Regulation of urokinase receptor proteolytic function by the tetraspanin CD82
ABSTRACT The high affinity interaction between the urokinase-type plasminogen activator (uPA) and its glycolipid-anchored cellular receptor (uPAR) promotes plasminogen activation and the efficient generation of pericellular proteolytic activity. We demonstrate here that expression of the tetraspanin CD82/KAI1 (a tumor metastasis suppressor) leads to a profound effect on uPAR function. Pericellular plasminogen activation was reduced by approximately 50-fold in the presence of CD82, although levels of components of the plasminogen activation system were unchanged. uPAR was present on the cell surface and molecularly intact, but radioligand binding analysis with uPA and anti-uPAR antibodies revealed that it was in a previously undetected cryptic form unable to bind uPA. This was not due to direct interactions between uPAR and CD82, as they neither co-localized on the cell surface nor could be co-immunoprecipitated. However, expression of CD82 led to a redistribution of uPAR to focal adhesions, where it was shown by double immunofluorescence labeling to co-localize with the integrin alpha(5)beta(1), which was also redistributed in the presence of CD82. Co-immunoprecipitation experiments showed that, in the presence of CD82, uPAR preferentially formed stable associations with alpha(5)beta(1), but not with a variety of other integrins, including alpha(3)beta(1). These data suggest that CD82 inhibits the proteolytic function of uPAR indirectly, directing uPAR and alpha(5)beta(1) to focal adhesions and promoting their association with a resultant loss of uPA binding. This represents a novel mechanism whereby tetraspanins, integrins, and uPAR, systems involved in cell adhesion and migration, cooperate to regulate pericellular proteolytic activity and may suggest a mechanism for the tumor-suppressive effects of CD82/KAI1.
Article: Tetraspanins at a glance[Show abstract] [Hide abstract]
ABSTRACT: Tetraspanins are a family of proteins with four transmembrane domains that play a role in many aspects of cell biology and physiology; they are also used by several pathogens for infection and regulate cancer progression. Many tetraspanins associate specifically and directly with a limited number of proteins, and also with other tetraspanins, thereby generating a hierarchical network of interactions. Through these interactions, tetraspanins are believed to have a role in cell and membrane compartmentalization. In this Cell Science at a Glance article and the accompanying poster, we describe the basic principles underlying tetraspanin-based assemblies and highlight examples of how tetraspanins regulate the trafficking and function of their partner proteins that are required for the normal development and function of several organs, including, in humans, the eye, the kidney and the immune system.Journal of Cell Science 08/2014; 127(17). DOI:10.1242/jcs.154906 · 5.33 Impact Factor
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ABSTRACT: Lipid rafts are the lateral assemblies of cholesterol, sphingomyelin, glycosphingolipids, and specific proteins within the cell plasma membrane. These microdomains are involved in a number of important cellular processes including membrane rearrangement, protein internalization, signal transduction, and the entry of viruses into a cell. Some of the lipid rafts are stabilized by special microdomain-forming proteins such as caveolins, SPFH domain-containing superfamily, tetraspanins, galectins, which maintain the integrity of rafts and regulate many resident proteins, thereby participating in nearly all life processes of cells. However, such classes of microdomain-forming proteins are still considered separately from each other. In this review we have tried to perform a complex analysis of microdomain-forming proteins in cell regulation by the example of EGFR receptors, integrins, and matrix metalloproteinases.Biochemistry (Moscow) Supplement Series A Membrane and Cell Biology 01/2013; 7(1). DOI:10.1134/S1990747812060037
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ABSTRACT: Invasion is the key requirement for cancer metastasis. Expression of β1,6 branched N-oligosaccharides associated with invasiveness, have been shown to promote adhesion to most Extra Cellular Matrix (ECM) and Basement Membrane (BM) components and haptotactic motility on ECM (fibronectin) but attenuate it on BM (laminin/matrigel) components. To explore the mechanism and to evaluate the significance of these observations in terms of invasion, highly invasive B16BL6 cells were compared with the parent (B16F10) cells or B16BL6 cells in which glycosylation was inhibited. We demonstrate that increased adhesion to matrix components induced secretion of MMP-9, important for invasion. Further, both the subunits of integrin receptors for fibronectin (α5β1) and laminin (α3β1) on B16BL6 cells were shown to carry these oligosaccharides. Although, glycosylation of receptors had no effect on their surface expression, it had same differential effect on cell spreading as haptotactic motility. Absence of correlation between invasiveness and expression of most tetraspanins (major regulators of integrin function) hints at an alternate mechanism. Here we show that glycosylation on α3β1 impedes its association with CD151and modulates spreading and motility of cells apparently to reach an optimum required for invasion of BM. These studies demonstrate the complex mechanisms used by cancer cells to be invasive.Experimental Cell Research 04/2014; 322:249-264. DOI:10.1016/j.yexcr.2014.02.004 · 3.37 Impact Factor