SAGA is an essential in vivo target of the yeast acidic activator Gal4p

Despite major advances in characterizing the eukaryotic transcriptional machinery, the function of promoter-specific transcriptional activators (activators) is still not understood. For example, in no case have the direct in vivo targets of a transcriptional activator been unambiguously identified, nor has it been resolved whether activators have a single essential target or multiple redundant targets. Here we address these issues for the prototype acidic activator yeast Gal4p. Gal4p binds to the upstream activating sequence (UAS) of GAL1 and several other GAL genes and stimulates transcription in the presence of galactose. Previous studies have shown that GAL1 transcription is dependent on the yeast SAGA (Spt/Ada/GCN5/acetyltransferase) complex. Using formaldehyde-based in vivo cross-linking, we show that the Gal4p activation domain recruits SAGA to the GAL1 UAS. If SAGA is not recruited to the UAS, the preinitiation complex (PIC) fails to assemble at the GAL1 core promoter, and transcription does not occur. SAGA, but not other transcription components, is also recruited by the Gal4p activation domain to a plasmid containing minimal Gal4p-binding sites. Recruitment of SAGA by Gal4p and stimulation of PIC assembly is dependent on several SAGA subunits but not the SAGA histone acetyl-transferase (HAT) GCN5. Based on these and other results, we conclude that SAGA is an essential target of Gal4p that, following recruitment to the UAS, facilitates PIC assembly and transcription.

Developmental regulation of transcription by a tissue-specific TAF homolog

Alternate forms of the general transcription machinery have been described in several tissues or cell types. However, the role of tissue-specific TBP-associated factors (TAF(II)s) and other tissue-specific transcription components in regulating differential gene expression during development was not clear. Here we show that the cannonball gene of Drosophila encodes a cell type-specific homolog of a more ubiquitously expressed component of the general transcription factor TFIID. cannonball is required in vivo for high level transcription of a set of stage- and tissue-specific target genes during male gametogenesis. Regulation of transcription by cannonball is absolutely required for spermatogenesis, as null mutations block meiotic cell cycle progression and result in a complete failure of spermatid differentiation. Our results demonstrate that cell type-specific TAF(II)s play an important role in developmental regulation of gene expression.

Crystal structure of a TAF1-TAF7 complex in human transcription factor IID reveals a promoter binding module

The general transcription factor IID (TFIID) initiates RNA polymerase II-mediated eukaryotic transcription by nucleating pre-initiation complex formation at the core promoter of protein-encoding genes. TAF1, the largest integral subunit of TFIID, contains an evolutionarily conserved yet poorly characterized central core domain, whose specific mutation disrupts cell proliferation in the temperature-sensitive mutant hamster cell line ts13. Although the impaired TAF1 function in the ts13 mutant has been associated with defective transcriptional regulation of cell cycle genes, the mechanism by which TAF1 mediates transcription as part of TFIID remains unclear. Here, we present the crystal structure of the human TAF1 central core domain in complex with another conserved TFIID subunit, TAF7, which biochemically solubilizes TAF1. The TAF1-TAF7 complex displays an inter-digitated compact architecture, featuring an unexpected TAF1 winged helix (WH) domain mounted on top of a heterodimeric triple barrel. The single TAF1 residue altered in the ts13 mutant is buried at the junction of these two structural domains. We show that the TAF1 WH domain has intrinsic DNA-binding activity, which depends on characteristic residues that are commonly used by WH fold proteins for interacting with DNA. Importantly, mutations of these residues not only compromise DNA binding by TAF1, but also abrogate its ability to rescue the ts13 mutant phenotype. Together, our results resolve the structural organization of the TAF1-TAF7 module in TFIID and unveil a critical promoter-binding function of TAF1 in transcription regulation.

Weight Gain and Metabolic Effects in Persons With HIV Who Switch to ART Regimens Containing Integrase Inhibitors or Tenofovir Alafenamide

BACKGROUND

The timing and magnitude of antiretroviral therapy-associated weight change attributions are unclear.

SETTING

HIV Outpatient Study participants.

METHODS

We analyzed 2007-2018 records of virally suppressed (VS) persons without integrase inhibitor (INSTI) experience who switched to either INSTI-based or another non-INSTI-based ART, and remained VS. We analyzed BMI changes using linear mixed models, INSTI- and tenofovir alafenamide (TAF) contributions to BMI change by linear mixed models-estimated slopes, and BMI inflection points.

RESULTS

Among 736 participants (5316 person-years), 441 (60%) switched to INSTI-based ART; the remainder to non-INSTI-based ART. The mean follow-up was 7.15 years for INSTI recipients and 7.35 years for non-INSTI. Preswitch, INSTI and non-INSTI groups had similar median BMI (26.3 versus 25.9 kg/m 2 , P = 0.41). INSTI regimens included raltegravir (178), elvitegravir (112), and dolutegravir (143). Monthly BMI increases postswitch were greater with INSTI than non-INSTI (0.0525 versus 0.006, P < 0.001). A BMI inflection point occurred 8 months after switch among INSTI users; slopes were similar regardless of TAF use immediately postswitch. Among INSTI + TAF users, during 8 months postswitch, 87% of BMI slope change was associated with INSTI use, 13% with TAF use; after 8 months, estimated contributions were 27% and 73%, respectively. For non-INSTI+TAF, 84% of BMI gain was TAF-associated consistently postswitch. Persons switching from TDF to TAF had greater BMI increases than others ( P < 0.001).

CONCLUSION

Among VS persons who switched ART, INSTI and TAF use were independently associated with BMI increases. During 8 months postswitch, BMI changes were greatest and most associated with INSTI use; afterward, gradual BMI gain was largely TAF-associated.

Pharmacokinetics of tenofovir alafenamide with and without cobicistat in pregnant and postpartum women living with HIV

OBJECTIVE

To evaluate the pharmacokinetics of tenofovir alafenamide (TAF) 10 mg with cobicistat and 25 mg without boosting in pregnant and postpartum women with HIV and to characterize TAF placental transfer and infant washout pharmacokinetics.

DESIGN

Open-label, multicenter phase IV prospective study of TAF pharmacokinetics during pregnancy, postpartum, delivery, and infant washout.

METHODS

Pregnant women receiving TAF 10 mg with cobicistat or TAF 25 mg without boosting as part of clinical care had intensive pharmacokinetic assessments performed during the second and third trimesters, and 6-12 weeks postpartum. Maternal and cord blood samples were collected at delivery, and washout pharmacokinetic samples were collected in infants. TAF concentrations were quantified using liquid chromatography/mass spectrometry. Comparisons between pregnancy and postpartum were made using geometric mean ratios (90% confidence intervals) and Wilcoxon signed-rank tests.

RESULTS

Thirty-one pregnant women receiving TAF 10 mg with cobicistat-boosting and 27 women receiving TAF 25 mg without boosting were enrolled. TAF exposures did not significantly differ between pregnancy and postpartum when administered as 10 mg with cobicistat. Antepartum TAF exposures with the 25 mg dose were 33-43% lower in comparison with postpartum, but comparable with those measured in nonpregnant adults. TAF was below the lower limit of quantitation in 43 of 44 cord blood, 41 of 45 maternal blood at delivery, and all infant washout samples.

CONCLUSION

TAF exposures were comparable or higher than those measured in nonpregnant adults during pregnancy and postpartum. These findings provide reassurance on adequate TAF exposures during pregnancy, and support efforts to expand the use of TAF in pregnant women with HIV.

Switching to tenofovir alafenamide versus continued therapy in chronic hepatitis B patients who were treated with entecavir: A prospective, multicenter, randomized controlled study

BACKGROUNDS

Entecavir (ETV) and tenofovir alafenamide fumarate (TAF) have been used widely to treat patients with chronic hepatitis B virus (HBV) infection, but it is still unclear how best to use these drugs. Although some studies compared the efficacies of treatment switch from ETV to TAF, there has been no randomized study.

METHODS

We performed a prospective multicenter randomized controlled study in which subjects were enrolled from April 2018 to June 2019 and observed for 2 years until March 2021 to clarify the efficacy and safety of switching from ETV to TAF.

RESULTS

Thirty-three patients were enrolled and randomized into 2 groups, and a total of 30 patients were evaluated; a TAF-switching group (n = 16) and an ETV-continuing group (n = 14). The mean age of the 30 patients was 61 years old and 18 patients (60%) were male. The serum HBV DNA in all patients were below detection limit. The mean change in hepatitis B surface antigen (HBsAg) levels after 2 years was not significantly different between the TAF and ETV groups (-0.08 vs -0.20 log IU/mL, P = .07). Comparing the group with a HBsAg decline (≤ -0.1 log IU/mL) and a group without a HBsAg decline in an overall analysis, the prior ETV duration was significantly shorter in the HBsAg-declined group (49 vs 92 months, P = .03). Although the eGFR levels tended to decrease in the TAF group compared to ETV (-6.15 vs -2.26 mL/min/1.73 m2, P = .09), no significant differences were observed in patients with baseline eGFR < 60 (-2.49 vs 0.40 mL/min/1.73 m2, P = .25).

CONCLUSION

The efficacy and safety were comparable in the TAF-switching group and the ETV-continuing group. Because the present study was conducted in limited patients, a larger study will be required.

Clinical Efficacy and Safety of Long-Term Treatment of Tenofovir Alafenamide vs Tenofovir Disoproxil Fumarate for Chronic Hepatitis B in Vietnam

INTRODUCTION

Hepatitis B virus (HBV) infection is a contagious condition posing a major public health risk in various nations, including Vietnam. In 2019, the Ministry of Health introduced tenofovir alafenamide (TAF) to treat patients with chronic HBV infection and reduce the long-term toxicity of tenofovir disoproxil fumarate (TDF). This study aimed to assess the effectiveness and safety of these 2 medications in individuals with hepatitis B e antigen (HBeAg)-positive chronic HBV.

METHODS

This retrospective cohort study included data collected from the medical records of patients with chronic HBV who visited the Liver Clinic at University Medical Center Ho Chi Minh City between 2018 and 2020.

RESULTS

After 2 years of treatment, the proportion of HBeAg loss in the TAF group was twice that of the TDF group (22.4% vs 11.2%), indicating a statistically significant difference in the probability of HBeAg loss (adjusted hazard ratio = 2.22; 95% confidence interval [CI] 1.43-3.42; P < 0.01). In addition, there was a statistically significant difference in the rate and ability of antiviral response between patients treated with TAF and TDF (65% vs 54.5%, respectively; adjusted hazard ratio = 1.34; 95% CI 1.08-1.69; P < 0.01). A total of 93.9% of patients achieved the goal of restoring alanine aminotransferase to normal, a higher percentage compared with the 81.2% in the TDF group, and the likelihood of achieving normal alanine aminotransferase levels with TAF was greater compared with those on TDF (adjusted hazard ratio = 1.67; 95% CI 1.38-2.01; P < 0.01). Moreover, there was a statistically significant difference in the variation in renal function between the TAF and TDF groups. Serum creatinine levels in the TAF group increased less than those in the TDF group by 0.03 mg/dL every 6 months (95% CI -0.04 to -0.01, P < 0.01), and the estimated glomerular filtration rate in the TAF group was higher than that in the TDF group every 6 months by 2.78 mL/min/1.73 m 2 (95% CI 0.98-4.57, P < 0.01). However, there was no statistically significant difference in the likelihood of HBeAg seroconversion between patients with chronic hepatitis B treated with TAF or TDF (adjusted hazard ratio = 1.79; 95% CI 0.91-3.53; P = 0.09), nor in the risk of adverse events between the 2 groups (adjusted odds ratio = 1.34; 95% CI 0.88-2.05; P = 0.17). In addition, although the HBsAg concentration in the TAF group was lower than in the TDF group by an average of 0.05 log 10 IU/mL every 6 months (95% CI -0.15 to 0.05), this difference also did not reach statistical significance ( P = 0.35).

DISCUSSION

TAF has been demonstrated to achieve some therapeutic efficacy goals and reduce nephrotoxicity better than TDF. However, no differences were found in seroconversion or adverse events between the patient groups.

CROI 2016: Hot Spots in HIV Infection and Advances in HIV Prevention

The 2016 Conference on Retroviruses and Opportunistic Infections (CROI) highlighted hot spots in HIV infection. Men who have sex with men (MSM), transgender populations, people who inject drugs, fisherfolk, migrants, adolescents, and older adults are heavily impacted in a number of regions. Stigma contributes to risk behaviors and HIV acquisition across populations. HIV testing is a crucial first step in the HIV care continuum, and several large community-based surveys are underway in Africa to increase HIV testing, linkage to care, and uptake of antiretroviral treatment. Advances in preexposure prophylaxis (PrEP) featured prominently at CROI 2016. Two large efficacy trials of a vaginal ring containing the investigational drug dapivirine demonstrated efficacy and safety in preventing HIV infections in women in Africa. Data on the safety of long-acting injectable PrEP and several investigational PrEP drugs and formulations were also presented. Knowledge and use of PrEP among MSM in the United States appears to be increasing, and high uptake was seen among black MSM when provided as part of a culturally tailored support program. The use of broadly neutralizing antibodies for HIV prevention is a novel and promising approach to be evaluated in efficacy trials.

Pharmacokinetics of Tenofovir Alafenamide With Boosted Protease Inhibitors in Pregnant and Postpartum Women Living With HIV: Results From IMPAACT P1026s

BACKGROUND

Tenofovir alafenamide (TAF) is a key component of HIV treatment, but pharmacokinetic data supporting the use of TAF during pregnancy are limited. In this study, we report pharmacokinetic, safety, and birth outcomes for TAF 25 mg with a boosted protease inhibitor in pregnant women living with HIV.

METHODS

IMPAACT P1026s was a multicenter, nonrandomized, open-label, phase IV prospective study. Pregnant women living with HIV receiving TAF 25 mg with a boosted protease inhibitor were eligible. Intensive pharmacokinetic assessments were performed during the second and third trimesters and 6-12 weeks postpartum. Maternal and cord blood samples were collected at delivery. Infant washout samples were collected through 5-9 days postbirth. Comparisons of paired pharmacokinetic data between pregnancy and postpartum were made using geometric mean ratios (GMR) [90% confidence intervals (CIs)] and Wilcoxon signed-rank tests with P < 0.10 considered significant.

RESULTS

Twenty-nine women were enrolled from the United States (median age 31 years and weight 84.5 kg during the third trimester; 48% Black, 45% Hispanic/Latina). TAF AUCtau did not significantly differ in the second [GMR 0.62 (90% CI: 0.29 to 1.34); P = 0.46] or third trimester [GMR 0.94 (90% CI: 0.63 to 1.39); P = 0.50] vs. postpartum and were comparable with historical data in nonpregnant adults. TAF was only quantifiable in 2/25 maternal delivery samples and below the limit of quantification in all cord blood and infant washout samples, likely because of the short half-life of TAF.

CONCLUSION

TAF AUCtau did not significantly differ between pregnancy and postpartum. These findings provide reassurance as TAF use during pregnancy continues to expand.

Choosing Initial Antiretroviral Therapy: Current Recommendations for Initial Therapy and Newer or Investigational Agents

There is general consistency among US and European guidelines regarding the initiation of antiretroviral therapy for HIV-infected individuals. Recent and ongoing trials comparing regimens may lead to reevaluation of initial treatment choices. The choice of antiretroviral regimen will also likely be affected by development, evaluation, and availability of newer drugs. This article reviews currently recommended regimens and characteristics of selected current investigational drugs, including the nucleotide analogue reverse transcriptase inhibitor tenofovir alafenamide, the nonnucleoside reverse transcriptase inhibitor doravirine, the integrase strand transfer inhibitor cabotegravir, the HIV entry inhibitor BMS-663068, and the HIV maturation inhibitor BMS-955176. This article summarizes a presentation by Roy M. Gulick, MD, MPH, at the IAS-USA continuing education program, Improving the Management of HIV Disease, held in New York, New York, in March 2015 and September 2015.