We have used baculovirus-expressed Rep68 that has been purified to homogeneity to reexamine the binding properties of the Rep protein. We find that Rep68 is capable of binding to a linear DNA sequence that is contained within a 25-bp sequence of the A stem of the adeno-associated virus (AAV) terminal repeat proximal to the B and C palindromes. This has been shown conclusively by demonstrating that Rep68 could specifically

Adeno-associated virus (AAV) uses three promoters, p5, p19, and p40, to regulate viral gene expression. The p5 and p19 promoters direct the synthesis of the viral regulatory proteins, Rep78 and -68 and Rep52 and -40, respectively. The p5 Rep proteins bind a linear 22-bp sequence, the Rep binding element (RBE), that is within both the terminal repeat (TR) and the p5 promoter. In the absence of helper virus, all four Rep proteins have been shown to reduce transcription from the viral p5 and p19 promoters. In this report, we focus on the roles of these proteins and the RBEs in controlling transcription during a productive infection, that is, in the presence of adenovirus. We find that in the presence of adenovirus, the p5 RBE represses p5 transcription while the RBE in the TR activates p5. However, both the TR RBE and the p5 RBE transactivate the p19 and p40 promoters. The fact that the p5 RBE-Rep complex can transactivate p19 and p40 while repressing p5 suggests that Rep78/68 is both a repressor and a transactivator. Rep repression of p5 is specific for the p5 RBE, as other p5 promoter elements do not support this activity. We also demonstrate that in the presence of adenovirus, the p19 Rep proteins, which do not bind to the RBE, can eliminate repression of the p5 promoter by Rep78 and Rep68. This may occur by the association of Rep52 with Rep78 or Rep68 to produce a Rep78/68-Rep52 protein complex which can be detected in vivo by immunoprecipitation. Finally, two Rep mutants that were deficient in RBE binding and transactivation but positive for p5 repression were identified. These mutants may define interaction domains involved in making contacts with other proteins that facilitate repression. These observations suggest a mechanism for controlling the p5 and p19 mRNA levels during a productive AAV infection.

Control of adeno-associated virus (AAV) transcription from the three AAV promoters (p5, p19, and p40) requires the adenovirus E1a protein and the AAV nonstructural (Rep) proteins. The Rep proteins have been shown to repress the AAV p5 promoter yet facilitate activation of the p19 and p40 promoters during a productive infection. To elucidate the mechanism of promoter regulation by the AAV Rep proteins, the cellular factors involved in mediating Rep activation of the p19 promoter were characterized. A series of protein-DNA binding experiments using extracts derived from uninfected HeLa cells was performed to identify cellular factors that bind to the p19 promoter. Electrophoretic mobility shift assays, DNase I protection analyses, and UV cross-linking experiments demonstrated specific interactions with the cellular factor SP1 (or an SP1-like protein) at positions ؊50 and ؊130 relative to the start of p19 transcription. Additionally, an unknown cellular protein (cellular AAV activating protein [cAAP]) with an approximate molecular mass of 34 kDa was found to interact with a CArG-like element at position ؊140. Mutational analysis of the p19 promoter suggested that the SP1 site at ؊50 and the cAAP site at ؊140 were necessary to mediate Rep activation of p19. Antibody precipitation experiments demonstrated that Rep-SP1 protein complexes can exist in vivo. Although Rep was demonstrated to interact with p19 DNA directly, the affinity of Rep binding was much lower than that seen for the Rep binding elements within the terminal repeat and the p5 promoter. Furthermore, the interaction of purified Rep68 with the p19 promoter in vitro was negligible unless purified SP1 was also added to the reaction. Thus, the ability of Rep to transactivate the p19 promoter is likely to involve SP1-Rep protein contacts that facilitate Rep interaction with p19 DNA.

High systolic blood pressure caused by endothelial dysfunction is a comorbidity of metabolic syndrome that is mediated by local inflammatory signals. Insulin-induced vasorelaxation due to endothelial nitric oxide synthase (eNOS) activation is highly dependent on the activation of the upstream insulin-stimulated serine/threonine kinase (AKT) and is severely impaired in obese, hypertensive rodents and humans. Neutralisation of circulating tumor necrosis factor-α (TNFα) with infliximab improves glucose homeostasis, but the consequences of this pharmacological strategy on systolic blood pressure and eNOS activation are unknown. To address this issue, we assessed the temporal changes in the systolic pressure of spontaneously hypertensive rats (SHR) treated with infliximab. We also assessed the activation of critical proteins that mediate insulin activity and TNFα-mediated insulin resistance in the aorta and cardiac left ventricle. Our data demonstrate that infliximab prevents the upregulation of both systolic pressure and left ventricle hypertrophy in SHR. These effects paralleled an increase in AKT/eNOS phosphorylation and a reduction in the phosphorylation of inhibitor of nuclear factor-κB (Iκβ) and c-Jun N-terminal kinase (JNK) in the aorta. Overall, our study revealed the cardiovascular benefits of infliximab in SHR. In addition, the present findings further suggested that the reduction of systolic pressure and left ventricle hypertrophy by infliximab are secondary effects to the reduction of endothelial inflammation and the recovery of AKT/eNOS pathway activation.

We have identified the sequence elements that are required for adeno-associated virus type 2 p40 promoter activity. Mutation of specific promoter elements showed that two Sp1 sites at approximately ؊50 (Sp1-50) and ؊70 (GGT-70) bp upstream of the start of the p40 messages were necessary for maximal promoter activity. As expected, the TATA site at ؊30 was also essential. In vitro DNA binding experiments confirmed that the Sp1-50 and GGT-70 sites were bound by Sp1 or Sp1-like proteins. Two other transcription elements, the ATF-80 and AP1-40 sites, may play a role in p40 activity. Mutation of these elements resulted in a modest decrease in p40 transcription, but DNA binding experiments did not clearly demonstrate binding of transcription factors to these sites. In contrast, a major late transcription factor site at ؊110 was shown to bind the transcription factor, but mutation of this site had no effect on p40 activity. In a previous report, we have shown that transactivation of the p40 promoter by the viral Rep proteins required an upstream Rep binding element (in the terminal repeat or the p5 promoter), an unidentified p19 promoter element, and a p40 promoter element (D. J . Pereira and N. Muzyczka, J. Virol. 71:1747-1756, 1997). Here we demonstrate that the CArG-140 element in the p19 promoter and the Sp1-50 element in the p40 promoter are the specific p19 and p40 elements required for Rep induction of p40. As in the case of the p19 promoter, Sp1 facilitates interaction of Rep with the p40 promoter by interaction of the two proteins. Furthermore, electron microscopy experiments demonstrated that when Rep is bound to an upstream Rep binding element, it can interact with a proximal Sp1 site by protein contacts and create a loop in the intervening DNA. This finding suggests a common mechanism whereby the Rep binding element in the TR or the p5 promoter induces p19 and p40 activity by interaction with their respective Sp1 sites.

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The adeno-associated virus type 2 (AAV) replication (Rep) proteins Rep78 and 68 (Rep78/68) exhibit a number of biochemical activities required for AAV replication, including specific binding to a 22-bp region of the terminal repeat, site-specific endonuclease activity, and helicase activity. Individual and clusters of charged amino acids were converted to alanines in an effort to generate a collection of conditionally defective Rep78/68 proteins. Rep78 variants were expressed in human 293 cells and analyzed for their ability to mediate replication of recombinant AAV vectors at various temperatures. The biochemical activities of Rep variants were further characterized in vitro by using Rep68 His-tagged proteins purified from bacteria. The results of these analyses identified a temperature-sensitive (ts) Rep protein (D40,42,44A-78) that exhibited a delayed replication phenotype at 32°C, which exceeded wild-type activity by 48 h. Replication activity was reduced by more than threefold at 37°C and was undetectable at 39°C. Stability of the Rep78 protein paralleled replication levels at each temperature, further supporting ats phenotype. Replication differences resulted in a 3-log-unit difference in virus yields between the permissive and nonpermissive temperatures (2.2 × 106 and 3 × 103, respectively), demonstrating that this is a relatively tight mutant. In addition to the ts Rep mutant, we identified a nonconditional mutant with a reduced ability to support viral replication in vivo. Additional characterization of this mutant demonstrated an Mg2+-dependent phenotype that was specific to Rep endonuclease activity and did not affect helicase activity. The two mutants described here are unique, in that Rep tsmutants have not previously been described and the D412A Rep mutant represents the first mutant in which the helicase and endonuclease functions can be distinguished biochemically. Further understanding of these mutants should facilitate our understanding of AAV replication and integration, as well as provide novel strategies for production of viral vectors.

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