STEROL-METABOLISM AND ORAL EPITHELIAL-CELL GROWTH

Previous studies have demonstrated that as the density of cultured ora l epithelial cells increases, there is a concomitant increase in phosp holipids and cholesterol ester synthesis and a decrease in that of cho lesterol and sterol precursors. Other studies have suggested that the effects of exogenous cholesterol sulfate may be similar to growth resp onses and influence metabolic steps related to cell density. To furthe r examine this possibility, in the present study lipid synthesis was m onitored in hamster cheek pouch epithelial cells in cultures establish ed at different cells densities and in the presence of varying amounts of exogenous cholesterol sulfate. Cell [C-14]acetate incorporation in to lipids was measured in cultures established at four densities rangi ng from very subconfluent to very dense (postconfluent) in two media, Dulbecco's modified Eagle's medium (DMEM) with 5% fetal bovine serum a nd KSFM, a non-serum containing keratinocyte medium. Results indicated that the relative proportion of radiolabel incorporated into differen t lipid classes changed with cell density. In DMEM, the percentage of radiolabel incorporated into total phospholipids and fatty acids incre ased significantly with increasing cell density whereas percent incorp oration into cholesterol, sterol precursors, and cholesterol esters si gnificantly decreased. In KSFM cultures, proportionate phospholipids l abeling was significantly increased in more dense cultures whereas cho lesterol and cholesterol esters labeling was significantly decreased. In subconfluent and confluent cultures exposed to 10 or 25 muM cholest erol sulfate, the relative proportions of phospholipid labeling also i ncreased significantly compared to dimethyl sulfoxide (solvent) contro ls, whereas sterol precursors, fatty acids, and cholesterol esters lab eling was significantly decreased. These results indicate that cholest erol sulfate can affect cellular lipid synthesis in a manner similar t o that which occurs with increasing cell density, and strengthen the h ypothesis that cholesterol sulfate may regulate lipid metabolic pathwa ys related to growth and differentiation.