BACKGROUND AND AIMS: The role of GATA factors in cancer has gained increasing attention recently, but the function of GATA6 in pancreatic ductal adenocarcinoma (PDAC) is controversial. GATA6 is amplified in a subset of tumours and was proposed to be oncogenic, but high GATA6 levels are found in well-differentiated tumours and are associated with better patient outcome. By contrast, a tumour-suppressive function of GATA6 was demonstrated using genetic mouse models. We aimed at clarifying GATA6 function in PDAC. DESIGN: We combined GATA6 silencing and overexpression in PDAC cell lines with GATA6 ChIP-Seq and RNA-Seq data, in order to understand the mechanism of GATA6 functions. We then confirmed some of our observations in primary patient samples, some of which were included in the ESPAC-3 randomised clinical trial for adjuvant therapy. RESULTS: GATA6 inhibits the epithelial-mesenchymal transition (EMT) in vitro and cell dissemination in vivo. GATA6 has a unique proepithelial and antimesenchymal function, and its transcriptional regulation is direct and implies, indirectly, the regulation of other transcription factors involved in EMT. GATA6 is lost in tumours, in association with altered differentiation and the acquisition of a basal-like molecular phenotype, consistent with an epithelial-to-epithelial (ET2) transition. Patients with basal-like GATA6low tumours have a shorter survival and have a distinctly poor response to adjuvant 5-fluorouracil (5-FU)/leucovorin. However, modulation of GATA6 expression in cultured cells does not directly regulate response to 5-FU. CONCLUSIONS: We provide mechanistic insight into GATA6 tumour-suppressive function, its role as a regulator of canonical epithelial differentiation, and propose that loss of GATA6 expression is both prognostic and predictive of response to adjuvant therapy. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

This work was supported, in part, by grants SAF2007-60860, SAF2011-29530 and ONCOBIO Consolider from Ministerio de Economía y Competitividad (Madrid, Spain), RTICC from Instituto de Salud Carlos III, grants 256974 and 289737 from European Union Seventh Framework Program to FXR and by grant P27361-B23 from the Austrian Science Fund (FWF) to PM. AB receives support from the Wellcome Trust, Cancer Research UK, the Medical Research Council (MRC), The Engineering and Physical Sciences Research Council (EPSRC), Pancreatic Cancer UK, the Chief Scientists Office (Scottish Government) and Pancreatic Cancer Action Network (USA). The Cancer Research UK Liverpool Clinical Trials Unit, the ESPAC trials, and the ESPAC tissue collections, storage and analyses are all funded by Cancer Research UK. PM was recipient of a Juan de la Cierva grant from Spanish Ministry of Science and Innovation. BSJr is recipient of a Ramón y Cajal Merit Award from the Spanish Ministry of Science and Innovation and a Clinic and Laboratory Integration Program (CLIP) grant from the Cancer Research Institute, NY.