Role of Ca2+ activation and bilobal structure of calmodulin in nuclear and nucleolar localization.
Ca2+ signalling to the nucleus is thought to occur by calmodulin entry into the nucleus where calmodulin has many functions. In the present study we have investigated the role of Ca2+ and the N- and C-terminal lobes of calmodulin in its subnuclear targeting by using fluorescently labelled calmodulin and its mutants and confocal microscopy. Our data show, first, that Ca2+ stimulation induces a reorganization of subnuclear structures to which apo-calmodulin can bind. Secondly, Ca2+-independent association of the C-terminal lobe is seen with subnuclear structures such as chromatin, the nuclear envelope and the nucleoli. Thirdly, Ca2+-dependent accumulation of both calmodulin and the C-terminal calmodulin lobe occurs in the nucleoli. The N-terminal lobe of calmodulin does not show significant binding to subnuclear structures although, similarly to the C-terminal lobe, it accumulates in the nucleoplasm of wheat germ agglutinin-blocked nuclei suggesting that a facilitated nuclear export mechanism exists for calmodulin.
Thorogate
Richard
R
Division of Basic Medical Sciences, St George's University of London, London SW17 0RE, UK.
Török
Katalin
K
D021581:Active Transport, Cell Nucleus; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000032:analysis / Q000737:chemistry* / Q000235:genetics; D002466:Cell Nucleolus / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D005456:Fluorescent Dyes; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D012235:Rhodamines / Q000737:chemistry / Q000378:metabolism
D002147:Calmodulin; D005456:Fluorescent Dyes; D012235:Rhodamines; D002118:Calcium