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Prenylation of Rho G-Proteins: a Novel Mechanism Regulating Gene Expression and Protein Stability in Human Trabecular Meshwork Cells

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Abstract

Endogenous prenylation with sesquiterpene or diterpene isoprenoids facilitates membrane localization and functional activation of small monomeric GTP-binding proteins. A direct effect of isoprenoids on regulation of gene expression and protein stability has also been proposed. In this study, we determined the role of sesquiterpene or diterpene isoprenoids on the regulation of Rho G-protein expression, activation, and stability in human trabecular meshwork (TM) cells. In both primary and transformed human TM cells, limiting endogenous isoprenoid synthesis with lovastatin, a potent HMG-CoA reductase inhibitor, elicited marked increases in RhoA and RhoB mRNA and protein content. The effect of lovastatin was dose-dependent with newly synthesized inactive protein accumulating in the cytosol. Supplementation with geranylgeranyl pyrophosphate (GGPP) prevented, while inhibition of geranylgeranyl transferase-I mimicked, the effects of lovastatin on RhoA and RhoB protein content. Similarly, lovastatin-dependent increases in RhoA and RhoB mRNA expression were mimicked by geranylgeranyl transferase-I inhibition. Interestingly, GGPP supplementation selectively promoted the degradation of newly synthesized Rho proteins which was mediated, in part, through the 20S proteasome. Functionally, GGPP supplementation prevented lovastatin-dependent decreases in actin stress fiber organization while selectively facilitating the subcellular redistribution of accumulated Rho proteins from the cytosol to the membrane and increasing RhoA activation. Post-translational prenylation with geranylgeranyl diterpenes selectively facilitates the expression, membrane translocation, functional activation, and turnover of newly synthesized Rho proteins. Geranylgeranyl prenylation represents a novel mechanism by which active Rho proteins are targeted to the 20S proteasome for degradation in human TM cells.

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Acknowledgments

This work was supported, in part, by grants from the Department of Veterans Affairs (C3638R and B3756-F (EBS), Pre-Doctoral Associated Health Rehabilitation Research Fellowship and C7506M (CVZ)), the Illinois Society for the Prevention of Blindness, the Midwest Eye Banks, and the Richard A. Peritt Charitable Foundation.

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Authors and Affiliations

  1. Research Service, Department of Veterans Affairs, Edward Hines Jr. VA Hospital, Hines, IL, 60141, USA

    Evan B. Stubbs Jr. & Cynthia L. Von Zee

  2. Department of Ophthalmology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL, 60153, USA

    Evan B. Stubbs Jr. & Cynthia L. Von Zee

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  1. Evan B. Stubbs Jr.
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  2. Cynthia L. Von Zee
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Correspondence to Evan B. Stubbs Jr..

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Stubbs, E.B., Von Zee, C.L. Prenylation of Rho G-Proteins: a Novel Mechanism Regulating Gene Expression and Protein Stability in Human Trabecular Meshwork Cells. Mol Neurobiol 46, 28–40 (2012). https://doi.org/10.1007/s12035-012-8249-x

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