| Autor: |
Valencia DA; Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, 90095., Koeberlein AN; Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, 90095., Nakano H; Department of Molecular, Cell, and Developmental Biology, University of California Los Angeles, Los Angeles, California, 90095.; Eli & Edythe Broad Center of Regenerative Medicine & Stem Cell Research, University of California Los Angeles, Los Angeles, California, 90095., Rudas A; Department of Computational Medicine, University of California Los Angeles, Los Angeles, California, 90095., Harui A; Divison of Pulmonary & Critical Care Medicine, Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, 90095., Spencer C; Department of Molecular, Cell, and Developmental Biology, University of California Los Angeles, Los Angeles, California, 90095., Nakano A; Department of Molecular, Cell, and Developmental Biology, University of California Los Angeles, Los Angeles, California, 90095.; Eli & Edythe Broad Center of Regenerative Medicine & Stem Cell Research, University of California Los Angeles, Los Angeles, California, 90095.; Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, 90095., Quinlan ME; Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, 90095.; Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, 90095. |
| Abstrakt: |
Contractility and cell motility depend on accurately controlled assembly of the actin cytoskeleton. Formins are a large group of actin assembly proteins that nucleate new actin filaments and act as elongation factors. Some formins may cap filaments, instead of elongating them, and others are known to sever or bundle filaments. The Formin HOmology Domain-containing protein (FHOD)-family of formins is critical to the formation of the fundamental contractile unit in muscle, the sarcomere. Specifically, mammalian FHOD3L plays an essential role in cardiomyocytes. Despite our knowledge of FHOD3L's importance in cardiomyocytes, its biochemical and cellular activities remain poorly understood. It has been proposed that FHOD-family formins act by capping and bundling, as opposed to assembling new filaments. Here, we demonstrate that FHOD3L nucleates actin and rapidly but briefly elongates filaments after temporarily pausing elongation, in vitro . We designed function-separating mutants that enabled us to distinguish which biochemical roles are reqùired in the cell. We found that human FHOD3L's elongation activity, but not its nucleation, capping, or bundling activity, is necessary for proper sarcomere formation and contractile function in neonatal rat ventricular myocytes. The results of this work provide new insight into the mechanisms by which formins build specific structures and will contribute to knowledge regarding how cardiomyopathies arise from defects in sarcomere formation and maintenance. |
