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Inhibition of cell growth by lovastatin is independent of ras function
J E DeClue1, W C Vass, A G Papageorge
1Laboratory of Cellular Oncology, National Cancer Institute, Bethesda, Maryland 20892.
Abstract:
We have investigated the inhibition of cell growth by lovastatin (previously known as mevinolin), an antagonist of hydroxymethylglutaryl coenzyme A reductase which blocks the processing and membrane localization of ras proteins via inhibition of polyisoprenylation. A series of NIH 3T3 cells transformed by oncogenes with activities that are dependent or independent of isoprenylated ras were studied, including cells transformed by myristylated ras protein that is isoprenylation independent. Treatment with lovastatin at concentrations ranging from 5 to 15 microM for up to 96 h resulted in a time- and dose-dependent inhibition of cell growth in all lines tested. The inhibition ranged from 25 to 50% when cells were treated with 5 microM lovastatin for 48 h, to 72-90% for cells treated with 15 microM lovastatin for 96 h. Cells transformed by c-ras, v-ras, v-src, v-raf, and the myristylated ras genes displayed similar sensitivities; the parental NIH 3T3 line was the most resistant of the lines tested. Metabolic labeling of control and lovastatin-treated cells with [35S]methionine or tritiated lipids revealed that 15 microM lovastatin blocked the processing of both endogenous ras and v-ras proteins yet had no effect on the lipidation of myristylated ras proteins. Addition of 300 microM mevalonic acid overcame the inhibition induced by 15 microM lovastatin. Thus the inhibition of cell growth in vitro by lovastatin did not show specificity for cells the transformation of which is dependent upon isoprenylated ras protein. It is therefore likely that the inhibition of other pathways affected by lovastatin, such as cholesterol biosynthesis or the processing of other cellular proteins, are responsible for the growth inhibition by lovastatin.
Insights
Lovastatin inhibits cell growth by blocking ras protein processing, but this effect isn't specific to ras-dependent cells. Other pathways, like cholesterol synthesis, likely contribute to lovastatin's growth inhibition.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Lovastatin (mevinolin) inhibits HMG-CoA reductase, impacting polyisoprenylation and ras protein localization.
- Ras proteins are crucial in cell signaling, and their proper function depends on post-translational modification like isoprenylation.
Purpose of the Study:
- To investigate the effect of lovastatin on the cell growth of NIH 3T3 cells transformed by various oncogenes.
- To determine if lovastatin's growth inhibition is specific to cells dependent on isoprenylated ras proteins.
Main Methods:
- Treatment of NIH 3T3 cell lines (transformed by c-ras, v-ras, v-src, v-raf, myristylated ras) with lovastatin (5-15 microM) for up to 96 hours.
- Metabolic labeling with [35S]methionine and tritiated lipids to assess protein processing and lipidation.
- Addition of mevalonic acid to evaluate its effect on lovastatin-induced growth inhibition.
Main Results:
- Lovastatin caused a time- and dose-dependent inhibition of cell growth across all tested cell lines (25-90% inhibition).
- Lovastatin blocked the processing of endogenous and v-ras proteins but not myristylated ras proteins.
- Mevalonic acid addition reversed the growth inhibition caused by lovastatin.
Conclusions:
- Lovastatin's inhibition of cell growth is not specific to cells reliant on isoprenylated ras proteins.
- The growth-inhibitory effects of lovastatin may be due to its impact on other cellular pathways, including cholesterol biosynthesis or the processing of other proteins.