S. Jane Flint
Modulation of host cell processes by adenoviral gene products
Human adenoviruses, which are widespread in the population, are non-enveloped viruses with double-stranded DNA genomes. The study of these viruses has yielded fundamental insights into the mechanisms by which genes are expressed in human cells, as well as the intricate circuits that control cell proliferation but become deranged during malignant transformation. There is considerable interest in developing derivatives of adenoviruses for therapeutic applications, for example, as gene transfer vectors and oncolytic viruses for cancer therapy. However, relatively little attention has been paid to the interactions among viral and cellular gene products required for optimal virus reproduction in normal human cells (as opposed to highly abnormally transformed cells derived from human tumors). Furthermore, the molecular functions of the products of genes routinely deleted from “therapeutic” adenoviruses are not fully understood. Our research seeks to address such issues, focusing on the contributions of the viral E1B 55 kDa protein to the infectious cycle in normal human cells: the gene for this protein is deleted from all adenovirus gene transfer vectors, and such deletion (in the absence of other alterations) confers tumor cell-selective reproduction and host cell lysis.
One function of this E1B protein implicated in the cell-selective reproduction is induction of selective export of viral mRNAs during the late phase of infection. This process requires assembly in infected cells of a virus-specific E3 ubiquitin ligase that contains the viral E1B 55 kDa and E4 Orf6 proteins, as well as several cellular proteins. We have established that this virus-specific enzyme targets one or more components of the major mRNA export pathway in mammalian cells, the Nxf1 pathway, and that efficient export of viral late mRNAs is more dependent on the E1B 55 kDa protein in normal than in tumor cells. As the relevant substrates of the virus specific E3 ubiquitin ligase have not been identified, we are applying proteomic methods to compare the populations of ubiquitinylated proteins in cells infected by mutant viruses defective for production of the E1B 55 kDa protein and their wild-type parent.
One of the first activities ascribed to the E1B 55 kDa pote9in was repression of transcription in simplified experimental systems, such as transient expression assays. However, the contribution of this function to viral reproduction was not known, until the results of our genome-wide analysis of cellular gene expression in infected normal human cells established that the E1B protein inhibits expression of a substantial number of genes. This set of genes proved to highly enriched for those associated with anti-viral defenses, particularly that mediated by the cytokine type I interferon. In fact, the E1B 55 kDa protein is required to block inhibition of viral reproduction by interferon, and when the E1B protein is not made, viral genome replication is inhibited severely in infected cells exposed to the interferon. The results of molecular and genetic analysis have established that this viral protein represses transcription of interferon-inducible genes and that his function correlates with preventing inhibition of viral DNA synthesis by interferon. This cytokine does not induce inhibition of synthesis of viral replication proteins, but rather leads to a block in formation of the specialized intranuclear structures in which viral DNA synthesis takes place, so-called viral replication centers. The mechanism by which the E1B 55 kDa protein represses transcription of specific human genes is currently under investigation, as is that by which the products of one or more of the some 130 human genes that are both interferon-inducible and E1B protein repressed disrupt formation of viral replication centers.
Jane Flint is a Professor of Molecular Biology at Princeton University. She became enthralled with science when introduced to the explanatory power of chemistry at age 13, and decided to pursue an undergraduate degree in Biochemistry. After graduate training in the same discipline at University College, London, Dr. Flint began postdoctoral studies at the Cold Spring Harbor Laboratory, New York, and helped develop the first transcriptional map of the human adenovirus DNA genome. She continued to investigate adenoviral gene expression in productively-infected and transformed cells as a postdoctoral fellow with Dr. Phillip Sharp, Massachusetts Institute of Technology, and from 1977, as Assistant Professor of Biochemical Sciences at Princeton University. Dr. Flint served as Associate Chair of that department and Director of the Program in Molecular Biology from 1982 until the Department of Molecular Biology was formed in 1984.
Dr. Flint's research focuses on investigation of the molecular mechanisms by which viral gene products modulate host cell pathways and anti-viral defenses to allow efficient reproduction in normal human cells of adenoviruses, viruses that are widely used in such therapeutic applications as gene transfer and cancer treatment. Dr. Flint's fascination with the marvelous variety in virus-host cell interactions, and her pleasure in writing, spurred her to lead a team of four authors of the popular text "Principles of Virology: Molecular Biology, Pathogenesis and Control". Her service to the scientific community includes membership of various editorial boards and several NIH study sections (including Chair of Biochemistry) and other review panels, and she is currently a member of the Biosafety Working Group of the NIH Recombinant DNA Advisory Committee. Dr. Flint was elected to the American Academy of Microbiology in 2000.
- Ph.D., University College, London
- B.S.c, (Class I, Hons) University College, London
- 1.Flint S. Viral Moulds and Cement: How Interactions among Human Adenovirus Hexons and Their Protein IX Cement May Buttress Human Adenovirus Particles. J Mol Biol. 2017;429(18):2752–2754. PMID: 28728981
- 1.Hung G, Flint S. Normal human cell proteins that interact with the adenovirus type 5 E1B 55kDa protein. Virology. 2017;504:12–24. PMCID: PMC5337154
- 1.Ortega-Esteban A, Condezo G, Pérez-Berná A, Chillón M, Flint J, Reguera D, San Martín C, de Pablo P. Mechanics of Viral Chromatin Reveals the Pressurization of Human Adenovirus. ACS Nano. 2015;9(11):10826–33. PMID: 26491879
- 1.DeHart C, Perlman D, Flint S. Impact of the adenoviral E4 Orf3 protein on the activity and posttranslational modification of p53. J Virol. 2015;89(6):3209–20. PMCID: PMC4337557
- 1.DeHart C, Chahal J, Flint S, Perlman D. Extensive post-translational modification of active and inactivated forms of endogenous p53. Mol Cell Proteomics. 2014;13(1):1–17. PMCID: PMC3879606
- 1.Chahal J, Flint S. The p53 protein does not facilitate adenovirus type 5 replication in normal human cells. J Virol. 2013;87(10):6044–6. PMCID: PMC3648133
- 1.Chahal J, Gallagher C, DeHart C, Flint S. The repression domain of the E1B 55-kilodalton protein participates in countering interferon-induced inhibition of adenovirus replication. J Virol. 2013;87(8):4432–44. PMCID: PMC3624377