Abstract
The Rho GTPases are involved in actin cytoskeleton organization and signal transduction. They need polyisoprenylation for membrane association and activation. Lovastatin, a hydroxymethylglutaryl coenzyme A inhibitor, prevents isoprene synthesis and thereby lipid modification of the Rho protein carboxy terminus. Because lovastatin causes rounding up of cultured cells, we investigated whether the compound acts on the actin cytoskeleton through Rho proteins. Lovastatin treatment decreased F-actin content in a time- and concentration-dependent manner. G-actin content remained unchanged. In lovastatin-treated NIH 3T3 cells, the amount of Rho protein which was ADP-ribosylated by Clostridium botulinum exoenzyme C3 decreased in membranes and increased in the cytosol fraction. Cycloheximide prevented lovastatin-induced rounding up of cells. However, after microinjection or direct application of exoenzyme C3, cells treated with cycloheximide and lovastatin rounded up again. On the contrary, lovastatin-treated, round Swiss 3T3 cells reverted to a flat morphology when microinjected with dominant active RhoA (Val14RhoA). Escherichia coli cytotoxic necrotizing factor (CNF1) which activates Rho proteins caused flattening of round, lovastatin-treated NIH 3T3 cells. These results suggest that lovastatin affects the actin cytoskeleton through inactivation of Rho proteins.
Footnotes
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Send reprint requests to: Dr. K. Aktories, Institut für Pharmakologie und Toxikologie, Universität Freiburg, Hermann-Herder-Str. 5, D-79104 Freiburg, Germany.
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↵1 This work was supported by the Deutsche Forschungsgemeinschaft.
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↵2 Present address: Psychiatrische Klinik Rheinau, CH-8462 Rheinau, Switzerland.
- Abbreviations:
- CNF1 and 2
- Escherichia colicytotoxic necrotizing factor 1 and 2
- F-actin
- filamentous actin
- G-actin
- globular actin
- GTPase
- guanosine 5′-triphosphate hydrolase
- HMG-CoA
- hydroxymethylglutaryl coenzyme A
- MVA
- mevalonic acid
- NAD
- nicotinamide adenine dinucleotide
- NBD-phalloidin
- (7-nitrobenz-2-oxa-1,3-diazol-4-yl)phalloidin
- RhoGDI
- Rho guanosine nucleotide dissociation inhibitor
- SDS-PAGE
- sodium dodecyl sulfate-polyacrylamide gel electrophoresis
- S.E.M.
- standard error of the mean
- Received February 10, 1997.
- Accepted July 7, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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