okadaic-acid and Cytomegalovirus-Infections

The devastating clinical consequences associated with human cytomegalovirus (HCMV) infection and reactivation underscores the importance of understanding triggers of HCMV reactivation in dendritic cells (DC). Here we show that ERK-mediated reactivation is dependent on the mitogen and stress activated kinase (MSK) family. Furthermore, this MSK mediated response is dependent on CREB binding to the viral major immediate early promoter (MIEP). Specifically, CREB binding to the MIEP provides the target for MSK recruitment. Importantly, MSK mediated phosphorylation of histone H3 is required to promote histone de-methylation and the subsequent exit of HCMV from latency. Taken together, these data suggest that CREB binding to the MIEP is necessary for the recruitment of the kinase activity of MSKs to initiate the chromatin remodelling at the MIEP required for reactivation. Thus the importance of CREB during HCMV reactivation is to promote chromatin modifications conducive for viral gene expression as well as acting as a classical transcription factor. Clearly, specific inhibition of this interaction between CREB and MSKs could provide a strategy for therapeutic intervention.

Topics: Antigens, Viral; Binding Sites; Cells, Cultured; Cyclic AMP Response Element-Binding Protein; Cytomegalovirus; Cytomegalovirus Infections; Dendritic Cells; DNA-Binding Proteins; Gene Expression Regulation, Viral; Histones; Humans; Immediate-Early Proteins; MAP Kinase Kinase 1; MAP Kinase Signaling System; Okadaic Acid; Phosphorylation; Promoter Regions, Genetic; Protein Binding; Trans-Activators; Virus Activation; Virus Latency

While the importance of cellular and viral kinases in HCMV replication has been demonstrated, relatively little is known about the activity of cellular phosphatases. We conducted a series of experiments designed to investigate the effect of HCMV infection on cellular serine/threonine phosphatase activity. We found that the abundance of two major cellular serine/threonine phosphatases, PP1 and PP2A, increases during HCMV infection. This was associated with an increase in threonine phosphatase activity in HCMV-infected cells. HCMV infection conferred resistance to the effects of the phosphatase inhibitors calyculin A (CA) and okadaic acid with regards to global protein hyperphosphorylation and the shutoff of protein synthesis. The protective effect of HCMV infection could be overcome at a high concentration of CA, suggesting that cellular phosphatase activity is required for critical cellular processes during HCMV infection. Specifically, phosphatase activity was required to limit the accumulation of phospho-eIF2alpha, but not phospho-PKR, during HCMV infection.

Topics: Animals; Cells, Cultured; Cytomegalovirus Infections; eIF-2 Kinase; Enzyme Inhibitors; Eukaryotic Initiation Factor-2; Humans; Marine Toxins; Mice; Okadaic Acid; Oxazoles; Phosphoprotein Phosphatases; Phosphorylation; Protein Biosynthesis