Myosin Va phosphorylated on Ser1650 is found in nuclear speckles and redistributes to nucleoli upon inhibition of transcription.
Nuclear actin and nuclear myosins have been implicated in the regulation of gene expression in vertebrate cells. Myosin V is a class of actin-based motor proteins involved in cytoplasmic vesicle transport and anchorage, spindle-pole alignment and mRNA translocation. In this study, myosin-Va, phosphorylated on a conserved serine in the tail domain (phospho-ser(1650) MVa), was localized to subnuclear compartments. A monoclonal antibody, 9E6, raised against a peptide corresponding to phosphoserine(1650) and flanking regions of the murine myosin Va sequence, was immunoreactive to myosin Va heavy chain in cellular and nuclear extracts of HeLa cells, PC12 cells and B16-F10 melanocytes. Immunofluorescence microscopy with this antibody revealed discrete irregular spots within the nucleoplasm that colocalized with SC35, a splicing factor that earmarks nuclear speckles. Phospho-ser(1650) MVa was not detected in other nuclear compartments, such as condensed chromatin, Cajal bodies, gems and perinucleolar caps. Although nucleoli also were not labeled by 9E6 under normal conditions, inhibition of transcription in HeLa cells by actinomycin D caused the redistribution of phospho-ser(1650) MVa to nucleoli, as well as separating a fraction of phospho-ser(1650) MVa from SC35 into near-neighboring particles. These observations indicate a novel role for myosin Va in nuclear compartmentalization and offer a new lead towards the understanding of actomyosin-based gene regulation.
Pranchevicius
Maria Cristina S
MC
Department of Cellular and Molecular Biology, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil.
Baqui
Munira M A
MM
Ishikawa-Ankerhold
Hellen C
HC
Lourenço
Elaine V
EV
Leão
Ricardo M
RM
Banzi
Silmara R
SR
dos Santos
Claudia Tavares
CT
Roque-Barreira
Maria C
MC
Barreira
Maria Cristina R
MC
Espreafico
Enilza M
EM
Larson
Roy E
RE
D000199:Actins / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000378:metabolism* / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D020409:Molecular Motor Proteins / Q000502:physiology*; D024701:Myosin Type V / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D010766:Phosphorylation; D051381:Rats; D012694:Serine / Q000378:metabolism; D014158:Transcription, Genetic
D000199:Actins; D020409:Molecular Motor Proteins; D012694:Serine; D024701:Myosin Type V