Microtubule anchoring and coupling of CD20 to the RhoA/Rock1 pathway

Abstract

CD20 is a B cell-specific four-helix transmembrane protein and a prominent target of therapeutic anti-CD20 antibodies. CD20 is localized within a membrane nanocluster harboring the IgD class B cell antigen receptor (IgD-BCR) where it functions as a gatekeeper for the resting state of naive B lymphocytes. How CD20 exerts its gatekeeper function is not yet known. Using Ramos and human peripheral blood B cells, we show here that the serine/threonine kinase PKC{delta}, constitutively phosphorylates serine residues at the cytosolic tails of CD20. The phosphorylated CD20 becomes a target for 14-3-3 adaptor proteins that link CD20 to the RhoA GDP/GTP exchange factor GEF-H1 and the microtubule (MT) network controlling the stability of the IgD-BCR nanocluster. The binding of anti-CD20 antibodies results in MT disassembly and the replacement of the GEF-H1/CD20 complex by a RhoA-GTP/ROCK1/CD20 complex which drives actomyosin contractility. Our study suggests that CD20 not only maintains the resting state, but also orchestrates the MT/actin switch in active B lymphocytes. This could have implications for treatment with anti-CD20 antibodies and may help to optimize therapeutic protocols. Graphic abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/656301v2_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@1cfe15aorg.highwire.dtl.DTLVardef@d3ee14org.highwire.dtl.DTLVardef@1b375eforg.highwire.dtl.DTLVardef@103c9dd_HPS_FORMAT_FIGEXP M_FIG C_FIG