Live-cell fluorescence imaging reveals the dynamics of protein kinase CK2 individual subunits.
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 (beta) subunits. To track the spatiotemporal dynamics of CK2 in living cells, we fused its catalytic alpha and regulatory beta 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-CK2alpha or GFP-CK2beta revealed the existence of CK2 subunit subpopulations exhibiting differential dynamics. Once in the nucleus, they diffuse randomly at different rates. Unlike CK2beta, CK2alpha 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 CK2alpha is dramatically changed by its association with CK2beta, the control of the nucleocytoplasmic distribution of each subunit may represent a unique potential regulatory mechanism for CK2 activity.
Filhol
Odile
O
INSERM EMI 104, Département Réponse et Dynamique Cellulaires, CEA, 38054 Grenoble, France.
Nueda
Arsenio
A
Martel
Véronique
V
Gerber-Scokaert
Delphine
D
Benitez
Maria José
MJ
Souchier
Catherine
C
Saoudi
Yasmina
Y
Cochet
Claude
C
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D047390:Casein Kinase II; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D019913:Nuclear Localization Signals; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases