The adenovirus E4 ORF6 and E1b 55 kDa proteins cooperate in a p53-independent manner to enhance transduction by recombinant adeno-associated virus vectors

Mechanisms of AAV transduction in glaucoma-associated human trabecular meshwork cells

BACKGROUND

Glaucoma is a chronic eye disease which leads to irreversible blindness. The trabecular meshwork tissue controls intraocular pressure (IOP), which is the major risk factor for glaucoma. Gene therapy treatment of chronic diseases requires the use of long-term expression, low toxicity and lack of immune response vectors. Adeno-associated viruses (AAV) possess these characteristics but have been unable to transduce the trabecular meshwork. Because of the importance of regulating elevated IOP by long-term gene therapy, we investigated mechanisms of AAV transduction to the human trabecular meshwork (TM).

METHODS

Primary human trabecular meshwork cells (HTM) and perfused organ cultures were infected with rAAV2-GFP, RGD-pseudotyped rAAV2-GFP alone, or combined with recombinant DeltaE1/E3 adenoviruses. Intracellular rAAV2 DNA and RNA were measured by relative quantitative and real-time TaqMan polymerase chain reaction (PCR). Host transcriptome was analyzed using high-density oligonucleotide microarrays. One transduction mechanism was tested using self-complementary AAV (scAAV).

RESULTS

The dramatic transduction enhancement obtained upon co-infection of rAAV2 with DeltaE1/E3 adenoviruses provides insights into transduction mechanisms in the HTM. Even if not transduced, rAAV2 enters TM cells. GeneChip analysis showed significant changes in host genes involved in cell cycle and DNA replication. Consequently, scAAV-GFP transduction was highly efficient. Other transduction-enhancement genes included coxsackie adenovirus receptor (CAR) and genes relevant to trabecular meshwork function.

CONCLUSIONS

The rate-limiting step of AAV transduction was not viral entry failure but, at least in part, host downregulation of DNA replication. Additional specific host genes might be involved. Our study revealed genes and mechanisms which led for the first time to efficient AAV transduction of the HTM.

Impurity of recombinant adeno-associated virus type 2 affects the transduction characteristics following subretinal injection in the rat

We recently reported that different purification methods of recombinant adeno-associated virus type 2 (rAAV2) affect the transduction characteristics following subretinal injection. In this study, we examined the roles of contaminant proteins from the HEK-293 cells and helper adenovirus, inactivation of helper adenovirus and cell stress induced by DNA-damaging agents in rAAV-mediated retinal transduction. Our results showed that contaminating factors/proteins resulting from the helper E1 deleted adenovirus are possibly responsible for efficient RPE transduction. Future studies of these factors will undoubtedly lead to development of new therapeutic approaches to PR- and RPE-specific retinal diseases.

Molecular regulation and biological function of adenovirus early genes: the E4 ORFs

Over the past few years there have been a number of interesting advances in our understanding of the functions encoded by the adenovirus early transcription unit 4 (Ad E4). A large body of recent data demonstrates that E4 proteins encompass an unexpectedly diverse collection of functions required for efficient viral replication. E4 gene products operate through a complex network of protein interactions with key viral and cellular regulatory components involved in transcription, apoptosis, cell cycle control and DNA repair, as well as host cell factors that regulate cell signaling, posttranslational modifications and the integrity of nuclear multiprotein complexes known as nuclear bodies (NBs) or PML oncogenic domains (PODs). As understood at present, some of the lytic functions overlap with roles in oncogenic transformation of primary mammalian cells. These observations, together with findings that E4 proteins substantially affect cell toxicity and the immune response of the host have profound implications for the development of Ad vectors for gene therapy. In this article we will summarize recent findings regarding the diverse functions of E4 gene products in the context of earlier work. We will emphasize the interaction of E4 proteins with cellular and viral interaction partners, the role of these interactions for lytic virus growth and how these interactions may contribute to viral oncogenesis. Finally, we will discuss their role in Ad vector and adeno-associated virus infections.