An unlikely player joins the ATM signalling network.
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Adaptor Proteins, Signal Transducing↗
Biomedical subjects
M F Lavin
Publications and source records attributed to M F Lavin.
ATM-dependent phosphorylation of nibrin in response to radiation exposure.
Mutations in the gene ATM are responsible for the genetic disorder ataxia-telangiectasia (A-T), which is characterized by cerebellar dysfunction, radiosensitivity, chromosomal instability and cancer predisposition. Both the A-T phenotype and the similarity of the ATM protein to other DNA-damage sensors suggests a role for ATM in biochemical pathways involved in the recognition, signalling and repair of DNA double-strand breaks (DSBs). There are strong parallels between the pattern of radiosensitivity, chromosomal instability and cancer predisposition in A-T patients and that in patients with Nijmegen breakage syndrome (NBS). The protein defective in NBS, nibrin (encoded by NBS1), forms a complex with MRE11 and RAD50 (refs 1,2). This complex localizes to DSBs within 30 minutes after cellular exposure to ionizing radiation (IR) and is observed in brightly staining nuclear foci after a longer period of time. The overlap between clinical and cellular phenotypes in A-T and NBS suggests that ATM and nibrin may function in the same biochemical pathway. Here we demonstrate that nibrin is phosphorylated within one hour of treatment of cells with IR. This response is abrogated in A-T cells that either do not express ATM protein or express near full-length mutant protein. We also show that ATM physically interacts with and phosphorylates nibrin on serine 343 both in vivo and in vitro. Phosphorylation of this site appears to be functionally important because mutated nibrin (S343A) does not completely complement radiosensitivity in NBS cells. ATM phosphorylation of nibrin does not affect nibrin-MRE11-RAD50 association as revealed by radiation-induced foci formation. Our data provide a biochemical explanation for the similarity in phenotype between A-T and NBS.
Ataxia Telangiectasia↗
Inactive free : total prostate specific antigen ratios in ejaculate from men with suspected and known prostate cancer, compared with young control men.
OBJECTIVE: To measure free : total prostate specific antigen (PSA) ratios in ejaculate from men with suspected and known prostate cancer, and in young control men, to determine if this ratio might be useful in discriminating benign from malignant prostatic conditions. Patients, subjects and methods Forty-seven men with prostate cancer (positive biopsies), 52 men with suspected prostate cancer but who had negative biopsies and 28 young men (< 30 years old) and with no family history of cancer, provided either a single ejaculate specimen (total 59) or multiple specimens (total 193) on subsequent occasions. Free and total PSA were measured using appropriate assays. All specimens were diluted in a PSA-negative female serum pool. RESULTS: The median free : total PSA ratios were 0.76-0.81 among the patient groups and control men, and there was no statistical difference between the groups. These data presumably only reflect the inactive component of free PSA, given that any alpha2-macroglobulin or alpha1-antichymotrypsin in the assay serum diluent was likely to have bound the active free PSA component in these samples. Similar results were obtained from those providing single and multiple samples, suggesting that a single specimen is sufficient to reflect the seminal plasma free : total PSA ratio over that period. There was no relationship between seminal plasma free : total PSA ratio and age for the controls or the positive biopsy group, although there was a negative relationship (i.e. a decline with age) that almost reached significance in those with negative biopsies (P = 0.058, R2 = 0.07). CONCLUSIONS: This is the first report of free : total PSA ratios in the ejaculate of men with suspected and known prostate cancer compared with young control men. Although no significant changes were detected in the free : total PSA ratios in ejaculate, these results may be confounded by differences in ratios with age, as is the case for serum PSA or different molecular forms of PSA. Indeed, these data suggest that a large proportion of free PSA in seminal plasma may be inactive. Further studies are needed to determine the potential utility of measuring free : total PSA, or other candidate markers, in ejaculate to better discriminate benign from malignant prostate disease.
Adult↗
Defective radiation signal transduction in ataxia-telangiectasia cells.
PURPOSE: The product of the gene ATM mutated in the human genetic disorder ataxia-telangiectasia (A-T) is predominantly present in the nucleus Compatible with a role in DNA-damage recognition and cell-cycle control. However, ATM is also present outside the nucleus in cytoplasmic and membrane associated vesicles, which may explain the more general signalling defect in A-T. This led us to investigate signalling events initiated by ionizing radiation, remote from the nucleus. MATERIALS AND METHODS: A-T and control lymphoblastoid cells were employed to study radiation-induced signalling at the level of protein activation using immunoprecipitation and immunoblotting. Flow cytometry was used to determine mobilization of intracellular Ca2+. RESULTS: Lymphoblastoid cells from A-T patients were found to be defective in the radiation-induced activation of protein tyrosine kinase p53/p56lyn. In control cells Ca2+ was mobilized in response to gamma-radiation largely from internal stores, and increased significantly over a 20 min period. This mobilization of Ca2+ was either absent or increased very slowly in A-T cells post-irradiation. The same pattern of release was observed after treatment with the radiometric agent, streptonigrin. In addition the phospatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin suppressed the release of Ca2+. CONCLUSION: These data demonstrate that ionizing radiation activates lyn kinase and leads to the release of Ca2+, and-for the first time-that these steps are ATM-dependent.
Ataxia Telangiectasia↗
Textilinins from Pseudonaja textilis textilis. Characterization of two plasmin inhibitors that reduce bleeding in an animal model.
The incidence of vein-graft occlusion associated with myocardial infarction and thrombosis following the use of the plasmin inhibitor, aprotinin, to reduce blood loss during vascular surgery has prompted the isolation of an alternative kinetically distinct inhibitor of plasmin from the venom of Pseudonaja textilis. This inhibitor has been called textilinin (Txln) and two distinct forms have been isolated from the Brown-snake venom (molecular weight, 6688 and 6692). A comparison of plasmin inhibitor constants for aprotinin and the Txlns 1 and 2 indicated that the former bound very tightly (inhibitor constant, Ki approximately 10(-11) mol/l), while both of the latter bound less tightly (Ki approximately 10(-9) mol/l). Homogeneity of Txlns 1 and 2 was confirmed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and mass spectrometry. A sequence difference of six amino acids was observed between the two forms of Txln. Txln 1 and 2 showed, respectively, 45 and 43% homology with aprotinin, while there was 58 and 55% homology, respectively, with a plasmin inhibitor from the venom of eastern Taipan, Oxyuranus scutellatus. Both Txlns have six cysteines, like other inhibitors of this group, and homology was determined by alignment of these cysteines. Both have been shown to reduce blood loss by about 60% in a murine tail vein bleeding model. It is proposed that the kinetic profiles of Txln 1 and 2 for plasmin allow the arrest of haemorrhage without the possible threat of thrombosis.
Amino Acid Sequence↗
Localization of a portion of extranuclear ATM to peroxisomes.
The gene mutated in the human genetic disorder ataxia-telangiectasia codes for a protein, ATM, the known functions of which include response to DNA damage, cell cycle control, and meiotic recombination. Consistent with these functions, ATM is predominantly present in the nucleus of proliferating cells; however, a significant proportion of the protein has also been detected outside the nucleus in cytoplasmic vesicles. To understand the possible role of extra-nuclear ATM, we initially investigated the nature of these vesicles. In this report we demonstrate that a portion of ATM co-localizes with catalase, that ATM is present in purified mouse peroxisomes, and that there are reduced levels of ATM in the post-mitochondrial membrane fraction of cells from a patient with a peroxisome biogenesis disorder. Furthermore the use of the yeast two-hybrid system demonstrated that ATM interacts directly with a protein involved in the import of proteins into the peroxisome matrix. Because peroxisomes are major sites of oxidative metabolism, we investigated catalase activity and lipid hydroperoxide levels in normal and A-T fibroblasts. Significantly decreased catalase activity and increased lipid peroxidation was observed in several A-T cell lines. The localization of ATM to peroxisomes may contribute to the pleiotropic nature of A-T.
Amino Acid Sequence↗
ATM is upregulated during the mitogenic response in peripheral blood mononuclear cells.
Patients with the human genetic disorder ataxia-telangiectasia (A-T) are characterized by immunodeficiency and a predisposition to develop lymphoid malignancies. The gene mutated in A-T patients, ATM, codes for a high molecular weight protein that is implicated in DNA damage recognition and cell cycle control. The ATM protein does not change in amount or cellular distribution throughout the cell cycle or in response to DNA damaging agents. Because peripheral blood mononuclear cells (PBMCs) are largely in a state of quiescence and can be readily stimulated to enter a proliferative phase and because A-T cells exhibit growth abnormalities and senescence, indicative of a general intracellular defect in signalling, we chose PBMCs to examine the relationship of ATM to the proliferative status of the cell. We show here that ATM protein is present at low levels in freshly isolated PBMCs and increases approximately 6-fold to 10-fold in response to a mitogenic stimulus, reaching a maximum after 3 to 4 days. A similar, but delayed response, was evident in the presence of serum only. This increase in ATM protein was accompanied by an increase in ATM kinase activity. While expression of ATM protein increased during proliferation, ATM mRNA expression was unchanged in stimulated and unstimulated cells and there was no evidence for increased ATM protein stability in the phytohemagglutinin (PHA)-treated cells. In keeping with the reduced levels of ATM in quiescent cells, the extent of radiation-induction of the p53 pathway was significantly lower than in mitogen-stimulated cells. Basal levels of p21 were elevated in quiescent cells, and the response to radiation was negligible or reduced compared with proliferating cells over a 2-hour period. Overall, the data suggest that the increase in ATM protein in proliferating cells is due to posttranscriptional regulation and points to a role for ATM in more general signalling.
Ataxia Telangiectasia↗
Frequent loss of heterozygosity at 1p36 in ovarian adenocarcinomas but the gene encoding p73 is unlikely to be the target.
Loss of heterozygosity (LOH) involving the distal part of the short arm of chromosome 1 occurs frequently in ovarian adenocarcinomas but the tumour suppressor gene(s) targeted by this event is unknown. We have used five microsatellite markers in a panel of 56 ovarian adenocarcinomas to determine which part of 1p34 - 36 is the focus of this LOH. LOH was considerably more common at 1p36 (43%) than at 1p34 - 35 (18%), and 11 tumours showed LOH at 1p36 but not at 1p34 - 35. These data strongly suggest the presence of a tumour suppressor gene inactivated in ovarian adenocarcinoma at 1p36. The p53 homologue, p73, has recently been isolated and mapped to 1p36 and therefore is a candidate for this tumour suppressor gene. However, RT - PCR and Western analyses revealed strong expression of p73 in ovarian adenocarcinoma cell lines but very low or undetectable levels in normal ovarian surface epithelial cells. Immunohistochemical analysis of primary ovarian tumours showed that only 3/22 (14%) contained p73 expressing cells. There was no association between 1p36 LOH and p73 expression in ovarian tumours, nor between p73 and p53 expression. These findings strongly suggest that p73 is not the target of 1p36 LOH in ovarian adenocarcinomas but indicate the presence of an, as yet unidentified, tumour suppressor gene in this region that plays an important role in ovarian tumorigenesis.
Adenocarcinoma↗
Eighth International Workshop on Ataxia-Telangiectasia (ATW8).
ATW8 was a unique opportunity to review the complex and growing field of ataxia-telangiectasia (A-T) research and to cross-fertilize ideas for new experimental designs. A-T biology now encompasses human and mouse neurology, neurobiology, immunology, radiobiology, cell signalling, cell cycle checkpoints, gametogenesis, and oncogenesis, as well as radiotherapy, cancer epidemiology, premature aging, cytogenetics, and DNA repair mechanisms. By an as yet undetermined mechanism, the ATM protein appears to sense double strand breaks (DSB) during meiosis or mitosis, or breaks consequent to the damage of free radicals which are generated during the metabolism of food. As a protein kinase, ATM then directly phosphorylates p53 and interacts with many other molecules involved in homologous and nonhomologous DSB repair, as well as in cell signalling. Some of these molecule targets include: c-abl, ATR, chk-1, chk-2, RPA, BRCA1, BRCA2, NFkappaB/IkappaB alpha, beta-adaptin, and perhaps ATM itself. Thus, ATM is a "hierarchical kinase," initiating many pathways simultaneously. Parallel sessions or longer meetings will clearly be necessary for future A-T workshops.
Animals↗
Chk1 complements the G2/M checkpoint defect and radiosensitivity of ataxia-telangiectasia cells.
Cells from patients with the human genetic disorder ataxia-telangiectasia (A-T) are defective in the activation of cell cycle checkpoints in response to ionizing radiation damage. In order to understand the role of ATM in checkpoint control we investigated whether Schizosaccaromyces pombe chk1, a protein kinase implicated in controlling the G2 DNA damage checkpoint, might alter the radiosensitive phenotype in A-T cells. The fission yeast chkl gene was cloned into an EBV-based vector under the control of a metallothionein promoter and transfected into A-T lymphoblastoid cells. Induction of chk1 enhanced the survival of an A-T cell line in response to radiation exposure as determined by cell viability and reduction of radiation-induced chromosome aberrations. This can be accounted for at least in part by the restoration of the G2 checkpoint to chk1 expressing cells. There was no evidence that chk1 expression corrected either the G1/S checkpoint or radioresistant DNA synthesis in S phase in these cells. These results suggest that chk1 when overexpressed acts downstream from ATM to restore the G2 checkpoint in these cells and correct the radiosensitive phenotype. These data allow us to dissociate individual checkpoint events and relate them to the radiosensitive phenotype in A-T cells.
Ataxia Telangiectasia↗
Single DNA sequence common to all chlamydial species employed for PCR detection of these organisms.
Chlamydial infection is responsible for a wide spectrum of diseases of the eye, genitourinary tract, and lung. This group of organisms is also implicated in the pathogenesis of coronary artery disease as well as arthritis. Since cross-species infection is widely reported (though probably underestimated), it is an advantage to have a rapid and reliable method to detect all forms of chlamydiae in patient samples. We have identified a 160/163-bp DNA fragment in Chlamydia which is highly conserved in all chlamydial species. A polymerase chain reaction method based on this sequence has been developed to detect, in clinical samples, chlamydiae which have been shown to be positive by fluorescent-staining immunoassay; this method can be utilized in combination with restriction endonuclease cleavage to identify individual chlamydial species. Thus we have developed a sensitive and rapid detection method and have used it on samples from patients with respiratory and genital infections.
Animals↗
ATM: the product of the gene mutated in ataxia-telangiectasia.
Ataxia-telangiectasia mutated (ATM) is the product of the gene mutated in the human genetic disorder ataxia-telangeictasia (A-T). It is a 370 kDa protein that is a member of the phosphatidyl inositol 3-kinases superfamily. A-T cells and those derived from Atm-/- mice are characterized by hypersensitivity to ionizing radiation and defective cell cycle checkpoints. Defects are observed at all cell cycle checkpoints in A-T cells post-irradiation including the G1/S interface where ATM plays an important role in the activation of the tumour suppressor gene product p53. Activation leads to the induction of p21/WAF1, inhibition of cyclin-dependent kinase activity, failure to phosphorylate key substrates such as the retinoblastoma protein and consequently G1 arrest. ATM also plays an important role in the regulation and surveillance of meiotic progression. Absence of ATM gives rise to a spectrum of defects including immunodeficiency, neurodegeneration, radiosensitivity and cancer predisposition. It is clear that a better definition of the role of ATM in DNA damage recognition, cell cycle control and cell signalling may assist in the treatment of the progressive neurodegeneration in this syndrome.
Animals↗
ATM: the protein encoded by the gene mutated in the radiosensitive syndrome ataxia-telangiectasia.
PURPOSE: To provide an update on the product of the ATM gene mutated in the human genetic disorder ataxia-telangiectasia (A-T). SUMMARY: The product of the ATM gene mutated in the human genetic disorder A-T is a 350 kDa protein that plays a central role in the regulation of a number of cellular processes. It is a member of the phosphatidylinositol 3-kinase superfamily, but is more likely a protein kinase similar to another member of that family, i.e. DNA-dependent protein kinase (DNA-PK). A-T cells and fibroblasts derived from the atm -/- mouse are hypersensitive to ionizing radiation and defective in cell cycle checkpoint control. At present the nature of the lesion in damaged DNA recognized by ATM remains uncertain, but it is evident that a small number of residual strand breaks remain unrepaired in A-T cells, which may well account for the radiosensitivity. On the other hand, considerable progress has been achieved in delineating the role of ATM in cell cycle checkpoint control. Defects are observed at all cell cycle checkpoints in A-T cells post-irradiation. At the G1 /S interface ATM has been shown to play a central role in radiation-induced activation of the tumour suppressor gene product p53. ATM binds to p53 in a complex fashion and activates the molecule in response to breaks in DNA by phosphorylating it at serine 15 close to the N-terminus and by controlling other phosphorylation and dephosphorylation changes on the molecule. This in turn leads to the induction of p21/WAF1 and other p53 effector proteins before inhibition of cyclin-dependent kinase activity and G1 arrest. Emerging evidence supports a direct role for ATM at other cell cycle checkpoints. Other proteins interacting with ATM include c-Abl a protein tyrosine kinase, beta-adaptin an endosomal protein and p21 a downstream effector of p53. The significance of these interactions is currently being investigated. ATM also plays an important role in the regulation and surveillance of meiotic progression. The localization of ATM to both the nucleus and other subcellular organelles implicates this molecule in a myriad of cellular processes. CONCLUSION: ATM is involved in DNA damage recognition and cell cycle control in response to ionizing radiation damage. There is evidence that ATM may also have a more general signalling role.
Animals↗
ATM protein synthesis patterns in sporadic breast cancer.
AIMS: The gene mutated in ataxia-telangiectasia (A-T), designated ATM (for "A-T mutated"), is believed to be associated with an increased risk of developing breast cancer. Most patients with A-T have null mutations of the ATM gene that appear to give rise to a truncated nonfunctional ATM protein. Therefore, the increased risk of breast cancer reported in A-T heterozygotes appears to be the result of haplo-insufficiency of ATM in breast tissues. This study aimed to determine whether reduced synthesis of ATM was also an important factor in sporadic breast cancer. METHODS: Paraffin wax embedded tissues from patients with breast invasive ductal carcinoma (IDC) (n = 42), patients with ductal carcinoma in situ (DCIS) (n = 17), and others with lymph node metastases (n = 14) were studied. A streptavidin-biotin-peroxidase system was used to stain tissue sections for the ATM protein using the ATM-4BA and CT-1 polyclonal and monoclonal antibodies, respectively. The protein truncation test was used to screen for mutations in the ATM gene in those patients who had greatly reduced ATM protein immunoreactivity in the primary carcinoma (n = 3). RESULTS: Most metastatic breast carcinomas in lymph nodes (71%) had greatly reduced or absent ATM protein synthesis, which was significant when compared with that observed in non-metastatic invasive breast carcinomas (p = 0.029; chi 2 test). Although not significant (p = 0.045; chi 2 test), some sporadic breast carcinomas (14 of 42) also had reduced or absent ATM protein immunoreactivity. The protein truncation test did not reveal any gross ATM gene abnormality in the cases tested, indicating that the patients were not A-T heterozygotes, who are predisposed to breast cancer. CONCLUSIONS: A reduction in immunohistochemically detectable ATM protein in sporadic breast carcinoma implicates ATM in the progression of the disease.
Adult↗
Hemps, a novel EGF-like protein, plays a central role in ascidian metamorphosis.
All chordates share several characteristic features including a dorsal hollow neural tube, a notochord, a pharynx and an endostyle. Unlike other chordate taxa, ascidians have a biphasic life-history with two distinct body plans. During metamorphosis, the larval nerve cord and notochord degenerate and the pharyngeal gill slits and endostyle form. While ascidians, like other marine invertebrates, metamorphose in response to specific environmental cues, it remains unclear how these cues trigger metamorphosis. We have identified a novel gene (Hemps) which encodes a protein with a putative secretion signal sequence and four epidermal growth factor (EGF)-like repeats which is a key regulator of metamorphosis in the ascidian Herdmania curvata. Expression of Hemps increases markedly when the swimming tadpole larva becomes competent to undergo metamorphosis and then during the first 24 hours of metamorphosis. The Hemps protein is localised to the larval papillae and anterior epidermis of the larva in the region known to be required for metamorphosis. When the larva contacts an inductive cue the protein is released, spreading posteriorly and into the tunic as metamorphosis progresses. Metamorphosis is blocked by incubating larvae in anti-Hemps antibodies prior to the addition of the cue. Addition of recombinant Hemps protein to competent larvae induces metamorphosis in a concentration-dependent manner. A subgroup of genes are specifically induced during this process. These results demonstrate that the Hemps protein is a key regulator of ascidian metamorphosis and is distinct from previously described inducers of this process in terrestrial arthropods and aquatic vertebrates.
Animals↗
Molecular detection of prostate cells in ejaculate and urethral washings in men with suspected prostate cancer.
PURPOSE: To determine whether prostatic cells were normally present in ejaculate and if the sensitivity and specificity of the detection of malignant prostate cells in ejaculate and urethral washings from men with suspected prostate cancer could be improved using the more sensitive molecular technique of reverse transcriptase-polymerase chain reaction (RT-PCR). MATERIALS AND METHODS: RT-PCR for prostate-specific antigen (PSA), prostate-specific membrane antigen (PSM) and Apoliprotein D (3 putative prostate-specific and/or cancer-specific markers) was performed on RNA extracts of ejaculate (80) and urethral washings (52) from 77 men with suspected prostate cancer and 12 young controls (<30 years of age) and urines from 5 men who had radical prostatectomies and 10 women. RESULTS: PSA, PSM and Apolipoprotein D expression was detected in ejaculates and urethral washings from both patient and control groups. No differences were observed in the results obtained for 58 men with suspected or 19 men with confirmed prostate cancer or the 18 vasectomized men within the patient group. Urines from the 5 men who had radical prostatectomies and 10 women were all negative for PSA, but PSM was detected in 2 female urines and in 3 radical prostatectomy samples. As few as 10 LNCaP prostate tumor cells could be detected by PSA RT-PCR when added to female urine. CONCLUSION: We have established a sensitive method of detecting prostatic cells in ejaculate and urethral washings and shown that PSA RT-PCR is a reliable indicator of prostate cells in these samples. However, RT-PCR for PSA, PSM and Apoliprotein D were not useful for discriminating malignant from non-malignant prostate cells.
Adult↗
A novel ionizing radiation-induced signaling pathway that activates the transcription factor NF-kappaB.
The signaling pathway through which ionizing radiation induces NF-kappaB activation is not fully understood. IkappaB-alpha, an inhibitory protein of NF-kappaB mediates the activation of NF-kappaB in response to various stimuli, including cytokines, mitogens, oxidants and other stresses. We have now identified an ionizing radiation-induced signaling pathway that is independent of TNF-alpha. IkappaB-alpha degradation is rapid in response to TNF-alpha induction, but it is absent in response to ionizing radiation exposure in cells from individuals with ataxia-telangiectasia (AT). Overexpression of wild-type ATM, the product of the gene defective in AT patients, restores radiation-induced degradation of IkappaB-alpha. Furthermore, phosphorylation of IkappaB-alpha by immunoprecipitated ATM kinase is increased in control fibroblasts and transfected AT cells following ionizing radiation exposure. These data provide support for a novel ionizing radiation-induced signaling pathway for activation of NF-kappaB and a molecular basis for the sensitivity of AT patients to oxidative stresses.
Acetylcysteine↗
Resistance to etoposide-induced apoptosis in a Burkitt's lymphoma cell line.
Burkitt's lymphoma cells that vary in their phenotypic characteristics show significantly different degrees of susceptibility to radiation-induced apoptosis. Propensity to undergo apoptosis is reflected in the degradation of substrates such as DNA-dependent protein kinase but the status of bcl-2, c-myc and p53 has been uninformative. In this study, we have focused on 2 Epstein-Barr virus (EBV)-associated Burkitt's cell lines, one (WW2) susceptible and the other (BL29) resistant to etoposide-induced apoptosis. Differences in expression of BHRF1, an EBV gene that is homologous to the Bcl-2 proto-oncogene and known to inhibit apoptosis, or changes in apoptosis inhibitory proteins (IAPs), did not appear to account for the difference in susceptibility in the 2 cell lines. Cytoplasmic extracts from etoposide-treated WW2 cells caused apoptotic changes in nuclei isolated from either BL29 or WW2 cells, whereas extracts from BL29 cells failed to do so. In addition, extracts from etoposide-treated WW2 cells degraded the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), an important indicator of apoptosis, but this protein was resistant to degradation by BL29 extracts. It appears likely that caspase 3 (CPP32) is involved in this degradation since it was activated only in the apoptosis susceptible cells and the pattern of cleavage of DNA-PKcs was similar to that reported previously with recombinant caspase 3. As observed previously, addition of caspase 3 to nuclei failed to induce morphological changes indicative of apoptosis, but addition of caspase 3 to nuclei in the presence of extract from the resistant cells led to apoptotic changes. We conclude that resistance to apoptosis in BL29 cells is due to a failure of etoposide to activate upstream effectors of caspase activity.
Apoptosis↗