Impaired regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase degradation in lovastatin-resistant cells.
L-90 cells were selected to grow in the presence of serum lipoproteins and 90 microM lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR). L-90 cells massively accumulate HMGR, a result of >10-fold amplification of the gene and 40-fold rise in mRNA, and also overexpress other enzymes of the mevalonate pathway. Western blot and promoter-luciferase analyses indicate that transcriptional regulation of sterol-responsive genes by 25-hydroxycholesterol or mevalonate is normal. Yet, none of these genes is regulated by lipoproteins, a result of severe impairment in the low density lipoprotein receptor pathway. Moreover, L-90 cells do not accelerate the degradation of HMGR or transfected HMGal chimera in response to 25-hydroxycholesterol or mevalonate. This aberrant phenotype persists when cells are grown without lovastatin for up to 37 days. The inability to regulate HMGR degradation is not due to its overproduction since in LP-90 cells, which were selected for lovastatin resistance in lipoprotein-deficient serum, HMGR is overexpressed, yet its turnover is regulated normally. Also, the rapid degradation of transfected alpha subunit of T cell receptor is markedly retarded in L-90 cells. These results show that in addition to gene amplification and overexpression of cholesterogenic enzymes, statin resistance can follow loss of regulated HMGR degradation.
Ravid
T
T
Department of Clinical Biochemistry, Sackler School of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel.
Avner
R
R
Polak-Charcon
S
S
Faust
J R
JR
Roitelman
J
J
D000818:Animals; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D006224:Cricetinae; D004351:Drug Resistance; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D017930:Genes, Reporter; D006888:Hydroxycholesterols / Q000494:pharmacology; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D008055:Lipids / Q000096:biosynthesis; D008074:Lipoproteins / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000378:metabolism; D008148:Lovastatin / Q000494:pharmacology*; D008798:Mevalonic Acid / Q000494:pharmacology; D008854:Microscopy, Electron; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000187:drug effects; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection
D006888:Hydroxycholesterols; D008055:Lipids; D008074:Lipoproteins; D008077:Lipoproteins, LDL; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D011993:Recombinant Fusion Proteins; C007997:25-hydroxycholesterol; D008148:Lovastatin; D006903:Hydroxymethylglutaryl CoA Reductases; D008798:Mevalonic Acid