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.