Evidence against a laminin receptor role for calsequestrin

Calsequestrin, a muscle calcium binding protein, has been shown to bind the extracellular matrix protein laminin and evidence has been presented that CAL (initially called aspartactin) is on the cell surface, consistent with a role as a laminin receptor (1). In this report, we present evidence that does not support a laminin receptor function for CAL. We found that CAL immunoreactivity could not be detected on live cultured chick myotubes unless they were permeabilized with detergent. Furthermore, polyclonal anti-CAL antibodies did not perturb myotube adhesion to laminin or the rate of myoblast fusion on laminin. Expression of the CAL cDNA in a melanoma cell line that was poorly adherent to laminin did not increase adhesion to laminin. In these cells, CAL could not be detected on the cell surface, and the majority of CAL was found to be secreted into the media.