Tumorvirus-specific Vaccination Strategies

Host cell restriction and dependency factors for Adeno-assocated viruses

Qingxin Chen, PhD student

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Introduction

Fig1. SUMOylation pathway factors and their z-scores identified in the screen are indicated
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Adeno-associated virus (AAV) is a single-stranded DNA-containing, nonpathogenic human parvovirus. In order to identify cellular factors could affect on rAAV-2 transduction, a high-throughput screen of siRNA libraries was performed. We identified Sae1/Sae2, Ubc9, Trim33 and Pias1 as host cell restriction factors. These cellular factors are key enzymes of the SUMOylation pathway, Therefore, we believe that SUMOylation pathway should be associated inevitably with AAV transduction. 

AAV entry and SUMOylation

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AAV transduction starts with cell attachment, followed by endocytosis, post-endocytic trafficking ending with the endosomal escape, nuclear translocation and finally uncoating, second strand synthesis and gene expression. In AAV transduction, postendocytic trafficking and cellular entry are regarded as rate limiting steps. Now we are proposing that the mechanism of AAV entry process is controlled by SUMOylation.

Table1. Prediction of putative SUMOylation sites in the AAV VP1 proteins.
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What is the target of SUMOylation in respect to AAV transduction? Is it the AAV capsid or a host cell factor? Whether the capsid proteins (consisting of VP1, VP2 and VP3) of rAAV2 possess a putative SUMOylation site or a Sumo interaction motif (SIM) was predicted by the freely available software GPS-SUMO (http://sumosp.biocuckoo.org/down.php) and in Table1 potential SUMOylation sites and SIMs of the capsid proteins of the currently known AAV serotypes are listed. Interestingly, nine of the thirteen serotypes seem to have a conserved target lysine at position K527 (according to serotype AAV2). Additionally, several other Lysine (K) residues are candidates as well. Previously it was shown that vectors in which some of these lysine were exchanged were significantly better transducing cell (Gabriel N et al. ), and Lochrie et al. showed that the single mutation K532A on AAV capsid surface could increase the transduction efficiency than AAV.

relevant publication

The SUMOylation pathway restricts gene transduction by adeno-associated viruses
Christina Hölscher, Florian Sonntag, Katharina Henrich, Qingxin Chen, Jürgen Beneke, Petr Matula, Karl Rohr, Lars Kaderali, Nina Beil, Holger Erfle,  Jürgen A. Kleinschmidt, and Martin Müller (2015) Plos. Pathogens 1;11(12): e1005281

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