Nonmuscle tropomyosin-4 requires coexpression with other low molecular weight isoforms for binding to thin filaments in cardiomyocytes

Helfman, D. M., Berthier, C., Grossman, J., Leu, M., Ehler, E., Perriard, E., Perriard, J. C. (February 1999) Nonmuscle tropomyosin-4 requires coexpression with other low molecular weight isoforms for binding to thin filaments in cardiomyocytes. Journal of Cell Science, 112 ( . pp. 371-80. ISSN 0021-9533 (Print)

URL: http://www.ncbi.nlm.nih.gov/pubmed/9885290

Abstract

Vertebrate tropomyosins (TMs) are expressed from four genes, and at least 18 distinct isoforms are generated via a complex pattern of alternative RNA splicing and alternative promoters. The functional significance of this isoform diversity is largely unknown and it remains to be determined whether specific isoforms are required for assembly and integration into distinct actin-containing structures. The ability of nonmuscle (TM-1, -2, -3, -4, -5(NM1), -5a or -5b) and striated muscle (skeletal muscle (&agr;)-TM) isoforms to incorporate into actin filaments of neonatal rat cardiomyocytes (NRCs) was studied using expression plasmids containing TM-fusions with GFP (green fluorescent protein) as well as with VSV- or HA-epitope tags. All isoforms, except of fibroblast TM-4, were able to incorporate into the I-band of NRCs. When TM-4 was co-transfected with other low molecular weight (LMW) isoforms of TM (TM-5, TM-5a and TM-5b), it was able to incorporate into sarcomeres of NRCs. This result was not obtained when TM-4 was co-transfected with high molecular weight (HMW) TMs (TM-1, TM-2 or skeletal muscle (&agr;)-TM). These data demonstrate that the ability of TM-4 to bind to actin filaments can be specifically influenced by its interaction with other LMW TM isoforms. In addition, cells that incorporated the muscle or nonmuscle GFP-TMs into their sarcomeres continued to beat and exhibited sarcomeric contraction. These studies provide the first in vivo demonstration of synergistic effects between TM isoforms for binding to actin filaments. These results have important implications in understanding actin filament dynamics in nonmuscle cell systems, especially during development and in transformed cells, where alterations in the ratio of different LMW isoforms might lead to changes in their interactions with actin filaments. Furthermore, these studies demonstrate that GFP-TM can be used to study thin-filament dynamics in muscle cells and actin filament dynamics in nonmuscle cells.

Item Type: Paper
Uncontrolled Keywords: Actins/metabolism Animals Cells, Cultured Fibroblasts/metabolism Muscle, Skeletal/metabolism Myocardium/ metabolism Protein Binding Protein Isoforms/metabolism Rats Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, P.H.S. Tropomyosin/analysis/ metabolism
Subjects: bioinformatics > genomics and proteomics > genetics & nucleic acid processing > protein structure, function, modification > protein types > actin
Investigative techniques and equipment > cell culture
organs, tissues, organelles, cell types and functions > cell types and functions > cell types > fibroblasts
organs, tissues, organelles, cell types and functions > cell types and functions > cell types > fibroblasts
organs, tissues, organelles, cell types and functions > cell types and functions > cell types > fibroblasts

bioinformatics > genomics and proteomics > genetics & nucleic acid processing > protein structure, function, modification > protein types
CSHL Authors:
Communities: CSHL labs > Helfman lab
Depositing User: Kathleen Darby
Date: February 1999
Date Deposited: 30 Apr 2014 15:23
Last Modified: 05 May 2014 16:58
Related URLs:
URI: http://repository.cshl.edu/id/eprint/29788

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