Regulation of lipoprotein receptors on a rat hepatoma cell line

The rat H-35 cultured hepatoma cell line expresses receptors for homologous lipoproteins. In previously reported experiments distinct receptors were identified for chylomicron remnants, HDL and LDL, by direct binding studies that yielded distinctive binding constants, cross competition assays, and by differential inhibitory effects of EDTA and suramin. In the present experiments, the regulation of expression of these receptors was assessed by growing cells either in the presence or absence of lipoproteins in the media and by growing cells to different densities (50-800 micrograms cell protein/dish). LDL binding to cells was increased by lipoprotein deprivation at all cell densities. LDL binding was inversely related to cell density when cells were grown in lipoprotein deficient serum (LPDS) but cell density did not affect LDL binding by cells grown in newborn calf serum (NBCS). By contrast HDL binding was not appreciably different whether cells were grown in NBCS or in LPDS. However, HDL binding was inversely related to cell density by cells grown either in LPDS or in NBCS. Binding of chylomicron remnants was increased by growth in LPDS at all densities, but altering growth density in either culture medium had little effect on the cellular binding of chylomicron remnants. The distinctive effects of these experimental perturbations on the binding of the 3 lipoprotein classes tend to confirm the presence of 3 separate receptor activities. The experiments also demonstrate that the responses at least of some of the receptors of the hepatoma cells in culture resemble those of hepatocytes in vivo and in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)