Control of cardiac myofilament activation and PKC-betaII signaling through the actin capping protein, CapZ |
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Authors: | Pyle W Glen La Rotta Gustavo de Tombe Pieter P Sumandea Marius P Solaro R John |
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Institution: | Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada N1G 2W1. gpyle@uoguelph.ca |
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Abstract: | Actin capping protein (CapZ) anchors the barbed ends of sarcomeric actin to the Z-disc. Myofilaments from transgenic mice (TG-CapZ) expressing a reduced amount of CapZ demonstrate altered function and protein kinase C (PKC) signaling Pyle WG, Hart MC, Cooper JA, Sumandea MP, de Tombe PP, and Solaro RJ., Circ. Res. 90 (2002) 1299-306]. The aims of the current study were to determine the direct effects of CapZ on myofilament function and on PKC signaling to the myofilaments. Our studies compared mechanical properties of single myocytes from TG-CapZ mouse hearts to wild-type myocytes from which CapZ was extracted using PIP(2). We found that myofilaments from CapZ-deficient transgenic myocardium exhibited increased Ca(2+) sensitivity and maximum isometric tension. The extraction of CapZ from wild-type myofilaments replicated the increase in maximum isometric tension, but had no effect on myofilament Ca(2+) sensitivity. Immunoblot analysis revealed that the extraction of CapZ was associated with a reduction in myofilament-associated PKC-beta(II) and that CapZ-deficient transgenic myofilaments also lacked PKC-beta(II). Treatment of wild-type myofilaments with recombinant PKC-beta(II) reduced myofilament Ca(2+) sensitivity, whereas this effect was attenuated in myofilaments from TG-CapZ mice. Our results indicate that cardiac CapZ directly controls maximum isometric tension generation, and establish CapZ as an important component in anchoring PKC-beta(II) at the myofilaments, and for mediating the effects of PKC-beta(II) on myofilament function. |
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Keywords: | CapZ actin capping protein PIP2 l-α-phosphatidylinositol-4" target="_blank">l-α-phosphatidylinositol-4 5-bisphosphate PKC protein kinase C EGTA ethylene glycol-bis(2-aminoethylether)-N N N′ N′-tetraacetic acid MOPS 3-morpholinopropanesulfonic acid PMSF phenylmethyl-sulfonyl fluoride SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis TG transgenic C-protein myosin binding C-protein Fmax isometric tension at maximally activating Ca2+ EC50 Ca2+ concentration required to generate 50% of maximum isometric tension |
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