κB-Ras and Ral GTPases regulate acinar to ductal metaplasia during pancreatic adenocarcinoma development and pancreatitis

Pancreatic ductal adenocarcinoma (PDAC) is associated with high mortality and therapy resistance. Here, we show that low expression of kappa B-Ras GTPases is frequently detected in PDAC and correlates with higher histologic grade. In a model of KRas(G12D)-driven PDAC, loss of kappa B-Ras accelerates tumour development and shortens median survival. kappa B-Ras deficiency promotes acinar-to-ductal metaplasia (ADM) during tumour initiation as well as tumour progression through intrinsic effects on proliferation and invasion. kappa B-Ras proteins are also required for acinar regeneration after pancreatitis, demonstrating a general role in control of plasticity. Molecularly, upregulation of Ral GTPase activity and Sox9 expression underlies the observed phenotypes, identifying a previously unrecognized function of Ral signalling in ADM. Our results provide evidence for a tumour suppressive role of kappa B-Ras proteins and highlight low kappa B-Ras levels and consequent loss of Ral control as risk factors, thus emphasizing the necessity for therapeutic options that allow interference with Ral-driven signalling. The molecular mechanisms of acinar-to-ductal metaplasia (ADM) in the course of pancreatitis and cancer development are unclear. Here, the authors show that loss of kappa B-Ras and consequent Ral activation promotes tumour initiation and progression through persistent ADM and enhanced cell proliferation