Inhibitors of Translation Induce Low Density Lipoprotein Receptor Gene Expression in Human Skin Fibroblasts

The effect of protein synthesis inhibitors on low density lipoprotein (LDL) receptor gene expression was examined in human skin fibroblasts. Incubations in cycloheximide led to a marked increase in LDL receptor mRNA abundance as detected by Northern or slot-blot hybridization analyses. Incubation in puromycin had a similar effect. After the addition of cycloheximide, induction of LDL receptor mRNA levels was rapid (peaking between 2 and 3 h) and transient (falling to control levels by 24 h). This incubation could not be accounted for by the modest stabilization of mature LDL receptor mRNA species produced by cycloheximide and was completely abolished by concurrent addition of actinomycin D. Nuclear run-off transcription assays demonstrated increased LDL receptor gene transcription after 20-min incubations in cycloheximide. Induction of LDL receptor mRNA by cycloheximide was partially resistant to sterol suppression and was at least additive with induction produced by growth activation of cells using platelet-derived growth factors. These results indicate that inhibition of protein synthesis leads to rapid stimulation of LDL receptor gene transcription by a mechanism which is partially resistant to sterol suppression. We further conclude that early stimulation of LDL receptor gene expression associated with growth-activation of quiescent cells is independent of new protein synthesis.