Retroviruses can infect a variety of species, including humans. Retroviral DNA integrates into the genome, resulting in persistent infections. Mammalian genomes are also under constant threat by endogenous retroviruses and retroelements. They thus have developed multiple mechanisms to restrict retroviral infections prior to proviral integration. Among the host restriction factors are APOBEC3 proteins with cytidine deaminase activity (CDA) that act during retroviral replication and that inhibit retrotransposition. There are 7 human A3 (hA3) family members (A3A-A3H), while rodents have a single A3 gene. All A3 proteins have CDA domains and can convert cytidines to uridines in reverse-transcribed single-stranded DNA, resulting in mutation of the viral DNA. While the human A3 proteins have been extensively studied in tissue culture, little is known about their action in vivo. Here, I propose to use transgenic mice that I recently created and express 2 human A3 proteins, A3A and A3G, with the goal of determining their ability to restrict retroviruses in vivo. A3A has a potent role in restricting viruses and retroelement retrotransposition in vitro, while A3G inhibits retroviruses such as HIV-1. Moreover, it has been suggested that A3 proteins play a critical role in preventing zoonoses and indeed, several human A3 proteins have been shown to restrict mouse retroviruses in vitro. Because of their potent antiviral activity, increasing A3 activity is currently being investigated as a target of ani-viral therapy but whether this has the potential to lead to cellular DNA damage or to drug-resistant retroviruses is not known. We will thus use these transgenic mice to test their effects on mouse mammary tumor virus (MMTV) and murine leukemia virus (MLV) infection, retroviruses for which the mouse is the natural host and which are only partially restricted by mouse A3 (mA3). Our laboratory (Dr. Susan Ross'laboratory at the University of Pennsylvania) pioneered the use of genetically modified mice, including mA3 knockout mice, to study host-retrovirus interactions in vivo. Thus, this project will provide me with training in retroviruses ad the generation of transgenic mouse models, while drawing on my previous training in viral pathogenesis in mice. This study will provide insight into the function of the A3 proteins in vivo, and also has the potential to create new models for testing therapeutic strategies for treating retroviral infections in humans.

Public Health Relevance

APOBEC 3 proteins (A3) are a family of cellular restriction factors that inhibit retrovirus infections by causing cytidine deamination in the retrovirus genome. There are 7 genes encoded by the A3 family (A3A-A3H) in humans. It has been found that A3A and A3G cause high levels of hypermutations in the retrovirus DNA and result in restriction of retrovirus infection in vitro. Using transgenic mice, this study will shed light to he function of A3A and A3G in vivo. The findings of this study regarding the in vivo function of A3 proteins will assist in developing new therapeutic strategies for the treatment of retrovirus infections.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Postdoctoral Individual National Research Service Award (F32)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1-F13-C (20))
Program Officer
Park, Eun-Chung
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Pennsylvania
Schools of Medicine
United States
Zip Code
Stavrou, Spyridon; Zhao, Wenming; Blouch, Kristin et al. (2018) Deaminase-Dead Mouse APOBEC3 Is an In Vivo Retroviral Restriction Factor. J Virol 92:
Stavrou, Spyridon; Aguilera, Alexya N; Blouch, Kristin et al. (2018) DDX41 Recognizes RNA/DNA Retroviral Reverse Transcripts and Is Critical for In Vivo Control of Murine Leukemia Virus Infection. MBio 9:
Cadena, Cristhian; Stavrou, Spyridon; Manzoni, Tomaz et al. (2016) The effect of HIV-1 Vif polymorphisms on A3G anti-viral activity in an in vivo mouse model. Retrovirology 13:45
Nakaya, Yuki; Stavrou, Spyridon; Blouch, Kristin et al. (2016) In Vivo Examination of Mouse APOBEC3- and Human APOBEC3A- and APOBEC3G-Mediated Restriction of Parvovirus and Herpesvirus Infection in Mouse Models. J Virol 90:8005-12
Stavrou, Spyridon; Blouch, Kristin; Kotla, Swathi et al. (2015) Nucleic acid recognition orchestrates the anti-viral response to retroviruses. Cell Host Microbe 17:478-88
Stavrou, Spyridon; Ross, Susan R (2015) APOBEC3 Proteins in Viral Immunity. J Immunol 195:4565-70
Stavrou, Spyridon; Crawford, Daniel; Blouch, Kristin et al. (2014) Different modes of retrovirus restriction by human APOBEC3A and APOBEC3G in vivo. PLoS Pathog 10:e1004145
Stavrou, Spyridon; Nitta, Takayuki; Kotla, Swathi et al. (2013) Murine leukemia virus glycosylated Gag blocks apolipoprotein B editing complex 3 and cytosolic sensor access to the reverse transcription complex. Proc Natl Acad Sci U S A 110:9078-83