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Molecular and Cellular Biology, February 2003, p. 975-987, Vol. 23, No. 3
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.3.975-987.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Live-Cell Fluorescence Imaging Reveals the Dynamics of Protein Kinase CK2 Individual Subunits

Odile Filhol,1 Arsenio Nueda,1,1 Véronique Martel,1 Delphine Gerber-Scokaert,1 Maria José Benitez,1 Catherine Souchier,2 Yasmina Saoudi,3 and Claude Cochet1*

INSERM EMI 104,1 INSERM U366, Département Réponse et Dynamique Cellulaires, CEA, 38054 Grenoble Cedex 9,3 INSERM U309, Institut Albert Bonniot, 38706 La Tronche, France2

Received 29 July 2002/ Returned for modification 16 September 2002/ Accepted 25 October 2002

Protein kinase CK2 is a multifunctional enzyme which has long been described as a stable heterotetrameric complex resulting from the association of two catalytic ({alpha} or {alpha}') and two regulatory (ß) subunits. To track the spatiotemporal dynamics of CK2 in living cells, we fused its catalytic {alpha} and regulatory ß subunits with green fluorescent protein (GFP). Both CK2 subunits contain nuclear localization domains that target them independently to the nucleus. Imaging of stable cell lines expressing low levels of GFP-CK2{alpha} or GFP-CK2ß revealed the existence of CK2 subunit subpopulations exhibiting differential dynamics. Once in the nucleus, they diffuse randomly at different rates. Unlike CK2ß, CK2{alpha} can shuttle, showing the dynamic nature of the nucleocytoplasmic trafficking of the kinase. When microinjected in the cytoplasm, the isolated CK2 subunits are rapidly translocated into the nucleus, whereas the holoenzyme complex remains in this cell compartment, suggesting an intramolecular masking of the nuclear localization sequences that suppresses nuclear accumulation. However, binding of FGF-2 to the holoenzyme triggers its nuclear translocation. Since the substrate specificity of CK2{alpha} is dramatically changed by its association with CK2ß, the control of the nucleocytoplasmic distribution of each subunit may represent a unique potential regulatory mechanism for CK2 activity.

* Corresponding author. Mailing address: INSERM EMI 104, Département Réponse et Dynamique Cellulaires, CEA, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. Phone: 33 4 38 78 42 04. Fax: 33 4 38 78 50 58. E-mail: ccochet1{at}cea.fr.

{dagger} Present address: Almirall Prodesfarma SA, Centro de Investigation, 08024 Barcelona, Spain.

Molecular and Cellular Biology, February 2003, p. 975-987, Vol. 23, No. 3
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.3.975-987.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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