THE PRESENCE AND PARTITIONING OF CALCIUM-BINDING PROTEINS IN HEPATIC AND CARDIAC NUCLEI

Calcium is an important signal in key nuclear events, including cell c ycle timing, regulation of gene expression, and activation of nuclear kinases and phosphatases. It is therefore important to identify calciu m binding proteins in the nucleus which may play roles in these functi ons, and to determine whether these proteins are located in the nuclea r envelope or in the nucleoplasm. Rat hepatic and pig cardiac nuclei w ere isolated and treated with a high salt solution to separate nucleop lasmic proteins from those associated with the nuclear envelope, The p resence of calcium binding proteins was then revealed by Stains-All st aining of electrophoretic gels and Ca-45(2+) overlays of Western blots . Four major calcium binding proteins were putatively identified in th e pig cardiac nuclei, and another three in the rat hepatic nuclei, Pro teins of 110, 93 and 35 kDa were observed in the pig cardiac nuclear e nvelope fraction, and another of 55 kDa in the pig cardiac high salt f raction, A 93-kDa protein was observed in the rat hepatic nuclear enve lope fraction, and others of 120 and 110 kDa in the rat hepatic high s alt fraction. A tentative identification has been made of the 93-kDa p rotein in each tissue type as calnexin, and of the cardiac 55 kDa prot ein as calsequestrin. This study, therefore, has putatively identified for the first time the presence of several calcium binding proteins w hich have distinct partitioning within hepatic and cardiac nuclei. Thi s localization may play an important functional role within the nuclei . (C) 1996 Academic Press Limited