Identification of a 51-kilodalton calmodulin binding protein that changes during estrogen-stimulated cell growth

Abstract

Calmodulin-binding proteins (CaMBPs) were analyzed during estrogen-stimulated growth in the human breast cancer cell line ZR-75-1. A variety of Ca2+-dependent and -independent CaMBPs were observed to be present in these cells. Calmodulin (CaM) binding to a 51-kilodalton protein was shown to be Ca2+-dependent. Moreover, binding to this protein was reduced in the estrogen-treated cells. This effect occurred early during estrogen-stimulated cell growth and was maintained during exponential growth in the presence of estrogen. 125I-labeled CaM overlay procedure of two-dimensional polyacrylamide gels reveals that this 51-kilodalton protein is composed of at least two distinct isoforms with different isoelectric points. Subcellular localization demonstrates that this protein resides exclusively in the microsomal fraction.Key words: calmodulin, calmodulin-binding protein, estrogen-stimulated cell growth.