Dissecting the role of iASPP, a novel crucial regulator of epidermal homeostasis, in squamous cell carcinoma

Abstract

Previous data have unveiled a novel autoregulatory feedback loop between iASPP and p63 in the stratified epithelia; this involves two microRNAs, miR-574-3p and miR-720, and is critical for epidermal homeostasis. The iASPP oncoprotein, an inhibitory member of the ASPP (apoptosis stimulating protein of p53) family, is a key inhibitor of p53 and NF-κB and is highly expressed in many cancers. Non-melanoma skin cancer, comprising of cutaneous squamous carcinoma (cSCC) and basal cell carcinoma, is currently the most common malignancy in the UK. In view of this newly-identified iASPP-p63 axis, I hypothesised a potential role for dysregulation of this feedback loop in the pathogenesis of cSCC and aimed to assess the role of iASPP in human cSCC. Protein and mRNA expression patterns were assessed in a panel of 10 cSCC cell lines generated by our group. In addition, immunostaining of iASPP and p63 was performed in 107 cSCC clinical samples of variable differentiation status. The data reveal an overall increase in expression of iASPP and ΔNp63 in cSCC but also suggest a significant alteration of the cellular localisation of iASPP dependent on the differentiation status of the tumour. To further assess the effects mediated by the iASPP/p63 axis, iASPP and p63 have been silenced by RNAi technology in a subset of cSCC cell lines. Whilst data shows the direct effects of iASPP and p63 upon each other’s expression are maintained in cSCC, epigenetic dysregulation of the feedback loop at the microRNA level may be occurring via a novel p63 regulator, miR-211-5p. Functionality of iASPP in cSCC (proliferation, apoptosis, cell motility/migration and invasiveness) provides evidence for a role of iASPP in preventing epithelial-mesenchymal transition in cSCC via a p63/miR-205-5. These findings provide potential future directions for development of clinical biomarkers and novel therapeutic targets for cSCC and may ultimately provide the tools for tackling the increasing morbidity and mortality associated with this malignancy.