PIP5K1A is a novel mutant KRAS effector and essential for pancreatic cancer cell survival

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PROJECT SUMMARY/ABSTRACT Phosphoinositides are lipid messengers that control essentially all aspects of human physiology such as survival, proliferation, and motility. Disregulation of phosphoinositide signaling thus is closely associated with human diseases including cancer. Phosphatidylinositol 4,5-bisphosphate (PI4,5P2) is the most abundant phosphoinositide species and has a fundamental role in cancer biology by controlling the activity and subcellular localization of PI4,5P2-binding proteins. The majority of cellular PI4,5P2 is generated by phosphatidyl inositol 4- phosphate 5-kinase type 1 (PIP5K1) and the alpha isoform (encoded by the PIP5K1A gene) is often found to be overexpressed in many types of cancer. However, the detailed molecular functions of PIP5K1A in cancer are poorly understood. In this study, we propose to investigate the molecular mechanisms by which PIP5K1A and its product PI4,5P2 synergistically control KRAS in pancreatic cancer which is one of the deadliest diseases with a median survival period of 4-6 months. KRAS is mutated in >90% of pancreatic cancer and mutant KRAS drives all steps of pancreatic cancer progression. Unfortunately, most of mutant KRAS in pancreatic cancer remains undruggable despite decades of extensive efforts. Thus, novel drugging strategies targeting mutant KRAS in pancreatic cancer is an utmost urgency. We found that PIP5K1A associates with mutant KRAS in pancratic cancer cells and, importantly, recombinant mutant KRAS binds to and stimulates the kinase activity of PIP5K1A in vitro. This finding points out that PIP5K1A is a novel KRAS effector. Consistently, PI4,5P2 production was increased in wild-type KRAS and more dramatically in mutant KRAS expressing cells compared to KRAS-null cells. Moreover, PIP5K1A protein expression was profoundly elevated in pancreatic cancer cells and tissues and depletion of PIP5K1A significantly reduced survival of pancreatic cancer cells harboring mutant KRAS. This makes PIP5K1A a key drug target in pancratic cancer. It is well-documented that PI4,5P2 binds to and activates KRAS by facilitating membrane association and clustering. We hypothesize that 1) KRAS stimulates PI4,5P2 production by PIP5K1A and the generated PI4,5P2 further activates KRAS and its downstream signaling, 2) this positive feedback mechanism sustains constitutive activation of KRAS signaling in pancreatic cancer, and 3) blockade of PIP5K1A consequently attenuates KRAS signaling, leading to pancreatic cancer cell death. To test these hypotheses we will explore 1) the protein-protein and protein-phosphoinositide interactions governing the PIP5K1A-KRAS axis at the molecular level and 2) the impacts of this novel mechanism in pancreatic cancer cell survival/proliferation and motility. This project will provide pivotal information how KRAS signaling is maintained in pancreatic cancer and illuminate new routes to target mutant KRAS by the understudied kinase PIP5K1A.