RalGAP complexes control secretion and primary cilia in pancreatic disease.

κB-Ras/RalGAP complexes limit the activity of Ral GTPases, which function in EGFR/Ras signaling. RalGAP expression is down-regulated in pancreatic cancer; however, the role of RalGAP and Ral GTPases in tumor development in vivo remained unclear. Here, we show that pancreatic RalGAPβ deficiency alone is sufficient to induce inflammation and neoplasia in vivo. We identify that this phenotype is triggered by disturbance of the secretory pathway and polarized exocytosis in acinar cells, demonstrating that RalGAP complexes uphold spatial control of Ral activity. We furthermore show that RALGAPβ deficiency results in defective primary cilium assembly, a process required for efficient acinar regeneration upon inflammation. Only primary cilium formation depends on κB-Ras proteins, suggesting that κB-Ras proteins are not essential for all RalGAP complex-controlled processes. In combination with an oncogenic mutation, RalGAPβ deficiency leads to a dramatic shortening of tumor latency and median survival. Our results highlight an important role of RalGAP/Ral signaling in upholding acinar cell identity and preventing pancreatic cancer development.