Format

Send to

Choose Destination
J Biol Chem. 2014 May 30;289(22):15705-17. doi: 10.1074/jbc.M114.571216. Epub 2014 Apr 16.

Oxysterol-binding protein (OSBP)-related protein 4 (ORP4) is essential for cell proliferation and survival.

Author information

1
From the Departments of Pediatrics, Biochemistry and Molecular Biology, and.
2
Physics and Atmospheric Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
3
From the Departments of Pediatrics, Biochemistry and Molecular Biology, and nridgway@dal.ca.

Abstract

Oxysterol-binding protein (OSBP) and OSBP-related proteins (ORPs) comprise a large gene family with sterol/lipid transport and regulatory activities. ORP4 (OSBP2) is a closely related paralogue of OSBP, but its function is unknown. Here we show that ORP4 binds similar sterol and lipid ligands as OSBP and other ORPs but is uniquely required for the proliferation and survival of cultured cells. Recombinant ORP4L and a variant without a pleckstrin homology (PH) domain (ORP4S) bind 25-hydroxycholesterol and extract and transfer cholesterol between liposomes. Two conserved histidine residues in the OSBP homology domain ORP4 are essential for binding phosphatidylinositol 4-phosphate but not sterols. The PH domain of ORP4L also binds phosphatidylinositol 4-phosphate in the Golgi apparatus. However, in the context of ORP4L, the PH domain is required for normal organization of the vimentin network. Unlike OSBP, RNAi silencing of all ORP4 variants (including a partial PH domain truncation termed ORP4M) in HEK293 and HeLa cells resulted in growth arrest but not cell death. ORP4 silencing in non-transformed intestinal epithelial cells (IEC)-18 caused apoptosis characterized by caspase 3 and poly(ADP-ribose) polymerase processing, DNA cleavage, and JNK phosphorylation. IEC-18 transformed with oncogenic H-Ras have increased expression of ORP4L and ORP4S proteins and are resistant to the growth-inhibitory effects of ORP4 silencing. Results suggest that ORP4 promotes the survival of rapidly proliferating cells.

KEYWORDS:

Apoptosis; Cholesterol; Lipid Transport; Oxysterol-binding Protein; Phosphatidylinositol 4-Phosphate; Phospholipid; RNA Interference (RNAi); Vimentin

PMID:
24742681
PMCID:
PMC4140924
DOI:
10.1074/jbc.M114.571216
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center