The Antiviral and Cancer Genomic DNA Deaminase APOBEC3H Is Regulated by an RNA-Mediated Dimerization Mechanism.

Human APOBEC3H and homologous single-stranded DNA cytosine deaminases are unique to mammals. These DNA-editing enzymes function in innate immunity by restricting the replication of viruses and transposons. APOBEC3H also contributes to cancer mutagenesis. Here, we address the fundamental nature of RNA in regulating human APOBEC3H activities. APOBEC3H co-purifies with RNA as an inactive protein, and RNase A treatment enables strong DNA deaminase activity. RNA-binding-defective mutants demonstrate clear separation of function by becoming DNA hypermutators. Biochemical and crystallographic data demonstrate a mechanism in which double-stranded RNA mediates enzyme dimerization. Additionally, APOBEC3H separation-of-function mutants show that RNA binding is required for cytoplasmic localization, packaging into HIV-1 particles, and antiviral activity. Overall, these results support a model in which structured RNA negatively regulates the potentially harmful DNA deamination activity of APOBEC3H while, at the same time, positively regulating its antiviral activity.

Exploring Social Support Dynamics After Bariatric Surgery: Insights From Patients and Providers.

INTRODUCTION: Weight loss after bariatric surgery is impacted by several factors, and social support is one of them. Our objective was to characterize patient and provider perceptions about social support after bariatric surgery. METHODS: We reported a secondary analysis of qualitative data acquired from semi-structured interviews conducted from January-November 2020 with bariatric surgery patients and providers. Participants included primary care providers, health psychologists, registered dietitians, bariatric surgeons, and patients with at least 1 y of follow-up after their bariatric procedure. Interview guides were designed using a hybrid of Andersen's Behavioral Model of Health Services and Torain's Framework for Surgical Disparities. Using directed content analysis, study team members generated codes, which were categorized into themes about social support pertaining to dietary habits, physical activity, and follow-up care. RESULTS: Forty-five participants were interviewed, including 24 patients (83% female; 79% White; mean age 50.6 ± 10.7 y) and 21 providers (six primary care providers, four health psychologists, five registered dieticians, and six bariatric surgeons). We identified four themes relating to social support affecting weight loss after surgery: (1) family involvement in helping patients adjust to the bariatric diet, (2) engagement in activities with partners/friends, (3) help with transportation to appointments, and (4) life stressors experienced by patients within their social relationships. CONCLUSIONS: Continued assessment of interpersonal factors after bariatric surgery is essential for weight loss maintenance. Providers can contribute by reinforcing the facilitators of social support and making referrals that may help patients overcome barriers to social support for sustained weight loss after surgery.

Identifying Intraoperative Behaviors Associated With Surgical Resident Teachability.

OBJECTIVE: The resident-attending dyad influences the intraoperative training of surgery residents. To better understand the role of trainees within the dyad, we hypothesized there is a measurable concept of "teachability," a combination of the trainee's observed skills and behaviors with their performance. This study aims to define teachability and identify discrete intraoperative behaviors that contribute to this concept. We posit that residents who are active learners as demonstrated by asking questions, proposing next steps, and initiating purposeful actions have higher teachability. DESIGN, SETTING, PARTICIPANTS: Previously recorded videos from 26 laparoscopic inguinal hernia repairs performed by two PGY-5 general surgery residents at a Midwest tertiary care center were qualitatively reviewed for intraoperative behaviors. A summative content analysis identified behaviors associated with increased teachability and improved operative performance assessment scores. RESULTS: Average frequencies of intraoperative behaviors for resident 1 and 2 (R1 and R2) were not significantly different, although R2 asked more medical knowledge and technical questions. While the rate of attending feedback was similar for both residents (x=3.82 vs 3.40, p=0.646), R1 consistently incorporated feedback (x=2.27 vs 0.40, p=0.001) whereas R2 needed frequent prompting (x=2.45 vs 1.55, p=0.239). R1 scored higher in all but one operative performance assessment category, including overall performance (x=4.17 vs 2.93, p=0.007), but R2 had a larger magnitude of overall improvement (+1 vs +2). CONCLUSIONS: Teachability is a dynamic component of the resident-attending dyad. While intraoperative active learning behaviors do not appear to be associated with teachability, asking questions may increase the magnitude of improvement in performance. Most importantly, the ability to incorporate intraoperative feedback in real time seems to be a critical aspect of teachability and warrants further research.

The Role of RNA in HIV-1 Vif-Mediated Degradation of APOBEC3H.

As many as five members of the APOBEC3 family of DNA cytosine deaminases are capable of inhibiting HIV-1 replication by deaminating viral cDNA cytosines and interfering with reverse transcription. HIV-1 counteracts restriction with the virally encoded Vif protein, which forms a hybrid ubiquitin ligase complex that directly binds APOBEC3 enzymes and targets them for proteasomal degradation. APOBEC3H (A3H) is unique among family members by dimerization through cellular and viral duplex RNA species. RNA binding is required for localization of A3H to the cytoplasmic compartment, for efficient packaging into nascent HIV-1 particles and ultimately for effective virus restriction activity. Here we compared wild-type human A3H and RNA binding-defective mutants to ask whether RNA may be a factor in the functional interaction with HIV-1 Vif. We used structural modeling, immunoblotting, live cell imaging, and split green fluorescence protein (GFP) reconstitution approaches to assess the capability of HIV-1 Vif to promote the degradation of wild-type A3H in comparison to RNA binding-defective mutants. The results combined to show that RNA is not strictly required for Vif-mediated degradation of A3H, and that RNA and Vif are likely to bind this single-domain DNA cytosine deaminase on physically distinct surfaces. However, a subset of the results also indicated that the A3H degradation process may be affected by A3H protein structure, subcellular localization, and differences in the constellation of A3H interaction partners, suggesting additional factors may also influence the fate and functionality of this host-pathogen interaction.