Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus-8 (HHV-8) causes a persistent infection, presenting latent and lytic replication phases during its life cycle. KSHV-related diseases are associated with deregulated expression of inflammatory cytokines, including IL-6 and IL-10, but the mechanisms underlying this dysregulation are unclear. Herein, we report a molecular mechanism for KSHV-induced gene expression. KSHV replication and transcription activator (K-RTA) is a molecular switch for the initiation of expression of viral lytic genes, and we describe, for the first time, that K-RTA significantly activates the promoter of the human gene. Of note, mutations involving a basic region of K-RTA reduced the association of K-RTA with the promoter. Moreover, the host-cell transcription factors, specificity proteins (SP) 1 and 3, play a pivotal cooperative role in K-RTA-mediated transactivation of the promoter. K-RTA can interact with SP1 and SP3 directly , and electrophoresis mobility shift assays (EMSAs) revealed co-operative interaction involving K-RTA, SP1, and SP3 in binding to the promoter. As DNase I footprinting assays indicated that K-RTA did not affect SP3 binding to the promoter, SP3 can function to recruit K-RTA to the promoter. These findings indicate that K-RTA can directly contribute to up-regulation via a functional interplay with the cellular transcription factors SP1 and SP3.