Phosphorylated l-caldesmon is involved in disassembly of actin stress fibers and postmitotic spreading.
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.
Kordowska
Jolanta
J
Muscle and Motility Group, Boston Biomedical Research Institute, Watertown, MA 02472, USA.
Hetrick
Tracy
T
Adam
Leonard P
LP
Wang
C-L Albert
CL
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D002645:Chickens; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008938:Mitosis / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D051381:Rats; D022502:Stress Fibers / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D014357:Trypsin / Q000502:physiology
D000199:Actins; D002148:Calmodulin-Binding Proteins; D014357:Trypsin