Control of Golgi- V-ATPase through Sac1-dependent co-regulation of PI(4)P and cholesterol

Sac1 is a conserved phosphoinositide phosphatase, whose loss-of-function compromises cell and organism viability. Here, we employed acute auxin-inducible Sac1 degradation to identify its immediate downstream effectors in human cells. Most of Sac1 was degraded in ∼1 h, paralleled by increased PI(4)P and decreased cholesterol in the trans-Golgi network (TGN) during the following hour, and superseded by Golgi fragmentation, impaired glycosylation, and selective degradation of TGN proteins by ∼4 h. The TGN disintegration resulted from its acute deacidification caused by disassembly of the Golgi V-ATPase. Mechanistically, Sac1 mediated TGN membrane composition maintained an assembly promoting conformation of the V 0 a2 subunit. Key phenotypes of acute Sac1 degradation were recapitulated in human differentiated trophoblasts, causing processing defects of chorionic gonadotropin, in line with loss-of-function intolerance of the human SACML1 gene. Collectively, our findings reveal that the assembly of the Golgi V-ATPase is controlled by the TGN membrane via Sac1 fuelled lipid exchange.