Melanoma secretion of transforming growth factor-beta 2 leads to loss of epidermal AMBRA1 threatening epidermal integrity and facilitating tumour ulceration

Background For patients with early American Joint Committee on Cancer (AJCC)-stage melanoma the combined loss of the autophagy regulatory protein AMBRA1 and the terminal differentiation marker loricrin in the peritumoral epidermis is associated with a significantly increased risk of metastasis. Objectives The aim of the present study was to evaluate the potential contribution of melanoma paracrine transforming growth factor (TGF)-beta signalling to the loss of AMBRA1 in the epidermis overlying the primary tumour and disruption of epidermal integrity. Methods Immunohistochemistry was used to analyse AMBRA1 and TGF-beta 2 in a cohort of 109 AJCC all-stage melanomas, and TGF-beta 2 and claudin-1 in a cohort of 30 or 42 AJCC stage I melanomas, respectively, with known AMBRA1 and loricrin (AMLo) expression. Evidence of pre-ulceration was analysed in a cohort of 42 melanomas, with TGF-beta 2 signalling evaluated in primary keratinocytes. Results Increased tumoral TGF-beta 2 was significantly associated with loss of peritumoral AMBRA1 (P < 0 center dot 05), ulceration (P < 0 center dot 001), AMLo high-risk status (P < 0 center dot 05) and metastasis (P < 0 center dot 01). TGF-beta 2 treatment of keratinocytes resulted in downregulation of AMBRA1, loricrin and claudin-1, while knockdown of AMBRA1 was associated with decreased expression of claudin-1 and increased proliferation of keratinocytes (P < 0 center dot 05). Importantly, we show loss of AMBRA1 in the peritumoral epidermis was associated with decreased claudin-1 expression (P < 0 center dot 05), parakeratosis (P < 0 center dot 01) and cleft formation in the dermoepidermal junction (P < 0 center dot 05). Conclusions Collectively, these data suggest a paracrine mechanism whereby TGF-beta 2 causes loss of AMBRA1 overlying high-risk AJCC early-stage melanomas and reduced epidermal integrity, thereby facilitating erosion of the epidermis and tumour ulceration.