ACTIVATING TRANSCRIPTION FACTOR 4 (ATF4) IS UPREGULATED BY HUMAN HERPESVIRUS 8 INFECTION, INCREASES VIRUS REPLICATION AND PROMOTES VIRUS PROANGIOGENIC PROPERTIES

Previous results from our group demonstrate that human herpesvirus 8 (HHV-8) triggers proangiogenic behavior in endothelial cells by promoting transcriptional activation and secretion of monocyte chemoattractant protein 1 (MCP-1), through activation of Nuclear Factor κB (NF-κB). However, inhibition of NF-κB still results in partial MCP-1 induction and consequent capillary-like structure formation, suggesting the involvement of another transcriptional pathway. Here we describe that HHV-8 infection upregulates cellular activating transcription factor 4 (ATF4), a member of the CREB family involved in the cell response to ER stress. Upregulation of ATF4 promotes HHV-8 infection, whereas its silencing decreases virus replication, transcription and antigen expression. Furthermore, ATF4 silencing decreases virus-induced MCP-1 production, as well as viral induction of tube-like structures in endothelial cells. We also show that ATF4 per se activates the MCP-1 promoter and induces proangiogenic properties in transfected endothelial cells. The elucidation of molecular mechanism involved in this process will result in a better understanding of the angiogenic process, its involvement in cancer and will help in designing novel therapies to reduce growth and vascularisation of Kaposi’s sarcoma.