The HPV16 E1 Carboxyl Domain Provides a Helper Function for Adeno-Associated Virus Replication

Recombinant adeno-associated virus (rAAV) is now in the clinic, yet production of rAAV remains problematic. We previously determined that human papillomavirus type 16 (HPV16) E1 protein boosts rAAV yields and E1 enhances AAV Rep78's replication-related biochemistries. Here, we deletion-mapped the helper domain within E1 to help glean its mechanism of action.

Rep78-E1 interaction was analyzed by Gal4-based yeast two-hybrid (Y2H)-cDNA assay. rAAV DNA replication was studied by AAV/helper plasmid transfection into HEK293 cells and Southern blot. Gene expression analysis was made of AAV and E1 plasmid transfection, cDNA generation, and then quantitative polymerase chain reaction. NCBI protein BLAST was used for the homology analysis.

Gal4-Y2H- cDNA assay found in vivo Rep78-E1-binding activity across E1, but the carboxyl-third (amino acids [aa] 421-649) of E1 contained the predominant DNA replication helper domain. The amino-half of E1 (aa 1-337) inhibited transcription of rep (p5 promoter) and cap (p40, trending lower) from non-replicating helper plasmid by quantitative (q)RT-PCR.

The aa 421-649 helper domain of HPV16 E1 includes the ATP-binding/helicase region of E1 which boosts rAAV production and has homology with the analogous region of parvovirus NS-1/Rep78 by NCBI protein BLAST, suggesting these biochemistries are responsible for the mechanism of action in E1 helper function.