Regulation of retinol uptake and esterification in MCF-7 and HepG2 cells by exogenous fatty acids.
The influence of extracellular fatty acids on the uptake and esterification of [3H]retinol bound to human retinol-binding protein (RBP), to RBP-transthyretin (TTR), or in dispersed form by the human hepatoma, HepG2, and human mammary epithelial carcinoma, MCF-7, cell lines was studied. The esterification of [3H]retinol was significantly increased in cells incubated with myristic, palmitic, stearic oleic, or linoleic acid-albumin complexes and was observed for all forms of [3H]retinol. Enhancement of [3H]retinol uptake was also observed in cells incubated with these fatty acids, but this increase was relatively small for the dispersed form as compared to that observed for [3H]retinol bound to RBP or RBP-TTR. Comparing equal concentrations of the [3H]retinol donors, cell uptake and esterification was greatest from the dispersed form and least from that bound to RBP-TTR. After preincubation of cells with oleate, uptake and esterification of [3H]retinol was increased but not to the extent observed when oleate and [3H]retinol donor were co-incubated. Incubation of cells with oleate resulted in rapid and correlated increases in the rates of [3H]retinol uptake and esterification which persisted until the steady state for [3H]retinol uptake was achieved. Beyond this time, net esterification of [3H]retinol continued in the presence of oleate. This kinetic pattern was observed for all [3H]retinol donors. These effects on [3H]retinol uptake and esterification were dose-dependent as the oleate to albumin ratio was varied from 0.5 to 3.0 and were observed across a physiological concentration range of RBP-3H-retinol. The data indicate that: 1) the fatty acid status of cells is a determinant of retinol uptake and esterification; and 2) the form of retinol presentation to cells is not qualitatively important for these processes.
Randolph
R K
RK
Department of Physiology and Biochemistry, Medical College of Pennsylvania, Philadelphia 19129.
Ross
A C
AC
D000818:Animals; D001693:Biological Transport, Active; D001943:Breast Neoplasms; D006528:Carcinoma, Hepatocellular; D004951:Esterification; D005227:Fatty Acids / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008113:Liver Neoplasms; D008892:Milk / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014801:Vitamin A / Q000378:metabolism*
D005227:Fatty Acids; D012177:Retinol-Binding Proteins; D014801:Vitamin A