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Journal of Virology, May 1999, p. 4208-4219, Vol. 73, No. 5
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Functional Interactions between Herpesvirus Oncoprotein MEQ and Cell Cycle Regulator CDK2

Juinn-Lin Liu,1,2 Ying Ye,3 Zheng Qian,1 Yongyi Qian,4 Dennis J. Templeton,4 Lucy F. Lee,2 and Hsing-Jien Kung1,5,*

Department of Molecular Biology and Microbiology1 and Institute of Pathology,4 School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106; Avian Disease and Oncology Laboratory, U.S. Department of Agriculture, Agricultural Research Station, East Lansing, Michigan 488232; Department of Pathology, Baylor College of Medicine, Houston, Texas 770303; and University of California Davis Cancer Center, Sacramento, California 958175

Received 29 May 1998/Accepted 12 January 1999

Marek's disease virus, an avian alphaherpesvirus, has been used as an excellent model to study herpesvirus oncogenesis. One of its potential oncogenes, MEQ, has been demonstrated to transform a rodent fibroblast cell line, Rat-2, in vitro by inducing morphological transformation and anchorage- and serum-independent growth and by protecting cells from apoptosis induced by tumor necrosis factor alpha, C2-ceramide, UV irradiation, or serum deprivation. In this report, we show that there is a cell cycle-dependent colocalization of MEQ protein and cyclin-dependent kinase 2 (CDK2) in coiled bodies and the nucleolar periphery during the G1/S boundary and early S phase. To our knowledge, this is the first demonstration that CDK2 is found to localize to coiled bodies. Such an in vivo association and possibly subsequent phosphorylation may result in the cytoplasmic translocation of MEQ protein. Indeed, MEQ is expressed in both the nucleus and the cytoplasm during the G1/S boundary and early S phase. In addition, we were able to show in vitro phosphorylation of MEQ by CDKs. We have mapped the CDK phosphorylation site of MEQ to be serine 42, a residue in the proximity of the bZIP domain. An indirect-immunofluorescence study of the MEQ S42D mutant, in which the CDK phosphorylation site was mutated to a charged residue, reveals more prominent cytoplasmic localization. This lends further support to the notion that the translocation of MEQ is regulated by phosphorylation. Furthermore, phosphorylation of MEQ by CDKs drastically reduces the DNA binding activity of MEQ, which may in part account for the lack of retention of MEQ oncoprotein in the nucleus. Interestingly, the localization of CDK2 in coiled bodies and the nucleolar periphery is observed only in MEQ-transformed Rat-2 cells, implicating MEQ in modifying the subcellular localization of CDK2. Taken together, our data suggest that there is a novel reciprocal modulation between the herpesvirus oncoprotein MEQ and CDK2.

* Corresponding author. Mailing address: UC Davis Cancer Center, Research Bldg., Rm. 2400B, 4501 X St., Sacramento, CA 95817. Phone: (916) 734-1538. Fax: (916) 734-2589. E-mail: hkung{at}ucdavis.edu.

Journal of Virology, May 1999, p. 4208-4219, Vol. 73, No. 5
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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