Rapid redistribution of CD20 to a low density detergent-insoluble membrane compartment.

CD20 is a B cell integral membrane protein capable of initiating growth-modulating signals in human B lymphocytes upon its engagement with monoclonal anti-CD20 antibodies. In this report, we demonstrate that treatment of B cells with CD20 antibodies induces rapid redistribution of CD20 into a detergent-insoluble membrane compartment. Redistribution is detected as early as 15 s, following antibody addition, and involves up to 95% of CD20 molecules, depending on the antibody used. All of the detergent-insoluble CD20 was found in the low density fractions of sucrose density gradients, indicating that CD20 redistributes to glycolipid-rich membrane domains, analogous to caveolae in some cell types. As CD20 has previously been shown to associate with Src family tyrosine kinases, their co-existence in these compartments suggests a link to the role of CD20 in signal transduction. This study provides insight into the mechanism by which CD20 communicates signals to the cell interior and indicates that the search for membrane-proximal intracellular signaling partners should be directed to the Triton-insoluble fraction.