Phosphorylated l-caldesmon is involved in disassembly of actin stress fibers and postmitotic spreading

• Published in: Experimental cell research 2006-01, Vol.312 (2), p.95-110
• Main Authors: Kordowska, Jolanta, Hetrick, Tracy, Adam, Leonard P., Albert Wang, C.-L.
• Format: Article
• Language: English
• Subjects: Actin; Actins - metabolism; Animals; Caldesmon; Calmodulin-Binding Proteins - genetics; Calmodulin-Binding Proteins - metabolism; Calmodulin-Binding Proteins - physiology; Cell Cycle - physiology; Cell Movement - physiology; Cells, Cultured; Chickens; Fibroblasts - cytology; Fibroblasts - metabolism; Focal adhesion; Gene Expression Regulation; Humans; Mitosis; Mitosis - physiology; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - metabolism; Mutation; Phosphorylation; Rats; Stress Fibers - metabolism; Stress Fibers - physiology; Time Factors; Trypsin - physiology
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1016/j.yexcr.2005.09.021

The function of the ubiquitous actin-binding protein, caldesmon (l-CaD) in mammalian non-muscle cells remains elusive. During mitosis, l-CaD becomes markedly phosphorylated at Ser497 and Ser527 (in the rat sequence), therefore, it has been suggested that l-CaD is involved in cytokinesis by inhibiting the actomyosin interaction until it is phosphorylated, although direct in vivo evidence is still missing. In the present study, we used F-actin staining and specific antibodies against these two phosphorylation sites of l-CaD to simultaneously monitor actin assembly and l-CaD phosphorylation. Our observations demonstrated that the level of l-CaD phosphorylation undergoes dynamic changes during the cell cycle. The spatial and temporal distributions of phospho-CaD do not correlate with cytokinesis per se, but rather, with the level of actin bundles in a reciprocal manner. The highest l-CaD phosphorylation level coincides with the disassembly of actin cytoskeleton during mitotic cell rounding. Ser-to-Ala mutations at these two positions prevent stress fibers from disassembly upon migratory stimulation. In addition, phospho-CaD appears to colocalize with nascent focal adhesion complexes during postmitotic spreading. These findings suggest that l-CaD phosphorylation plays an important role not only in cytoskeleton remodeling during cell shape changes, but also in cell spreading and migration.