Calreticulin affects beta-catenin-associated pathways

Calreticulin, a Ca2+ storage protein and chaperone in the endoplasmic retic ulum, also modulates cell adhesiveness. Overexpression of calreticulin corr elates with (i) increased cell adhesiveness, (ii) increased expression of N -cadherin and vinculin, and (iii) decreased protein phosphorylation on tyro sine. Among proteins that are dephosphorylated in cells that overexpress ca lreticulin is beta -catenin, a structural component of cadherin-dependent a dhesion complexes, a member of the armadillo family of proteins and a part of the Wnt signaling pathway. We postulate that the changes in cell adhesiv eness may be due to calreticulin-mediated effects on a signaling pathway fr om the endoplasmic reticulum, which impinges on the Wnt signaling pathway v ia the cadherin/catenin protein system and involves changes in the activity of protein-tyrosine kinases and/or phosphatases.