scholarly journals Bcl-xL inhibition enhances Dinaciclib-induced cell death in soft-tissue sarcomas

2018 ◽  
Author(s):  
Santi Rello-Varona ◽  
Miriam Fuentes-Guirado ◽  
Roser López-Alemany ◽  
Aida Contreras-Pérez ◽  
Núria Mulet-Margalef ◽  
...  
Keyword(s):  
Cell Death ◽  
Protein Synthesis ◽  
Soft Tissue ◽  
Liver Toxicity ◽  
Soft Tissue Sarcomas ◽  
Mitochondrial Pathway ◽  
Chemotherapy Drugs ◽  
Model Drug

AbstractSoft-tissue sarcomas (STS) are an uncommon and heterogeneous group of malignancies that result in high mortality. Metastatic STS have very bad prognosis due to the lack of effective treatments. Dinaciclib is a model drug for the family of CDK inhibitors. Its main targets are cell cycle regulator CDK1 and protein synthesis controller CDK9. We present data supporting Dinaciclib ability to inactivate in vitro different STS models at nanomolar concentrations. Moreover, the different rhythms of cell death induction allow us to further study into the mechanism of action of the drug. Cell death was found to respond to the mitochondrial pathway of apoptosis. Anti-apoptotic Bcl-xL was identified as the key regulator of this process. Bcl-xL showed a slower decay curve after protein synthesis disruption that in tolerant cell lines was enough to delay apoptosis, as its action cannot be countered by the relative low levels of pro-apoptotic BH3 proteins BIM and PUMA. Combination of Dinaciclib with BH3-mimetics led to quick and massive apoptosis induction in vitro, but in vivo assessment was prevented due to liver toxicity. Additionally, Bcl-xL inhibitor A-1331852 also synergized with conventional chemotherapy drugs as Gemcitabine. Thus, Bcl-xL targeted therapy arises as a major opportunity to the treatment of STS.

scholarly journals Characterization of cell-death pathways in Punta Toro virus-induced hepatocyte injury

2008 ◽  
Vol 89 (9) ◽  
pp. 2175-2181 ◽  
Author(s):  
Fangling Xu ◽  
Xiaodong Liang ◽  
Robert B. Tesh ◽  
Shu-Yuan Xiao
Keyword(s):  
Cell Death ◽  
Hepg2 Cells ◽  
Antigen Expression ◽  
Mitochondrial Pathway ◽  
Cellular Viability ◽  
Tnf Receptor ◽  
Extrinsic Pathway ◽  
Punta Toro Virus

Punta Toro virus (PTV; genus Phlebovirus, family Bunyaviridae) causes apoptosis of hepatocytes in vivo in experimentally infected hamsters and in vitro in cultured HepG2 cells. Screening for expression of apoptosis-related genes has shown alterations in the genes for tumour necrosis factor-α (TNF-α) and the TNF receptor family. This study examined the roles of the TNF receptor-related extrinsic pathway and the Bcl-2 family-associated mitochondrial pathway in PTV-induced cell death. The effects of caspase inhibitors (caspIs) and TNF on cellular viability, virus replication, and morphological and biochemical changes in apoptosis were examined in HepG2 cells at different time points after infection with PTV (Adames strain). The results showed that caspIs dampened the virus-induced reduction in cellular viability, partially suppressed and delayed viral titres and antigen expression, and partially decreased the expression of apoptotic genes, caspase activities and DNA fragmentation. TNF treatment further decreased cellular viability after PTV infection and increased the level of apoptosis, whilst caspIs partially inhibited these effects. These findings indicate that TNF, caspase-8 and caspase-9 contribute to PTV-induced hepatocytic apoptosis and that additional mediators are probably also involved in this process. These mediators from different pathways correlated with one another and may be interlinked.

scholarly journals P09.14 Blocking counterregulation of unfolded protein response by targeted protein synthesis inhibition produces highly synergistic cell death in several cancer entities

2020 ◽  
Vol 8 (Suppl 2) ◽  
pp. A59.1-A59
Author(s):  
F Gsottberger ◽  
C Meier ◽  
S Petkovic ◽  
L Mellenthin ◽  
M Krumbholz ◽  
...  
Keyword(s):  
Cell Death ◽  
Protein Synthesis ◽  
Unfolded Protein Response ◽  
Therapeutic Window ◽  
Protein Synthesis Inhibition ◽  
Synthesis Inhibition ◽  
Unfolded Protein ◽  
Protein Response

BackgroundBecause tumor cells have high proliferation rates the demand for energy on the one hand and proteins on the other hand is high. In line, protein folding machinery of the ER is heavily used. 2-Deoxyglucose (2-DG) not only blocks energy synthesis by inhibiting glycolysis but also blocks synthesis of mannosyl leading to impaired N-linked glycosylation, accumulation of misfolded proteins, and increased unfolded protein response (UPR). However, due to compensatory events, UPR-induced apoptosis is hampered. Therefore, we combined 2-DG with targeted protein synthesis inhibition by immunotoxins, consisting of an antibody and pseudomonas exotoxin, to enhance UPR mediated cell death.Materials and MethodsEstablished cell lines and patient-derived B-ALL samples were treated in vitro with various protein synthesis inhibitors and UPR-inducers. Drug synergy was determined mathematically as fold-increase over additivity. Biochemical studies were performed using western blots. In vivo enhancement was tested using systemic xenograft models.ResultsThe combination of Moxetumomab and 2-DG achieved a two to nine-fold synergy in vitro. Synergy was abrogated by the addition of Mannose suggesting UPR as cause of synergistic cell death. Similarly, Moxetumomab enhanced UPR-inducers Bortezomib and tunicamycin and protein synthesis inhibition by cycloheximide and puromycin enhanced 2-DG suggesting a conserved mechanism. Using HB21, an immunotoxin targeting human transferrin-receptor, breast cancer, hepatocellular carcinoma, and glioblastoma were sensitized to 2-DG induced cell death. Biochemically, 2-DG increased XBP-1-cleavage, expression of pro-apoptotic CHOP and of anti-apoptotic BIP. Moxetumomab, however, blocked the upregulation of BIP while maintaining CHOP correlating with synergistic increase in PARP-cleavage and apoptosis. In two systemic mouse models, bone marrow (BM) lymphoma infiltration was not reduced by 2-DG or tunicamycin alone but was reduced after treatment with Moxetumomab alone by 5-fold in the JeKo-1 and by 16-fold in the Ramos model, respectively. The combination of Moxetumomab and 2-DG achieved a three-fold synergy in the JeKo-1 model and achieved MRD-negative BM status in the Ramos model. Against patient-derived B-ALL of the Burkitt’s type, 2-DG and Moxetumomab were up to 5-fold more active in vitro and up to 7-fold more active in mouse xenografts in vivo.ConclusionsCell death after persisting unfolded protein response is synergistically enhanced by tumor-cell specific inhibition of protein synthesis against four distinct tumor entities at physiologically achievable concentrations. Our approach of immunotoxin-induced targeted protein synthesis inhibition opens a novel, so far undescribed therapeutic window which may warrant clinical evaluation.Disclosure InformationF. Gsottberger: None. C. Meier: None. S. Petkovic: None. L. Mellenthin: None. M. Krumbholz: None. M. Metzler: None. A. Mackensen: None. F. Müller: None.

scholarly journals Assessment of Efficiency and Safety of Apatinib in Advanced Bone and Soft Tissue Sarcomas: A Systematic Review and Meta-Analysis

2021 ◽  
Vol 11 ◽  
Author(s):  
Zuoyao Long ◽  
Mengquan Huang ◽  
Kaituo Liu ◽  
Minghui Li ◽  
Jing Li ◽  
...  
Keyword(s):  
Soft Tissue ◽  
Soft Tissue Sarcoma ◽  
Adverse Events ◽  
Fixed Effects ◽  
Meta Analysis ◽  
Soft Tissue Sarcomas ◽  
Progression Free Survival ◽  
Cochrane Library

BackgroundPrevious studies, both in vitro and in vivo, have established that apatinib has anti-tumor properties. However, insufficient empirical evidence of the efficacy and safety of apatinib has been published for bone and soft tissue sarcoma, the reported results differing widely. Here, we conducted a meta-analysis to assess the efficacy and toxicity of apatinib for the treatment of bone and soft tissue sarcoma.MethodsPubmed, Medline, Web of Science, ScienceDirect, Ovid, Embase, Cochrane Library, Scopus, Vip (China), Cnki (China), Wanfang (China), and CBM (China) databases and literature from conferences were searched for studies of apatinib for the treatment of bone and soft tissue sarcomas, published from the inception of each database to Sep 1, 2020, without language restrictions. Primary outcomes were efficacy and toxicity of apatinib for the treatment of bone and soft tissue sarcoma, including treatment response, progression-free survival (PFS), and the incidence of adverse events. After extraction of data and methodological quality evaluation, random or fixed-effects models, as appropriate, were selected to calculate pooled effect estimates using R software (Version 3.4.1).ResultsA total of 21 studies with 827 participants were included in the present meta-analysis. The mean MINORS score was 10.48 ± 1.75 (range: 7-13), indicating evidence of moderate quality. Pooled outcomes indicated that overall response rate (ORR) and disease control rate (DCR) were 23.85% (95% CI: 18.47%-30.21%) and 79.16% (95% CI: 73.78%-83.68%), respectively. Median PFS ranged from 3.5 to 13.1 months, with a mean of 7.08 ± 2.98 months. Furthermore, the rates of PFS (PFR) after 1, 6, and 12 months were 99.31%, 44.90%, and 14.31%, respectively. Drug-related toxicity appears to be common in patients administered apatinib, for which hand-foot syndrome (41.13%), hypertension (36.15%), and fatigue (20.52%) ranked the top three most common adverse events. However, the incidence of grade 3-4 adverse events was relatively low and manageable.ConclusionsBased on the best evidence currently available, apatinib demonstrates promising clinical efficacy and an acceptable safety profile for the treatment of advanced bone and soft tissue sarcoma, although additional high-quality clinical studies are required to further define its properties and toxicity.

Detection of MSC-like cells in soft tissue sarcoma cell lines and primary tumors

2009 ◽  
Vol 27 (15_suppl) ◽  
pp. 11000-11000
Author(s):  
S. Wirths ◽  
E. Malenke ◽  
T. Wiesner ◽  
H. Buehring ◽  
J. Hartmann ◽  
...  
Keyword(s):  
Soft Tissue ◽  
Cell Lines ◽  
Primary Tumor ◽  
Growth Factor Receptor ◽  
Soft Tissue Sarcomas ◽  
Proliferative Capacity ◽  
Differentiation Potential ◽  
Primary Tumors

11000 Background: Soft tissue sarcomas (STS) are a heterogeneous group of mesodermal tumors hypothetically originating from mesenchymal stem cells (MSC). While the expression profile of bone marrow derived MSCs and their in vitro differentiation potential have been examined extensively, knowledge regarding the in vivo counterparts of MSC is still evolving. We hypothesized that MSC-like cells within STS could represent sarcoma initiating cells. Methods: To target rare human cell populations including MSCs, an exclusive antibody panel was developed. The target antigens include platelet-derived growth factor receptor-β (CD140b), HER-2/erbB2 (CD340), TNFRSF16 (CD217), frizzled-4 (CD344), the recently described W8B2 antigen, as well as several surface antigens identified by novel antibodies. To define the expression pattern of MSC-markers in STS, both cell lines and primary tumor samples in suspension and in snap frozen sections were investigated. To reveal functional differences between identified rare tumor populations single cell proliferation kinetics were investigated after FACS-sorting. Results: All cell lines und primary tumor samples revealed expression of selected markers. Antigens identifying subpopulations within all sarcoma samples investigated, were selected for functional studies. These included frizzled-4, TNFRSF16, W5C5 and W8B2. Liposarcoma (SW872), leiomyosarcoma (SK-LMS) and fibrosarcoma (HT1080) cell lines enclosed subpopulations with differential expression of above markers and by FACS based limiting dilution it was demonstrated that only fractions of viable cells contained proliferative capacity. Cells lacking expression of CD271 had lower proliferative capacity compared to mock sorted HT1080 or SK-LMS, while CD271+ SW872 had significantly higher proliferation. The antigen defined by W5C5 identified cells with high proliferative capacity compared to control in SW872 and SK-LMS and its lack in HT1080 identified a subpopulation with largely reduced proliferation. Conclusions: Subpopulations within STS cell lines and primary sarcoma tissue express novel MSC-markers and display increased proliferative capacity, potentially reflecting the existence of sarcoma initiating cells. No significant financial relationships to disclose.

A phase II study of intravenous (IV) wild-type reovirus (Reolysin) in the treatment of patients with bone and soft tissue sarcomas metastatic to the lung

2009 ◽  
Vol 27 (15_suppl) ◽  
pp. 10524-10524 ◽  
Author(s):  
A. C. Mita ◽  
K. Sankhala ◽  
J. Sarantopoulos ◽  
J. Carmona ◽  
S. Okuno ◽  
...  
Keyword(s):  
Side Effects ◽  
Soft Tissue ◽  
Phase Ii ◽  
Performance Status ◽  
Single Agent ◽  
Soft Tissue Sarcomas ◽  
In Vivo Studies ◽  
Open Label

10524 Background: Reolysin is a Dearing strain, naturally occurring, ubiquitous human reovirus. The PKR (double stranded RNA-activated protein kinase) is inhibited and therefore the virus replicates specifically in transformed cells possessing an activated Ras pathway producing lysis. In vitro and in vivo studies with Reolysin in sarcoma cell lines revealed significant antitumor activity. Methods: This phase II open-label, single agent study was designed to characterize the efficacy and safety of Reolysin given IV every 28 days in patients (pts) with bone or soft tissue sarcoma with lung metastasis using a Simon two-stage design. 38 pts were accrued to the first stage. If 1 or more pts experience clinical benefit (prolonged SD > 6 months, partial or complete response) up to 52 pts could be accrued. The agent will be considered active if 3 or more responses or prolonged SD are observed. Results: Since July 2007, 43 pts age 19–76 (median 49) were enrolled (20 female) and received a total of 141 cycles (range 1–18). All pts had performance status 1 (29 pts) or 0 (14 pts). 38 pts received prior chemotherapy, radiotherapy, biological agents or combinations for their metastatic disease, 15 pts received more than 3 chemotherapy regimens. The sarcoma subtypes included: synovial sarcoma (13 pts), osteosarcoma (7 pts), leiomyosarcoma (7 pts), MFH (5 pts), Ewing/PNET (1 pt), chordoma (1 pt), others (9 pts). Side effects were mild to moderate (grade 1–2) and included constitutional symptoms fever, chills, fatigue. Two pts experienced respiratory side effects (cough and dyspnea) and 2 pts had diarrhea. Hematological side effects included grade 2–3 neutropenia (6 pts) and grade 2 thrombocytopenia (2 pts). One patient experienced grade 2 AST elevation. 33 pts are evaluable for response to date: 14 pts (42%) had SD for 2+ months including 5 pts having SD for more than 6 months. Conclusions: Utilization of single agent reovirus for treatment of sarcoma is a novel and unique therapeutic approach to date. Reolysin is well tolerated and shows promise for the treatment of metastatic sarcoma. Primary efficacy goals have been met. Accrual is ongoing to a total of 52 pts. [Table: see text]

scholarly journals Neuroprotection by Osteopontin in Stroke

2005 ◽  
Vol 25 (2) ◽  
pp. 217-225 ◽  
Author(s):  
Robert Meller ◽  
Susan L Stevens ◽  
Manabu Minami ◽  
Jennifer A Cameron ◽  
Sonya King ◽  
...  
Keyword(s):  
Cell Death ◽  
Protein Synthesis ◽  
Protective Effect ◽  
Cortical Neuron ◽  
Neuroprotective Effect ◽  
Protein Synthesis Inhibitor ◽  
Synthesis Inhibitor ◽  
In Vivo Models

Osteopontin (OPN) is a secreted extracellular phosphoprotein involved in diverse biologic functions, including inflammation, cell migration, and antiapoptotic processes. Here we investigate the neuroprotective potential of OPN to reduce cell death using both in vitro and in vivo models of ischemia. We show that incubation of cortical neuron cultures with OPN protects against cell death from oxygen and glucose deprivation. The effect of OPN depends on the Arg–Gly–Asp (RGD)-containing motif as the protective effect of OPN in vitro was blocked by an RGD-containing hexapeptide, which prevents integrin receptors binding to their ligands. Osteopontin treatment of cortical neuron cultures caused an increase in Akt and p42/p44 MAPK phosphorylation, which is consistent with OPN-inducing neuroprotection via the activation of these protein kinases. Indeed, the protective effect of OPN was reduced by inhibiting the activation of Akt and p42/p44 MAPK using LY294002 and U0126, respectively. The protective effect of OPN was also blocked by the protein synthesis inhibitor cycloheximide, suggesting that the neuroprotective effect of OPN required new protein synthesis. Finally, intracerebral ventricular administration of OPN caused a marked reduction in infarct size after transient middle cerebral artery occlusion in a murine stroke model. These data suggest that OPN is a potent neuroprotectant against ischemic injury.

scholarly journals Differential Efficacy of Caspase Inhibitors on Apoptosis Markers during Sepsis in Rats and Implication for Fractional Inhibition Requirements for Therapeutics

2004 ◽  
Vol 199 (2) ◽  
pp. 199-207 ◽  
Author(s):  
Nathalie Méthot ◽  
JingQi Huang ◽  
Nathalie Coulombe ◽  
John P. Vaillancourt ◽  
Dita Rasper ◽  
...  
Keyword(s):  
Cell Death ◽  
Dna Fragmentation ◽  
Caspase 3 ◽  
Apoptotic Cell ◽  
Mitochondrial Pathway ◽  
Caspase Inhibitors ◽  
Caspase Inhibition ◽  
Caspase Activated Dnase

A rodent model of sepsis was used to establish the relationship between caspase inhibition and inhibition of apoptotic cell death in vivo. In this model, thymocyte cell death was blocked by Bcl-2 transgene, indicating that apoptosis was predominantly dependent on the mitochondrial pathway that culminates in caspase-3 activation. Caspase inhibitors, including the selective caspase-3 inhibitor M867, were able to block apoptotic manifestations both in vitro and in vivo but with strikingly different efficacy for different cell death markers. Inhibition of DNA fragmentation required substantially higher levels of caspase-3 attenuation than that required for blockade of other apoptotic events such as spectrin proteolysis and phosphatidylserine externalization. These data indicate a direct relationship between caspase inhibition and some apoptotic manifestations but that small quantities of uninhibited caspase-3 suffice to initiate genomic DNA breakdown, presumably through the escape of catalytic quantities of caspase-activated DNase. These findings suggest that putative caspase-independent apoptosis may be overestimated in some systems since blockade of spectrin proteolysis and other cell death markers does not accurately reflect the high degrees of caspase-3 inhibition needed to prevent DNA fragmentation. Furthermore, this requirement presents substantial therapeutic challenges owing to the need for persistent and complete caspase blockade.

scholarly journals Pyrroline-5-Carboxylate Reductase 1: A Novel Target for Sensitizing Myeloma to Cytotoxic Agents By Inhibition of PRAS40-Mediated Protein Synthesis

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 1574-1574
Author(s):  
Inge Oudaert ◽  
Hatice Satilmis ◽  
Philip Vlummens ◽  
Anke Maes ◽  
Elke De Bruyne ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Cell Death ◽  
Protein Synthesis ◽  
Apoptotic Cell ◽  
Myeloma Cell ◽  
Tumor Burden ◽  
Rpmi 8226 ◽  
Carboxylate Reductase

Abstract Introduction Multiple myeloma (MM) remains an incurable cancer despite advances in therapy. Therefore, the search for new targets is still essential to uncover potential treatment strategies. Metabolic changes, induced by the hypoxic bone marrow, contribute to both cancer cell survival and drug resistance. In this study, we aimed to identify which metabolic changes and downstream pathways are involved in myeloma cell growth and persistence. Methods Correlation of pyrroline-5-carboxylate reductase 1 and 2 (PYCR1 and PYCR2) with overall survival was investigated in the gene-expression data of MM patients (MMRF CoMMpass trial). To perform a tracer study, RPMI-8226 cells were supplemented with 13C-glutamine for 48h in both normoxia and hypoxia (<1% O 2, by chamber). For further in vitro investigation, 2 human MM cell lines (OPM-2 and RPMI-8226) were used. Proline concentrations in cell lysates were measured by ELISA-based proline assay kit. We used siRNA to establish a knockdown of PYCR1 and/or PYCR2. Levels of apoptosis were measured using AnnexinV and 7-AAD positivity on flow cytometry. Differential protein expression was evaluated with western blot. Proliferation was measured by assessing BrdU incorporation through flow cytometry. Pargyline was used as a PYCR1 inhibitor. All in vitro experiments were performed in hypoxic conditions. For the in vivo murine experiment, C57BL/KalwRij mice were inoculated with 1 million of eGFP+ 5TGM1 cells, and treated with vehicle, bortezomib (0.6 mpk, 2x/week, starting day 14), pargyline (100 mpk, 5x/week, starting day 1) or combination of both. Tumor burden was measured by flow cytometry when vehicle mice reached end-stage. Results Pyrroline-5-carboxylate reductase 1 and 2 (PYCR1 and PYCR2) are 2 mitochondrial enzymes that facilitate the last step in the enzymatic conversion of glutamine to proline. High expression of both enzymes correlated with a lower overall survival in the CoMMpass trial. Moreover, MM cells from relapse/refractory patients expressed significant higher levels of PYCR1. We performed a tracer study with RPMI-8226 cells, revealing an increased conversion of 13C-glutamine to proline in hypoxia compared to normoxia. We confirmed these results by increased proline production after 48h of hypoxic culture. SiRNA-mediated knockdown of PYCR1 or both PYCR1/2 combined with bortezomib increased apoptotic cell death in OPM-2 and RPMI-8226, which we confirmed by detecting upregulation of cleaved PARP and cleaved CASPASE 3 levels. In contrast, PYCR2 knockdown combined with bortezomib did not significantly alter apoptosis. Further investigation revealed that PYCR1 knockdown reduced proliferation, and led to a decrease in p-AKT, p-p42/44 MAPK and c-MYC levels. Mechanistically, we found that PYCR1 silencing affected protein synthesis, as shown by a downregulation of p-PRAS40, p-MTOR, p-p70, p-S6, p-4EBP1 and p-EIF4e levels. Next, we evaluated whether the clinically relevant anti-hypertensive agent and PYCR1 inhibitor, pargyline, was capable of inducing myeloma cell death. In vitro, pargyline reduced proline production, MM viability and increased apoptotic cell death. Pargyline was also capable of reducing viability in CD138+ cells of primary patient samples . Finally, in vivo combination of pargyline with bortezomib significantly reduced tumor burden in the 5TGM1 model. On protein level, we also observed a significant decrease in p-4EBP1 and p-EIF4e in the freshly isolated 5TGM1 cells for the combination therapy. Conclusion Hypoxia increased glutamine-to-proline conversion in myeloma cells by stimulating PYCR activity. Knockdown of PYCR1 and PYCR1/2 increased bortezomib efficacy and inhibited proliferation. Mechanistically, PYCR1 interference reduced PRAS40-mediated protein synthesis. Pargyline, a PYCR1 inhibitor, also reduced MM viability and increased apoptosis. In vivo, pargyline combined with bortezomib significantly reduced tumor burden in the 5TGM1 model compared to both single agents. In conclusion, this study identifies PYCR1 as a novel target in MM therapy. Disclosures De Veirman: Active Biotech AB: Research Funding. OffLabel Disclosure: Pargyline is a antihypertensive agent and irreversible MAO B inhibitor that also inhibits PYCR1. Pargyline is not approved by the FDA as a PYCR1 inhibitor.

scholarly journals Pro-apoptotic Bid induces membrane perturbation by inserting selected lysolipids into the bilayer

2005 ◽  
Vol 387 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Alexander GOONESINGHE ◽  
Elizabeth S. MUNDY ◽  
Melanie SMITH ◽  
Roya KHOSRAVI-FAR ◽  
Jean-Claude MARTINOU ◽  
...  
Keyword(s):  
Cell Death ◽  
Membrane Surface ◽  
Death Receptor ◽  
Mitochondrial Pathway ◽  
Full Length ◽  
Membrane Perturbation ◽  
C Terminus ◽  
Biochemical Level

Bid is a BH3-only member of the Bcl-2 family that regulates cell death at the level of mitochondrial membranes. Bid appears to link the mitochondrial pathway with the death receptor-mediated pathway of cell death. It is generally assumed that the f.l. (full-length) protein becomes activated after proteolytic cleavage, especially by apical caspases like caspase 8. The cleaved protein then relocates to mitochondria and promotes membrane permeabilization, presumably by interaction with mitochondrial lipids and other Bcl-2 proteins that facilitate the release of apoptogenic proteins like cytochrome c. Although the major action may reside in the C-terminus part, tBid (cleaved Bid), un-cleaved Bid also has pro-apoptotic potential when ectopically expressed in cells or in vitro. This pro-apoptotic action of f.l. Bid has remained unexplained, especially at the biochemical level. In the present study, we show that f.l. (full-length) Bid can insert specific lysolipids into the membrane surface, thereby priming mitochondria for the release of apoptogenic factors. This is most effective for lysophosphatidylcholine species that we report to accumulate in mitochondria during apoptosis induction. A Bid mutant that is not pro-apoptotic in vivo is defective in lysophosphatidylcholine-mediated membrane perturbation in vitro. Our results thus provide a biochemical explanation for the pro-apoptotic action of f.l. Bid.

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