The R-Ras interaction partner ORP3 regulates cell adhesion

Abstract

Oxysterol-binding protein (OSBP)-related protein 3 (ORP3) is highly expressed in epithelial, neuronal and hematopoietic cells, as well as in certain forms of cancer. We assessed the function of ORP3 in HEK293 cells and in human macrophages. We show that ORP3 interacts with R-Ras, a small GTPase regulating cell adhesion, spreading and migration. Gene silencing of ORP3 in HEK293 cells results in altered organization of the actin cytoskeleton, impaired cell-cell adhesion, enhanced cell spreading and an increase of β1 integrin activity–effects similar to those of constitutively active R-Ras(38V). Overexpression of ORP3 leads to formation of polarized cell-surface protrusions, impaired cell spreading and decreased β1 integrin activity. In primary macrophages, overexpression of ORP3 leads to the disappearance of podosomal structures and decreased phagocytotic uptake of latex beads, consistent with a role in actin regulation. ORP3 is phosphorylated when cells lose adhesive contacts, suggesting that it is subject to regulation by outside-in signals mediated by adhesion receptors. The present findings demonstrate a new function of ORP3 as part of the machinery that controls the actin cytoskeleton, cell polarity and cell adhesion.

Impaired SUMOylation of nuclear receptor LRH-1 promotes nonalcoholic fatty liver disease

“…OSBPL3, a member of subfamily III, contains a conserved sterol-binding OSBP homology domain (OHD) as well as a phosphatidylinositol lipid species-binding pleckstrin homology (PH) domain and two 2-phenylalanines in an acidic tract (FFAT) domains that bind to the vesicle-associated membrane protein-associated (VAMP-associated) protein (VAP) (39,41,42). Recently, it has been shown that this last interaction can activate R-RAS, thus reorganizing the actin cytoskeleton and affecting cell polarity and cell-cell adhesion (43). Future studies will be necessary to dissect the exact mechanisms by which OSBPL3 modulates SREBP-1 processing, but its association with the ER could indicate a possible site of regulation.…”

Identification of Patients with Recurrent Glioblastoma Who May Benefit from Combined Bevacizumab and CCNU Therapy: A Report from the BELOB Trial

“…OSBPL3 binds to the phosphoinositides PIP2 and PIP3 and can interact with the small GTPase R-RAS (48,49). OSBPL3 was shown to play a role in the regulation of the actin cytoskeleton and cellular adhesion (49).…”

Functions of OSBP/ORP Family Proteins and Their Relation to Dyslipidemia

“…The expression in cerebellum, heart, and liver of most isoforms was negligible. Lehto et al described that ORP3 was expressed at high levels in kidney tubule epithelia and in the human embryonic kidney cell line HEK293 (Lehto, Mayranpaa et al 2008). They also described that the endogenous ORP3 protein in HEK293 cells localized at the ER and the PM, especially thin filopodial cell-surface projections.…”

“…ORP2 presents on LD and has a functional role in the regulation of neutral lipid metabolism, possibly as a factor that integrates the cellular metabolism of triglycerides (TG) with that of cholesterol (Hynynen, Suchanek et al 2009). ORP3 may play an important role in efficient directed membrane trafficking (Lehto, Mayranpaa et al 2008). But the direct evidence that ORP3 functions to regulate dyslipidemia is yet to be reported.…”

“…Molecular functions related to dyslipidemia: The direct evidence that ORP3 functions to regulate Dyslipidemia is yet to be reported. ORP3 interacts with R-Ras, a small GTPase regulating cell adhesion, spreading and migration (Lehto, Mayranpaa et al 2008). Gene silencing of ORP3 and overexpression of ORP3 in HEK293 cells or primary macrophages demonstrate the function of ORP3 as part of the machinery that controls the actin cytoskeleton, cell polarity and cell adhesion.…”