[YAP induces chromosomal instability in liver cancer patients]. / YAP induziert chromosomale Instabilität in Leberkrebspatienten.

BACKGROUND: The Hippo/YAP signaling pathway is a central regulator of organ growth and cell proliferation. Activation of the transcriptional co-activator and oncogene YAP (yes-associated protein) supports the development of liver cancer. AIMS: The aim of this work was to analyze the molecular mechanisms which are responsible for YAP-induced hepatocarcinogenesis. METHODS: YAP was silenced using siRNAs in liver cancer cell lines and effects on target gene expression were analyzed via real-time polymerase chain reaction (PCR) and western immunoblotting. Immunoprecipitation and chromatin immunoprecipitation was used to study interacting proteins and binding to target gene promoter regions, respectively. Transgenic mice with liver-specific and inducible YAP expression were used for in vivo analysis. Gene expression data from hepatocellular carcinoma (HCC) patients were used to analyze YAP-dependent gene signatures and to correlate with clinical data. HCC tissue microarrays were analyzed using immunohistochemistry. RESULTS: Together with the transcription factors TEAD4 and FOXM1, YAP induces the expression of genes which are responsible for the development of chromosomal instability (CIN). The overexpression of these CIN genes characterizes liver cancer patients with a poor prognosis. Mechanistically, YAP/TEAD4 and FOXM1 bind to the promoter regions of the CIN genes to directly regulate their expression. The treatment of YAP-transgenic mice with a specific FOXM1 inhibitor reduces the YAP-dependent hepatomegaly, CIN gene expression and CIN. The analysis of human HCC tissue samples confirms the statistical correlation between YAP, FOXM1 and CIN. DISCUSSION: These results reveal a new oncogenic mechanism of the Hippo/YAP signaling pathway and identify YAP and FOXM1 as potential targets for targeted therapies.

[Nonautonomous effects of oncogenic YAP in hepatocarcinogenesis]. / Nichtautonome Effekte des Onkogens YAP in der Hepatokarzinogenese.

BACKGROUND: The transcriptional coactivator yes-associated protein (YAP) is a strong oncogene in liver cancer development. OBJECTIVES: To investigate if and how YAP-induced paracrine-acting factors are regulated in hepatocytes and liver cancer cells. MATERIAL AND METHODS: Transcriptome analysis and proteomics of murine wildtype and YAP-transgenic hepatocytes were performed to identify paracrine-acting proteins. Molecular and biochemical techniques were used to examine the mechanisms of YAP-dependent gene regulation. Gene expression data from HCC (hepatocellular carcinoma) patients was evaluated. RESULTS: Several YAP-dependent, secreted factors (e. g. CXCL10, GDF15, PDGFB) were identified. YAP regulates these factors through transcription factors of the TEAD (TEA domain) protein family. Moreover, the dysregulation of the YAP-target genes is often associated with poor HCC patient prognosis. CONCLUSIONS: YAP induces the expression of paracrine-acting factors that may affect the tumor microenvironment and therefore support carcinogenesis. This multicellular network could allow the development of novel and specific perturbation approaches.

Snap-fits and upper limb functional limitations in German automotive workers.

BACKGROUND: The use of snap-fit fasteners in automotive assembly has increased in the last 10 years. Their impact on musculoskeletal function of the upper limbs in assembly workers is not well described. AIMS: To investigate the association between snap-fit assembly and upper limb functional limitations (ULFLs) in workers after a large-scale expansion of snap-fit assembly by a German automotive company. METHODS: Cross-sectional data on blue-collar production workers' exposure to snap-fit assembly and ULFLs were collected from medical check-ups and company registers. The association between duration of snap-fit assembly and ULFLs, and the dose-response relationship between the two were analysed using logistic regression, adjusted for body mass index, gender and employment duration before snap-fit exposure. RESULTS: The study group included 10722 workers. Within the company, 8.4, 6.9 and 10.3% were exposed to snap-fit 1-12, 13-24 and ≥25 months, respectively. After adjusting for confounders, snap-fit exposure for 1-12 months [odds ratio (OR) = 1.59, 95% confidence interval (CI) 0.88-2.88] and 13-24 months (OR = 1.48, 95% CI 0.76-2.88) was not statistically significantly associated with ULFLs compared with an unexposed group. However, exposure to ≥25 months of snap-fit assembly was statistically significant associated with ULFLs showing >2-fold risk (OR = 2.44, 95% CI 1.52-3.92). No clear dose-response relationship was found. CONCLUSIONS: Our study suggests a negative long-term impact from snap-fit assembly on workers' upper limb function. Company physicians should be vigilant for signs of upper limb musculoskeletal disorders among workers exposed to snap-fit assembly.

Cetuximab induced aseptic meningitis.

We report a 67-year-old man with recurrent advanced oropharyngeal squamous cell carcinoma who developed aseptic meningitis, with first symptoms arising approximately 9hours after the first administration of cetuximab, and review the literature to identify key signs and symptoms of this condition. Cetuximab is a monoclonal antibody targeting the epidermal growth factor receptor which has been rarely associated with aseptic meningitis. Besides the case description, a MEDLINE search was performed. In five patients identified in the literature and our patient, the leading signs and symptoms included headache, neck stiffness and high fever developing within a few hours of the first cetuximab administration. Cerebrospinal fluid (CSF) analysis revealed severe pleocytosis (range: 528-2300/µl) with dominance of neutrophils (⩾87%). Clinical recovery within 1-2weeks was accompanied by normalization of CSF cell count within 4-7days. Re-challenge with cetuximab at a reduced dose caused recurrent aseptic meningitis in one of three patients. In summary, aseptic meningitis is a rare complication after first cetuximab exposure that the clinician should be aware of. CSF analysis is the key to diagnosis and recovery is usually complete within days to weeks after withdrawal of the drug. Re-challenge may be considered but bears the risk of recurrence.

Treatment of gout in a renal transplant patient leading to severe thrombocytopenia.

WHAT IS KNOWN AND OBJECTIVE: Allopurinol (AP) inhibits the xanthine oxidase, which may indirectly lead to myelotoxicity when used in combination with azathioprine (AZA). CASE SUMMARY: A 79-year-old female developed symptomatic thrombocytopenia after combination therapy with AZA (75 mg/day) and AP (100 mg/day) - after AP had been stopped. Concentrations of the myelotoxic 6-thioguanine-nucleotides metabolite of AZA were increased. Thrombocyte counts normalized within 8 days of discontinuation of AZA. WHAT IS NEW AND CONCLUSION: The effect of a drug interaction in a patient with decreased elimination capacity may take several weeks to become apparent and may in fact do so even after the drug has been stopped. Concurrent AZA and AP therapy demands cautious use.

[Antibiotic therapy: impact and resistance]. / Antibiotikatherapie: Wirkung und Resistenz.

BACKGROUND: Many achievements in modern medicine, such as in transplantation medicine, cancer therapy, surgery, and intensive care medicine would have been impossible without effective treatment of bacterial infections. Antibiotic resistance is on the rise; the reasons for this are complex and vary greatly. OBJECTIVE: Knowledge about the impact of antibiotics and mechanisms of antibiotic resistance, which are the cornerstones of calculated and targeted antibiotic therapy, is imperative. RESULTS: This review describes the pharmacodynamics of relevant antibiotics in emergency and intensive care medicine. Commonly resistant bacteria with clinical relevance and the respective mechanisms of resistance are highlighted. Furthermore, the use of antiinfectives for reserve treatment of severe infections is discussed. CONCLUSION: Understanding the mechanisms of resistance and effects of antibiotics are fundamental for efficient and successful treatment of bacterial infections and for the reduction of resistant species.

[Outpatient physiotherapy for patients with knee pain in northern Germany]. / Heilmittelversorgung in der ambulanten Physiotherapie bei Kniebeschwerden.

BACKGROUND: Physiotherapy, in comparison to occupational therapy and speech therapy, is the most frequently prescribed treatment in Germany. Nationally there is only scarce information available on indications, treatment approaches and development of health condition throughout therapy. Present work encompasses only small sample sizes and insufficient follow-up periods. AIM: To describe, how patients with knee complaints are treated based on a physiotherapy referral and how their health condition changes during therapy. METHODS: A descriptive-exploratory secondary analysis of data from a prospective multicentre observational study was conducted. The Bother index of the Musculoskeletal Function Assessment Questionnaire (German, 16-Item version) and an 11-step box scale on pain intensity were utilised as outcome criteria. RESULTS: Data of 160 patients, age 47.4 (SD 10.8), 51% female, approximately 51% with previous arthroscopy, were analysed. The response rate 6 months after therapy approximately amounted to 50%. Main therapy approaches were strengthening, stretching and manual therapy, combined with home exercises. Impairment in daily life as well as pain improved substantially during therapy (SES range 0.6-1.75). CONCLUSION: The conducted study brought up insights for physiotherapy health service for pa-tients with cartilage or meniscal problems, based on a sample size not accessible for Germany before. After reviewing the international literature it may be assumed, that the clearly active character of the therapy and the combination of different treatment approaches are of relevance for the presented reduction of impairment in daily life.

Mollow quintuplets from coherently excited quantum dots.

Charge-neutral excitons in semiconductor quantum dots (QDs) have a small finite energy separation caused by the anisotropic exchange splitting. Coherent excitation of neutral excitons will generally excite both exciton components, unless the excitation is parallel to one of the dipole axes. We present a polaron master equation model to describe two-exciton pumping using a coherent continuous wave pump field in the presence of a realistic anisotropic exchange splitting. We predict a five-peak incoherent spectrum, namely a Mollow quintuplet under general excitation conditions. We experimentally confirm such spectral quintuplets for In(Ga)As QDs and obtain very good agreement with theory.

[Prescriptions in outpatient physiotherapy for low back pain - descriptive analysis to relate indication key and everyday impairment]. / Heilmittelverordnungen in der ambulanten Physiotherapie bei Rückenbeschwerden - deskriptive Analyse zum Abgleich von Indikationsschlüssel und Alltagsbeeinträchtigung.

BACKGROUND: In Germany, in comparison to occupational therapy and speech therapy, physiotherapy is the most often prescribed treatment, with a prescription volume of 3 billion Euro in 2009. The catalogue of prescribable therapies (CPT; "Heilmittelkatalog") is a matter of controversial discussion. It represents the rationale which should support the physician in adhering to the efficiency principle. AIM: To describe the coded indications used by physicians to justify a physiotherapy prescription for patients with back pain, in order to verify its plausibility. Furthermore, we aimed to describe the manner in which patient subgroups differ regarding factors given in the CPT to allocate patients to various domains of indication. METHODS: A descriptive-exploratory secondary analysis of data from a prospective multicentre (84 private physiotherapy practices) observational trial was conducted. The Bother index of the Musculoskeletal Function Assessment Questionnaire (German, 16-Item version), the Work Ability Index and an 11-step box scale on pain intensity were measured as outcome. RESULTS: Coded indications related to dysfunction/pain due to joint-blockages dominated clearly (WS1a 30%, WS2a 35.3%). Patients who were allocated to the domains of indication WS1 and WS2 did not differ regarding botherment in daily life at the beginning of therapy (SES=0.05). CONCLUSION: It is hardly possible to identify clear prescription patterns. Results did not show any clear differences regarding major criteria for efficient prescription in line with the CPT. The weaknesses discussed should be targeted in future studies and should be considered during subsequent revisions of the CPT.

Teicoplanin pharmacokinetics in critically ill patients on continuous veno-venous hemofiltration.

Pharmacokinetics of teicoplanin (TP) was assessed in critically ill patients on continuous veno-venous hemofiltration (CVVH), in eleven patients, after the first dose and in another four after repeated administration. The TP peak concentration amounted to 55.44 +/- 15.90 microg/ml and 81.28 +/- 28.55 microg/ml (mean +/- SD), the trough concentration 6.4 +/- 1.7 microg/ml and 21.3 +/- 5.0 microg/ml, the half-life 15.7 +/- 5.7 and 35.1 +/- 12.3 h, the apparent volume of distribution 0.84 +/- 0.22 and 0.48 +/- 0.09 l/kg and the TP clearance 39 +/- 12 and 11 +/- 4 ml/h/kg after the first dose and after repeated administration, respectively. The mean sieving coefficient of TP was 0.15. After a 1,200 mg loading dose, daily maintenance doses of 600 - 1,800 mg were required for achieving trough levels of 15 - 25 microg/ml. Therapeutic drug monitoring is indispensable during CVVH because of a considerable variability of TP pharmacokinetics.

Children's blood lead and standardized test performance response as indicators of neurotoxicity in metropolitan New Orleans elementary schools.

This study analyzes pre-Katrina variation in aggregate student performance and children's blood lead (BPb) in 117 elementary school districts in metropolitan New Orleans. Fourth grade student achievement on Louisiana Educational Assessment Program (LEAP) tests were analyzed as a function of BPb for children 1-6 years old within school districts, controlling for student-teacher ratios, percent of students eligible for a free or discounted lunch, and school racial demography. Measures of performance across subject areas (English Language Arts, Science, Mathematics, and Social Studies) include school Achievement Test Scores (ATS) and indices of agreement and variation in student achievement. ATS are measured on a 5-point scale, corresponding to achievement categories of advanced=5 to unsatisfactory=1. Regression results show that median BPb (microg/dL) and percent of children with BPb > or =10 microg/dL are significantly associated with reductions in test scores across all subjects and depress variation in student performance across achievement categories. These data suggest that assisting children with improved school performance requires alleviation of pre-school Pb exposure and its associated neurotoxic damage. Cost-benefit calculations suggest that it is more cost effective to pay for onetime primary prevention instead of paying continuous expenses focused on reversing neurotoxic damage.

[Rehabilitation of construction industry workers considering special workplace demands--results of the "RehaBau" pilot study]. / Arbeitsplatzorientierte Rehabilitation von Bauarbeitern--Ergebnisse der Pilotstudie "RehaBau".

In a descriptive study, 122 construction industry workers were treated in an especially workplace-oriented inpatient rehabilitation measure. Effects were assessed by written questionnaires using the SF-36 questionnaire, the questionnaire for employees self-assessment (FBS) and further standardized instruments for job strain and demand at time intervals of 0, 4 and 13 months from rehabilitation participation. Along with high rehabilitation satisfaction, improvement of quality of life and decreasing disability complaints are reported, which keep stable and significant for at least one year and thus are indicators of sustainable rehabilitation success.

Backbone dynamics for the wild type and a double H52R/T56W mutant of the vnd/NK-2 homeodomain from Drosophila melanogaster.

The (15)N relaxation behavior and heteronuclear Overhauser effect data for the wild type and an H52R/T56W double mutant protein that encompasses the vnd/NK-2 homeodomain from Drosophila melanogaster were used to characterize and describe the protein backbone dynamics. This investigation, which includes a description of a model structure for the H52R/T56W double mutant vnd/NK-2 homeodomain, was carried out for the two proteins in both the free and DNA-bound states. The double residue replacement at positions 52 and 56 within the DNA recognition helix of vnd/NK-2 has been shown to lead to a significant secondary structural modification resulting in an increase in the length of the recognition helix for the unbound protein. These structural changes are accompanied by corresponding changes in the T(1) and T(1)(rho) relaxation times as well as in the heteronuclear Overhauser effect (XNOE) values that show that the structural stability of the protein is enhanced by the two residue replacements. The values of the rotational anisotropy, D(parallel)/D(perpendicular), derived from analysis of the (15)N T(1) and T(1)(rho) relaxation values are small (1.189 for the unbound homeodomain and 1.110 for the bound homeodomain; both analyzed as prolate ellipsoids of revolution). A comparison of the T(2) values of the wild type and double mutant homeodomain reveals the presence of a low-frequency exchange contribution for the wild type analogue. These relaxation studies show that the motional behavior of the protein primarily reflects the tertiary structure and stability of the homeodomain backbone as well as the respective changes induced upon site-directed residue replacement or DNA binding.

BCL-2, BCL-X(L) sequester BH3 domain-only molecules preventing BAX- and BAK-mediated mitochondrial apoptosis.

Critical issues in apoptosis include the importance of caspases versus organelle dysfunction, dominance of anti- versus proapoptotic BCL-2 members, and whether commitment occurs upstream or downstream of mitochondria. Here, we show cells deficient for the downstream effectors Apaf-1, Caspase-9, or Caspase-3 display only transient protection from "BH3 domain-only" molecules and die a caspase-independent death by mitochondrial dysfunction. Cells with an upstream defect, lacking "multidomain" BAX, BAK demonstrate long-term resistance to all BH3 domain-only members, including BAD, BIM, and NOXA. Comparison of wild-type versus mutant BCL-2, BCL-X(L) indicates these antiapoptotics sequester BH3 domain-only molecules in stable mitochondrial complexes, preventing the activation of BAX, BAK. Thus, in mammals, BH3 domain-only molecules activate multidomain proapoptotic members to trigger a mitochondrial pathway, which both releases cytochrome c to activate caspases and initiates caspase-independent mitochondrial dysfunction.

The vnd/NK-2 homeodomain: thermodynamics of reversible unfolding and DNA binding for wild-type and with residue replacements H52R and H52R/T56W in helix III.

The conformational stabilities of the vnd (ventral nervous system defective)/NK-2 homeodomain [HD(wt); residues 1-80 that encompass the 60-residue homeodomain] and those harboring mutations in helix III of the DNA recognition site [HD(H52R) and HD(H52R/T56W)] have been investigated by differential scanning calorimetry (DSC) and ellipticity changes at 222 nm. Thermal unfolding reactions at pH 7.4 are reversible and repeatable in the presence of 50-500 mM NaCl with DeltaC(p) = 0.52 +/- 0.04 kcal K(-1) mol(-1). A substantial stabilization of HD(wt) is produced by 50 mM phosphate or by the addition of 100-500 mM NaCl to 50 mM Hepes, pH 7.4, buffer (from T(m) = 35.5 degrees C to T(m) 43-51 degrees C; DeltaH(vH) congruent with 47 +/- 5 kcal mol(-1)). The order of stability is HD(H52R/T56W) > HD(H52R) > HD(wt), irrespective of the anions present. Progress curves for ellipticity changes at 222 nm as a function of increasing temperature are fitted well by a two-state unfolding model, and the cooperativity of secondary structure changes is greater for mutant homeodomains than for HD(wt) and also is increased by adding 100 mM NaCl to Hepes buffer. A 33% quench of the intrinsic tryptophanyl residue fluorescence of HD(wt) by phosphate binding (K(D)' = 2.6 +/- 0.3 mM phosphate) is reversed approximately 60% by DNA binding. Thermodynamic parameters for vnd/NK-2 homeodomain proteins binding sequence-specific 18 bp DNA have been determined by isothermal titration calorimetry (10-30 degrees C). Values of DeltaC(p) are +0.25, -0.17, and -0.10 +/- 0.04 kcal K(-1) mol(-1) for HD(wt), HD(H52R), and HD(H52R/T56W) binding duplex DNA, respectively. Interactions of homeodomains with DNA are enthalpically controlled at 298 K and pH 7.4 with corresponding DeltaH values of -6.6 +/- 0.5, -10.8 +/- 0.1, and -9.0 +/- 0.6 kcal mol(-1) and DeltaG' values of -11.0 +/- 0.1, -11.0 +/- 0.1, and -11.3 +/- 0.3 kcal mol(-1) with a binding stoichiometry of 1.0 +/- 0.1. Thermodynamic parameters for DNA binding are not predicted from homeodomain structural changes that occur upon complexing to DNA and must reflect also solvent and possibly DNA rearrangements.

Telomere dysfunction alters the chemotherapeutic profile of transformed cells.

Telomerase inhibition has been touted as a novel cancer-selective therapeutic goal based on the observation of high telomerase levels in most cancers and the importance of telomere maintenance in long-term cellular growth and survival. Here, the impact of telomere dysfunction on chemotherapeutic responses was assessed in normal and neoplastic cells derived from telomerase RNA null (mTERC(-/-)) mice. Telomere dysfunction, rather than telomerase per se, was found to be the principal determinant governing chemosensitivity specifically to agents that induced double-stranded DNA breaks (DSB). Enhanced chemosensitivity in telomere dysfunctional cells was linked to therapy-induced fragmentation and multichromosomal fusions, whereas telomerase reconstitution restored genomic integrity and chemoresistance. Loss of p53 function muted the cytotoxic effects of DSB-inducing agents in cells with telomere dysfunction. Together, these results point to the combined use of DSB-inducing agents and telomere maintenance inhibition as an effective anticancer therapeutic approach particularly in cells with intact p53-dependent checkpoint responses.

Expression studies and mutational analysis of the androgen regulated homeobox gene NKX3.1 in benign and malignant prostate epithelium.

PURPOSE: The NKX-3.1gene is an androgen regulated prostate specific homeobox gene that is believed to have a vital role in normal prostate development. In mice the homologue NKx3.1 is exclusively expressed in prostate epithelium. In humans NKX3.1 expression is also restricted to the prostate but to our knowledge the cellular location has not been described. Furthermore, since NKX3.1 maps to chromosomal band 8p21, a region with high loss of heterozygosity in prostate cancer, the gene has been proposed to have tumor suppressor function. In this study we demonstrate that in human prostates NKX3.1 is expressed exclusively in secretory epithelial cells and the level of NKX3.1 expression remains invariant in normal tissue and in tissue showing various grades of prostate cancer. In the 19 cases examined the DNA sequences of the NKX3.1 gene were identical and no mutation was detected. MATERIALS AND METHODS: Frozen tissue from patients who underwent radical prostatectomy was used for this study. For in situ hybridization experiments a 377 bp fragment corresponding to a portion of the 3' untranslated region of the NKX3.1 gene was amplified by polymerase chain reaction and cloned into the pCRII plasmid vector Invitrogen. Antisense or sense [33P] uridine triphosphate labeled RNA probes were generated with SP6 or T7 RNA polymerase and hybridized to the tissue sections. Slides were exposed to photographic emulsion and visualized on autoradiography. Laser capture microdissection was performed to procure pure populations of malignant epithelium. DNA was isolated by digesting samples in proteinase K buffer. Polymerase chain reaction and direct sequencing was performed using standard protocols. RESULTS: In vitro hybridization showed that NKX3.1 expression was restricted to secretory epithelial cells within benign prostate glands. No expression was detected in stroma or infiltrating lymphocytes. NKX3.1 was expressed in all grades of malignant epithelium in all 25 cases examined. Direct sequencing of the coding region of NKX3.1 revealed the wild-type sequence in all 18 microdissected cancers analyzed. CONCLUSIONS: Based on our studies we propose that NKX3.1 gene expression is restricted to benign and malignant secretory epithelium within the prostate but NKX3.1 does not appear to be a classic tumor suppressor gene responsible for prostate cancer initiation. These findings are consistent with the role of NKX3.1 in the development of normal prostate epithelium and maintenance of normal secretory function. Thus, NKX3.1 may represent a useful molecular marker for benign and malignant prostate epithelium.

Posttranslational N-myristoylation of BID as a molecular switch for targeting mitochondria and apoptosis.

Many apoptotic molecules relocate subcellularly in cells undergoing apoptosis. The pro-apoptotic protein BID underwent posttranslational (rather than classic cotranslational) N-myristoylation when cleavage by caspase 8 caused exposure of a glycine residue. N-myristoylation enabled the targeting of a complex of p7 and myristoylated p15 fragments of BID to artificial membranes bearing the lipid composition of mitochondria, as well as to intact mitochondria. This post-proteolytic N-myristoylation serves as an activating switch, enhancing BID-induced release of cytochrome c and cell death.

Telomere dysfunction impairs DNA repair and enhances sensitivity to ionizing radiation.

Telomeres are specialized nucleoprotein complexes that serve as protective caps of linear eukaryotic chromosomes. Loss of telomere function is associated with rampant genetic instability and loss of cellular viability and renewal potential. The telomere also participates in processes of chromosomal repair, as evidenced by the 'capture' or de novo synthesis of telomere repeats at double-stranded breaks and by the capacity of yeast telomeres to serve as repositories of essential components of the DNA repair machinery, particularly those involved in non-homologous end-joining (NHEJ). Here we used the telomerase-deficient mouse, null for the essential telomerase RNA gene (Terc), to assess the role of telomerase and telomere function on the cellular and organismal response to ionizing radiation. Although the loss of telomerase activity per se had no discernable impact on the response to ionizing radiation, the emergence of telomere dysfunction in late-generation Terc-/- mice imparted a radiosensitivity syndrome associated with accelerated mortality. On the cellular level, the gastrointestinal crypt stem cells and primary thymocytes showed increased rates of apoptosis, and mouse embryonic fibroblasts (MEFs) showed diminished dose-dependent clonogenic survival. The radiosensitivity of telomere dysfunctional cells correlated with delayed DNA break repair kinetics, persistent chromosomal breaks and cytogenetic profiles characterized by complex chromosomal aberrations and massive fragmentation. Our findings establish a intimate relationship between functionally intact telomeres and the genomic, cellular and organismal response to ionizing radiation.

tBID, a membrane-targeted death ligand, oligomerizes BAK to release cytochrome c.

TNFR1/Fas engagement results in the cleavage of cytosolic BID to truncated tBID, which translocates to mitochondria. Immunodepletion and gene disruption indicate BID is required for cytochrome c release. Surprisingly, the three-dimensional structure of this BH3 domain-only molecule revealed two hydrophobic alpha-helices suggesting tBID itself might be a pore-forming protein. Instead, we demonstrate that tBID functions as a membrane-targeted death ligand in which an intact BH3 domain is required for cytochrome c release, but not for targeting. Bak-deficient mitochondria and blocking antibodies reveal tBID binds to its mitochondrial partner BAK to release cytochrome c, a process independent of permeability transition. Activated tBID results in an allosteric activation of BAK, inducing its intramembranous oligomerization into a proposed pore for cytochrome c efflux, integrating the pathway from death receptors to cell demise.