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Multisite phosphorylation of oxysterol-binding protein regulates sterol binding and activation of sphingomyelin synthesis.

ABSTRACT: The endoplasmic reticulum (ER)-Golgi sterol transfer activity of oxysterol-binding protein (OSBP) regulates sphingomyelin (SM) synthesis, as well as post-Golgi cholesterol efflux pathways. The phosphorylation and ER-Golgi localization of OSBP are correlated, suggesting this modification regulates the directionality and/or specificity of transfer activity. In this paper, we report that phosphorylation on two serine-rich motifs, S381-S391 (site 1) and S192, S195, S200 (site 2), specifically controls OSBP activity at the ER. A phosphomimetic of the SM/cholesterol-sensitive phosphorylation site 1 (OSBP-S5E) had increased in vitro cholesterol and 25-hydroxycholesterol-binding capacity, and cholesterol extraction from liposomes, but reduced transfer activity. Phosphatidylinositol 4-phosphate (PI(4)P) and cholesterol competed for a common binding site on OSBP; however, direct binding of PI(4)P was not affected by site 1 phosphorylation. Individual site 1 and site 2 phosphomutants supported oxysterol activation of SM synthesis in OSBP-deficient CHO cells. However, a double site1/2 mutant (OSBP-S381A/S3D) was deficient in this activity and was constitutively colocalized with vesicle-associated membrane protein-associated protein A (VAP-A) in a collapsed ER network. This study identifies phosphorylation regulation of sterol and VAP-A binding by OSBP in the ER, and PI(4)P as an alternate ligand that could be exchanged for sterol in the Golgi apparatus.

SUBMITTER: Goto A

PROVIDER: S-EPMC3442410 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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Multisite phosphorylation of oxysterol-binding protein regulates sterol binding and activation of sphingomyelin synthesis.

Goto Asako A Liu Xinwei X Robinson Carolyn-Ann CA Ridgway Neale D ND

Molecular biology of the cell 20120808 18

The endoplasmic reticulum (ER)-Golgi sterol transfer activity of oxysterol-binding protein (OSBP) regulates sphingomyelin (SM) synthesis, as well as post-Golgi cholesterol efflux pathways. The phosphorylation and ER-Golgi localization of OSBP are correlated, suggesting this modification regulates the directionality and/or specificity of transfer activity. In this paper, we report that phosphorylation on two serine-rich motifs, S381-S391 (site 1) and S192, S195, S200 (site 2), specifically contro ...[more]

PMID: 22875984

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Project description:Sphingomyelin (SM) and cholesterol content is positively correlated in cellular membranes, and in several pathological and experimental conditions there is evidence for coregulation. The potential role of oxysterols and oxysterol binding protein (OSBP) in mediating the coregulation of cholesterol and SM was examined using Chinese hamster ovary (CHO) and cholesterol auxotrophic, sterol regulatory defective (SRD) 6 cells. SRD 6 cells grown in the presence or absence of cholesterol for 24 h displayed a 30-50% reduction in SM synthesis compared with control CHO 7 cells. SM synthesis in CHO 7 and cholesterol-supplemented SRD 6 cells was stimulated 2-fold by 25-hydroxycholesterol, but cholesterol-starved SRD 6 cells were unresponsive. Basal and 25-hydroxycholesterol-stimulated SM synthesis was also inhibited in lovastatin-treated wild-type CHO-K1 cells. Lack of 25-hydroxycholesterol activation of SM synthesis in cholesterol-starved SRD 6 and lovastatin-treated CHO-K1 cells was correlated with dephosphorylation of OSBP. In SRD 6 cells, this was evident after 12 h of cholesterol depletion, it occurred equally at all phosphorylation sites and was exacerbated by 25-hydroxycholesterol. Unlike CHO 7 cells, where OSBP was observed in small vesicles and the cytoplasm, OSBP in cholesterol-starved SRD 6 cells was constitutively localized in the Golgi apparatus. Supplementation with non-lipoprotein cholesterol promoted redistribution to vesicles and the cytoplasm. Similarly, OSBP in CHO-K1 cells grown in delipidated serum was predominantly in the Golgi apparatus. Low-density lipoprotein (LDL) supplementation of CHO-K1 cells caused the redistribution of OSBP to the cytoplasm and small vesicles, and this effect was blocked by pharmacological agents ¿3-beta-[2-(diethylamino)ethoxy]androst-5-en-17-one and progesterone¿, which inhibited LDL cholesterol efflux from lysosomes. The results showed that localization of OSBP between the Golgi apparatus and a cytoplasmic/vesicular compartment was responsive to changes in cholesterol content and trafficking. In cholesterol depleted SRD 6 cells, this was accompanied by dephosphorylation of OSBP and attenuation of 25-hydroxycholesterol activation of SM synthesis.

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Multisite phosphorylation of oxysterol-binding protein regulates sterol binding and activation of sphingomyelin synthesis.

Publications

Multisite phosphorylation of oxysterol-binding protein regulates sterol binding and activation of sphingomyelin synthesis.

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