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.

Kaposi's sarcoma–associated herpesvirus (KSHV) is responsible for the pathogenesis of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman disease. The expression of immunosuppressive genes, such as IL‐10 and CD274/PD‐L1 is observed during KSHV‐associated pathogenesis, and the modulation of the host immune system by KSHV contributes to establishing viral persistence in the host. Understanding the mechanism that allows the virus to evade host cell immunity would be helpful in order to develop therapeutic strategies for KSHV malignancy. In this study, we show that KSHV replication and transcriptional activator (K‐RTA), an essential activator of the viral lytic cycle, transactivates the CD274/PD‐L1 gene promoter. Mechanistically, we demonstrate that the binding of K‐RTA to the cellular specificity protein 1 (SP1) is critical for K‐RTA–mediated CD274/PD‐L1 promoter activation. These findings suggest that K‐RTA cooperates with intracellular SP1 to activate the expression of CD274/PD‐L1, which helps the virus regulate immune checkpoints to escape and survive.