Regulation of low-density-lipoprotein-receptor mRNA by insulin in human hepatoma Hep G2 cells

Abstract

The low-density-lipoprotein (LDL)-receptor mRNA content of human hepatoma (Hep G2) cells has been estimated from densitometric scans of autoradiograms obtained following the hybridisation of Northern blots of a poly(A)-rich RNA fraction with a 32P-labelled cDNA probe for the LDL-receptor gene. The recovery of beta-actin mRNA was used to correct for losses occurring during the preparation of the poly(A)-rich RNA. The content of LDL-receptor mRNA was reduced when the cells were pre-incubated in medium containing foetal calf serum, 25-hydroxycholesterol, or LDL, compared to that measured in cells which had been pre-incubated in medium containing lipoprotein-deficient serum (LPDS). When insulin (100 mU/ml) was included in pre-incubation medium containing LPDS, the amount of LDL-receptor mRNA increased approximately twofold. The level of beta-actin mRNA was not significantly increased by insulin treatment. Addition of insulin to incubation medium containing LPDS also overcame the suppressive effect of exogenous LDL on the cellular content of mRNA for the LDL receptor. These findings suggest that one action of insulin in these cells may be to promote transcription of the LDL-receptor gene by a mechanism that can override the sterol regulatory pathway.