Targeting plasma membrane phosphatidylserine content to inhibit oncogenic KRAS function

The small GTPase KRAS, which is frequently mutated in human cancers, must be localized to the plasma membrane (PM) for biological activity. We recently showed that the KRASC-terminal membrane anchor exhibits exquisite lipid-binding specificity for select species of phosphatidylserine(PtdSer). We, therefore, investigated whether reducing PM PtdSer content is sufficient to abrogate KRASoncogenesis. Oxysterol-related binding proteins ORP5 and ORP8 exchange PtdSer synthesized in the ER for phosphatidyl-4-phosphate synthesized in the PM. We show that depletion of ORP5 or ORP8 reduced PM PtdSer levels, resulting in extensive mislocalization of KRASfrom the PM. Concordantly, ORP5 or ORP8 depletion significantly reduced proliferation and anchorage-independent growth of multiple KRAS-dependent cancer cell lines, and attenuated KRASsignaling in vivo. Similarly, functionally inhibiting ORP5 and ORP8 by inhibiting PI4KIIIα-mediated synthesis of phosphatidyl-4-phosphate at the PM selectively inhibited the growth of KRAS-dependent cancer cell lines over normal cells. Inhibiting KRASfunction through regulating PM lipid PtdSer content may represent a viable strategy for KRAS-driven cancers.