Hypoxia and hypoxia inducible factors (HIFs) play important roles in the Kaposi's sarcoma-associated herpesvirus (KSHV) life cycle. KSHV is the causative agents of Kaposi's sarcoma (KS) and other AIDS related malignancies. Kaposi's sarcoma is a highly vascular tumor， which preferentially develops in the lower extremities of the body where blood vessels are often poorly oxygenated. The main cellular responses to hypoxia are mediated mainly by two isoforms of HIF， HIF-1α and HIF-2α. Both HIF-1α and HIF-2α have common as well as distinct functions， although they are similar in structure and function. Previously， we showed that the KSHV ORF34 protein binds HIF-1α and facilitates its degradation through... More
Hypoxia and hypoxia inducible factors (HIFs) play important roles in the Kaposi's sarcoma-associated herpesvirus (KSHV) life cycle. KSHV is the causative agents of Kaposi's sarcoma (KS) and other AIDS related malignancies. Kaposi's sarcoma is a highly vascular tumor， which preferentially develops in the lower extremities of the body where blood vessels are often poorly oxygenated. The main cellular responses to hypoxia are mediated mainly by two isoforms of HIF， HIF-1α and HIF-2α. Both HIF-1α and HIF-2α have common as well as distinct functions， although they are similar in structure and function. Previously， we showed that the KSHV ORF34 protein binds HIF-1α and facilitates its degradation through the ubiquitin-proteasome pathway causing negative regulation of HIF-1α-dependent genes (Haque and Kousoulas， J Virol. 87:2164-73， 2013). Herein， we show that the ORF34 gene is involved in the regulation of KSHV lytic gene expression， since deletion of the ORF34 resulted in reduced immediate early and early lytic gene expression and blocked late gene expression. Coimmunoprecipitation experiments revealed that the ORF34 protein physically interacted with HIF-2α in transfected， as well as in KSHV-infected cells. Utilization of ORF34 truncations revealed that three distinct domains bind HIF-2α and that both bHLH and PAS domains of HIF-2α interacted with ORF34. Unlike HIF-1α， dose dependent co-expression of ORF34 stabilized the HIF-2α protein ensuring HIF-2α dependent transcriptional activity. The ORF34 protein enhanced HIF-2α ubiquitination at the bHLH and PAS domains. The results show that the KSHV ORF34 protein is involved in the KSHV life cycle by regulating the expression of HIF-1α & HIF-2α proteins.The Hypoxia inducible factors-1α (HIF-1α) and -2α (HIF-2α) are transcription factors which play important roles in the Kaposi's sarcoma-associated herpesvirus (KSHV) latent and lytic gene replication. Herein， we show that the ORF34 gene is involved in the regulation of KSHV lytic gene expression， since deletion of the ORF34 resulted in reduced immediate early and early lytic gene expression and blocked late gene expression. In addition， we demonstrate that the KSHV ORF34 protein binds and stabilizes HIF-2α， in contrast to its role in binding HIF-1α and causing its degradation via the proteasome pathway. Thus， the KSHV ORF34 protein plays a regulatory role in the KSHV life cycle by regulating HIF-1α and HIF-2α expression.
