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Journal of Virology, February 2000, p. 1158-1167, Vol. 74, No. 3
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Activation of the Mitogen-Activated Protein Kinase p38 by Human Cytomegalovirus Infection through Two Distinct Pathways: a Novel Mechanism for Activation of p38

Robert A. Johnson,1,2 Shu-Mei Huong,2 and Eng-Shang Huang1,2,3,4,*

Department of Microbiology and Immunology,1 Lineberger Comprehensive Cancer Center,2 Department of Medicine,3 and Curriculum of Genetics and Molecular Biology,4 University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295

Received 28 July 1999/Accepted 1 November 1999

Recent evidence indicates activated mitogen-activated protein kinase (MAPK) p38 has a critical function in human cytomegalovirus (HCMV) viral DNA replication in infected human fibroblasts. To elucidate the mechanism of HCMV-mediated p38 activation, we have performed a detailed analysis of p38 activation and the kinases associated with this activation at different times postinfection. We demonstrate that p38 kinase activity is strongly increased following viral infection. Inhibition of this activity significantly inhibited HCMV-induced hyperphosphorylation of pRb and phosphorylation of heat shock protein 27, suggesting that p38 activation is involved in virus-mediated changes in host cell metabolism throughout the course of infection. We then provide evidence that p38 activation is mediated by different mechanisms at early times versus later times of infection. At early times of infection (8 to 14 h postinfection [hpi]), when p38 activation is first observed, no significant activation of the three kinases which can directly phosphorylate p38 (namely, MKK3, MKK6, and MKK4) is detected. Using vectors which express dominant negative proteins, we demonstrate that basal MKK6 kinase activity is necessary for HCMV-mediated p38 activation at these early times of infection (12 hpi). Then, we use ATP depletion to show that at 12 hpi, HCMV inhibits dephosphorylation of activated p38. These two experiments suggest that HCMV activates p38 by inhibition of dephosphorylation of p38. In contrast to early times of infection, at later times of infection (48 to 72 hpi), increased MKK3/6, but not MKK4, activity is observed. These results indicate that at early times of HCMV infection, increased steady-state levels of activated p38 is mediated at least in part by inhibition of dephosphorylation of p38, while at later times of infection p38 activation is due to increased activity of the upstream kinases MKK3 and MKK6. These findings indicate that HCMV has developed multiple mechanisms to ensure activation of the MAPK p38, a kinase critical to viral infection.

* Corresponding author. Mailing address: 32-026 Lineberger Comprehensive Cancer Center, CB# 7295, University of North Carolina, Chapel Hill, NC 27599-7295. Phone: (919) 966-4323. Fax: (919) 966-4303. E-mail: eshuang{at}med.unc.edu.

Journal of Virology, February 2000, p. 1158-1167, Vol. 74, No. 3
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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