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Effect of Cell Density and Confluency on Cholesterol Metabolism in Cancer Cells in Monolayer Culture¹

The Cecil H. and Ida Green Center for Reproductive Biology Sciences, and Departments of Obstetrics and Gynecology and Biochemistry, University of Texas Southwestern Medical School, Dallas, Texas 75235

Cholesterol metabolism in four gynecological cancer cell lines in monolayer culture was evaluated as a function of cell density. The rate of uptake and degradation of [¹²⁵I]iodinated low-density lipoprotein increased during the first 24 to 48 hr of culture, but decreased thereafter. Once the cells became confluent, the rate of metabolism of [¹²⁵I]iodinated low-density lipoprotein was only one-tenth that in cells which were in the preconfluent state. The specific activity of 3-hydroxy-3-methylglutaryl coenzyme reductase increased during the first 24 to 48 hr of culture and subsequently declined, reaching a nadir after confluency was attained. The rate of incorporation of [¹⁴C]oleate into cholesteryl esters was low when the cells were in the log-exponential phase of replication but increased gradually as cell density increased. The highest specific activity of acylcoenzyme A: cholesterol acyltransferase was attained after the cells became confluent. Generally speaking, there was an inverse relationship between the specific activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on the one hand, and the rate of [¹²⁵I]iodinated low-density lipoprotein metabolism and cholesteryl ester synthesis, on the other. It is concluded that cholesterol metabolism in cancer cells in monolayer culture is regulated, in part, by the rate of cell division. In the cancer cells utilized in this study, it is apparent that cholesterol metabolism was subject to the same regulatory mechanisms as are present in nonneoplastic cells.

¹ Supported in part by NIH Grants 5-P01-AG00306 and 1-R01-HD13234.

² Postdoctoral trainee supported in part by NIH Training Grant 1-T32-HD-07190. To whom requests for reprints should be addressed, at Department of Obstetrics and Gynecology, The University of Texas Southwestern Medical School, 5323 Harry Hines Boulevard, Dallas, Texas 75235.

Received 7/16/80. Accepted 11/ 3/80.