癌细胞必须维持其增殖的脂质供应,并通过上调脂肪生成基因程序来做到这一点。固醇调节元件结合蛋白(SREBPs)通过充当脂肪酸和胆固醇合成和摄取所需基因的转录激活因子而充当脂质稳态的调节剂。SREBPs已被认为是多种癌症的化疗靶点,然而,尚不清楚哪些SREBP靶基因对肿瘤发生至关重要。使用平行的体外和体内CRISPR基因敲除筛选,我们确定萜类骨架生物合成基因对胰腺导管腺癌(PDAC)肿瘤的发展至关重要.具体来说,我们鉴定了甲羟戊酸途径的非甾醇类异戊二烯产物,香叶基香叶基二磷酸(G3GPP),作为肿瘤生长的必需脂质。机械上,我们观察到,使用他汀类药物和SREBP抑制剂限制甲羟戊酸途径活性协同诱导细胞凋亡,并导致小G蛋白异戊烯化破坏,对细胞信号传导途径具有多效性作用.最后,我们证明了在原位异种移植小鼠模型中,香叶基香叶基二磷酸合成酶1(GGPS1)敲低可显著降低肿瘤负荷.这些发现表明PDAC肿瘤相对于其他脂质如胆固醇和脂肪酸选择性地需要GGb,并且这是胰腺癌细胞的可靶向脆弱性。
OBJECTIVE: Cancer cells must maintain lipid supplies for their proliferation and do so by upregulating lipogenic gene programs. The sterol regulatory element-binding proteins (SREBPs) act as modulators of lipid homeostasis by acting as transcriptional activators of genes required for fatty acid and cholesterol synthesis and uptake. SREBPs have been recognized as chemotherapeutic targets in multiple cancers, however it is not well understood which
SREBP target genes are essential for tumorigenesis. In this study, we examined the requirement of
SREBP target genes for pancreatic ductal adenocarcinoma (PDAC) tumor growth.
METHODS: Here we constructed a custom CRISPR knockout library containing known
SREBP target genes and performed in vitro 2D culture and in vivo orthotopic xenograft CRISPR screens using a patient-derived PDAC cell line. In vitro, we grew cells in medium supplemented with 10% fetal bovine serum (FBS) or 10% lipoprotein-deficient serum (LPDS) to examine differences in gene essentiality in different lipid environments. In vivo, we injected cells into the pancreata of nude mice and collected tumors after 4 weeks.
RESULTS: We identified terpenoid backbone biosynthesis genes as essential for PDAC tumor development. Specifically, we identified the non-sterol isoprenoid product of the mevalonate pathway, geranylgeranyl diphosphate (GGPP), as an essential lipid for tumor growth. Mechanistically, we observed that restricting mevalonate pathway activity using statins and
SREBP inhibitors synergistically induced apoptosis and caused disruptions in small G protein prenylation that have pleiotropic effects on cellular signaling pathways. Finally, we demonstrated that geranylgeranyl diphosphate synthase 1 (GGPS1) knockdown significantly reduces tumor burden in an orthotopic xenograft mouse model.
CONCLUSIONS: These findings indicate that PDAC tumors selectively require GGPP over other lipids such as cholesterol and fatty acids and that this is a targetable vulnerability of pancreatic cancer cells.