Expression of a 24 kDa GTP-binding protein (Gn24) is increased in lovastatin treated human erythroleukemia cells.
A major 27 kDa particulate and a minor 24 kDa cytosolic GTP-binding protein was detected in HEL cells upon incubation with [alpha-32P]GTP of nitrocellulose blots containing polypeptides separated using SDS-PAGE. Addition of lovastatin (30 microM) to HEL cells in culture inhibited protein synthesis by approximately 35%. However, this treatment resulted in a 5-fold increase, as quantitated by [alpha-32P]GTP binding, in the amount of cytosolic 24 kDa GTP-binding protein. Addition of cycloheximide plus lovastatin to cells in culture abolished the observed increase in 24 kDa GTP-binding protein. Incubation of cells with lovastatin plus [R,S]-[5-(3)H] mevalonolactone resulted in the incorporation of radioactivity into several polypeptides in both the cytosolic and particulate fractions including a polypeptide of molecular mass of 24 kDa in the cytosol. The mobility of this 24 kDa isoprenylated protein on SDS-PAGE was identical to that of the GTP-binding protein increased in response to lovastatin. However, the 24 kDa protein remained in the cytosol after undergoing isoprenylation. The 24 kDa protein was distinct from the HEL cell, G25K/CDC42Hs GTP-binding protein and the GTP-binding protein that was a substrate for botulinum toxin C3 catalyzed ADP-ribosylation. Results demonstrate that lovastatin specifically increases the expression of a 24 kDa GTP-binding protein in HEL cells and that, isoprenylation of low molecular mass GTP-binding protein(s) may have function(s) in addition to its role in the targetting of these proteins to cell membrane.
Bhullar
R P
RP
Department of Oral Biology, University of Manitoba, Winnipeg, Canada.
D036002:ADP Ribose Transferases / Q000378:metabolism; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D001905:Botulinum Toxins; D003513:Cycloheximide / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects*; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism / Q000473:pathology*; D008148:Lovastatin / Q000494:pharmacology*; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D017368:Protein Prenylation; D011499:Protein Processing, Post-Translational; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000924:Anticholesteremic Agents; D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D009363:Neoplasm Proteins; D011500:Protein Synthesis Inhibitors; D003513:Cycloheximide; D008148:Lovastatin; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins