Although the BCL-2 family constitutes a crucial checkpoint in apoptosis, the intricate interplay between these family members remains elusive. Here, we demonstrate that BIM and PUMA, similar to truncated BID (tBID), directly activate BAX-BAK to release cytochrome c. Conversely, anti-apoptotic BCL-2-BCL-X(L)-MCL-1 sequesters these 'activator' BH3-only molecules into stable complexes, thus preventing the activation of BAX-BAK. Extensive mutagenesis of BAX-BAK indicates that their activity is not kept in check by BCL-2-BCL-X(L)-MCL-1. Anti-apoptotic BCL-2 members are differentially inactivated by the remaining 'inactivator' BH3-only molecules including BAD, NOXA, BMF, BIK/BLK and HRK/DP5. BAD displaces tBID, BIM or PUMA from BCL-2-BCL-X(L) to activate BAX-BAK, whereas NOXA specifically antagonizes MCL-1. Coexpression of BAD and NOXA killed wild-type but not Bax, Bak doubly deficient cells or Puma deficient cells with Bim knockdown, indicating that activator BH3-only molecules function downstream of inactivator BH3-only molecules to activate BAX-BAK. Our data establish a hierarchical regulation of mitochondrion-dependent apoptosis by various BCL-2 subfamilies.

statement: Chest computed tomography scans for the primary screening or diagnosis of coronavirus disease 2019 would not be beneficial in a low-prevalence region due to the substantial rate of false-positives.This copy is for personal use only. To order printed copies, contact reprints@rsna.org I n P r e s s Key Results• The pooled sensitivity and specificity were 94% (95% CI: 91%, 96%) and 37% (95% CI: 26%, 50%), respectively, for chest CT. The pooled sensitivity of reverse transcriptasepolymerase chain reaction (RT-PCR) was 89% (95% CI: 81%, 94%).• In low-prevalence (<10%) countries, the positive predictive value of RT-PCR (range: 47.3%, 84.3%) was more than ten times higher than that of CT scans (range: 1.5%, 8.3%).The negative predictive value of both methods ranged from 99.0% to 99.9%. AbbreviationsCI = confidence interval, COVID-19 = coronavirus disease 2019, NPV = negative predictive value, ORF = open reading frame, PPV = positive predictive value, PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-analyses, QUADAS-2 = Quality Assessment of Diagnostic Accuracy Studies-2, RT-PCR = reverse transcriptase-polymerase chain reaction, SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2, WHO = World Health Organization I n P r e s s Abstract Background: Recent studies have suggested that chest computed tomography (CT) scans could be used as a primary screening or diagnostic tool for coronavirus disease 2019 (COVID-19) in epidemic areas.Purpose: To perform a meta-analysis to evaluate diagnostic performance measures, including predictive values, of chest CT and initial reverse transcriptase-polymerase chain reaction (RT-PCR). studies on COVID-19 that reported the sensitivity and/or specificity of CT scans and/or RT-PCR assays. The pooled sensitivity and specificity were estimated by using random-effects models. The actual prevalence (i.e., the proportion of confirmed patients among those tested) in eight countries was obtained from web sources, and the predictive values were calculated. Meta-regression was performed to reveal the effect of potential explanatory factors on the diagnostic performance measures. Results:The pooled sensitivity was 94% (95% CI: 91%, 96%; I 2 =95%) for chest CT and 89% (95% CI: 81%, 94%; I 2 =90%) for RT-PCR. The pooled specificity was 37% (95% CI: 26%, 50%; I 2 =83%) for chest CT. The prevalence of COVID-19 outside China ranged from 1.0% to 22.9%. For chest CT scans, the positive predictive value (PPV) ranged from 1.5% to 30.7%, and the negative predictive value (NPV) ranged from 95.4% to 99.8%. For RT-PCR, the PPV ranged from 47.3% to 96.4%, while the NPV ranged from 96.8% to 99.9%. The sensitivity of CT was affected by the distribution of disease severity, the proportion of patients with comorbidities, and the proportion of asymptomatic patients (all p < 0.05). The sensitivity of RT-PCR was negatively associated with the proportion of elderly patients (p = 0.01). Conclusion:Outside of China where there is a low-prevalence of COVID-19 (1-22.9%), chest CT screening...

SUMMARY While activation of BAX/BAK by BH3-only molecules (BH3s) is essential for mitochondrial apoptosis, the underlying mechanisms remain unsettled. Here, we demonstrate that BAX undergoes stepwise structural reorganization leading to mitochondrial targeting and homo-oligomerization. The α1 helix of BAX keeps the α9 helix engaged in the dimerization pocket, rendering BAX as a monomer in cytosol. The activator BH3s, tBID/BIM/PUMA, attack and expose the α1 helix of BAX, resulting in secondary disengagement of the α9 helix and thereby mitochondrial insertion. Activator BH3s remain associated with the N-terminally exposed BAX through the BH1 domain to drive homo-oligomerization. BAK, an integral mitochondrial membrane protein, has bypassed the first activation step, explaining its faster killing kinetics than BAX. Furthermore, death signals initiated at ER induce BIM and PUMA to activate mitochondrial apoptosis. Accordingly, deficiency of Bim/Puma impedes ER stress-induced BAX/BAK activation and apoptosis. Our study provides mechanistic insights regarding the spatiotemporal execution of BAX/BAK-governed cell death.