p63a proteins with SV40 large tumour antigen was also detected and ectopic expression of DNp63a can extend the lifespan of rat embryo ®broblasts. Taken together the results indicate that p63 proteins may play a role in replicative senescence either by competition for p53 DNA binding sites or by direct interaction with p53 protein bound to DNA. Oncogene (2002) 21, 981 ± 989.

p63 and epithelial biology

“…The DNA binding specificity of p53, mediated by the DNA binding domain of the protein, is the major determinant of the spectrum of genes that p53 regulates [67][68][69]. The DNA binding domain of p63 retains significant homology to that of p53, and p63 proteins can bind to p53 consensus DNA binding sites in vitro and in vivo [9,10,70]. However, the divergent biological roles of these two genes imply that they regulate distinct subsets of target genes.…”

Constitutive expression of ?N-p63? isoform in human thymus and thymic epithelial tumours

“…A complex network links p63 to the other members of the p53 family, as both TAp63 and TA-p73 are required for p53-dependent apoptosis after DNA damage, and p53, in turn, has the ability to mediate DN-p63 degradation, thus balancing its oncogenic properties [15,33]. The fine-tuning of different p63 isoforms in the basal and differentiating compartments is necessary to maintain the regenerative quality of epithelial stem cells, as well as the regulation of epidermalmesenchyme interactions, replicative senescence, and angiogenesis [12,14,37]. All these functions render p63 essential during embryonic life for the correct development of limb, craniofacial and epithelial differentiation [29,48].…”

The role of P63 in cancer, stem cells and cancer stem cells

“…p63+/-mice have a shortened life span and display features of accelerated aging, and p63 deficiency also activates enhanced expression of senescent markers [68,70]. Early studies showed that upon senescence, ΔNp63 proteins decreased in abundance, whereas TAp63 isoforms accumulated in serially passaged rat embryo fibroblasts [71]. Recently, Guo et al [72] used a new TAp63-specific mouse model to show that TAp63 isoforms inhibit tumorigenesis in vivo and are robust mediators of senescence.…”