PO-160 Downregulation of the oncofetal gene SALL4 in melanoma leads to invasion and metastasis by differential acetylation mediated through binding to HDACs

IntroductionThe transcription factor Sall4 is a well-known developmental regulator involved in embryonic patterning and stem cell maintenance. More recently Sall4 has been suggested to be an oncofetal gene due to being expressed in many fetal tissues and malignant tumours but only rarely in normal adult tissues. The re-expression of such genes in cancer might reflect crucial processes during development, which are reactivated in neoplasias such as increased migratory and invasive capacities. Sall4 is discussed as novel marker and target in some solid tumours and haematological malignancies, however its role in melanoma is unknown.Material and methodsTo address a putative role of Sall4 in melanoma, we used the Tyr::NrasQ61KINK4a−/− murine melanoma model, which spontaneously develops metastatic melanoma. Those mice were crossed with Tyr::CreERT2Sall4lox/loxR26R::GFP mice, allowing us to conditionally ablate Sall4 in melanocytes and to trace Cre activity via GFP expression. We further used human melanoma patient-derived primary cell cultures for in vitro experiments and the same cell lines as xenographs in immunocompromised mice.Results and discussionsMice lacking Sall4 did not form primary tumours compared to the control animals however strikingly had more GFP +melanoma metastases in the lungs. Sall4lox/wt animals formed tumours like control animals but also showed more lung metastases. Through RNA Sequencing on siSALL4-treated human melanoma cell lines we found that SALL4 decrease correlates with upregulation of melanoma invasiveness genes and functionally increased invasiveness in vitro. We further found by Co-IP that SALL4 binds to members of the histone deacetylase family (HDACs) and by running a ChIP-Seq for H3K27ac, we could indeed verify that knocking down SALL4 lead to increased histone acetylation of enhancer regions of the mentioned invasiveness genes. Interestingly, HDAC inhibitor (HDACi) treatment in vitro resulted in an invasiveness gene expression pattern very similar to SALL4 knock down and HDACi treatment of xenograph tumours also lead to an expression profile hinting towards increased invasiveness in vivo.ConclusionAll in all we found that downregulation of Sall4 in melanoma leads to increased acetylation and expression of invasiveness genes in vitro and increased metastasis in vivo, with both phenotypes being closely mimicked by HDAC inhibitor application.