Expression of the p53 homologue p63alpha and DeltaNp63alpha in normal and neoplasticcells

Abstract

A burgeoning family of p53-related genes have been described recently, including p73 and p63. Both these genes encode proteins with many similarities to p53 but also with the potential for forming a range of related species by alternative promoter usage and alternative splicing. In order to begin the characterization of p63, we generated a polyclonal serum (designated SC1) that recognizes the C-terminus of p63alpha. We have shown that this reagent recognizes p63alpha but not p53 nor p73. By western blot analysis both p63alpha and the N-terminal truncated form of p63alpha (DeltaNp63alpha) were found in a range of cell lines. Similar immunoblot analysis of tissues reveals considerable complexity with at least four SC1-immunoreactive isoforms being identified. In immunohistological studies SC1 immunoreactivity is widely detectable, being predominantly associated with proliferative compartments in epithelia. However, non-proliferative populations can also show SC1 immunostaining. No simple relationship between the isoforms identified by immunoblotting of tissue lysates and the tissue immunostaining characteristics was identified. A previously unrecognized species intermediate in mobility between p63alpha and DeltaNp63alpha was found in several tissues, including nerve and peripheral blood lymphocytes. Interestingly, there is suppression of p63alpha expression in HaCat cells in a time- and concentration-dependent manner after UV and MMS treatment. Our data provide further information about the complexity of p63 and the SC1 serum will prove to be a useful tool in further studies of this p53 homologue.

p63α and ΔNp63α can induce cell cycle arrest and apoptosis and differentially regulate p53 target genes

“…The levels of actin were determined as a loading control ( Figure 2, lower panel). Only the DNp63a isoform of p63 was detected in ME-180 cells, which is consistent with previous reports of predominant expression of DN variants (Crook et al, 2000;De Laurenzi et al, 2000;Hall et al, 2000;Yang et al, 1998). Additionally, p73 was undetectable in the H1299 cell line (data not shown).…”

“…In addition, MDM2 was not activated by DNp63a. Therefore, the predominant expression of DN isoforms in epithelial tissues (Crook et al, 2000;De Laurenzi et al, 2000;Hall et al, 2000;Yang et al, 1998) may result from the lack of negative regulation by MDM2.…”

“…In addition, overexpression of p63g can suppress growth and induce apoptosis (Osada et al, 1998;Yang et al, 1998). In contrast to p53 and p73, p63 expression has been reported to be suppressed under conditions of DNA damage (Hall et al, 2000;Liefer et al, 2000). P63 knockout mice exhibit major limb, craniofacial, and epithelial defects, indicating that p63 is critical for proper epithelial development (Mills et al, 1999;Yang et al, 1999).…”

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

“…Moreover, the 60 KDa protein was recognized by H-129, indicating that it was an a isoform but smaller than the authentic full-length 68 KDa DNp63a. Various additional splice forms have been described by Hall and colleagues and explained by the existence of multiple splice variants (Hall et al, 2000); the 60 KDa DNp63a may be one such splice variant. The most likely candidate for the 65 KDa protein is DNp63b (Yang et al, 1998).…”

The role of p53 protein family in gastrointestinal malignancies

“…1 In contrast, columnar surface and crypt epithelium in the cardia, antrum, duodenum, jejunum, ileum and colon have weaker staining or show no staining at all for p63. 1,2 p73…”