Itch/AIP4 Associates with and Promotes p63 Protein Degradation

Abstract

ABSTRACTp63, a protein related to the tumor suppressor p53, is a transcription factor that plays an important role in epidermal differentiation and limb development. The gene has two distinct promoters that allow the formation of proteins that either contain (TA) or lack (∆N) a transactivation domain. In addition, alternative splicing at the 3' end generates proteins with different C-termini, denoted α, β and γ for a total of six isoforms. ∆Np63α isoform is the main isoform expressed at all stages of development, however the relative contribution of individual p63 isoform during ectodermal differentiation and organogenesis is still far from understood. Overexpression of ∆Np63 led to increased growth of transformed cells in vitro and in vivo while treatment of keratinocytes with ultraviolet irradiation causes downregulation of ∆Np63 proteins and their corresponding mRNA. The p63 gene locus is often amplified in squamous cell carcinomas while alterations in the relative levels of TA and ∆Np63 correlate with prognosis in several human cancers suggesting that fine regulation of p63 intracellular levels must be of pivotal importance in controlling cell proliferation, death and differentiation. Despite its relevance little is known on the mechanisms controlling p63 protein levels. Here we show that Itch/AIP4, a HECT E3-ubiquitin ligase, promotes p63 degradation. Using a set of p63 deletion mutants, we have identified a region and two critical lysine residues of p63, associated to human Split-Hand and Foot Malformation-4 (SHFM-4) syndrome, which are involved in the mechanism of Itch-mediated p63 degradation.

WW domain-containing E3 ubiquitin protein ligase 1 targets p63 transcription factor for ubiquitin-mediated proteasomal degradation and regulates apoptosis

“…Increasing evidence suggests that protein ubiquitination and degradation have an important function for the p63 activity. [23][24][25]33 Two other WWP1 family members, Itch and Nedd4, have been previously reported to target p63 proteins for proteasomal degradation. 24,25 However, the expression levels of Itch in breast cancer are not altered 34 although the expression of Nedd4 has been found to be overexpressed in invasive bladder cancer cells.…”

Reduced expression of ΔΝp63α in cervical squamous cell carcinoma

“…Suggesting that diminished ΔNp63α is associated with di erentiation of cervical squamous cancer, and might be also related with progression from super cial to invasive tumours. e regulation of ΔNp63α expression is involved in ubiquitin-proteasome degradation mediated by HECT domain family members such as ITCH and WWP1 [25][26][27][28], the transcriptional regulation of nuclear transcription factors, and the inhibition of protein translation by miR-203 [29]. Persistent infection with high-risk human papillomavirus (HR-HPV) is closely associated with cervical cancer [30], and HR-HPV can bind to their receptors speci cally expressed in cervical basal cells [31][32][33], the integration of HR-HPV DNA into host cells can disrupt normal cervical sqaumous di erentiation by altering several transcriptional factors to promote the initiation of the carcinogenic process [34][35][36][37][38], and their coding proteins,E6 and E7 contribute to disorganised layer formation and hyperplasia in organotypic cultures [35,39], us, HR-HPV infection probably contribute to ΔNp63α inactivation during tumourigenesis.…”

MDM2 and Fbw7 cooperate to induce p63 protein degradation following DNA damage and cell differentiation

“…Recently, we have demonstrated that the homeodomain Dlx3 protein triggers proteasome-dependent Np63 degradation (Di Costanzo et al, 2009) whereas Np63 proteasomal degradation, in response to genotoxic stress, has been proposed to involve RACK1 (Li et al, 2009). Also, the E3 ubiquitin ligases NEDD4 and ITCH/AIP4 have both been found to be involved in the control of p63 steady state level (Rossi et al, 2006a;Rossi et al, 2006b).…”

“…p63 protein stability is regulated by protein modifications such as phosphorylation, ubiquitylation and sumoylation (Ghioni et al, 2005;Rossi et al, 2006a;Rossi et al, 2006b). Proteasomes and lysosomes have both been found to be involved in p63 protein degradation (Watson and Irwin, 2006).…”