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Isoprenoid requirement for intracellular transport and processing of murine leukemia virus envelope protein
1Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822.
Abstract:
Lovastatin blocks the biosynthesis of the isoprenoid precursor, mevalonate. When Friend murine erythroleukemia (MEL) cells are cultured in medium containing lovastatin, the precursor of murine leukemia virus envelope glycoprotein (gPr90env) fails to undergo proteolytic processing, which normally occurs in the Golgi complex. Consequently, newly synthesized envelope proteins are not incorporated into viral particles that are shed into the culture medium. gPr90env appears to be localized in a pre-Golgi membrane compartment, based on its enrichment in subcellular fractions containing NADPH-cytochrome c reductase activity and the sensitivity of its carbohydrate chains to digestion with endoglycosidase H. Arrest of gPr90env processing occurs at concentrations of lovastatin that are not cytostatic, and the effect of the inhibitor is prevented by addition of mevalonate to the medium. The low molecular mass GTP-binding proteins, rab1p and rab6p, which are believed to function in early steps of the exocytic pathway, are normally modified posttranslationally by geranylgeranyl isoprenoids. However, in MEL cells treated with 1 microM lovastatin, nonisoprenylated forms of these proteins accumulate in the cytosol prior to arrest of gPr90env processing. These observations suggest that lovastatin may prevent viral envelope precursors from reaching the Golgi compartment by blocking the isoprenylation of rab proteins required for ER to Golgi transport.
Insights
Lovastatin inhibits viral glycoprotein processing in Friend murine erythroleukemia cells by blocking mevalonate synthesis. This prevents viral envelope proteins from reaching the Golgi, impacting viral particle formation.
Area of Science:
- Cell Biology
- Virology
- Biochemistry
Background:
- Lovastatin inhibits mevalonate biosynthesis, a key pathway for isoprenoid precursor production.
- Viral envelope glycoproteins undergo essential post-translational modifications in the Golgi complex.
- Rab proteins are crucial for intracellular transport, including ER to Golgi trafficking.
Purpose of the Study:
- To investigate the effect of lovastatin on viral envelope glycoprotein processing in Friend murine erythroleukemia (MEL) cells.
- To determine the mechanism by which lovastatin disrupts viral protein transport.
- To explore the role of isoprenylation in the exocytic pathway.
Main Methods:
- Culturing MEL cells in medium containing lovastatin.
- Analyzing the proteolytic processing and localization of murine leukemia virus envelope glycoprotein (gPr90env).
- Assessing the post-translational modification of rab1p and rab6p using subcellular fractionation and enzymatic digestion.
Main Results:
- Lovastatin treatment arrested gPr90env processing and prevented its incorporation into viral particles.
- gPr90env accumulated in a pre-Golgi compartment, indicated by its association with NADPH-cytochrome c reductase and sensitivity to endoglycosidase H.
- Non-isoprenylated forms of rab1p and rab6p accumulated in the cytosol of lovastatin-treated cells.
- The inhibitory effect of lovastatin was reversible by mevalonate addition.
Conclusions:
- Lovastatin disrupts viral envelope glycoprotein transport to the Golgi complex in MEL cells.
- The findings suggest that lovastatin-induced blockade of rab protein isoprenylation impairs ER to Golgi transport.
- This mechanism highlights the critical role of isoprenoids in viral protein maturation and exocytic pathway function.