Annexin 6 is a putative cell surface receptor for chondroitin sulfate chains

Chondroitin sulfate proteoglycans, including PG-M/versican, inhibit cell-substratum adhesion. They achieve this through their chondroitin sulfate chains. In order to define the molecular mechanism for this inhibition, we investigated the influence of these chains on cell attachment to substratum, the first step in cell adhesion. Chondroitin sulfate chains did not prevent cell attachment. In fact, a variety of cells attached to chondroitin sulfate, implying the existence of putative receptors and/or binding proteins for this extracellular matrix glycosaminoglycan. Detergent-extracted human fibroblast membrane protein extracts were examined by affinity chromatography in the presence of Ca(2+) on chondroitin sulfate immobilized on agarose CL-6B. A 68 kDa and a 35 kDa protein were isolated, sequenced and demonstrated to be annexin 6 and annexin 4, respectively. Next we used A431 cells devoid of annexin 6 expression to verify that annexin 6 is the receptor for this glycosaminoglycan. We confirmed that A431 cells were unable to attach to the chondroitin sulfate substratum and that the stable transfectants expressing annexin 6 conferred the ability to attach to chondroitin sulfate chains. Further, the presence of annexin 6 on the cell surface was confirmed by fluorescence-activated cell sorting analysis using the annexin 6 antibody; annexin 4 is not present on the cell surface. In summary, annexin 6 is a candidate receptor for chondroitin sulfate chains.