HM1.24 Is Internalized from Lipid Rafts by Clathrin-mediated Endocytosis through Interaction with α-Adaptin

Abstract

HM1.24/Bst2/CD317 is a protein highly expressed in multiple myeloma cells and has unique topology with two membrane anchor domains, an NH 2 -terminal transmembrane domain and a glycosylphosphatidylinositol attached to the COOH terminus. We show here that human HM1.24 is localized not only on the cell surface but also in the trans-Golgi network and/or recycling endosomes, where it resides in detergent-resistant microdomains, lipid rafts. In contrast to other glycosylphosphatidylinositol-anchored proteins, HM1.24 was internalized from lipid rafts on the cell surface by clathrin-mediated endocytosis. Interestingly, a non-canonical tyrosine-based motif, which contains two tyrosine residues, Tyr-6 and Tyr-8, present in the NH 2 -terminal cytoplasmic tail, was essential for endocytosis through interaction with an ␣-adaptin, but not 2-subunit, of the AP-2 complex. Indeed, an appendage domain of ␣-adaptin was identified as a protein interacting with the cytoplasmic tail of HM1.24. Furthermore, overexpression of the appendage domain of ␣-adaptin in cells depleted of ␣-adaptin could rescue the clathrin-mediated endocytosis of HM1.24 but not of the transferrin receptor. Taken together, our findings suggest that clathrin-dependent endocytosis of human HM1.24 from the cell surface lipid rafts is mediated by direct interaction with ␣-adaptin.

HIV-1 Accessory Protein Vpu Internalizes Cell-surface BST-2/Tetherin through Transmembrane Interactions Leading to Lysosomes

“…Because a very recent report has suggested that Vpu would act after the physiological endocytosis of BST-2 via AP-2 (48), we examined whether or not a BST-2 mutant deficient in constitutive endocytosis could be insensitive to Vpu. To do this we introduced mutations into a non-canonical tyrosine-based motif containing two tyrosine residues at positions 6 and 8 in the CT domain of BST-2 (Y6A/Y8A), which has been known to be essential for clathrin-mediated internalization of this protein (32,49). Protein expressions were confirmed by immunoblotting, showing more intensive bands in the endocytosis mutant Y6A/Y8A than in WT as expected (Fig.…”

The role of BST‐2/Tetherin in host protection and disease manifestation

“…The C‐terminal membrane anchor is thought to be a second TM domain rather than a GPI anchor 12. The cytoplasmic tail of BST‐2 contains a highly conserved double tyrosine motif (6 Y 7 × 8 Y ) implicated in clathrin‐dependent endocytosis of BST‐2 13 and in nuclear factor κ‐B (NF‐κB) activation 14, 15, 16, 17 (Fig. 1).…”

“…Although the function of BST‐2 glycosylation for inhibition of virus release is unclear 11, 22, this post‐translational modification is important for proper folding and trafficking of BST‐2 through the endoplasmic reticulum (ER) and the Golgi 23. BST‐2 molecule associates with lipid rafts 1, 9, 13, 24, 25, 26 through the GPI anchor 9 (Fig. 1).…”

The Size and Conservation of a Coiled-coil Structure in the Ectodomain of Human BST-2/Tetherin Is Dispensable for Inhibition of HIV-1 Virion Release

“…In addition, BST-2 is modified by N-linked glycosylation at two sites in the BST-2 ectodomain (20,23,29,30); however, the functional importance of BST-2 glycosylation for inhibition of virus release is under debate (29,30). Finally, BST-2 protein associates with lipid rafts at the cell surface and on internal membranes (23,(31)(32)(33)(34) and the C-terminal TM region has been implicated with raft targeting of BST-2 (23).…”