Association of Calponin with Desmin Intermediate Filaments*
- From the ‡Muscle Research Group, Boston Biomedical Research Institute, Boston, Massachusetts 02114, ¶Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0521, and ‖Department of Neurology, Harvard Medical School, Boston, Massachusetts 02115 and Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts 02111
Abstract
Our previous immunoelectron microscopy studies of chicken gizzard smooth muscle cells showed that in certain areas the distribution of anti-calponin exhibits a high degree of overlap with β-actin, filamin, and in particular, desmin, suggesting that in situ a fraction of calponin may be associated with intermediate filaments of the cytoskeleton. In this work we further explore this idea by studying the interaction between calponin and desmin. We found that at physiological salt concentrations, calponin bound only weakly to synthetic desmin intermediate filaments. On the other hand, calponin bound strongly to nonfilamentous desmin tetramers and was incorporated into intermediate filaments when the two proteins were mixed in a buffer containing 6 m urea and dialyzed into a buffer containing 0.15 m NaCl. Anti-calponin was found to label a portion of intermediate filaments and dense bodies isolated from gizzard tissues. Our findings suggest that in chicken gizzard smooth muscle cells, calponin may be an integral component of desmin intermediate filaments in the vicinity of dense bodies. Since calponin is also known to bind actin, we hypothesize that one of the functions of calponin might be to bridge intermediate filaments with actin in dense bodies.
Footnotes
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↵* This work was supported by National Institutes of Health Grant P01-AR41637.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Boston Biomedical Research Institute, 20 Staniford St., Boston, MA 02114. Tel.: 617-742-2010; Fax: 617-523-6649; E-mail:mabuchi{at}bbri.harvard.edu.
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↵1 The abbreviations used are: CP, calponin; CaD, caldesmin; DTT, dithiothreitol; IEM, immunoelectron microscopy; IF, intermediate filament; PAGE, polyacrylamide gel electrophoresis; SMC, smooth muscle cells; Tm, tropomyosin.
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- Received January 30, 1997.
- Revision received June 24, 1997.
