Our Science – Felber Website
Barbara K. Felber, Ph.D.
Posttranscriptional Control of Gene Expression
Our research focuses on the regulation of gene expression, in particular the mechanisms controlling cellular and viral mRNA expression. A critical step in the mRNA metabolism is the transport of the mRNA from the nucleus to the cytoplasm. Analysis of retroviral systems, pioneered by research on HIV-1, have shed light into some important aspects of nuclear mRNA export and these studies have provided critical insight into mechanisms governing cellular mRNA and protein transport. We are utilizing retroviral systems to identify and study mechanisms of mRNA metabolism using a combination of biochemistry, functional genomics, and proteomics. The dissection of the mechanisms of posttranscriptional control and nucleocytoplasmic trafficking of macromolecules are relevant to understand processes involved in cellular gene expression as well as virus expression. Since posttranscriptional regulation is an essential step in virus propagation, our studies also focus on the understanding of this regulatory step in pathogenesis of HIV and SIV. Recent data from my lab identified the cellular PSF protein as a factor interacting with distinct HIV-1 mRNAs and inhibiting their expression, hence virus production. The role of PSF in the posttranscriptional regulation of cellular mRNAs is under investigation.
The identification of CTE and CTE-related RNA transport elements as well as their receptor, the cellular TAP/NXF1 protein, enabled us to further dissect its mechanism of function. NXF1 is also the key receptor for cellular mRNAs, and we demonstrated that this function is conserved in metazoa. We also found that TAP/NXF1 binds to the splicing factor U2AF35 which provides a novel link between splicing and export of mRNA. We are currently examining the role of the other members of the NXF family. In collaboration with George Pavlakis (Vaccine Branch), we identified a novel RNA transport element RTE, which appears to hijack the NXF transport pathway. RTE interactions and mechanism of function are under investigation.
Pathogenesis of SIV and Prevention of AIDS
Live-attenuated SIV strains provide an important model to study cellular and viral determinants that contribute to disease development and they also provide a unique tool to study mechanisms leading to protective immunity. We study the regulated expression of HIV which is mediated via the viral Rev protein with the goal to evaluate the role of Rev in pathogenesis. Our discovery of other RNA export mechanisms (mediate via cellular RNA export factors and retrovial RNA export elements CTE, RTE) provided the key tools to generate HIV and SIV variants that have the Rev/RRE regulatory system replaced. CTE or RTE provide us also with useful tools to achieve efficient expression of HIV and SIV structural protein in simple DNA vectors used as vaccine approaches against AIDS. Importantly, we found that our Rev-independent SIV strains are not pathogenic in rhesus macaques, which demonstrates that the Rev regulation plays an important role in pathogenicity of SIV. Replacement of the natural regulatory controls of Rev-RRE by the CTE provides a novel approach to lower the virulence of a pathogenic lentivirus. These studies provide critical information about the establishment and maintenance of host immune responses during chronic retroviral infections with distinct pathogenic outcomes. Macaques immunized with attenuated viruses develop persistent humoral and cellular immune responses, able to protect the animals from highly pathogenic SIV challenge. Therefore, these live-attenuated SIV strains provide us not only with a unique tool to dissect cellular and viral determinants that contribute to AIDS development, but are also useful for studying correlates of protective immunity. These studies will provide critical information about the establishment and maintenance of host immune responses during chronic retroviral infections with distinct pathogenic outcomes.
To study prevention of AIDS, we have a long-standing collaboration with George Pavlakis (Human Retrovirus Section, Vaccine Branch), and we have generated efficient DNA expression vectors, which are currently evaluated as vaccines against SIV and HIV. This work is based on the previous recognition that RNA elements (called INS) present within the gag/pol and env coding regions of HIV are responsible for nuclear retention and instability of the transcripts in the absence of Rev, and that these elements can be eliminated by changing the RNA composition without affecting the amino acid sequence. These RNA optimized gag and env expression vectors mediate the development of protective immune responses in vaccinated macaques when used as DNA only as well as DNA prime vaccine modality. On-going studies focus on the use of further optimized DNA based vaccine vectors and on evaluating their efficacy both as preventive and therapeutic vaccination modalities.
Our collaborators include Marta Marthas, California Regional Primate Center, University of California-Davis; Ruth Ruprecht, Dana-Farber Cancer Institute; David Weiner, University of Pennsylvania; Genoveffa Franchini, NIH; George N. Pavlakis, NCI-Frederick; and J. Thomas August, Johns Hopkins University School of Medicine.
This page was last updated on 2/19/2013.