The major immediate early (MIE) gene of cytomegalovirus plays a key role in determining the activation and replication of cytomegalovirus, which represents the most important event signaling the onset of virus-induced disease relapse. The viral-encoded chemokine receptor homolog US28 can constitutively activate many cellular transcription factors, which can bind to the promoter/enhancer of the MIE gene and activate its transcription. Using reporter gene assays in HEK293 cells, we found that US28 enhanced the transcription efficiency of MIE and other genes via cAMP response element-binding protein (CREB). Inhibition of CREB partially blocked the effect of US28, whereas forskolin enhanced this effect. There was a direct correlation between CREB and transcription of MIE gene. These data, together with the broad-spectrum effect of cellular transcription factors, suggest that US28 may be involved in the very early transcription of the host cell during virus activation.