Download Nuclear localization of CK2 associated with the progression of cell

REGULATORY ROLE OF CK2 DURING THE PROGRESSION OF
CELL CYCLE
Miwako K. Homma* and Yoshimi Homma
Department of Biomolecular Science, Fukushima Medical University
School of Medicine, Fukushima 960-1295, Japan
*[email protected]
INTRODUCTION Protein kinase CK2 is a ubiquitous eukaryotic Ser/Thr kinase.
Genetic, biochemical and cell biological studies indicate that the enzyme is involved in
the control of cell division and in signal transduction. We have characterized potent
roles for CK2 in the progression of cell cycle.
METHOD For cell synchronization, logarithmically growing cells were starved in
0.2% FBS for 48h and were collected in G0 or released into fresh medium containing
10% FBS to obtain cell populations synchronized at S phase or pro-metaphase. CK2,
APC and eIF5 were immunoprecipitated separately from synchronized cells. CK2
activity was determined by a p81 filter method. Proteins associated with CK2 were
identified by mass spectrometric analysis.
RESULTS We found that CK2 directly interacts with the tumor suppressor protein
adenomatous polyposis coli (APC) in a cell cycle-dependent manner. The C-terminal
region of APC suppressed the kinase activity of CK2, although APC-CK2 interactions
involved the N-terminal region of APC. The inhibitory region localized between amino
acid residues 2086-2394, and over-expression of this fragment in cultured colorectal
carcinoma cells suppressed cell proliferation rates as well as colony formation on soft
agar. We further identified eukaryotic translational initiation factor 5 (eIF5) as a
downstream target for CK2, that was phosphorylated by CK2 in vivo and in vitro. The
phosphorylation levels of eIF5 and its association with CK2 changed dramatically
during the progression of cell cycle. We determined the phosphorylation sites in eIF5
produced by CK2 and eIF5 mutants that lack those phosphorylation sites perturbed
synchronous progression of cells through the S to M phase.
DISCUSSION These findings provide insight into understanding the molecular link
between APC and the regulation of phosphorylation-dependent signal transduction. In
colorectal carcinoma cells, truncated APC mutants lacking the C-terminal domain bind
to CK2 but fail to effectively suppress CK2 activity. The results indicate that
hetero-complex formation between CK2 and full-length APC regulates CK2 activity in
vivo and has regulatory effects on cell cycle progression, which seems to be defective in
truncated APC mutants that are frequently observed in colorectal carcinomas. These
results suggest that growth inhibitory effects of APC may be regulated by CK2. Also,
CK2 carries out its growth promoting effect through eIF5 and the results suggest the
critical role for its phosphorylation by CK2 on the progression of cell cycle.
ACKNOWLEDGMENT
This work was supported in part by Yamada Science Foundation (Osaka) and by
grants-in-aid from the Ministry of Education, Culture, Sports, Science and Technology
of Japan.
REFERENCES
1. Homma, M.K., and Homma, Y. (2002) Proc. Natl. Acad. Sci. USA 99, 5959-5964
2. Litchfield, D.W. (2003) Biochem. J. 369, 1-15
3. Ahmed, K., Gerber, D.A., and Cochet, C.,(2002) Trends Cell Biol. 12, 226-230