虽然PIKFYVE磷脂酰肌醇激酶抑制剂可以在体外和体内选择性地消除PIKFYVE依赖的人类癌细胞，但其选择性的基础仍然不清楚。在这里，我们展示了，对PIKFYVE抑制剂WX8的细胞敏感性不与PIKFYVE表达、巨噬细胞自噬/自噬流量、BRAFV600E突变或有争议的抑制剂特异性有关。PIKYVE依赖性来自于PIP5K1C磷脂酰肌醇激酶的缺陷，该酶是将磷脂酰肌醇-4-磷酸（PtdIns4P）转化为与溶酶体稳态、内体运输和自噬相关的磷脂酰肌醇-4,5-双磷酸（PtdIns[4,5]P2/PIP2）所需的酶。PtdIns（4,5）P2通过两个独立的途径产生。一个需要PIP5K1C；另一个需要PIKFYVE和PIP4K2C将PtdIns3P转化为PtdIns（4,5）P2。在PIKFYVE依赖性细胞中，低浓度的WX8特异性地体内抑制PIKFYVE，从而增加其底物PtdIns3P的水平，同时抑制PtdIns（4,5）P2的合成和抑制溶酶体功能和细胞增殖。在更高的浓度下，WX8在体内同时抑制PIKFYVE和PIP4K2C，从而加强这些效应，进一步扰乱自噬并诱导细胞死亡。WX8不改变PtdIns4P的水平。因此，在WX8耐药的细胞中抑制PIP5K1C可使其转变为敏感细胞，在WX8敏感的细胞中过表达PIP5K1C可增加其对WX8的抵抗力。这一发现表明，PIKFYVE依赖性癌症可以通过低水平的PIP5K1C在临床上鉴定，并用PIKFYVE抑制剂治疗。

Although PIKFYVE phosphoinositide kinase inhibitors can selectively eliminate PIKFYVE-dependent human cancer cells in vitro and in vivo, the basis for this selectivity has remained elusive. Here we show that the sensitivity of cells to the PIKFYVE inhibitor WX8 is not linked to PIKFYVE expression, macroautophagic/autophagic flux, the BRAFV600E mutation, or ambiguous inhibitor specificity. PIKYVE dependence results from a deficiency in the PIP5K1C phosphoinositide kinase, an enzyme required for conversion of phosphatidylinositol-4-phosphate (PtdIns4P) into phosphatidylinositol-4,5-bisphosphate (PtdIns[4,5]P2/PIP2), a phosphoinositide associated with lysosome homeostasis, endosome trafficking, and autophagy. PtdIns(4,5)P2 is produced via two independent pathways. One requires PIP5K1C; the other requires PIKFYVE and PIP4K2C to convert PtdIns3P into PtdIns(4,5)P2. In PIKFYVE-dependent cells, low concentrations of WX8 specifically inhibit PIKFYVE in situ, thereby increasing the level of its substrate PtdIns3P while suppressing PtdIns(4,5)P2 synthesis and inhibiting lysosome function and cell proliferation. At higher concentrations, WX8 inhibits both PIKFYVE and PIP4K2C in situ, which amplifies these effects to further disrupt autophagy and induce cell death. WX8 did not alter PtdIns4P levels. Consequently, inhibition of PIP5K1C in WX8-resistant cells transformed them into sensitive cells, and overexpression of PIP5K1C in WX8-sensitive cells increased their resistance to WX8. This discovery suggests that PIKFYVE-dependent cancers could be identified clinically by low levels of PIP5K1C and treated with PIKFYVE inhibitors.