Structural and functional analysis of the Rous Sarcoma virus negative regulator of splicing and demonstration of its activation by the 9G8 SR protein

Understanding and Rescuing the Splicing Defect Caused by the Frequent ABCA4 Variant c.4253+43G>A Underlying Stargardt Disease

Pathogenic variants in ABCA4 are the underlying molecular cause of Stargardt disease (STGD1), an autosomal recessive macular dystrophy characterized by a progressive loss of central vision. Among intronic ABCA4 variants, c.4253+43G>A is frequently detected in STGD1 cases and is classified as a hypomorphic allele, generally associated with late-onset cases. This variant was previously reported to alter splicing regulatory sequences, but the splicing outcome is not fully understood yet. In this study, we attempted to better understand its effect on splicing and to rescue the aberrant splicing via antisense oligonucleotides (AONs). Wild-type and c.4253+43G>A variant-harboring maxigene vectors revealed additional skipping events, which were not previously detected upon transfection in HEK293T cells. To restore exon inclusion, we designed a set of 27 AONs targeting either splicing silencer motifs or the variant region and screened these in maxigene-transfected HEK293T cells. Candidate AONs able to promote exon inclusion were selected for further testing in patient-derived photoreceptor precursor cells. Surprisingly, no robust splicing modulation was observed in this model system. Overall, this research helped to adequately characterize the splicing alteration caused by the c.4253+43G>A variant, although future development of AON-mediated exon inclusion therapy for ABCA4 is needed.

The RNA-Binding Proteins SRP14 and HMGB3 Control HIV-1 Tat mRNA Processing and Translation During HIV-1 Latency

HIV-1 Tat protein is essential for virus production. RNA-binding proteins that facilitate Tat production may be absent or downregulated in resting CD4+ T-cells, the main reservoir of latent HIV in people with HIV (PWH) on antiretroviral therapy (ART). In this study, we examined the role of Tat RNA-binding proteins on the expression of Tat and control of latent and productive infection. Affinity purification coupled with mass spectrometry analysis was used to detect binding partners of MS2-tagged tat mRNA in a T cell-line model of HIV latency. The effect of knockdown and overexpression of the proteins of interest on Tat transactivation and translation was assessed by luciferase-based reporter assays and infections with a dual color HIV reporter virus. Out of the 243 interactions identified, knockdown of SRP14 (Signal Recognition Particle 14) negatively affected tat mRNA processing and translation as well as Tat-mediated transactivation, which led to an increase in latent infection. On the other hand, knockdown of HMGB3 (High Mobility Group Box 3) resulted in an increase in Tat transactivation and translation as well as an increase in productive infection. Footprinting experiments revealed that SRP14 and HMGB3 proteins bind to TIM-TAM, a conserved RNA sequence-structure in tat mRNA that functions as a Tat IRES modulator of tat mRNA. Overexpression of SRP14 in resting CD4+ T-cells from patients on ART was sufficient to reverse HIV-1 latency and induce virus production. The role of SRP14 and HMGB3 proteins in controlling HIV Tat expression during latency will be further assessed as potential drug targets.

Designing and evaluation of MERS-CoV siRNAs in HEK-293 cell line

Background

The MERS-CoV was identified for the first time from Jeddah, Saudi Arabia in 2012 from a hospitalized patient. This virus has now been spread to 27 countries with a total of 858 deaths and 2494 confirmed cases and has become a serious concern for the human population. Camels are well known for the transmission of the virus to the human population.

Methods

In this report, we have discussed the designing, prediction, and evaluation of potential siRNAs against the orf1ab gene of MERS-CoV. The online software was used to predict and design the siRNAs and finally, total twenty-one siRNA were filtered out from four hundred and sixty-two sIRNAs as per their scoring and specificity criteria. We have used only ten siRNAs to evaluate their cytotoxicity and efficacy by reverse transfection approach in HEK-293-T cell lines.

Results

Based on the results and data generated; no cytotoxicity was observed for any siRNAs at various concentrations in HEK-293-T cells. The ct value of real-time PCR showed the inhibition of viral replication in siRNA-1, 2, 4, 6, and 9. The data generated provided the preliminary information and encouraged us to evaluate the remaining siRNAs separately as well as in combination to analyses the replication of MERS-CoV inhibition in other cell lines.

Conclusion

Based on the results obtained; it is concluded that the prediction of siRNAs using online software resulted in the filtration of potential siRNAs with high accuracy and strength. This technology can be used to design and develop antiviral therapy not only for MERS-CoV but also against other viruses.