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Tropomyosin variants describe distinct functional subcellular domains in differentiated vascular smooth muscle cells.

ABSTRACT: Tropomyosin (Tm) is known to be an important gatekeeper of actin function. Tm isoforms are encoded by four genes, and each gene produces several variants by alternative splicing, which have been proposed to play roles in motility, proliferation, and apoptosis. Smooth muscle studies have focused on gizzard smooth muscle, where a heterodimer of Tm from the ?-gene (Tmsm-?) and from the ?-gene (Tmsm-?) is associated with contractile filaments. In this study we examined Tm in differentiated mammalian vascular smooth muscle (dVSM). Liquid chromatography-tandem mass spectrometry (LC MS/MS) analysis and Western blot screening with variant-specific antibodies revealed that at least five different Tm proteins are expressed in this tissue: Tm6 (Tmsm-?) and Tm2 from the ?-gene, Tm1 (Tmsm-?) from the ?-gene, Tm5NM1 from the ?-gene, and Tm4 from the ?-gene. Tm6 is by far most abundant in dVSM followed by Tm1, Tm2, Tm5NM1, and Tm4. Coimmunoprecipitation and coimmunofluorescence studies demonstrate that Tm1 and Tm6 coassociate with different actin isoforms and display different intracellular localizations. Using an antibody specific for cytoplasmic ?-actin, we report here the presence of a ?-actin cortical cytoskeleton in dVSM cells. Tm1 colocalizes with cortical cytoplasmic ?-actin and coprecipitates with ?-actin. Tm6, on the other hand, is located on contractile bundles. These data indicate that Tm1 and Tm6 do not form a classical heterodimer in dVSM but rather describe different functional cellular compartments.

SUBMITTER: Gallant C

PROVIDER: S-EPMC3118631 | biostudies-literature | 2011 Jun

REPOSITORIES: biostudies-literature

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Tropomyosin variants describe distinct functional subcellular domains in differentiated vascular smooth muscle cells.

Gallant Cynthia C Appel Sarah S Graceffa Philip P Leavis Paul P Lin Jim Jung-Ching JJ Gunning Peter W PW Schevzov Galina G Chaponnier Christine C DeGnore Jon J Lehman William W Morgan Kathleen G KG

American journal of physiology. Cell physiology 20110202 6

Tropomyosin (Tm) is known to be an important gatekeeper of actin function. Tm isoforms are encoded by four genes, and each gene produces several variants by alternative splicing, which have been proposed to play roles in motility, proliferation, and apoptosis. Smooth muscle studies have focused on gizzard smooth muscle, where a heterodimer of Tm from the α-gene (Tmsm-α) and from the β-gene (Tmsm-β) is associated with contractile filaments. In this study we examined Tm in differentiated mammalian ...[more]

PMID: 21289288

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Project description:BackgroundGenome-wide association studies have identified many genetic loci that are robustly associated with coronary artery disease (CAD). However, the underlying biological mechanisms are still unknown for most of these loci, hindering the progress to medical translation. Evidence suggests that the genetic influence on CAD susceptibility may act partly through vascular smooth muscle cells (VSMCs).MethodsWe undertook genotyping, RNA sequencing, and cell behavior assays on a large bank of VSMCs (n>1499). Expression quantitative trait locus and splicing quantitative trait locus analyses were performed to identify genes with an expression that was influenced by CAD-associated variants. To identify candidate causal genes for CAD, we ascertained colocalizations of VSMC expression quantitative trait locus signals with CAD association signals by performing causal variants identification in associated regions analysis and the summary data-based mendelian randomization test. Druggability analysis was then performed on the candidate causal genes. CAD risk variants were tested for associations with VSMC proliferation, migration, and apoptosis. Collective effects of multiple CAD-associated variants on VSMC behavior were estimated by polygenic scores.ResultsApproximately 60% of the known CAD-associated variants showed statistically significant expression quantitative trait locus or splicing quantitative trait locus effects in VSMCs. Colocalization analyses identified 84 genes with expression quantitative trait locus signals that significantly colocalized with CAD association signals, identifying them as candidate causal genes. Druggability analysis indicated that 38 of the candidate causal genes were druggable, and 13 had evidence of drug-gene interactions. Of the CAD-associated variants tested, 139 showed suggestive associations with VSMC proliferation, migration, or apoptosis. A polygenic score model explained up to 5.94% of variation in several VSMC behavior parameters, consistent with polygenic influences on VSMC behavior.ConclusionsThis comprehensive analysis shows that a large percentage of CAD loci can modulate gene expression in VSMCs and influence VSMC behavior. Several candidate causal genes identified are likely to be druggable and thus represent potential therapeutic targets.

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Tropomyosin variants describe distinct functional subcellular domains in differentiated vascular smooth muscle cells.

Publications

Tropomyosin variants describe distinct functional subcellular domains in differentiated vascular smooth muscle cells.

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