VIP17/MAL, a lipid raft-associated protein, is involved in apical transport in MDCK cells

Abstract

Apical proteins are sorted and delivered from the trans-Golgi network to the plasma membrane by a mechanism involving sphingolipid-cholesterol rafts. In this paper, we report the effects of changing the levels of VIP17/ MAL, a tetraspan membrane protein localized to post-Golgi transport containers and the apical cell surface in MDCK cells. Overexpression of VIP17/MAL disturbed the morphology of the MDCK cell layers by increasing apical delivery and seemingly expanding the apical cell surface domains. On the other hand, expression of antisense RNA directed against VIP17/MAL caused accumulation in the Golgi and/or impaired apical transport of different apical protein markers, i.e., inf luenza virus hemagglutinin, the secretory protein clusterin (gp80), the transmembrane protein gp114, and a glycosylphosphatidylinositol-anchored protein. However, antisense RNA expression did not affect the distribution of E-cadherin to the basolateral surface. Because VIP17/MAL associates with sphingolipid-cholesterol rafts, these data provide functional evidence that this protein is involved in apical transport and might be a component of the machinery clustering lipid rafts with apical cargo to form apical transport carriers.

Rafts in oligodendrocytes: Evidence and structure–function relationship

“…One protein that might promote raft clustering is MAL, which is also known as MVP17 (myelin vesicular protein 17; Kim et al, 1995) and VIP17 (vesicular integral protein 17; Zacchetti et al, 1995). MAL is a 17 kDa non-glycosylated integral membrane protein that localizes in the Golgi (Puertollano et al, 1999) and is required for apical targeting in epithial cells (Cheong et al, 1999;Martin-Belmonte et al, 2000;Puertollano et al, 1999). In OLGs, MAL has been shown to be a component of GSL-rafts (Frank et al, 1998;Frank, 2000;Kim et al, 1995;Kim and Pfeiffer, 2002;Schaeren-Wiemers et al, 1995) and to end up in compact myelin (Frank et al, 1998).…”

α-Synuclein and Its A30P Mutant Affect Actin Cytoskeletal Structure and Dynamics

“…The DNA fragments coding for human wt and A30P ␣-synucleins including the stop codon were inserted into the pEGFP-N1 vector for transfection in N2A cells. The same DNA fragments were inserted in pOPRSVI-1 vector (Cheong et al, 1999). The resulting constructs were transfected into MDCK cells expressing the lac repressor (McCarthy et al, 1996).…”

Clustering and Lateral Concentration of Raft Lipids by the MAL Protein

“…MAL is a compact hydrophobic 17-kDa protein with four predicted transmembrane helices that localizes to the epithelium's apical membrane domain (Alonso and Weissman, 1987;Cheong et al, 1999;. In epithelia, it has been shown to be essential for the apical sorting of several proteins, including GPI-anchored proteins Martin-Belmonte et al, 2000).…”