Melanoma secretion of TGFβ-2 leads to loss of epidermal AMBRA1 threatening epidermal integrity and facilitating tumour ulceration.

BACKGROUND For patients with early AJCC stage melanoma the combined loss of the autophagy-regulatory protein AMBRA1 and the terminal differentiation marker loricrin in the peritumoural 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 TGFβ 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 TGFβ2 in a cohort of 109 all AJCC stage melanomas, and TGFβ2 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 TGFβ2 signalling evaluated in primary keratinocytes. RESULTS Increased tumoural TGFβ2 was significantly associated with loss of peritumoural AMBRA1 (P < 0.05), ulceration (P < 0.001), AMLo high-risk status (P < 0.05) and metastasis (P < 0.01). TGFβ2 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 < 0.05). Importantly, we show loss of AMBRA1 in the peritumoural epidermis was associated with decreased claudin- 1 expression (P < 0.05), parakeratosis (P < 0.01) and cleft formation in the dermal-epidermal junction (P < 0.05). CONCLUSIONS Collectively these data suggest a paracrine mechanism whereby TGFβ2 causes loss of AMBRA1 overlying high-risk early AJCC stage melanomas and reduced epidermal integrity, thereby facilitating erosion of the epidermis and tumour ulceration.