INHIBITION OF RETINOIC ACID RECEPTOR FUNCTION AND RETINOIC ACID-REGULATED GENE-EXPRESSION IN MOUSE MELANOMA-CELLS BY CALRETICULIN - A POTENTIAL PATHWAY FOR CYCLIC-AMP REGULATION OF RETINOID ACTION

Calcium is a second messenger that controls a wide variety of cellular functions. Because of its multiple actions, there is a stringent requ irement for calcium ho meostasis, and this is achieved in part by a sy stem of transport and storage proteins such as calreticulin located in the endoplasmic reticulum, Calreticulin is also found in the nucleus, suggesting that it may have a role in transcriptional regulation. It has been reported that calreticulin can inhibit steroid-regulated gene transcription by preventing receptor binding to DNA, Here we report t hat overexpression of the calreticulin gene in B16 mouse melanoma cell s resulted in a decrease in retinoic acid (RA)-stimulated reporter gen e expression, Gel shift analysis showed that purified calreticulin inh ibited the binding of endogenous RAR 60 a beta-RA response element oli gonucleotide, only if added prior to the addition of the oligonucleoti de. Co-immunoprecipitation studies suggest a physical interaction betw een RAR and calreticulin. Transfection of the calreticulin gene into B 16 cells inhibited the RA induction of protein kinase C alpha, a marke r of RA induced differentiation. We also found that cyclic AMP increas ed the expression of calreticulin, Cyclic AMP may act to antagonize RA action by both decreasing RAR expression (Y, Xiao, D, Desai, T, Quick , and R, M, Niles, J, Cell Physiol., in press) and stimulating calreti culin levels,