Regulation of caldesmon activity by Cdc2 kinase plays an important role in maintaining membrane cortex integrity during cell division.
To study the mitosis-specific phosphorylation of caldesmon (CaD), we generated a mutant of the C-terminal fragment (amino acids 244-538) of human fibroblast CaD (CaD39-6F), as well as a mutant of the full-length CaD (CaD-6F), in which all six potential phosphorylation sites for Cdc2 kinase were abolished. The mitotic CaD39-6F-overexpressing cells required more time to progress from anaphase start to 50% cytokinesis, exhibited larger size, and abnormally formed numerous small blebs. In contrast, overexpression of the wild-type C-terminal fragment of CaD (CaD39) did not result in abnormal bleb formation, but led to larger size and prolonged the time requirement between anaphase start and 50% cytokinesis. Similar abnormal blebs were also observed in the CaD-6F-overexpressing cells. CaD-6F-overexpressing cells did not show larger size but required more time to progress from anaphase start to 50% cytokinesis. These results suggest that mitosis-specific phosphorylation of CaD plays a role in inhibiting bleb formation and that the N-terminal fragment of CaD is required for cell size determination.
Li
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Department of Biological Sciences, University of Iowa, 138 Biology Building, Iowa City, Iowa 52242-1324, USA.
Wessels
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Wang
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Lin
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Soll
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Lin
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D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D016466:CHO Cells; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D002462:Cell Membrane / Q000502:physiology*; D048429:Cell Size; D006224:Cricetinae; D005347:Fibroblasts; D015870:Gene Expression; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017354:Point Mutation; D013997:Time Factors; D014335:Tropomyosin / Q000032:analysis / Q000302:isolation & purification
D000199:Actins; D002148:Calmodulin-Binding Proteins; D014335:Tropomyosin; D016203:CDC2 Protein Kinase