Expression of nuclear matrix proteins in rat liver tissue

We have studied the synthesis of nuclear matrix proteins as it occurs in the rat liver. To investigate their kinetics in tissue, nuclear matrix proteins were prepared from liver of rats injected with radioactive methionine. Synthesis of lamins was not observed in quiescent hepatocytes although they were the principal proteins of this subcellular fraction, suggesting that lamins are very stable in the liver. When hepatocytes were stimulated to divide by partial hepatectomy, only synthesis of lamin B was initiated. Many proteins not visible on Coomassie blue-stained gels were detectable by autoradiography. In the nuclear matrix extracts of quiescent hepatocytes, one of the most prominently labeled ones was a protein of 70 kDa. After hepatectomy, an additional protein of 62 kDa was detectable. These proteins were visible 1 h after the injection of radioactivity, but were no longer observed in nuclear matrices prepared 24 h after injection. These experiments indicate that in addition to lamins, two nuclear matrix proteins are present in the rat liver that were not detected previously, perhaps because of their rapid turnover.