A CD317/tetherin–RICH2 complex plays a critical role in the organization of the subapical actin cytoskeleton in polarized epithelial cells

Abstract

CD317/tetherin is a lipid raft–associated integral membrane protein with a novel topology. It has a short N-terminal cytosolic domain, a conventional transmembrane domain, and a C-terminal glycosyl-phosphatidylinositol anchor. We now show that CD317 is expressed at the apical surface of polarized epithelial cells, where it interacts indirectly with the underlying actin cytoskeleton. CD317 is linked to the apical actin network via the proteins RICH2, EBP50, and ezrin. Knocking down expression of either CD317 or RICH2 gives rise to the same phenotype: a loss of the apical actin network with concomitant loss of apical microvilli, an increase in actin bundles at the basal surface, and a reduction in cell height without any loss of tight junctions, transepithelial resistance, or the polarized targeting of apical and basolateral membrane proteins. Thus, CD317 provides a physical link between lipid rafts and the apical actin network in polarized epithelial cells and is crucial for the maintenance of microvilli in such cells.

Simian immunodeficiency virus envelope glycoprotein counteracts tetherin/BST-2/CD317 by intracellular sequestration

“…3C) of SIVtan Env. When expressed alone in 293T cells, HA-tagged tetherin localized at the cell surface, as well as in intracellular compartments, consistent with previous observations (8,19,20). On co-expression of SIVtan Env the tetherin was now mostly intracellular with a perinuclear distribution.…”

Membrane Anchoring by a C-terminal Tryptophan Enables HIV-1 Vpu to Displace Bone Marrow Stromal Antigen 2 (BST2) from Sites of Viral Assembly

“…has been proposed to link lipid rafts to each other and to the actin cytoskeleton (19,40), whereas HIV assembly sites are known to include both lipid rafts and TEMs (20 -22). In light of this, we wondered whether the displacement of BST2 from viral assembly sites by Vpu might disrupt the organization of membrane microdomains at assembly sites.…”

“…In support of this, we show using immunofluorescence microscopy that Trp-76 is required for the displacement of BST2 from viral assembly sites by Vpu. Because BST2 has been proposed to link lipid rafts to each other (4,18) and to the actin cytoskeleton (19), we considered that Vpu might distort the membrane topology of viral assembly sites through its influence on BST2. Instead, we observed that cellular markers of lipid rafts and tetraspanin-enriched membrane domains (TEMs), proteins that define the assembly sites of HIV-1 virions (20 -22), remained associated with Gag, the viral structural protein that drives viral assembly, despite the Vpu-induced redistribution of BST2.…”

CD317/Tetherin is an organiser of membrane microdomains

“…This places the N-terminal cytosolic domain of tetherin in a suitable position to interact with the actin cytoskeleton, which it does (indirectly) (Rollason et al, 2009). Consistent with this interaction is the fact that knocking down expression of tetherin in polarised epithelial cells leads to a complete loss of the sub-apical cortical actin network and a commensurate loss of apical microvilli (Rollason et al, 2009).…”