Calreticulin is the major calcium binding protein found in smooth muscle sarcoplasmic reticulum (SR) and non-muscle endoplasmic reticulum (ER) membranes. Calreticulin can inhibit the binding of androgen receptor to its hormone-responsive DNA element and can inhibit androgen receptor and retinoic acid receptor transcriptional activities in vivo, as well as retinoic acid-induced neuronal differentiation.