Living myocardial slices for the study of nucleic acid-based therapies

Gene therapy based on viral vectors offers great potential for the study and the treatment of cardiac diseases. Here we explore the use of Living Myocardial Slices (LMS) as a platform for nucleic acid-based therapies. Rat LMS and Adeno-Associated viruses (AAV) were used to optimise and analyse gene transfer efficiency, viability, tissue functionality, and cell tropism in cardiac tissue. Human cardiac tissue from failing (dilated cardiomyopathy) hearts was also used to validate the model in a more translational setting. LMS were cultured at physiological sarcomere length for 72-h under electrical stimulation. Two recombinant AAV serotypes (AAV6 and AAV9) at different multiplicity of infection (MOI) expressing enhanced green fluorescent protein (eGFP) were added to the surface of rat LMS. AAV6 at 20,000 MOI proved to be the most suitable serotype without affecting LMS contractility or kinetics and showing high transduction and penetrability efficiency in rat LMS. This serotype exhibited 40% of transduction efficiency in cardiomyocytes and stromal cells while 20% of the endothelial cells were transduced. With great translational relevance, this protocol introduces the use of LMS as a model for nucleic acid-based therapies, allowing the acceleration of preclinical studies for cardiac diseases.

What is the best surgical option after failure of graciloplasty in patients with recurrent rectovaginal fistula? A study of 19 consecutive patients

BACKGROUND

Management of recurrent rectovaginal fistula (rRVF) remains challenging despite the good results of graciloplasty reported in the literature. However, little is known about how to avoid a permanent stoma if graciloplasty fails. The aim of our study was to report the management of rRVF after failure of graciloplasty.

METHODS

A retrospective study was performed on consecutive patients with rRVF after failure of graciloplasty treated at our institution in January 2005-December 2021.

RESULTS

There were 19 patients, with a median age at graciloplasty of 39 years (range 25-64 years). Etiologies of RVF were Crohn's disease (CD) (n = 10), postoperative (n = 5), post-obstetrical (n = 3), and unknown (n = 1). After failure of graciloplasty, 45 new procedures were performed, all of them with a covering stoma: trans-anal repairs (n = 31), delayed colo-anal anastomosis (DCAA) (n = 4), biological mesh interposition (n = 3), second graciloplasty (n = 3), stoma only (n = 2) and redo ileal pouch-anal anastomosis (IPAA) (n = 2). One patient was not re-operated on and instead treated medically for CD. After a mean follow-up of 63 ± 49 months, success (i.e., absence of stoma or RVF) was obtained in 11 patients (58%): 4/4 DCAA (100%), 5/31 after local repair (16%), 1 after stoma creation alone (50%) and 1 after redo IPAA (50%). Second graciloplasty and biologic mesh interposition all failed. All 8 patients with failed intervention had CD.

CONCLUSIONS

In cases of rRVF after failed graciloplasty, reoperation is possible, although the chance of success is relatively low. The best results were obtained with DCAA. CD is a predictor of poor outcome.

Nucleic acid-based therapies using living myocardial slices

Background

Gene therapy based on viral vectors is a promising new approach and offers great potential for the study and the treatment of cardiac diseases. Nucleic acid-based transfection of human heart tissue could be considered a valid and translational alternative to the use of transgenic animal models in cardiovascular research.

Purpose

Here we explore the use of Living Myocardial Slices (LMS) as a platform for nucleic acid-based therapies. Rat LMS and Adeno-Associated viruses (AAV) were used to optimise and analyse gene transfer efficiency, viability, tissue functionality, and cell tropism in cardiac tissue. Human cardiac samples from failing (dilated cardiomyopathy) hearts were also used to validate the human model. In addition, we transfected and tested for the first time the regenerative effect of AAV-miR-199a in both healthy and pathologically overloaded LMS.

Methods

LMS (300 μm thick) were prepared and glued to PTFE-coated holders, mounted on custom stretchers, and cultured at physiological sarcomere length for 72-hours under electrical stimulation. Two recombinant AAV serotypes (AAV-6 and AAV-9) at different multiplicity of infection (MOI) expressing green fluorescent protein (GFP) or the miR-199 transgene were added to the surface of the LMS.

Results

AAV6 proved to be the most suitable serotype and 20,000 MOI the most efficient dose, as these conditions were proven not to affect LMS contractility and to have the highest transduction and penetrability efficiency. This serotype exhibited preferential cell tropism to cardiomyocytes and stromal cells (40% of transduction in both) in rat LMS, with lower efficiency in endothelial cells, (20% of transduction). In contrast, AAV6 in human failing LMS showed higher transduction efficiency in endothelial cells and myofibroblasts. Treatment with miR-199a significantly increased the active force of pathologically overstretched LMS, downregulated the expression of its target genes, and affected the proliferative capacity of LMS.

Conclusion

LMS can be used as a model for nucleic acid-based therapies and their transfection protocol can be adapted to samples obtained from failing human hearts. With great translational relevance, this model would accelerate preclinical studies of novel nucleic acid-based therapies for heart failure.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): British Heart Foundation

C-reactive protein monitoring after ileocecal resection and stoma closure reduces length of hospital stay: a prospective case-matched study in 410 patients with Crohn's disease

BACKGROUND

The aim of this study was to evaluate a C-reactive protein (CRP)-driven monitoring discharge strategy for patients with Crohn's disease (CD) undergoing laparoscopic ileo-cecal resection (ICR) and if needed, temporary stoma closure (SC).

METHODS

Four hundred and ten patients who underwent laparoscopic ICR for CD: 153 patients (CRP group) between June 2016 and June 2020 at our department, had a CRP-driven monitoring discharge on postoperative day (POD) 3 and were discharged on POD 4 if CRP < 100 mg/L. These patients were matched (according to age, sex, body mass index, type of CD (and stoma or not) to 257 patients who underwent laparoscopic ICR for CD between January 2009 and May 2016, without CRP monitoring (Control group). For SC, 79 patients with CRP monitoring were matched with 88 control patients. Primary outcome was overall length of hospital stay (LHS). Secondary outcomes were discharge on POD 4 for SC and POD 4 and POD 6 for ICR, 3-month postoperative overall morbidity and severe morbidity rates, surgical site infection, readmission rates, and CRP level in cases of morbidity at 3 months.

RESULTS

For ICR without stoma, mean LHS was significantly shorter in the CRP group than in the control group (6.9 ± 2 days vs 8.3 ± 6 days, p = 0.017). Discharge occurred on POD 6 (or before) in 73% of the patients (CRP group) vs 60% (Control group) (p = 0.027). For ICR with stoma, LHS was 8 days for both groups (p = 0.612). For SC, LHS was significantly shorter in the CRP group than in the control group (5.5 ± 3 days vs 7.1 ± 4 days; p = 0.002). Discharge occurred on POD 4 in 62% (CRP group) vs 30% (Control) (p = 0.003). Postoperative 3-month overall and severe morbidity, and rehospitalization rates were similar between groups.

CONCLUSIONS

CRP-driven monitoring discharge strategy after laparoscopic ICR for CD is associated with a significant reduction of LHS, without increasing morbidity, reoperation or rehospitalisation rates.

Will our cardiomyopathy patients accept gene therapy?

Novel techniques such as gene therapy are becoming available in an attempt to cure inherited diseases. Before these new therapies can be offered to patients, we need to be aware of potential reservations or objections, not only from patients and their surroundings but also from the public. In addition, legal issues and costs need attention before curative gene therapy can be applied in the clinic. As this therapeutic approach is closer to becoming a reality, now is the right time to start the debate.

AAV9-mediated engineering of autotransplanted kidney of non-human primates

Ex vivo gene transfer to the graft before transplantation is an attractive option for circumventing systemic side effects of chronic antirejection therapy. Gene delivery of the immunomodulatory protein cytotoxic T-lymphocyte-associated protein 4-immunoglobulin (CTLA4-Ig) prevented chronic kidney rejection in a rat model of allotransplantation without the need for systemic immunosuppression. Here we generated adeno-associated virus type 2 (AAV2) and AAV9 vectors encoding for LEA29Y, an optimized version of CTLA4-Ig. Both LEA29Y vectors were equally efficient for reducing T-cell proliferation in vitro. Serotype 9 was chosen for in vivo experiments owing to a lower frequency of preformed antibodies against the AAV9 capsid in 16 non-human primate tested sera. AAV9-LEA29Y was able to transduce the kidney of non-human primates in an autotransplantation model. Expression of LEA29Y mRNA by renal cells translated into the production of the corresponding protein, which was confined to the graft but not detected in serum. Results in non-human primates represent a step forward in maintaining the portability of this strategy into clinics.

Intravenous lipid infusion and total plasma fatty acids positively modulate plasma acylated ghrelin in vivo

BACKGROUND & AIMS

Ghrelin is a gastric orexigenic hormone whose activating acylation plays a relevant role in the regulation of energy balance. Nutritional modulators of ghrelin acylation and plasma acylated ghrelin (AG) concentration remain however largely undefined. We aimed at investigating whether circulating free fatty acids (FFA) contribute to regulate plasma AG and its ratio (AG/TG) to total hormone (TG).

METHODS

Plasma FFA, TG, AG and AG/TG were measured in a primary outpatient care setting in a community-based population cohort of 850 individuals (age 54 ± 10 years, M/F: 408/442) from the North-East Italy MoMa study. 150-min intravenous lipid infusions in rodents (10% lipids, 600 μl/h) were used to investigate the potential causal role of FFA in the regulation of plasma ghrelin profile.

RESULTS

Plasma FFA were associated positively with AG and AG/TG while negatively with TG (P < 0.01). Associations between FFA, AG and AG/TG remained statistically significant (P < 0.02) in multiple regression analysis including HOMA insulin resistance and metabolic confounders, and both AG and AG/TG but not TG increased through plasma FFA quartiles (P < 0.01). Consistent with these findings, intravenous lipid infusion with plasma FFA elevation caused elevations of AG and AG/TG (P < 0.05) with no TG modifications.

CONCLUSIONS

The current findings demonstrate a novel role for circulating FFA availability to up-regulate plasma AG, which could involve FFA-induced stimulation of ghrelin acylation.

Plasma total and unacylated ghrelin predict 5-year changes in insulin resistance

BACKGROUND & AIMS

Ghrelin is a gastric hormone circulating in acylated (AG) and unacylated (UG) forms, and higher plasma total ghrelin (TG) and UG may be cross-sectionally associated with lower insulin resistance in metabolic syndrome patients. The potential value of ghrelin forms in predicting insulin resistance and its time-related changes in community-based population cohorts remains unknown.

METHODS

We measured TG, AG and calculated UG (TG-AG) in 716 individuals from the North-East-Italy MoMa study (age: 55 ± 9 years, BMI: 29 ± 5 kg/m(2), M/F:349/367) to test the hypothesis that circulating TG and UG, but not AG are negatively associated with insulin resistance (HOMA). We further hypothesized that baseline TG and UG negatively predict 5-year HOMA changes in a 350-individual subgroup.

RESULTS

Baseline TG and UG were associated negatively with HOMA after adjusting for gender and body mass index (BMI). Baseline gender- and BMI-adjusted TG and UG were also negatively associated with HOMA at 5-year follow-up (n = 350), and changes in TG and UG were negatively associated with changes in HOMA (P < 0.05) after adjustment for anthropometric and metabolic confounders. No statistically significant correlations were observed between AG and baseline or 5-year HOMA.

CONCLUSIONS

In a North-East Italy community-based population cohort, plasma TG and UG but not AG are negatively associated with HOMA. TG and UG and their changes also independently predict 5-year HOMA changes. TG and UG are therefore novel potential modulators of insulin resistance and may contribute to predict its time-related changes in humans.

Effect of vascular endothelial growth factor gene therapy on post-traumatic peripheral nerve regeneration and denervation-related muscle atrophy

Functional recovery after peripheral nerve injury depends on both improvement of nerve regeneration and prevention of denervation-related skeletal muscle atrophy. To reach these goals, in this study we overexpressed vascular endothelial growth factor (VEGF) by means of local gene transfer with adeno-associated virus (AAV). Local gene transfer in the regenerating peripheral nerve was obtained by reconstructing a 1-cm-long rat median nerve defect using a vein segment filled with skeletal muscle fibers that have been previously injected with either AAV2-VEGF or AAV2-LacZ, and the morphofunctional outcome of nerve regeneration was assessed 3 months after surgery. Surprisingly, results showed that overexpression of VEGF in the muscle-vein-combined guide led to a worse nerve regeneration in comparison with AAV-LacZ controls. Local gene transfer in the denervated muscle was obtained by direct injection of either AAV2-VEGF or AAV2-LacZ in the flexor digitorum sublimis muscle after median nerve transection and results showed a significantly lower progression of muscle atrophy in AAV2-VEGF-treated muscles in comparison with muscles treated with AAV2-LacZ. Altogether, our results suggest that local delivery of VEGF by AAV2-VEGF-injected transplanted muscle fibers do not represent a rational approach to promote axonal regeneration along a venous nerve guide. By contrast, AAV2-VEGF direct local injection in denervated skeletal muscle significantly attenuates denervation-related atrophy, thus representing a promising strategy for improving the outcome of post-traumatic neuromuscular recovery after nerve injury and repair.

VEGF gene therapy: therapeutic angiogenesis in the clinic and beyond

Despite the enormous progress made in terms of prevention and early intervention, a pressing need remains to develop innovative therapeutic strategies for ischemic cardiovascular disorders, including acute myocardial infarction, chronic cardiac ischemia, peripheral artery disease and stroke. The induction of new blood vessel formation by delivering angiogenic genes to ischemic tissues continues to appear as a promising, alternative strategy to currently available therapies. In aspiring to induce therapeutic angiogenesis, the members of the vascular endothelial growth factor (VEGF) family have long been recognized as major molecular tools. Remarkably, VEGF family members have recently been recognized to also exert multiple, non-angiogenic effects on various cell types, including neurons, skeletal muscle and cardiac cells. Here, we critically review the VEGF-based therapies that have already reached clinical experimentation and highlight the pleiotropic activities of VEGF factors that might create new opportunities for therapeutic application.

Adeno-associated viral vector-mediated human vascular endothelial growth factor gene transfer stimulates angiogenesis and wound healing in the genetically diabetic mouse

AIMS/HYPOTHESIS

We studied the gene therapy efficacy of diabetes-associated wound healing disorder with an adeno-associated virus (AAV) vector expressing the 165-amino acid isoform of human vascular endothelial growth factor-A (VEGF-A) by using an incisional skin-wound model produced on the back of female diabetic C57BL/KsJ db+/db+ mice and their normal littermates ( db+/+m).

METHODS

Animals were randomized to receive intradermally into the wound edges either rAAV-LacZ (a control gene), or rAAV-VEGF165. Animals were killed on different days (7 and 14 days after skin injury) and wounded skin tissues were used for gene marker studies, histological evaluation and immunohistochemistry, and wound breaking strength analysis. Furthermore we studied the VEGF mature protein in the wounds.

RESULTS

We found that AAV vectors are highly efficient for gene transfer to the mouse skin, displaying an exquisite tropism for the panniculus carnosus by using the beta-galactosidase activity assay. We confirmed the increased expression of the angiogenic factor at day 7 by measuring the wound content of the mature protein. Delivery of VEGF165 to incisional skin wounds of diabetic mice resulted in a remarkable induction of new vessel formation with consequent improvement in the wound healing process. The rAAV-VEGF165 gene improved wound healing in diabetic mice through the stimulation of angiogenesis, reepithelization, synthesis and maturation of extracellular matrix. Moreover the recombinant AAV encoding the human VEGF165 increased the breaking strength of the wound and enhanced the wound content of VEGF.

CONCLUSION/INTERPRETATION

Our study suggests that VEGF gene transfer might represent a new approach to treat wound healing disorders associated with diabetes.

Recombinant AAV vector encoding human VEGF165 enhances wound healing

Delivery of therapeutic genes represents an appealing possibility to accelerate healing of wounds that are otherwise difficult to treat, such as those in patients with metabolic disorders or infections. Experimental evidence indicates that in such conditions potentiation of neo-angiogenesis at the wound site might represent an important therapeutic target. Here we explore the efficacy of gene therapy of wound healing with an adeno-associated virus (AAV) vector expressing the 165 amino acid isoform of vascular endothelial growth factor-A (VEGF-A). By gene marker studies, we found that AAV vectors are highly efficient for gene transfer to the rat skin, displaying an exquisite tropism for the panniculus carnosus. Gene expression from these vectors is sustained and persistent over time. Delivery of VEGF165 to full thickness excisional wounds in rats resulted in remarkable induction of new vessel formation, with consequent reduction of the healing time. Histological examination of treated wounds revealed accelerated remodeling of epidermis and dermis, with formation of a thick granular layer, containing numerous newly formed capillaries, as well as vessels of larger size. These data underline the importance of neo-angiogenesis in the healing process and indicate that VEGF gene transfer might represent a novel approach to treat wound healing disorders.

Involvement of cellular double-stranded DNA break binding proteins in processing of the recombinant adeno-associated virus genome

Unlike postmitotic tissues in vivo, transduction of cultured cells is poor with recombinant adeno-associated virus (rAAV). The ability of rAAV to transduce cells is greatly enhanced by a variety of agents that induce DNA damage and is elevated in cells defective in the ataxia telangiectasia gene product (ATM), showing increased genomic instability. Here we show that DNA double-stranded break (DSB) repair pathways are involved in the regulation of rAAV transduction efficiency. By quantitative chromatin immunoprecipitation, we found that Ku86 and Rad52 proteins associate with viral DNA inside transduced cells. Both proteins are known to competitively recognize hairpin structures and DNA termini and to promote repair of DSBs, the former by facilitating nonhomologous end joining and the latter by initiating homologous recombination. We found that rAAV transduction is increased in Ku86-defective cells while it is inhibited in Rad52 knockout cells. These results suggest that binding of Rad52 to the rAAV genome might be involved in processing of the vector genome through a homologous recombination pathway.

Visualization of in vivo direct interaction between HIV-1 TAT and human cyclin T1 in specific subcellular compartments by fluorescence resonance energy transfer

Human cyclin T1, a component of the P-TEFb kinase complex, was originally identified through its biochemical interaction with the Tat transactivator protein of human immunodeficiency virus type 1 (HIV-1). Current understanding suggests that binding of Tat to P-TEFb is required to promote efficient transcriptional elongation of viral RNAs. However, the dynamics and the subnuclear localization of this process are still largely unexplored in vivo. Here we exploit high resolution fluorescence resonance energy transfer (FRET) to visualize and quantitatively analyze the direct interaction between Tat and cyclin T1 inside the cells. We observed that cyclin T1 resides in specific subnuclear foci which are in close contact with nuclear speckles and that Tat determines its redistribution outside of these compartments. Consistent with this observation, strong FRET was observed between the two proteins both in the cytoplasm and in regions of the nucleus outside of cyclin T1 foci and overlapping with Tat localization. These results are consistent with a model by which Tat recruits cyclin T1 outside of the nuclear compartments where the protein resides to promote transcriptional activation.

Changes in thymic function in HIV-positive patients treated with highly active antiretroviral therapy and interleukin-2

Despite its potent antiviral activity, highly active antiretroviral therapy (HAART) only exerts a marginal effect on CD4+ T-cell regeneration in HIV-infected subjects. Combination therapies aimed at boosting T-cell activity and maturation may provide an important contribution to the restoration of immune function. Here, we report the results obtained by a two-year follow-up of a cohort of HIV-infected patients treated with a combination of HAART and interleukin-2 (IL-2). In these patients, in addition to a series of quantitative virological and immunological parameters, we investigated T-cell regeneration by an immunophenotypic assay monitoring CD4+ naïve T cells, and by analysis of thymic function, through the quantification of the excision DNA products of T-cell receptor rearrangement (TRECs) in lymphocytes. Compared with HAART alone, we found that the IL-2 combination therapy was equally effective in reducing the levels of viremia and marginally more effective in decreasing proviral DNA load. Strikingly, the IL-2 combination produced a marked increase in the number of CD4+ T cells bearing a naïve phenotype (CD45RA+, CD62L+), which was apparent for over 96 weeks after therapy. To assess whether these cells were the product of improved T-cell generation, we exploited a competitive quantitative molecular assay to quantify TRECs in peripheral blood lymphocytes. Surprisingly, we found that the levels of these molecules were unchanged in these patients. These findings indicate that improved thymic function does not account for the early rise of CD4 naïve cells in HIV-positive patients treated with IL-2, and suggest that alternative mechanisms of T-cell maturation and differentiation are responsible for this event.

Pentosan polysulfate as an inhibitor of extracellular HIV-1 Tat

HIV-1 Tat protein, released from HIV-infected cells, may act as a pleiotropic heparin-binding growth factor. From this observation, extracellular Tat has been implicated in the pathogenesis of AIDS and of AIDS-associated pathologies. Here we demonstrate that the heparin analog pentosan polysulfate (PPS) inhibits the interaction of glutathione S-transferase (GST)-Tat protein with heparin immobilized to a BIAcore sensor chip. Competition experiments showed that Tat-PPS interaction occurs with high affinity (K(d) = 9.0 nm). Also, GST.Tat prevents the binding of [(3)H]heparin to GST.Tat immobilized to glutathione-agarose beads. In vitro, PPS inhibits GST.Tat internalization and, consequently, HIV-1 long terminal repeat transactivation in HL3T1 cells. Also, PPS inhibits cell surface interaction and mitogenic activity of GST.Tat in murine adenocarcinoma T53 Tat-less cells. In all assays, PPS exerts its Tat antagonist activity with an ID(50) equal to approximately 1.0 nm. In vivo, PPS inhibits the neovascularization induced by GST.Tat or by Tat-overexpressing T53 cells in the chick embryo chorioallantoic membrane. In conclusion, PPS binds Tat protein and inhibits its cell surface interaction, internalization, and biological activity in vitro and in vivo. PPS may represent a prototypic molecule for the development of novel Tat antagonists with therapeutic implications in AIDS and AIDS-associated pathologies, including Kaposi's sarcoma.

Coherent dynamics of photoexcited green fluorescent proteins

The coherent dynamics of vibronic wave packets in the green fluorescent protein is reported. At room temperature the nonstationary dynamics following impulsive photoexcitation displays an oscillating optical transmissivity pattern with components at 67 fs (497 cm(-1)) and 59 fs (593 cm(-1)). Our results are complemented by ab initio calculations of the vibrational spectrum of the chromophore. This analysis shows the interplay between the dynamics of the aminoacidic structure and the electronic excitation in the primary optical events of green fluorescent proteins.

Genetic determinants of ethanol-induced liver damage

BACKGROUND

Although a clear correlation exists between cumulative alcohol intake and liver disease, only some of the alcohol abusers develop signs of ethanol-induced liver damage. To identify some of the genetic variations predisposing persons to alcoholic liver disease (ALD), a genetic study was performed in heavy drinkers from the cohort of the Dionysis study, a survey aimed at evaluating liver disease in the open population of two towns in Northern Italy (6917 individuals).

MATERIALS AND METHODS

158 heavy drinkers (approximately 85% of all heavy drinkers in the population; daily alcohol intake > 120 g in males and >60 g in females) were investigated by the analysis of nine polymorphic regions, mapping in exons III and IX of the alcohol-dehydrogenase (ADH)-2 gene, in exon VIII of the ADH3 gene, in intron VI, in the promoter region of the cytochrome P4502E1 (CYP2E1) gene, and in the promoter region of the tumor necrosis factor-alpha gene.

RESULTS

Heavy drinkers with or without ALD significantly differed for the distribution of alleles of the cytochrome P4502E1 (CYP2E1) and alcohol-dehydrogenase-3 (ADH-3) genes. In one town, allele C2 in the promoter region of the CYP2E1 gene had a frequency of 0.06 in healthy heavy drinkers, of 0.19 in heavy drinkers with ALD (p = 0.012), and of 0.33 in heavy drinkers with cirrhosis (p = 0.033). In the other town, whose inhabitants have different genetic derivation, a prominent association between ALD and homozygosity for allele ADH3*2 of ADH3 was found, with a prevalence of 0.31 in heavy drinkers with ALD and of 0.07 in healthy heavy drinkers controls (p = 0.004). CONCLUSIONS. Both heterozygosity for allele C2 of CYP2E1 and homozygosity for allele ADH3*2 of ADH3 are independent risk factors for ALD in alcohol abusers. The relative contribution of these genotypes to ALD is dependent on their frequency in the population. Overall, heavy drinkers lacking either of these two genotypes are 3.2 and 4.3 times more protected from developing ALD and cirrhosis respectively.

Multiple modes of transcriptional regulation by the HIV-1 Tat transactivator

Regulation of HIV-1 gene expression by the viral Tat transactivator is a critical step in the viral life cycle. Tat acts as a highly unusual transcription factor that interacts with a stem-loop RNA structure (TAR) found at the 5' end of all viral transcripts. There, it induces a modification of chromatin at the HIV-1 long terminal repeat (LTR) promoter and stimulates the recruitment of elongation-competent RNA polymerase II complexes capable of processive transcription. Increase of transcriptional elongation is the consequence of the interaction of Tat with cyclin T1, the cyclin component of CDK9, which phosphorylates the carboxy-terminal domain of RNA polymerase II to enhance its processivity. Tat-induced transcriptional activation of the LTR promoter is concomitant with recruitment of the transcriptional coactivators p300 and the highly homologue cAMP-responsive transcription factor binding protein (CBP). These large proteins act at the level of transcriptional initiation by bridging the basal transcription machinery with specific transcriptional activators. Furthermore, p300/CBP are histone acetyl-transferases capable of modulating the interaction of nucleosomes with DNA and with chromatin remodeling complexes. Besides histones, Tat itself is a substrate for the enzymatic activity of p300/CBP and of the associated factor P/CAF, suggesting a regulatory role of acetylation on the protein itself. Devising a unifying model for LTR activation that includes activities of Tat at the levels of both transcriptional initiation and transcriptional elongation is a challenging task at this moment. Nevertheless, protein localization studies indicate that both cyclin T1 and p300/CBP co-localize in specific subnuclear compartments, thus suggesting participation of both proteins in the formation of multimolecular complexes governing coordinated steps of transcriptional activation.

Internalization of HIV-1 tat requires cell surface heparan sulfate proteoglycans

Tat, the transactivator protein of human immunodeficiency virus-1, has the unusual capacity of being internalized by cells when present in the extracellular milieu. This property can be exploited for the cellular delivery of heterologous proteins fused to Tat both in cell culture and in living animals. Here we provide genetic and biochemical evidence that cell membrane heparan sulfate (HS) proteoglycans act as receptors for extracellular Tat uptake. Cells genetically defective in the biosynthesis of fully sulfated HS are selectively impaired in the internalization of recombinant Tat fused to the green fluorescent protein, as evaluated by both flow cytometry and functional assays. In wild type cells, Tat uptake is competitively inhibited by soluble heparin and by treatment with glycosaminoglycan lyases specifically degrading HS chains. Cell surface HS proteoglycans also mediate physiological internalization of Tat green fluorescent protein released from neighboring producing cells. In contrast to extracellular Tat uptake, both wild type cells and cells genetically impaired in proteoglycan synthesis are equally proficient in the extracellular release of Tat, thus indicating that proteoglycans are not required for this process. The ubiquitous distribution of HS proteoglycans is consistent with the efficient intracellular delivery of heterologous proteins fused with Tat to different mammalian cell types.

Adeno-associated virus type 2 rep protein inhibits human papillomavirus type 16 E2 recruitment of the transcriptional coactivator p300

Infection by human adeno-associated virus type 2 (AAV2) is a possible protective factor in the development of cervical carcinomas associated with human papillomaviruses (HPV). The replicative proteins of AAV2 (Rep) have been implicated in the inhibition of papillomavirus replication and transforming activities, although the molecular events underlying these effects are poorly understood. We observed that each of the four forms of AAV2 Rep inhibited the E1- and E2-driven replication of oncogenic HPV type 16 (HPV16). Rep40, corresponding to the C-terminal domain of all Rep proteins, inhibited both HPV DNA replication and HPV16 E2-mediated transactivation. Rep40 specifically bound the N-terminal transactivation domain of HPV16 E2 both in vitro and in vivo. This interaction was found to specifically disrupt the binding of E2 to the cellular transcriptional coactivator p300. Accordingly, the inhibitory effect of Rep on HPV16 E2 transactivation was rescued by the overexpression of p300. These data indicate a novel role of Rep in the down-regulation of papillomaviruses through inhibition of complex formation between the HPV16 E2 transcriptional activator and its cellular coactivator, p300.

Thrombospondin-1/HIV-1 tat protein interaction: modulation of the biological activity of extracellular Tat

Tat protein, a trans-activating factor of the human immunodeficiency virus type 1, acts also as an extracellular molecule modulating gene expression, cell survival, growth, transformation, and angiogenesis. Here we demonstrate that human thrombospondin-1 (TSP), a plasma glycoprotein and constituent of the extracellular matrix, binds to glutathione-S-transferase (GST)-Tat protein but not to GST. Scatchard plot analysis of the binding of free GST-Tat to immobilized TSP reveals a high-affinity interaction (Kd equal to 25 nM). Accordingly, TSP inhibits cell internalization and HIV-1 LTR trans-activating activity of extracellular Tat in HL3T1 cells with ID50 equal to 10-30 nM. Also, TSP inhibits cell interaction and mitogenic activity of extracellular Tat in T53 Tat-less cells. TSP is instead ineffective when administered after the interaction of Tat with cell surface heparan-sulfate proteoglycans has occurred, in keeping with its ability to prevent but not disrupt Tat/heparin interaction in vitro. Finally, TSP inhibits the autocrine loop of stimulation exerted by endogenous Tat in parental T53 cells. Accordingly, TSP overexpression inhibits cell proliferation, angiogenic activity, and tumorigenic capacity of stable T53 transfectants. Our data demonstrate the ability of TSP to bind to Tat protein and to affect its LTR trans-activating, mitogenic, angiogenic, and tumorigenic activity. These findings suggest that TSP may be implicated in the progression of AIDS and in AIDS-associated pathologies by modulating the bioavailability and biological activity of extracellular Tat.