Regulation of G-protein alpha i2 subunit expression by oxidized low-density lipoprotein.
Oxidized low-density lipoprotein (LDL) inhibits signalling pathways mediated by pertussis toxin-sensitive guanine nucleotide-binding proteins (Gi proteins). To determine whether this inhibition is due to altered G protein alpha i subunit expression, mRNA and protein levels of alpha i isoforms were assessed in bovine aortic endothelial cells treated with oxidized LDL (0-100 micrograms/ml, 0-72 h). Oxidized LDL did not affect the expression of alpha i3, but did cause time- and concentration-dependent decrease in alpha i2 mRNA and protein resulting in a 3.2- and 3.5-fold reduction, respectively, after 72 h. This decrease in alpha i2 coincided with a 86% decrease in alpha i2 GTPase activity. Nuclear run-off studies did not show any significant effect of oxidized LDL on alpha i2 or alpha i3 transcription. In the presence of actinomycin D, oxidized LDL shortened the t1/2 of alpha i2 mRNA from 16 h to 8 h which was attenuated by cycloheximide. In addition, pulse-chase labelling with [35S]methionine revealed that oxidized LDL reduced the t1/2 of alpha i2 protein from 27 to 14 h. Our results indicate that oxidized LDL can modulate receptor-Gi coupling by downregulating the expression of alpha i2, but not alpha i3. The mechanism involves both mRNA destabilization and protein degradation.
Liao
J K
JK
Cardiovascular Division, Brigham & Women's Hospital, Boston, Massachusetts, USA.
Clark
S L
SL
D000595:Amino Acid Sequence; D000818:Animals; D001011:Aorta / Q000166:cytology; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D005786:Gene Expression Regulation; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction
D008077:Lipoproteins, LDL; D012333:RNA, Messenger; D019204:GTP-Binding Proteins