KSHV-encoded LANA bypasses transcriptional block through the stabilization of RNA Pol II in hypoxia

Abstract

ABSTRACTHypoxia results from an insufficient supply of oxygen, which results in physiological stress in biological systems. Cells respond to this unfavorable condition by reducing critical cellular functions, which include replication, transcription, and translation. Oncogenic Kaposi sarcoma-associated virus (KSHV) undergoes lytic reactivation in hypoxic conditions. Furthermore, reactivation requires the synthesis of specific viral proteins, both structural and non-structural. Therefore, the virus manipulates the cellular microenvironment to ensure efficient functioning of the cellular transcription machinery, including RNA polymerase II (Pol II), by protecting it from hypoxia-mediated degradation. In this study, we demonstrated that hypoxia induces degradation of RNA Pol II via ubiquitination mediated by the NEDD4 E3 ligase, which results in transcription inhibition. However, in KSHV-infected cells during hypoxia, the virus-encoded latency-associated nuclear antigen interacts with NEDD4, inhibiting its E3 ubiquitin ligase activity and requires complex formation with hypoxia inducible factor HIF1α. This activity inhibits the polyubiquitination of RNA Pol II to maintain steady transcription levels necessary for the synthesis of the essential viral genes needed for successful lytic reactivation.IMPORTANCEHypoxia can induce the reactivation of Kaposi sarcoma-associated virus (KSHV), which necessitates the synthesis of critical structural proteins. Despite the unfavorable energetic conditions of hypoxia, KSHV utilizes mechanisms to prevent the degradation of essential cellular machinery required for successful reactivation. Our study provides new insights on strategies employed by KSHV-infected cells to maintain steady-state transcription by overcoming hypoxia-mediated metabolic stress to enable successful reactivation. Our discovery that the interaction of latency-associated nuclear antigen with HIF1α and NEDD4 inhibits its polyubiquitination activity, which blocks the degradation of RNA Pol II during hypoxia, is a significant contribution to our understanding of KSHV biology. This newfound knowledge provides new leads in the development of novel therapies for KSHV-associated diseases.

Keywords

• hypoxia
• KSHV
• lytic reactivation
• RNA Polymerase II
• ubiquitination