The Influence of Host Factors on Retroviral Integration into Chromatin Templates

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DESCRIPTION (provided by applicant): Retroviral infections cause a variety of cancers in animals, and a number of diverse diseases in humans such as leukemia and acquired immune deficiency syndrome. The process of integration is critical for retroviral function, yet the host factors that interface with, and undoubtedly influence the integration process are still poorly understood. Little is known about the factors influencing where and how retroviruses select integration sites within the genome of their hosts, and few integrase interacting proteins have been identified and verified. We have been studying retroviral integration with the long-term goal of developing interventions that can modulate the process towards several therapeutic ends, including design of benign retroviral-based gene targeting vectors and avoiding insertional mutagenesis. Identification of cellular factors that potentiate integration into host genomes may allow us to design inhibitors of the integration reaction, an outcome that would be extremely useful in designing anti-HIV-1 and other anti-retroviral drugs. The goal of this project is to identify and characterize host factors that interact with retroviral integrase and modulate the results of viral integration. This study uses the most commonly used retroviral vector in gene therapy trials, Moloney murine leukemia virus (MoMLV), as a model retrovirus for in vitro and in vivo experiments, and we include comparative studies with HIV-1 in our research plan. We hypothesize that host factors affecting chromatin structure are key modulators of integration via direct interactions with the viral integrase protein. Aim 1: We will determine the effect of transcription-induced chromatin alteration on retroviral integration patterns using our novel and innovative in vivo integration assay. In this system, transcription initiation from the extensively characterized mouse mammary tumor virus long terminal repeat (MMTV LTR) occurs in response to steroid hormones, and we will use this feature to map MoMLV integration events with and without hormone. Aim 2: We will also determine the role of integrase-interacting chromatin-associated host factors in integration and virus infectivity. We have identified a number of integrase-interacting host factors in cDNA screens, and we will use RNA interference (RNAi) in mammalian cell lines to knockdown two proteins initially, both of which are chromatin binding factors. Using this technique, we show that one of these proteins inhibits virus infectivity. We will also map integration events into the chimeric bovine papilloma virus-MMTV LTR episomes in the presence and absence of hormone in these lines. These studies will advance the retroviral integration field by identifying at least two key host factors and by providing an in vivo integration system that will enable us to examine specific steps of the integration reaction in detail, and identify new targets for antiviral therapy. PUBLIC HEALTH RELEVANCE: Identification of host factors critical for integration is important for two reasons. First, to design benign retroviral-based-gene targeting vectors to avoid insertional mutagenesis. Second, this information would be extremely useful in designing anti-HIV, anti-oncogenic, and other anti-retroviral drugs.