Kes1p shares homology with human oxysterol binding protein and participates in a novel regulatory pathway for yeast Golgi-derived transport vesicle biogenesis.

Abstract

The yeast phosphatidylinositol transfer protein (Sec14p) is required for biogenesis of Golgi‐derived transport vesicles and cell viability, and this essential Sec14p requirement is abrogated by inactivation of the CDP‐choline pathway for phosphatidylcholine biosynthesis. These findings indicate that Sec14p functions to alleviate a CDP‐choline pathway‐mediated toxicity to yeast Golgi secretory function. We now report that this toxicity is manifested through the action of yeast Kes1p, a polypeptide that shares homology with the ligand‐binding domain of human oxysterol binding protein (OSBP). Identification of Kes1p as a negative effector for Golgi function provides the first direct insight into the biological role of any member of the OSBP family, and describes a novel pathway for the regulation of Golgi‐derived transport vesicle biogenesis.

A role for yeast oxysterol-binding protein homologs in endocytosis and in the maintenance of intracellular sterol-lipid distribution

“…The OSH gene family and secretion The deletion of KES1/OSH4 suppresses the lethality associated with loss of SEC14, an essential gene required for Golgi vesicle budding, even though deletion of OSH4 has no detectable effect on Golgi secretory transport (Fang et al, 1996). The implication is that OSH4 does not facilitate Golgi secretion but rather acts as a repressor of SEC14-dependent Golgi transport.…”

“…Moreover, several reports suggest that OSBP homologs regulate vesicular trafficking through the Golgi (Fang et al, 1996;Xu et al, 2001). To test whether OSH genes affected vesicular trafficking of proteins from the ER to the vacuole, the maturation of CPY precursors in OSH mutants was analyzed.…”

“…SEC14 encodes a phospholipid transfer protein, which creates a membrane lipid composition that promotes Golgi-derived secretory transport (Bankaitis et al, 1990). The deletion of OSH4/KES1, but none of the other OSHs, bypasses the essential requirement for SEC14 (Fang et al, 1996;Beh et al, 2001). This indicates that this SEC14 interaction is specific to OSH4, and that OSH4 is a negative regulator of SEC14-dependent secretion.…”

Roles of Phosphoinositides and of Spo14p (phospholipase D)-generated Phosphatidic Acid during Yeast Sporulation

“…YEp352 PIK1 (Flanagan et al, 1993), pGALHA-STT4 -8 (Cutler et al, 1997; generous gift of Maria Cardenas, Duke University Medical Center, Durham, NC), and YEp24-CSR1/SFH2 (Santos and Snyder, 2000; generous gift of Beatriz Santos, Universidad de Salamanca, Salamanca, Spain) are all described in detail in the references cited. pRE352 (kes1::URA3, which removes the N-terminal 262 amino acids of Kes1p; Fang et al, 1996), and pME1827 (cki1::LEU2, which removes 757 base pairs in the middle of the 1749-base pair ORF; Rudge et al, 2001) were used to generate chromosomal disruption/deletions of kes1 and cki1, respectively. Finally, plasmids encoding in vivo phosphoinositide-specific reporters, pRS426GFP-PH(FAPP1) and pRS426GFP-2xPH(PLC␦), are described in detail elsewhere (Stefan et al, 2002; generous gift of Scott Emr and Christopher Stefan, University of California at San Diego, La Jolla, CA).…”

Phospholipase D activity is required for suppression of yeast phosphatidylinositol transfer protein defects

“…The case for how Sec14p stimulates Golgi secretory function is derived primarily from analyses of mutations that permit efficient Golgi secretory activity (and cell viability) in the face of sec14 deletion mutations (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Characterization of these 'bypass Sec14p' mutations suggests that Sec14p maintains the integrity of a critical Golgi diacylglycerol (DAG) pool that is somehow required for Golgi secretory function (4,7).…”