Bcl-2 protects murine erythroleukemia cells from p53-dependent and -independent radiation-induced cell death

Biomarkers for response to neoadjuvant chemoradiation for rectal cancer

Locally advanced rectal cancer (LARC) is currently treated with neoadjuvant chemoradiation. Although approximately 45% of patients respond to neoadjuvant therapy with T-level downstaging, there is no effective method of predicting which patients will respond. Molecular biomarkers have been investigated for their ability to predict outcome in LARC treated with neoadjuvant chemotherapy and radiation. A literature search using PubMed resulted in the initial assessment of 1,204 articles. Articles addressing the ability of a biomarker to predict outcome for LARC treated with neoadjuvant chemotherapy and radiation were included. Six biomarkers met the criteria for review: p53, epidermal growth factor receptor (EGFR), thymidylate synthase, Ki-67, p21, and bcl-2/bax. On the basis of composite data, p53 is unlikely to have utility as a predictor of response. Epidermal growth factor receptor has shown promise as a predictor when quantitatively evaluated in pretreatment biopsies or when EGFR polymorphisms are evaluated in germline DNA. Thymidylate synthase, when evaluated for polymorphisms in germline DNA, is promising as a predictive biomarker. Ki-67 and bcl-2 are not useful in predicting outcome. p21 needs to be further evaluated to determine its usefulness in predicting outcome. Bax requires more investigation to determine its usefulness. Epidermal growth factor receptor, thymidylate synthase, and p21 should be evaluated in larger prospective clinical trials for their ability to guide preoperative therapy choices in LARC.

Advances in regulation mechanism of hepatocyte apoptosis in nonalcoholic fatty liver disease

The pathogenic mechanism of nonalcoholic fatty liver disease (NAFLD) still remains unclear. In recent years, many studies indicate that abnormal hepatocyte apoptosis exists in NAFLD, confirming the close relationship between NAFLD and hepatocyte apoptosis. The regulation of cell apoptosis includes two: positive or negative. In this paper, we review the research advances in the regulation of hepatocyte apoptosis during the pathogenesis of NAFLD.

Heavy ion beams induce survivin expression in human hepatoma SMMC-7721 cells more effectively than X-rays

High linear energy transfer (LET) heavy ion radiation is more effective in inducing biological damage than low-LET X-rays or gamma-rays. Heavy ion beam provides good dose localization (Bragg peak) in critical cancer tissue and gives higher relative biological effectiveness in cell killing across the dose peak, so high-LET heavy ion beam is superior to low-LET radiation in cancer treatment. Survivin, as a member of the inhibitor of apoptosis protein family, might help cancerous cells to overcome the G2/M apoptotic checkpoint and favor the aberrant progression of transformed cells through mitosis. Survivin expression in the human hepatoma SMMC-7721 cell line after exposure to low-LET X-ray and high-LET carbon ion irradiation was investigated in this study. Compared with X-ray irradiation, the carbon ion beam clearly caused G2/M arrest and promoted the expression of the survivin gene in a dose-dependent manner. Clonogenic survival assay showed that SMMC-7721 cells were more radiosensitive to the high-LET carbon ions than to the X-rays, and the radiosensitivity was promoted after treatment with specific survivin short interfering RNA. Differential survivin expression at both transcriptional and translational levels was found for SMMC-7721 cells following low- and high-LET irradiation. The overexpression of survivin in SMMC-7721 cells is probably an important reason why the cancerous cells have radioresistance to strong stimulus such as dense ionizing high-LET radiation. However, the direct killing effect on cancerous cells by high-LET radiation might be more significant than the apoptosis inhibition through the overexpression of survivin following heavy ion irradiation.

The Involvement of MAPK Signaling Pathways in Determining the Cellular Response to p53 Activation

The effect of ERK, p38, and JNK signaling on p53-dependent apoptosis and cell cycle arrest was investigated using a Friend murine erythroleukemia virus (FVP)-transformed cell line that expresses a temperature-sensitive p53 allele, DP16.1/p53ts. In response to p53 activation at 32 degrees C, DP16.1/p53ts cells undergo p53-dependent G(1) cell cycle arrest and apoptosis. As a result of viral transformation, these cells express the spleen focus forming env-related glycoprotein gp55, which can bind to the erythropoietin receptor (EPO-R) and mimics many aspects of EPO-induced EPO-R signaling. We demonstrate that ERK, p38 and JNK mitogen-activated protein kinases (MAPKs) are constitutively active in DP16.1/p53ts cells. Constitutive MEK activity contributes to p53-dependent apoptosis and phosphorylation of p53 on serine residue 15. The pro-apoptotic effect of this MAPK kinase signal likely reflects an aberrant Ras proliferative signal arising from FVP-induced viral transformation. Inhibition of MEK alters the p53-dependent cellular response of DP16.1/p53ts from apoptosis to G(1) cell cycle arrest, with a concomitant increase in p21(WAF1), suggesting that the Ras/MEK pathway may influence the cellular response to p53 activation. p38 and JNK activity in DP16.1/p53ts cells is anti-apoptotic and capable of limiting p53-dependent apoptosis at 32 degrees C. Moreover, JNK facilitates p53 protein turnover, which could account for the enhanced apoptotic effects of inhibiting this MAPK pathway in DP16.1/p53ts cells. Overall, these data show that intrinsic MAPK signaling pathways, active in transformed cells, can both positively and negatively influence p53-dependent apoptosis, and illustrate their potential to affect cancer therapies aimed at reconstituting or activating p53 function.

Zonal necrosis prevented by transduction of the artificial anti-death FNK protein

Protection of cells from necrosis would be important for many medical applications. Here, we show protein transduction domain (PTD)-FNK therapeutics based on protein transduction to prevent necrosis and acute hepatic injury with zonal death induced by carbon tetrachloride (CCl4). PTD-FNK is a fusion protein comprising the HIV/Tat PTD and FNK, a gain-of-function mutant of anti-apoptotic Bcl-x(L). PTD-FNK protected hepatoma HepG2 from necrotic death induced by CCl4, and additionally, increased the apoptotic population among cells treated with CCl4. A concomitant treatment with a pan-caspase inhibitor Z-VAD-FMK (N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone), which alone could not prevent the necrosis, protected these cells from the apoptosis. When pre-injected intraperitoneally, PTD-FNK markedly reduced zonal liver necrosis caused by CCl4. Moreover, injection of PTD-FNK accompanied by Z-VAD-FMK suppressed necrotic injury even after CCl4 administration. These results suggest that PTD-FNK has great potential for clinical applications to prevent cell death, whether from apoptosis or necrosis, and organ failure.

Hydroxylamine potentiates the effect of low dose hydrogen peroxide in glioma cells independent of p53

We had earlier shown that higher concentration of hydrogen peroxide (H(2)O(2)) induced p53-dependent apoptosis in glioma cell line with wild type p53 but had minimal effect on cells with mutated p53. Here we show a potentiating effect of hydroxylamine (HA), an inhibitor of catalase, on a nontoxic dose of H(2)O(2) in glioma cells. HA sensitized both p53 wild type and mutated glioma cells to 0.25 mM H(2)O(2). Potentiating effect of HA was independent of p53. Higher levels of reactive oxygen species (ROS) generation were observed in cells treated with HA+H(2)O(2) as compared to cells treated with each component alone in both the cell lines. Dimethyl sulfoxide (DMSO) protected cells. Cytosolic cytochrome c and activated caspase 3 were detected at 4h. The results suggest that higher levels of intracellular ROS, generated by HA+H(2)O(2) act as a molecular switch in activating a rapidly acting p53-independent mitochondrial apoptotic pathway.

A role for survivin in radioresistance of pancreatic cancer cells

Using gene-transduced pancreatic cancer cells, we examined whether survivin expression is directly involved in regulation of radiosensitivity. Ordinarily radiosensitive MIAPaCa-2 cells transduced with wild-type survivin gene (MS cells) proliferated more rapidly than cells transduced with control vector. MS cells were significantly less radiosensitive than control vector-transduced cells. Radiation-induced activity of caspase-3, but not caspase-7, was significantly inhibited in MS cells. On the other hand, transduction of a dominant-negative mutant survivin gene into radioresistant PANC-1 cells augmented radiosensitivity. Further, the radiation-induced increase in caspase-3 activity was enhanced, indicating that survivin function was truly inhibited. These results indicate that survivin expression directly down-regulates radiosensitivity.

p53, BCL-2, and Ki-67 expression according to tumor response after concurrent chemoradiotherapy for advanced rectal cancer

BACKGROUND

Concurrent chemoradiotherapy (CCRT) for locally advanced rectal cancer is an important modality for curative resection, but tumors show wide spectrum response. The purpose of this study was to investigate any correlation among related genetic mutations, proliferative index, and tumor response after CCRT.

METHODS

This study included 23 patients with rectal cancer, who were preoperatively staged as at least T3 N1 or T4 (determined by transrectal ultrasonography and MRI). Enrolled patients were given 5-FU 450 mg/m2/day and leucovorin 20 mg/m2/day intravenously for 5 days during weeks 1 and 5 of radiotherapy (45-54 Gy). Surgical resection was performed 4 weeks after completion of the scheduled treatment. Tumor response was classified as CR (complete response), PR (partial response: 50% diminution of tumor volume and downstaging), and NR (no response). Paraffin-embedded tissue obtained before chemoradiotherapy was studied by immunohistochemical staining for p53, BCL-2, and Ki-67. The extent of tumor response was correlated with proliferative activity and was measured by immunostaining Ki-67 proliferative antigen and the expression of p53 and BCL-2 oncoproteins.

RESULTS

All patients were resectable. CR was obtained in 4 patients, PR in 10 patients, and NR in 9 patients. The p53 mutation was noted in 16 patients: NR in 5 patients, PR in 9 patients, and CR in 2 patients (P = .638). BCL-2 expression was noted in 11 patients: NR in 4 patients, PR in 3 patients, and CR in 4 patients (P = .799). The Ki-67 labeling index was NR: 615.4+/-47.2; PR: 663.2+/-20.4; and CR: 765.5+/-58.3 (CR + PR vs. NR, P = .029).

CONCLUSIONS

Immunohistochemical expression of p53 and BCL-2 does not correlate with tumor response after CCRT, but Ki-67 labeling may be a useful parameter for radiosensitive tumors selected for CCRT.

Role of apoptosis in the response of lung carcinomas to anti-cancer treatment

Resistance of tumor cells to treatment often accounts for the failure of traditional forms of anti-cancer therapy. It is well known that tumors from the same histological group and stage of development are highly heterogeneous in their sensitivity to therapy. Among the factors that can influence tumor sensitivity are DNA repair capacity, distribution of cells throughout the cell cycle, proliferation potential, etc. In many cases, anti-cancer therapy eliminates tumor cells via apoptosis, an active form of cell death characterized by cell shrinkage and the removal of cells in a neat, orderly fashion. However, this process is not always efficient. In the present review, the precise role that apoptosis plays in the response of lung carcinomas to chemotherapy and radiation treatment is discussed.

Survivin as a radioresistance factor in pancreatic cancer

We examined whether survivin acts as a constitutive and inducible radioresistance factor in pancreatic cancer cells. Using a quantitative TaqMan reverse transcription-polymerase chain reaction for survivin mRNA in five pancreatic cancer cell lines, we found an inverse relationship between survivin mRNA expression and radiosensitivity. PANC-1 cells, which had the highest survivin mRNA levels, were most resistant to X-irradiation; MIAPaCa-2 cells, which showed the least survivin mRNA expression, were the most sensitive to X-irradiation. Our results suggested that survivin could act as a constitutive radioresistance factor in pancreatic cancer cells. To determine whether radioresistance is enhanced by induction of survivin expression by irradiation, PANC-1 and MIAPaCa-2 cells were subjected to sublethal doses of X-irradiation followed by a lethal dose. Survivin mRNA expression was increased significantly in both PANC-1 and MIAPaCa-2 cell lines by pretreatment with a sublethal dose of X-irradiation, as was cell survival after exposure to the lethal dose. In this system, enzymatic caspase-3 activity was significantly suppressed in cells with acquired resistance. These results suggest that survivin also acts as an inducible radioresistance factor in pancreatic cancer cells. Survivin, then, appears to enhance radioresistance in pancreatic cancer cells; inhibition of survivin mRNA expression may improve the effectiveness of radiotherapy.

Increased frequencies of gene and chromosome mutations after X-irradiation in mouse embryonal carcinoma cells transfected with the bcl-2 gene

Preimplantation stage mouse embryos are known to be highly sensitive to the killing effect of DNA-damaging agents such as radiation. Interestingly, however, this stage of development is well protected from radiation induction of malformation and carcinogenesis in postnatal life. In recent years, it has become clear that the stem cells of preimplantation stage embryos undergo extensive apoptosis after DNA damage. It has been postulated that this apoptosis is likely to be responsible for the resistance to malformation, by excluding cells carrying deleterious DNA damage. We have tested the possible role of apoptosis in elimination of gene and chromosome mutations in undifferentiated mouse embryonal carcinoma cell line, F9, transfected with human bcl-2 cDNA. The colony radiosensitivity of F9 cells was not affected by overexpression of the bcl-2 gene, but the apoptotic cell death was suppressed, as examined by DNA ladder assay and Hoechst staining. This suppression was accompanied by an increase in the frequencies of hprt mutation and micronucleus formation after X-irradiation. These results support the idea that maintenance of genomic integrity during early development is likely to be executed by apoptotic elimination of cells at risk.

Cell death is prevented in thalamic fields but not in injured neocortical areas after permanent focal ischaemia in mice overexpressing the anti-apoptotic protein Bcl-2

Previous studies have suggested that various apoptotic-related proteins could be involved in the death process induced by cerebral ischaemia. In order to further clarify their role and examine how the anti-apoptotic protein Bcl-2 could influence this process, the time-course of mRNA expression of various cell death genes was studied from 1 to 14 days following permanent occlusion of the middle cerebral artery in wild-type (WT) and Bcl-2 transgenic mice, within and outside the area of infarction. No differences of the infarct sizes were observed between the two groups of mice, showing that the extent of neuronal injury could not have been lowered by the Bcl-2 transgene. Seven days after the ischaemic insult, the mRNA expression of the cell death gene effector cpp32 was dramatically upregulated in the penumbra of WT and Bcl-2 transgenic mice. Interestingly, the cpp32 transcript was markedly induced from 3 days in the ipsilateral thalamus of the two groups of mice. However, apoptotic bodies were observed in the thalamic field of WT but not transgenic mice. This suggests that cpp32 mRNA may be induced in an attempt to kill the injured cells and, in contrast to the penumbra, cell death in the thalamus may be prevented in Bcl-2 transgenic mice. Based on these results, the pathophysiological mechanisms that underly neuronal damage following ischaemia need consideration in order to evaluate the extent of neuroprotection that may be afforded by the Bcl-2 anti-apoptotic protein. Although the present study does not confirm previous data showing a protective role of Bcl-2 in neocortical infarcted areas, it suggests that anti-apoptotic therapies may constitute a possible treatment for areas of the brain remote from those directly affected by ischaemia.

The role of PDGF-dependent suppression of apoptosis in differentiating 3T3-L1 preadipocytes

In a chemically defined serum-free culture system, platelet-derived growth factor (PDGF) as the only externally applied growth factor, in concert with corticosterone, 3-isobutyl-1-methylxanthine (IBMX) and low insulin (1nM), stimulates adipose conversion of 3T3-L1 preadipocytes. Omission of PDGF during the induction period results in loss of differentiation competence and apoptotic cell death. Induction of apoptosis is shown to be clearly mediated by PDGF withdrawal, since neither corticosterone nor IBMX affect the apoptotic behaviour of 3T3-L1 cells. Cell viability in the absence of the survival factor PDGF could be achieved by application of high insulin (1 microM) or ectopical expression of the anti-apoptotic proto-oncogene Bcl-2. However, PDGF-independent suppression of cell death does not trigger adipose conversion in the presence of corticosterone and IBMX. Therefore, we conclude that suppression of apoptosis per se is not permissive for differentiation of 3T3-L1 preadipocytes and PDGF might exert some additional differentiation-promoting effect(s).

Higher spontaneous apoptotic index in small cell compared with non-small cell lung carcinoma cell lines; lack of correlation with Bcl-2/Bax

Spontaneous apoptosis was assessed in ten small-cell (SCLC) and five non-small cell (NSCLC) lung carcinoma cell lines by the TUNEL assay and chromatin cleavage. TUNEL staining showed significantly higher apoptotic index (AI) in SCLC (2-20%) compared with NSCLC lines (0.2-1%) in untreated exponentially growing cells. Six out of ten SCLC and none of the NSCLC showed DNA fragmentation when analysed by agarose gel electrophoresis. Field inversion pulse gel electrophoresis was used in a subset of cell lines and showed the presence of high molecular weight fragments in untreated SCLC lines U-1285 and U-1906 cells, but not in the NSCLC line U-1810. Important molecular determinants of apoptosis were studied by Western blot. Bcl-2 was detected at highest level in SCLC. There was no correlation between the ratio Bcl-2/Bax and AI in all tested cell lines. Neither p53 nor c-Myc protein status correlated to AI. Pro-caspase-3 was expressed in all cell lines without correlation to AI and no difference between the SCLC and NSCLC groups was found. In conclusion, this study shows a high degree of spontaneous apoptosis in SCLC lines compared to NSCLC lines unrelated to Bcl-2/Bax ratio.

Targeting cancer cell death with a bcl-XS adenovirus

Transformation is a complex cellular process that requires several genetic abnormalities. In many cases, one of these abnormalities is an inhibition of PCD, which provides a selective advantage for tumor cells. This has been recently shown in an in vivo model, where overexpression of Bcl-XL, is a crucial step in the progression from hyperplasia to neoplasia and is accompanied by a significant decrease in tumor apoptosis [56]. Frequently, overexpression of a member of the Bcl-2 family results in a block in cell death and appears to nullify many built-in cellular defense mechanisms against cancer. Such a block presents a problem because radiation and chemotherapy, standard cancer treatments, ultimately exert their effect by induction of apoptosis and would also be made less effective. Therefore, to better treat cancer it may be necessary to develop novel methods to overcome the effects of the Bcl-2 family. One way to approach this problem is to target the cause--the molecular machinery that allows a cancer cell to survive. Advances in our understanding of apoptosis has identified the Bcl-2 family as a mediator of most apoptosis pathways, including those initiated by oncogenes, tumor suppressor genes, growth factor withdrawal, and external damaging signals. Therefore, functional inhibition of Bcl-2 family members is lethal to many cancer cells. Using gene transfer technology, we can now deliver genes that accomplish this goal. Further investigation will reveal whether this translates to improved therapy in the future.

[Significance of apoptotic processes in radiotherapy. I]

According to a considerable amount of publications apoptosis plays an important role for radio- and chemotherapy. The most important results related to this issue will be described in 2 independent articles, covering the following topics: Part I: I. definition, morphology, biochemical processes, II. clinical relevant detection assays, III. signal transduction. Part II: significance of apoptosis for radio- and chemotherapy.

Role of p53 and p21/WAF1 detection in patient selection for preoperative radiotherapy in rectal cancer patients

BACKGROUND

Recent studies showed that p53 and p21 may play major roles in determining tumor radiosensitivity through the apoptosis pathway. The aim of this study was to investigate the predicting value of radiosensitivity in human rectal carcinoma.

METHODS

p53 and p21/WAF1 expressions in formalin fixed, paraffin-embedded, preradiation biopsy samples from 49 patients with primary rectal carcinoma were analyzed immunohistochemically. p53 and p21 expressions and their relationships with histopathologic changes after radiation and other clinical features were evaluated.

RESULTS

Expressions of p53 and p21/WAF1 were 49 and 28.6 percent, respectively. In 36.7 percent of total tumors, significant histopathologic effect can be observed. There was a significant inverse expression of p53 and p21. Most of the p53(+) or p21(-) tumors were radioresistant, and the majority of p53(-) or p21(+) tumors were radiosensitive. Tumors size in the radiosensitive, p53(-), or p21(+) group decreased more significantly than in radioresistant, p53(+), or p21(-) group (P < 0.01), and patients with radioresistant, p53(+), or p21(-) tumors had more local recurrence, more distant metastasis, and a shorter five-year survival rate than those with radiosensitive, p53(-), or p21(+) tumors, but without statistic significance. No statistically significant correlation can be observed between other tumor clinical features and radiosensitivity, p53, or p21 expressions.

CONCLUSION

Immunohistochemistry detection of p53 and p21 expressions may be useful parameters for more radiosensitive patients selected for preoperative radiotherapy.

Mechanisms of cycloheximide-induced apoptosis in liver cells

Cycloheximide in sublethal doses caused apoptosis in liver cells in vivo, inducing c-myc, c-fos, c-jun and p53 genes and accumulation of sphingosine, a toxic product of the sphingomyelin cycle. These data support the hypothesis that continuous synthesis of labile protective proteins is required to restrain apoptosis in liver; sphingosine might be important in mediating cycloheximide-induced apoptosis as an endogenous modulator of protein kinase C activity.

Suppression of apoptosis by overexpression of Bcl-2 or Bcl-xL promotes survival and mutagenesis after oxidative damage

Apoptosis is the physiological process by which unwanted cells in an organism are killed. Bcl-2, a membrane-bound cytoplasmic protein, and its close relative Bcl-xL, are both effective inhibitors of apoptosis induced by a wide variety of stimuli in many different cell types. In a previous study, we reported that suppression of apoptosis by Bcl-2 or Bcl-xL, markedly elevates the levels of radiation-induced mutations at the specific locus thymidine kinase. We investigated the effect of the Bcl-2 or Bcl-xL overproduction on hydrogen peroxide-induced mutagenesis. Oxidative DNA damage has been implicated in biological processes such as mutagenesis, carcinogenesis and aging. Overexpression of either Bcl-2 or Bcl-xL enhances oxidative stress mutagenesis in cells with wild type p53 as well as with mutated p53 protein. These results support the hypothesis that apoptosis plays a crucial role in maintaining genomic integrity by selectively eliminating highly mutated cells from the population.

Effect of p53 overexpression on radiation sensitivity of human colon cancer cells

Substantial controversy surrounds our understanding of the effect of p53 status on radiation sensitivity. To assess directly the role of p53 expression on radiation sensitivity, we chose a conditional expression system using a temperature-sensitive murine p53 that permitted each cell line to act as its own control. We found that the conditional expression of wild type p53 induced cell death (both apoptotic and nonapoptotic), changes in cell cycle distribution (arrest in G1 and G2, which resulted in a marked depletion of S-phase cells and an increase in the fraction of cells in G2), and an increase in the radiation resistance of G1 cells. These counterbalancing effects resulted in no significant effect on overall radiosensitivity. These findings demonstrate that wild type p53 function can produce a variety of effects that can modulate radiation sensitivity and may explain why p53 status alone has not been a strong predictor of radiosensitivity.

Apoptosis and necrosis in toxicology: a continuum or distinct modes of cell death?

Mounting evidence indicates that apoptosis rather than necrosis predominates in many cytolethal toxic injuries. Associated cell death models of apoptosis and necrosis are either: (1) totally separate death modes, (2) a continuum whereby they are extremes of biochemically overlapping death pathways, or (3) essentially distinct processes with only limited molecular and cell biology overlap. We conclude that the current balance of evidence favours the third of these options. The established axiom that, even when considering the same toxicant, injury amplitude (dose) is a primary determinant of whether cells die via active cell death (apoptosis) or failure of homeostasis (necrosis) remains valid. Tissue selectivity of toxicants can stem from the apoptotic or necrotic thresholds at which different cells die, as well as targeting factors such as toxicokinetics, receptor recognition, bioactivation, and cell-specific lesions.

Expression and Regulation of Bcl-2, Bcl-xl, and Bax Correlate With p53 Status and Sensitivity to Apoptosis in Childhood Acute Lymphoblastic Leukemia

Bcl-2 and its homologue, Bcl-xl, encode membrane-associated proteins that protect neoplastic cells from DNA damage-induced apoptosis, whereas Bax is a Bcl-2 antagonist that promotes cell death. In the present study, we examined the expression and regulation of these genes at both the mRNA and protein level in 22 pediatric acute lymphoblastic leukemia (ALL) cell lines, as well as their sensitivity to apoptosis after exposure to ionizing radiation (IR). Eleven of 22 lines expressed wild-type (wt) p53, 4 expressed mutant p53, and 7 did not express p53 (p53-null). Nine of 22 (41%) lines expressed Bcl-2; of these, 8 were wt-p53+ and 1 expressed mutant p53. Bcl-2 was not expressed in any p53-null lines. In contrast, all 22 lines were positive for Bcl-xl and Bax, although expression level varied. Treatment with IR (10 Gy) induced both downregulation of Bcl-2 and upregulation of Bax at 2 to 5 hours post-IR in 5 of 8 (63%) wt-p53+ lines, leading to apoptosis. Conversely, lines that failed to both downregulate Bcl-2 and upregulate Bax after IR were resistant to apoptosis. Although levels of Bcl-xl expression varied among the 22 lines, high levels of Bcl-xl were observed in 5 of 7 (71%) p53− lines. There were no obvious changes in the expression of Bcl-xl in these lines after IR. However, among the p53-null lines, resistance to IR was observed only in those expressing high levels of Bcl-xl. These results suggest that expression of Bcl-2 but not Bcl-xl is p53-dependent and that IR-induced downregulation of Bcl-2 and upregulation of Bax occur in most wt-p53+ lines and are associated with radiosensitivity. Furthermore, high-level expression of Bcl-xl occurs predominantly in p53-null lines and is associated with resistance to IR-induced apoptosis in these lines, indicating differential expression and regulation of Bcl-2 and Bcl-xl in pediatric ALL.

Neuroprotective action of cycloheximide involves induction of bcl-2 and antioxidant pathways

The ability of the protein synthesis inhibitor cycloheximide (CHX) to prevent neuronal death in different paradigms has been interpreted to indicate that the cell death process requires synthesis of "killer" proteins. On the other hand, data indicate that neurotrophic factors protect neurons in the same death paradigms by inducing expression of neuroprotective gene products. We now provide evidence that in embryonic rat hippocampal cell cultures, CHX protects neurons against oxidative insults by a mechanism involving induction of neuroprotective gene products including the antiapoptotic gene bcl-2 and antioxidant enzymes. Neuronal survival after exposure to glutamate, FeSO4, and amyloid beta-peptide was increased in cultures pretreated with CHX at concentrations of 50-500 nM; higher and lower concentrations were ineffective. Neuroprotective concentrations of CHX caused only a moderate (20-40%) reduction in overall protein synthesis, and induced an increase in c-fos, c-jun, and bcl-2 mRNAs and protein levels as determined by reverse transcription-PCR analysis and immunocytochemistry, respectively. At neuroprotective CHX concentrations, levels of c-fos heteronuclear RNA increased in parallel with c-fos mRNA, indicating that CHX acts by inducing transcription. Neuroprotective concentrations of CHX suppressed accumulation of H2O2 induced by FeSO4, suggesting activation of antioxidant pathways. Treatment of cultures with an antisense oligodeoxynucleotide directed against bcl-2 mRNA decreased Bcl-2 protein levels and significantly reduced the neuroprotective action of CHX, suggesting that induction of Bcl-2 expression was mechanistically involved in the neuroprotective actions of CHX. In addition, activity levels of the antioxidant enzymes Cu/Zn-superoxide dismutase, Mn-superoxide dismutase, and catalase were significantly increased in cultures exposed to neuroprotective levels of CHX. Our data suggest that low concentrations of CHX can promote neuron survival by inducing increased levels of gene products that function in antioxidant pathways, a neuroprotective mechanism similar to that used by neurotrophic factors.

bcl-2 over-expression delays radiation-induced apoptosis without affecting the clonogenic survival of human prostate cancer cells

In this study we evaluated the effect of over-expression of the bcl-2 gene, a potent apoptosis suppressor, on radiation-induced apoptotic cell death in 2 human prostate cancer cell lines, androgen-independent PC-3 cells and androgen-sensitive LNCaP cells. Cells were transfected with the bcl-2 gene and bcl-2 transfectant clones isolated under neomycin selection; bcl-2 gene integration and level of mRNA and protein expression in the cloned transfectants were examined by Southern, Northern and Western blot analyses, respectively. Parental, neo control and bcl-2-expressing cells were exposed to single or fractionated doses of ionizing irradiation, and the cellular response to radiation was determined at 24, 48 and 72 hr post-irradiation, on the basis of: (i) loss of cell viability, (ii) clonogenic survival and (iii) induction of apoptotic DNA fragmentation. At 24 hr post-irradiation all cell lines, i.e., parental and bcl-2 transfectants, failed to form colonies, though the majority of bcl-2-expressing cells did not exhibit apoptotic morphology; bcl-2 over-expression in both cell lines reduced apoptosis 48 hr post-irradiation from 20-25% to 5% at a dose of 2,000 cGy. By 72 hr, bcl-2 over-expression afforded a 3-fold protection from radiation-induced apoptosis. There was no significant difference, however, in the clonogenic survival of the parental and bcl-2-expressing cells. Furthermore, there was a 24 hr delay in induction of the apoptosis marker gene SGP-2/TRPM-2 in the bcl-2-expressing cells, co-incidental with the delay in apoptotic DNA fragmentation.

Mcl-1, a Bcl-2 Family Member, Delays the Death of Hematopoietic Cells Under a Variety of Apoptosis-Inducing Conditions

Mcl-1 is a member of the Bcl-2 family that was identified based on increased expression in myeloblastic leukemia cells undergoing differentiation. Mcl-1 was previously found to be similar to Bcl-2 in causing a delay in apoptotic cell death in Chinese hamster ovary cells. The work described here was aimed at determining whether Mcl-1 could also exert such an effect in hematopoietic cells, because endogenous Mcl-1 expression is prominent in the hematopoietic system. A further aim was to assess the effects of Mcl-1 in cells exposed to a variety of cytotoxic stimuli, because Bcl-2 is known to have a broad spectrum of activity. To approach these aims, FDC-P1 murine myeloid progenitor cells were transfected with vectors driving either constitutive or inducible expression of Mcl-1. The introduced Mcl-1 gene was found to cause a prolongation of viability under various conditions that cause apoptotic cell death, including exposure to cytotoxic agents (the chemotherapeutic drug etoposide, calcium ionophore, or UV irradiation) and the withdrawal of required growth factors. In addition, Mcl-1 was found to interact with Bax, a member of the Bcl-2 family that promotes cell death as a homodimer but that can heterodimerize with Bcl-2 to promote cell viability. Although Mcl-1 prolonged cell viability, it did not prevent eventual cell death upon continuous exposure to a cytotoxic agent. Prolongation of viability was maximal when expression of Mcl-1 was induced before the application of the apoptotic stimulus, although some increase occurred if Mcl-1 was induced shortly thereafter and before overt apoptosis. Taken as a whole, these findings provide further parallels between Mcl-1 and Bcl-2, showing that Mcl-1 can interact with Bax in hematopoietic FDC-P1 cells and can prolong cell viability under a variety of cytotoxic conditions.