Effect of nonspecific phospholipid transfer protein on cholesterol esterification in microsomes from Morris hepatomas.

The content of cholesterol and cholesterol ester as well as the levels of acyl coenzyme A:cholesterol acyltransferase activity were determined in the microsomes from Morris hepatomas 7777, 5123D, and 7787. The free cholesterol content, expressed per mg microsomal protein, was significantly increased only in the microsomes from Morris hepatoma 7777 [47.8 +/- 0.4 micrograms (S.D.); p less than 0.001] and hepatoma 7787 (37.6 +/- 6.2 micrograms; p less than 0.01) as compared to normal liver (28.8 +/- 2.4 micrograms). The cholesterol ester content in the microsomes of the three different tumors did not significantly differ from that of normal liver (2.1 +/- 1.2 micrograms cholesterol per mg microsomal protein). The microsomal acyl coenzyme A:cholesterol acyltransferase activity was decreased in Morris hepatoma 7777 (8.6 +/- 2.3 pmol/min/mg protein; p less than 0.01) and in hepatoma 5123D (7.5 +/- 1.7 pmol/min/mg protein; p less than 0.02), and was normal in the hepatoma 7787 (16.5 +/- 7.8 pmol/min/mg protein) as compared to rat liver (16.0 +/- 2.9 pmol/min/mg protein). In a previous study (B. J. H. M. Poorthuis and K. W. A. Wirtz, Biochim. Biophys. Acta, 710: 99-105, 1982), this acyltransferase activity was shown to be stimulated by preincubation of rat liver microsomes with cholesterol-containing vesicles and the nonspecific phospholipid transfer protein. In this paper, a similar 4-fold stimulation of activity was observed for the microsomes of the various hepatomas investigated. The possible role of the nonspecific phospholipid transfer protein in intracellular cholesterol esterification is discussed.