Inhibiting membrane association of RAS has long been considered a rational approach to anticancer therapy, which led to the development of farnesyltransferase inhibitors (FTIs). However, FTIs proved ineffective against KRAS-driven tumors. To reveal alternative therapeutic strategies, we carried out a genome-wide CRISPR-Cas9 screen designed to identify genes required for KRAS4B membrane association. We identified five enzymes in the prenylation pathway and SAFB, a nuclear protein with both DNA and RNA binding domains. Silencing SAFB led to marked mislocalization of all RAS isoforms as well as RAP1A but not RAB7A, a pattern that phenocopied silencing FNTA, the prenyltransferase α subunit shared by farnesyltransferase and geranylgeranyltransferase type I. We found that SAFB promoted RAS membrane association by controlling FNTA expression. SAFB knockdown decreased GTP loading of RAS, abrogated alternative prenylation, and sensitized RAS-mutant cells to growth inhibition by FTI. Our work establishes the prenylation pathway as paramount in KRAS membrane association, reveals a regulator of prenyltransferase expression, and suggests that reduction in FNTA expression may enhance the efficacy of FTIs.

长期以来，抑制RAS的膜缔合一直被认为是抗癌治疗的合理方法，从而导致了法呢基转移酶抑制剂（FTI）的发展。但是，FTI被证明对KRAS驱动的肿瘤无效。为了揭示替代治疗策略，我们进行了全基因组CRISPR-Cas9筛选，旨在鉴定KRAS4B膜结合所需的基因。我们在异戊二烯化途径和SAFB（一种具有DNA和RNA结合域的核蛋白）中鉴定了5种酶。沉默SAFB会导致所有RAS同种型以及RAP1A而不是RAB7A出现明显的错误定位，这是FNTA表型沉默的模式，异戊二烯基转移酶α亚基由法呢基转移酶和I型香叶基香叶基转移酶共有。我们发现，SAFB通过控制FNTA表达来促进RAS膜缔合。SAFB敲低降低了RAS的GTP负荷，废除了替代的异戊二烯化，并使RAS突变细胞对FTI的生长抑制敏感。我们的工作将异戊二烯化途径确立为KRAS膜缔合的首要条件，揭示了异戊二烯基转移酶表达的调节剂，并表明FNTA表达的减少可能会增强FTI的功效。