Inverse correlation between expression of phosphatidylethanolamine N-methyltransferase-2 and growth rate of perinatal rat livers

Our previous studies have implicated the liver-specific phosphatidylethanolamine N-methyltransferase-2 (PEMT2) in suppression of hepatocarcinoma proliferation (Cui et al. (1994) J. Biol. Chem. 269, 24531-24533). It was not known if this phenomenon in cell culture had relevance to liver growth and PEMT2 expression in an intact animal. Hence, we investigated the relationship between normal proliferation of liver and the expression of PEMT2 during the perinatal period of developing rats. PEMT2 protein was completely absent, and PEMT activity was very low, in prenatal livers in which liver growth is rapid. At birth, a decrease of liver growth coincided with the rapid appearance in liver of a high level of PEMT2 protein that was sustained throughout adult life. Northern blots revealed that the postnatal expression of PEMT2 correlated with the level of its mRNA. Immunohistochemical staining of liver sections showed a distinctive pattern of PEMT2 expression at birth. A high level of PEMT2 was expressed in defined extranuclear regions of hepatocytes from newborn rats whereas the protein was dispersed in the extranuclear areas in adult hepatocytes. The inverse correlation between the rate of liver growth and PEMT2 expression together with other results suggest that this enzyme, or its product, is involved in control of normal liver proliferation. (C) 1997 Elsevier Science B.V.