title: Regulation of microfilament organization by Kaposi sarcoma-associated herpes virus-cyclin.CDK6 phosphorylation of caldesmon.
abstract: Kaposi sarcoma-associated herpes virus (KSHV) encodes a D-like cyclin (K-cyclin) that is thought to contribute to the viral oncogenicity. K-cyclin activates cellular cyclin-dependent kinases (CDK) 4 and 6, generating enzymes with a substrate selectivity deviant from CDK4 and CDK6 activated by D-type cyclins, suggesting different biochemical and biological functions. Here we report the identification of the actin- and calmodulin-binding protein caldesmon (CALD1) as a novel K-cyclin.CDK substrate, which is not phosphorylated by D.CDK. CALD1 plays a central role in the regulation of microfilament organization, consequently controlling cell shape, adhesion, cytokinesis and motility. K-cyclin.CDK6 specifically phosphorylates four Ser/Thr sites in the human CALD1 carboxyl terminus, abolishing CALD1 binding to its effector protein, actin, and its regulator protein, calmodulin. CALD1 is hyperphosphorylated in cells following K-cyclin expression and in KSHV-transformed lymphoma cells. Moreover, expression of exogenous K-cyclin results in microfilament loss and changes in cell morphology; both effects are reliant on CDK catalysis and can be reversed by the expression of a phosphorylation defective CALD1. Together, these data strongly suggest that K-cyclin expression modulates the activity of caldesmon and through this the microfilament functions in cells. These results establish a novel link between KSHV infection and the regulation of the actin cytoskeleton.
authors.affiliation: Cancer Research UK Centre for Cell and Molecular Biology, Chester Beatty Laboratories, The Institute of Cancer Research, 237 Fulham Road, SW3 6JB London, United Kingdom.
authors.forename: Maria Emanuela
authors.initials: ME
authors.lastname: Cuomo
authors.forename: Axel
authors.initials: A
authors.lastname: Knebel
authors.forename: Georgina
authors.initials: G
authors.lastname: Platt
authors.forename: Nick
authors.initials: N
authors.lastname: Morrice
authors.forename: Philip
authors.initials: P
authors.lastname: Cohen
authors.forename: Sibylle
authors.initials: S
authors.lastname: Mittnacht
mesh_terms: D000199:Actins / Q000737:chemistry; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D015967:Gene Expression Regulation, Viral; D006367:HeLa Cells; D019288:Herpesvirus 8, Human / Q000378:metabolism*; D006801:Humans; D013058:Mass Spectrometry; D051379:Mice; D008856:Microscopy, Fluorescence; D041681:NIH 3T3 Cells; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D016160:Retinoblastoma Protein / Q000378:metabolism; D012685:Sepharose / Q000737:chemistry; D012694:Serine / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013379:Substrate Specificity; D013912:Threonine / Q000737:chemistry; D013997:Time Factors
chemical_list: D000199:Actins; D002148:Calmodulin-Binding Proteins; D010455:Peptides; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D013912:Threonine; D012694:Serine; D012685:Sepharose; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6