Cyclin G2 is a centrosome-associated nucleocytoplasmic shuttling protein that influences microtubule stability and induces a p53-dependent cell cycle arrest.
Cyclin G2 is an atypical cyclin that associates with active protein phosphatase 2A. Cyclin G2 gene expression correlates with cell cycle inhibition; it is significantly upregulated in response to DNA damage and diverse growth inhibitory stimuli, but repressed by mitogenic signals. Ectopic expression of cyclin G2 promotes cell cycle arrest, cyclin dependent kinase 2 inhibition and the formation of aberrant nuclei [Bennin, D. A., Don, A. S., Brake, T., McKenzie, J. L., Rosenbaum, H., Ortiz, L., DePaoli-Roach, A. A., and Horne, M. C. (2002). Cyclin G2 associates with protein phosphatase 2A catalytic and regulatory B' subunits in active complexes and induces nuclear aberrations and a G(1)/S-phase cell cycle arrest. J Biol Chem 277, 27449-67]. Here we report that endogenous cyclin G2 copurifies with centrosomes and microtubules (MT) and that ectopic G2 expression alters microtubule stability. We find exogenous and endogenous cyclin G2 present at microtubule organizing centers (MTOCs) where it colocalizes with centrosomal markers in a variety of cell lines. We previously reported that cyclin G2 forms complexes with active protein phosphatase 2A (PP2A) and colocalizes with PP2A in a detergent-resistant compartment. We now show that cyclin G2 and PP2A colocalize at MTOCs in transfected cells and that the endogenous proteins copurify with isolated centrosomes. Displacement of the endogenous centrosomal scaffolding protein AKAP450 that anchors PP2A at the centrosome resulted in the depletion of centrosomal cyclin G2. We find that ectopic expression of cyclin G2 induces microtubule bundling and resistance to depolymerization, inhibition of polymer regrowth from MTOCs and a p53-dependent cell cycle arrest. Furthermore, we determined that a 100 amino acid carboxy-terminal region of cyclin G2 is sufficient to both direct GFP localization to centrosomes and induce cell cycle inhibition. Colocalization of endogenous cyclin G2 with only one of two GFP-centrin-tagged centrioles, the mature centriole present at microtubule foci, indicates that cyclin G2 resides primarily on the mother centriole. Copurification of cyclin G2 and PP2A subunits with microtubules and centrosomes, together with the effects of ectopic cyclin G2 on cell cycle progression, nuclear morphology and microtubule growth and stability, suggests that cyclin G2 may modulate the cell cycle and cellular division processes through modulation of PP2A and centrosomal associated activities.
Arachchige Don
Aruni S
AS
The Department of Pharmacology, University of Iowa, Iowa City, IA 52242-1109, USA.
Dallapiazza
Robert F
RF
Bennin
David A
DA
Brake
Tiffany
T
Cowan
Colleen E
CE
Horne
Mary C
MC
D054758:A Kinase Anchor Proteins; D021581:Active Transport, Cell Nucleus; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D002453:Cell Cycle; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D018385:Centrosome / Q000378:metabolism*; D056767:Cyclin G2; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D006801:Humans; D008870:Microtubules / Q000502:physiology*; D017239:Paclitaxel / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D054648:Protein Phosphatase 2; D017434:Protein Structure, Tertiary; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
D054758:A Kinase Anchor Proteins; C119719:AKAP9 protein, human; D048868:Adaptor Proteins, Signal Transducing; C101593:CCNG2 protein, human; C493956:CDKN1A protein, human; D056767:Cyclin G2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D003598:Cytoskeletal Proteins; D003902:Detergents; C432785:PPP2R1B protein, human; D016159:Tumor Suppressor Protein p53; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D017239:Paclitaxel