Clustering Induces a Lateral Redistribution of α2β1 Integrin from Membrane Rafts to Caveolae and Subsequent Protein Kinase C-dependent Internalization

Abstract

Integrin ␣2␤1 mediates the binding of several epithelial and mesenchymal cell types to collagen. The composition of the surrounding plasma membrane, especially caveolin-1-and cholesterol-containing membrane structures called caveolae, may be important to integrin signaling. On cell surface ␣2␤1 integrin was located in the raft like membrane domain, rich in GPI-anchored proteins, rather than in caveolae. However, when antibodies were used to generate clusters of ␣2␤1 integrin, they started to move laterally on cell surface along actin filaments. During the lateral movement small clusters fused together. Finally ␣2␤1 integrin was found inside caveolae and subsequently internalized into caveosome-like perinuclear structures. The internalization process, unlike cluster formation or lateral redistribution, was dependent on protein kinase C␣ activity. Caveolae are known to be highly immobile structures and ␣2␤1 integrin clusters represent a previously unknown mechanism to activate endocytic trafficking via caveolae. The process was specific to ␣2␤1 integrin, because the antibody-mediated formation of ␣V integrin clusters activated their internalization in coated vesicles and early endosomes. In addition to natural ligands human echovirus-1 (EV1) gains entry into the cell by binding to ␣2␤1 and taking advantage of ␣2␤1 internalization via caveolae. INTRODUCTIONCaveolae are cave-like invaginations of the cell surface (for reviews see Kurzchalia and Parton, 1999;Parton 2003). They have been described as highly immobile and not involved in constitutive endocytic trafficking (Thomsen et al., 2002). Their internalization can be activated, for example, by the phosphatase inhibitor okadaic acid (Parton et al., 1994). In endothelial cells the interaction of albumin docking protein gp60 and caveolin-1 initiates the endocytosis of caveolae (Minshall et al., 2000). Caveolins are membrane proteins that are molecular markers of caveolae and shown to be crucial for the formation of these structures (Fra et al., 1995). Caveolins can be associated with cell surface growth factor receptors (Couet et al., 1997) and cell adhesion receptors (Wary et al., 1996(Wary et al., , 1998Wei et al., 1999) and caveolae might therefore play a role in cellular signaling. In addition, caveolae have been suggested to participate in the uptake of folate by pinocytosis, but this is still under discussion (Parton, 2003). Caveolin-deficient mice have given novel insight into the function of caveolae. Caveolin-1 gene knockout leads to pulmonary defects, vasoconstriction, or dilatation abnormalities and resistance to diet-induced obesity (Drab et al., 2001;Razani et al., 2001;Schubert et al., 2001;Sotgia et al., 2002;Razani et al., 2002). Simian virus 40 (SV40) has been shown to be internalized through caveolae and detailed studies focused on the virus entry mechanism have produced a lot of new information about the biology of caveolae (Pelkmans et al., 2001. We have recently shown that human echovirus 1 (EV1) is another virus using caveolae in its entry (Mar...

Virus trafficking – learning from single-virus tracking

“…After a dynamin-dependent pinching process, the SV40-loaded caveolae leaves the plasma membrane and enters the caveosome before finally reaching the ER through microtubule-dependent transport. Polyoma virus and Echovirus 1 also enter cells through a similar pathway to SV40 (REFS [22][23][24] ).…”

Pathologic Caveolin-1 Regulation of PTEN in Idiopathic Pulmonary Fibrosis

“…1 Prior studies suggest that caveolin-1 may associate with integrin and regulate integrin signaling. [25][26][27][28] Since we have found that during control fibroblast interaction with collagen, PTEN associates with caveolin-1 and suppresses activation of Akt, we were interested in determining whether ␤1 integrin also associates with caveolin-1 in a protein complex. We found that an endogenous protein complex consisting of caveolin-1, ␤1 integrin, and PTEN could be coprecipitated from normal fibroblasts ( Figure 5, A and B).…”

Pharmacoproteomic Analysis of a Novel Cell-permeable Peptide Inhibitor of Tumor-induced Angiogenesis

“…Clathrin-independent and caveolae-mediated internalization of integrins has been described for certain integrins including integrin ␣ 2 ␤ 1 . Caveolin-1 is associated with some integrins including ␣ v ␤ 3 and ␣ 5 ␤ 1 , and integrin ␣ 2 ␤ 1 redistributes to caveolae after integrin clustering (76). ␤ 1 integrins play an important role in the process of endocytosis of fibronectin and fibronectin matrix fibrils by caveolin-mediated event (75).…”