Svenja Kriener  

Home Institution
Charité Universitätsmedizin Berlin

Host Institution(s)
Rockefeller University, New York
Aaron Diamond AIDS Research Center
Mentor: Vivian Simon, M.D., Ph.D.

E-Mail: enja_98@hotmail.com
Research Topic
see Abstract
Personal Reactions to the U.S. Experience
One Saturday night I was at the Brooklyn Museum of Art, where I basically could be found on the first Saturday of the month, since they offered not only free entrance to the museum and the ongoing exhibitions, but also various events and special programs. So, this night at around 10 PM, I was in the big hall where the dance lesson was taking place. It was really packed, and the band was playing some nice Brazilian songs for a samba class. I was looking at the crowd, and in that instant it really struck me that what I loved about New York and about living in that huge, incredible city, were two things. The first thing was that there you could be who you were; you could dress as you felt like, and you could wear whatever you wanted to wear, and come as close to your dreams of yourself as possible. Whatever you would wear on any random day, even if it's a bad hair day for you, almost nobody will give you a wry look or think something like "Ooh, what a weirdo!2 You were totally free to come as you are or to start singing whenever or wherever you felt like it. And that's fantastic!
The other thing I realized was that all these moving people on the dance floor were so different from each other. Not only were there women and men, old and young, but also black, white, yellow, red, the whole beautiful variety of mankind was on display for me, around me. And still they were all enjoying the same music, listening to the same song, moving to the same rhythm, holding hands and all having a great time together! New York City is made up of such a motley crew that you sometimes forgot that there were still people who suffer from inequality, injustice, or racism, even there. But on Saturdays at the Art Museum you could catch a promising glimpse of how wonderful the world could be ... "free at last"!
Greatest Difficulties Encountered
It was not the visa procedure ;)! It was finding myself in a hospital, but this time as a patient, and it was not at all like it was on ER on TV! Lying there, many different thoughts were turning in my head. There I was as a patient, seeing all my illusions about American medical care come crashing down. I not only encountered the most unfriendly people I met during my whole stay in the U.S., but also some incompetent ones. Nevertheless, I was probably lucky. It was a private hospital, I had all the medical insurance I needed, and I was a med student. But still I was extremely challenged as a patient as well as a doctor.
Most humorous incident
Sometimes, especially when you are abroad and alone, it feels so good and is so comforting to realize that the world is actually pretty small ... ;) Even while you are in NYC, you'll probably bump into some known faces once in a while. My funniest coincidence started right at the airport, in front of the immigration, where I met another med student from my home institution who was doing part of her Practical Year in NYC. Since I moved a lot in NYC, I had a hard time keeping everybody updated on my address. Just after having moved to my fourth and final domicile, I dropped her an e-mail, and proposed to have dinner at my place that night, since we were now both living in the Upper East Side. She agreed and asked for the address. My answer "63rd and York." Her answer "Oh, me too, what number?" "500." "You mean that big building? Can't be true! Which elevator do you take, the one on the right hand side?" "Yes, you also? On which floor are you living" "23 and you?" "Same with me!! 23B - Incredible!" "Wow, we are direct neighbors! My apartment is 23A. Isn't that funny?! I'll be knocking at your door in a minute!"
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Abstract on Research Topic
Neutralization capabilities of the DNA-editing enzymes APOBEC3G and APOBEC3F determine Vif protein function and HIV-1 mutagenesis
Authors: Svenja Kriener, Viviana Simon

Background:
Host cells use DNA-editing enzymes such as APOBEC3G and APOBEC3F as ways to curb invasion from viruses. In turn, human immunodeficiency viruses (HIV) and other retroviruses use an efficient, although unusual approach to the “gene silencing” of these cellular enzymes: the viral gene vif counters the antiretroviral activity of the cytidine deaminases APOBEC3G and APOBEC3F by inducing their degradation. It is conceivable, however, that Vif-mediated protection of HIV-1 genomes from host-mediated viral cDNA deamination is not absolute in vivo. We found Vif variants that selectively fail to neutralize APOPOBEC3G and/or APOBEC3F activity, and proviruses that appeared to be independently hypermutated as a result of APOBEC3G and/or APOBEC3F action. These studies indicate that natural variation in Vif function may profoundly impact the extent and direction of viral sequence evolution within HIV-1 infected individuals. Since APOBEC3G enzymes induce hypermutations in different dinucleotides contexts the understanding of how activity against one enzyme but not the other is maintained is relevant for viral evolution. In performing the experiments we aim to demonstrate that the DNA-editing enzymes APOBEC3G and APOBEC3F influence basic properties of the virus and play an eminent role in HIV-1 diversification.

Material and Methods:
We determine the domains in the 5’ region of Vif that are essential for the interaction by GT-pull down and co-immunoprecipitation experiments using naturally occurring and deletion Vif mutants. Then we transfect 293T cells with the Vif mutants expression plasmid, prepare cell lysates and incubate these with agarose beads that have been coated with GST, GST-APOBEC3F, GST-APOBEC3G, GST-Cullin5 and GST-ElonginC. Bound proteins are eluted and subjected to westen blot analysis with antiVif monoclonal antibodies. Also reciprocal immunoprecipitation is performed.

Conclusion:
The experiments demonstrate that there are regions in the N-terminal portion of Vif that interact with the APOBEC enzymes. The selective Vif acivity correlates with enzyme binding and reduced or abrogated Vif:APOBEC enzyme binding leads to preferential deamination of the viral genome in a GG dinucleotide or GA dinucleotide context.