To replicate in the host cell, viruses commandeer cellular signaling pathways. Cytomegalovirus (CMV) is a DNA virus with that is widespread in the population but usually causes disease only in immunocompromised individuals and is also a viral cause of birth defects. One of the actions of CMV in the host cell is to stimulate MAP kinase pathways. Both p38 and ERK kinases are activated by CMV infection through activation map kinase kinases and inhibition of phosphatases. One result of Map kinase activation by CMV is activation of transcription of viral genes, increasing the production of viral gene products. Both p38 and ERK kinases contribute to the activation of viral genes by cellular transcription factors acting through the viral UL4 promoter at upstream and basal transcription elements. Another target of prolonged p38 activation during infection is Rb, contributing to viral replication. Activation of MKK1 and MKK2 leads to Erk1 and Erk2 activation, and phosphorylation of downstream targets. The MEKK1 kinase regulates the immediate early promoter indirectly through downstream kinase signaling and perhaps more directly through activation of NF-kB. Map kinase pathways activated by CMV converge on increased transcription of viral genes and increased replication of the viral genome. Better understanding of the mechanisms involved in the interaction of CMV with cellular signaling machinery will provide improved ways to treat CMV-mediated disease.
