122 AMBRA1 and SQSTM1; Prognostic and surgical excision biomarkers for cSCC

Abstract

Two challenges limiting the management of patients with cutaneous squamous cell carcinoma (cSCC) are the ability to accurately define surgical excision margins and accurate prognostication, empasising the acute need for novel credible biomarkers able to identify high risk tumour subsets. Autophagy, (a lysosomal process for removing damaged organelles/excess proteins) is essential for cellular differentiation with key regulatory proteins known to display prognostic significance in cutaneous malignancy. In this context we demonstrate increased expression of AMBRA1 in normal skin from the basal layer to the stratum corneum, in-line with keratinocyte differentiation. Western blot analysis of CCD1106 or primary human keratinocytes undergoing calcium-induced differentiation in vitro revealed a significant increase in AMBRA1 expression while knockdown of AMBRA1 in primary human keratinocytes was associated with loss of Loricrin expression and significantly increased proliferation. Semi quantitative immunohistochemical expression of AMBRA1 in a cohort of well or poorly differentiated primary cSCCs revealed decreased expression was associated with a poorly differentiated phenotype. Coupled with observations showing AMBRA1 loss promotes cell proliferation and tumorigenesis in an animal model of cSCC and data indicating AMBRA1 loss in primary cSCC tumours is associated with elevated cytoplasmic SQSTM1 (p62) and a poorly differentiated phenotype, these data suggest changes in the level and/or subcellular localization of AMBRA1 and p62 reflect pathological changes related to deregulation of keratinocyte differentiation and a high risk phenotype. Combined expression of AMBRA1 and p62 may thus provide a novel biomarker able to define adequate excison margins at initial excision as well as the risk of tumour progression/recurrence, informing more effective management and follow up regimes for patients with cSCC.