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J C Reed

Publications and source records attributed to J C Reed.

At least 361 records · Page 20Linked to original sources
PubMed1996

Rapid modulation of the apoptosis regulatory genes, bcl-2 and bax by prolactin in rat Nb2 lymphoma cells.

The Nb2 rat lymphoma represents a useful model for investigation of molecular events coupled to PRL-induced proliferation. Moreover, recent evidence has also demonstrated the utility of this system to study mechanisms linked to programmed cell death (apoptosis). Thus, glucocorticosteroids activate apoptosis in lactogen-dependent Nb2 cells, whereas the addition of PRL abrogates this effect. The present study was conducted to determine whether PRL stimulation in lactogen-dependent Nb2-11 or autonomous Nb2-SFJCD1 cultures alters expression of bcl-2 or bax, genes that suppress or facilitate apoptosis, respectively. We demonstrate that PRL stimulation in stationary Nb2-11 cultures significantly increased the level of bcl-2 messenger RNA (mRNA) within 3 h (15-fold) and its protein product by 6 h, time points previously shown to correspond with G1 cell cycle progression. In Nb2-SFJCD1 cells, bcl-2 mRNA was found to be constitutively present. Addition of PRL to these lactogen-independent cultures further enhanced its expression at the mRNA and protein levels with a kinetic pattern similar to that observed in the PRL-dependent line. Results from stability studies indicated that increased bcl-2 mRNA evoked by PRL in Nb2 cell lines was most likely not attributable to increased stability of its transcripts. Furthermore, the rapid increase in its expression in PRL-stimulated Nb2-11 cells was not altered by inhibition of protein synthesis suggesting a direct action of the hormone. PRL also increased bax mRNA by 8 h in Nb2-11 cultures. However, hormone stimulation markedly attenuated the level of the Bax protein from 2-6 h. In contrast, bax expression in Nb2-SFJCD1 cultures remained unaltered by the addition of the hormone. These results demonstrate that altered expression of bcl-2 and bax are each associated with PRL-stimulated cell cycle progression in Nb2 cells. Moreover, bcl-2 appears to be an immediate-early gene induced by PRL in the hormone-dependent line and may represent an important regulator of early G1 cell cycle progression most likely by suppressing cell death mechanisms.

Animals↗
PubMed1996

Expression of the cell death-inducing gene bax in carcinomas developed from the follicular cells of the thyroid gland.

The expression of apoptosis-regulating proteins, Bcl-2, Bax, Mcl-1, and Bcl-X, was evaluated by immunohistochemical methods in 39 cases of thyroid carcinomas. Normal thyroid tissues showed a consistent expression of Bcl-2 and Mcl-1 whereas Bax and Bcl-X proteins were essentially absent from most follicular thyroid cells. Bax expression was observed in all papillary carcinomas (n = 23) and in 8 of 10 follicular carcinomas. The intensity of Bcl-2 immunostaining was generally higher in follicular tumors (n = 10) than in papillary carcinomas (n = 21 of 23). However, in undifferentiated tumors, both Bax and Bcl-2 were weakly expressed. Mcl-1 protein expression was similar to that of Bax in papillary and follicular tumors, but was also frequently detectable in undifferentiated tumors. Bcl-X immunostaining was seen in all undifferentiated tumors (n = 6), in 22 of 23 papillary tumors, and in 5 of 10 follicular tumors. Our findings show that the regulation of bcl-2 family gene expression is different in normal thyroid tissue compared to that of its neoplastic counterpart and varies with the tumor subtype. In particular, unlike normal thyroid epithelium, the apoptosis-blocking gene bcl-X and the apoptosis-inducing gene bax are frequently expressed in thyroid carcinomas derived from the follicular cells. Thus, alterations in the expression of these bcl-2 family genes may contribute to the pathogenesis of thyroid carcinomas.

Adenocarcinoma, Follicular↗
PubMed1996

Apoptosis in the terminal endbud of the murine mammary gland: a mechanism of ductal morphogenesis.

Ductal morphogenesis in the rodent mammary gland is characterized by the rapid penetration of the stromal fat pad by the highly proliferative terminal endbud and subsequent formation of an arborized pattern of ducts. The role of apoptosis in ductal morphogenesis of the murine mammary gland and its potential regulatory mechanisms was investigated in this study. Significant apoptosis was observed in the body cells of the terminal endbud during the early stage of mammary ductal development. Apoptosis occurred predominately in defined zones of the terminal endbud; 14.5% of the cells within three cell layers of the lumen were undergoing apoptosis compared to 7.9% outside this boundary. Interestingly, DNA synthesis in the terminal endbud demonstrated a reciprocal pattern; 21.1% outside three cell layers and 13.8% within. Apoptosis was very low in the highly proliferative cap cell laver and in regions of active proliferation within the terminal endbud. In comparison to other stages of murine mammary gland development, the terminal endbud possesses the highest level of programmed cell death observed to date. These data suggest that apoptosis is an important mechanism in ductal morphogenesis. In p53-deficient mice, the level of apoptosis was reduced, but did not manifest a detectable change in ductal morphology, suggesting that p53-dependent apoptosis is not primarily involved in formation of the duct. Immunohistochemical examination of the expression of the apoptotic checkpoint proteins, Bcl-x, Bax and Bcl-2, demonstrated that they are expressed in the terminal endbud. Bcl-x and Bcl-2 expression is highest in the body cells and lowest in the nonapoptotic cap cells, implying that their expression is associated with increased apoptotic potential. Bax expression was distributed throughout the terminal endbud independent of the observed pattern of apoptosis. A functional role for Bcl-2 family members in regulating endbud apoptosis was demonstrated by the significantly reduced level of apoptosis observed in WAP-Bcl-2 transgenic mice. The pattern of apoptosis and ductal structure of endbuds in these mice was also disrupted. These data demonstrate that p53-independent apoptosis may play a critical role in the early development of the mammary gland.

Animals↗
PubMed1996

Bcl-x gene expression in Hodgkin's disease.

Bcl-x is a Bcl-2-family protein that has been previously detected in cortical thymocytes, plasma cells, and activated lymphocytes. We report here on the high detection rate of the Bcl-x protein found in 86% of Hodgkin's disease samples and on the significance regarding its complex role among the Bcl-2-family of proteins: Bcl-x is known to heterodimerize with Bcl-2 (an anti-apoptosis protein) and with Bax, a potent inducer of cell death. Moreover, recent evidences show that Bcl-x may induce multiple drug resistance in vitro, suggesting that chemical or biological interactions with this protein may have potential therapeutic value in Hodgkin's disease.

Apoptosis↗
PubMed1996

Expression of p53, bcl-2, bax, bcl-x2 and c-myc in radiation-induced apoptosis in Burkitt's lymphoma cells.

Apoptosis, a form of physiological cell death, is a genetically determined program essential for normal development and maintenance of tissues, which has been linked to a variety of gene products. We have examined the susceptibility to radiation-induced apoptosis of cell lines derived from the human B cell tumour, Burkitt's lymphoma (BL), displaying a variety of phenotypic characteristics and expressing genes implicated in apoptosis at different levels. The susceptibility to apoptosis following gamma radiation varied significantly amongst the lines. Cell lines with wild type p53 were susceptible to radiation-induced apoptosis but two of five BL lines with only mutant p53 allele also displayed similar susceptibility. Some BL cell lines that expressed bcl-2 at levels comparable with Epstein-Barr virus (EBV) transformed normal B cells were highly susceptible to gamma radiation-induced apoptosis, whereas others expressing low levels were resistant. When these lines were analysed for bax and bcl-X(L) expression again no correlation was observed with susceptibility or resistance to apoptosis. Two BL cell lines having deregulated expression of c-myc were resistant to the induction of apoptosis while two others which had regulated c-myc expression were susceptible. Thus the status of p53, c-myc, bcl-2, bcl-X(L) and bax is not sufficiently informative in BL lines to predict susceptibility to radiation-induced apoptosis.

Journal Article↗
PubMed1996

Apoptotic and necrotic myocyte cell deaths are independent contributing variables of infarct size in rats.

Programmed cell death in the myocardium has been linked to ischemia reperfusion injury as well as to excessive mechanical forces associated with increases in ventricular loading. Moreover, hypoxia activates the suicide program of cardiac myocytes in vitro. Because the supplied portion of the ventricular wall is ischemic and subjected to high levels of systolic and diastolic stresses (acutely after coronary artery occlusion), apoptosis and necrosis may contribute independently to myocyte cell death after infarction. Therefore, myocardial infarction was produced in rats, and, after the determination of ventricular hemodynamics, the contribution of apoptotic and/or necrotic myocyte cell death to infarct size was measured quantitatively from 20 minutes to 7 days after coronary artery occlusion. Programmed cell death was assessed by the terminal deoxynucleotidyl transferase assay and by the electrophoretic detection of DNA laddering. Myocyte necrosis was evaluated by myosin monoclonal Ab labeling. Moreover, the expression of Bcl-2, Bax, and Fas proteins in myocytes was examined by immunocytochemistry. Myocyte cell death by apoptosis and necrosis comprised nearly 3 million myocytes at 2 hours. Apoptotic cell death involved 2.8 million cells and necrotic cell death only 90,000 myocytes. Apoptosis continued to represent the major independent form of myocyte cell death, affecting 6.6 million myocytes at 4.5 hours. Myocyte necrosis peaked at 1 day, including 1.1 million myocytes. DNA electrophoretic analysis confirmed these observations by showing nucleosomal ladders at 2-3 hours, 4.5 hours, 1 day, and 2 days after coronary artery occlusion. Myocytes showing both DNA strand breaks and myosin labeling were a prominent aspect of myocardial damage only after 6 hours. Finally, the expression of Bcl-2 and Fas in myocytes increased 18-fold and 131-fold, respectively. In conclusion, programmed myocyte cell death is the major form of myocardial damage produced by occlusion of a major epicardial coronary artery, whereas necrotic myocyte cell death follows apoptosis and contributes to the progressive loss of cells with time after infarction. The enhanced expression of Fas may be implicated in the activation of apoptosis in spite of the increase in Bcl-2, which tends to preserve cell survival.

Animals↗
PubMed1996

Immunohistochemical analysis of bcl-2, bax, bcl-X, and mcl-1 expression in prostate cancers.

Proteins encoded by bcl-2 family genes are important regulators of programmed cell death and apoptosis. Alterations in the expression of these apoptosis-regulating genes can contribute to the origins of cancer, as well as adversely influence tumor responses to chemo- and radiotherapy. Using antibodies specific for the Bcl-2, Bax, Bcl-X, and Mcl-1 proteins in combination with immunohistochemical methods, we examined for the first time the expression of these bcl-2 family genes in 64 cases of adenocarcinoma of the prostate, including 10 Gleason grade 2 to 4 tumors, 21 grade 5 to 7 tumors, 17 grade 8 to 10 tumors, 8 lymph node metastases, and 8 bone metastases. In addition, 24 cases of prostatic intraepithelial neoplasia (PIN) or PIN coexisting with carcinoma were also evaluated. All immunostaining results were scored with regard to approximate percentage of positive tumor cells and relative immunostaining intensity. Expression of the anti-apoptotic protein Bcl-2 was present in 16 of 64 (25%) adenocarcinomas and tended to be more frequent in high grade tumors (Gleason grade 8 to 10; 41%) and nodal metastases (38%) than in lower grade (Gleason 2 to 7) primary tumors (16%; P < 0.05). Bcl-X was expressed in all 64 (100%) tumors evaluated. Bcl-X immunointensity was generally stronger in high grade primary tumors (grade 8 to 10) and metastases compared with PIN and low grade neoplasms (P < 0.0001). In addition, the proportion of specimens with > 50% Bcl-X-immunopositive tumor cells also was higher in advanced grade primary tumors (Gleason 8 to 10) and metastases than in PIN and low grade tumors (Gleason 2 to 7; P < 0.005). The anti-apoptotic protein Mcl-1 was expressed in 52 of 64 (81%) tumors, compared with only 9 of 24 (38%) cases of PIN (P < 0.001). In addition, the percentage of Mcl-1-positive cells was typically higher in Gleason grade 8 to 10 tumors and metastases than in PIN or lower grade tumors (P = 0.025). In contrast, the pro-apoptotic protein Bax was expressed in all prostate cancers evaluated, with high percentages of immunopositive cells and strong immunointensity typically occurring regardless of tumor grade. The findings suggest that expression of several anti-apoptotic members of the bcl-2 gene family, including bcl-2, bcl-X, and mcl-1 increases during progression of prostate cancers, a finding that may be relevant to the hormone-insensitive, metastatic phenotype of most advanced adenocarcinomas of the prostate.

Adenocarcinoma↗
PubMed1996

Protective effect of transforming growth factor-beta 1 on beta-amyloid neurotoxicity in rat hippocampal neurons.

Neurodegeneration associated with Alzheimer's disease is believed to involve toxicity to beta-amyloid (A beta) and related peptides. Treatment of cultured rat hippocampal neurons with A beta 1-40 (1 microM) or the active fragment A beta 25-35 (1 microM) for 5 days led to a approximately 40-50% decrease in neuronal viability. The hydrophilic antioxidant ascorbic acid (300 microM) and the lipophilic antioxidant 2-mercaptoethanol (10 microM) both protected significantly against A beta neurotoxicity. Despite the protective effects of these antioxidants, both acute and chronic treatments with A beta 25-35 did not increase production of superoxide anions, as monitored with the fluorescent probe hydroethidine. Similarly, overexpression of Cu/Zn-superoxide dismutase using adenovirus-mediated gene transfer did not protect against A beta neurotoxicity. A beta neurotoxicity, however, was prevented in cultures infected with a recombinant, replication-defective adenovirus overexpressing the Ca2+ binding protein calbindin D28k. Transforming growth factor-beta 1 (TGF-beta 1) has been shown to protect neurons against both Ca(2+)- and free radical-mediated neuronal degeneration. We found that A beta neurotoxicity was significantly attenuated by single treatments with TGF-beta 1 (0.1-10 ng/ml) and prevented by repetitive treatments (10 ng/ml/day). The protective effects of TGF-beta 1 were associated with a preservation of mitochondrial potential and function, as determined with rhodamine-123-based microfluorimetry. Because both increased oxidative stress and pathophysiological Ca2+ fluxes can impair mitochondrial function, preservation of mitochondrial potential by TGF-beta 1 could be directly associated with its protection against A beta neurotoxicity. The ability of TGF-beta 1 to increase the expression of the anti-apoptotic proteins Bcl-2 and Bcl-XL is discussed in this context.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1996

Decreased DNA repair but normal apoptosis in ultraviolet-irradiated skin of p53-transgenic mice.

p53 tumor suppressor plays a vital role in the cellular responses to genotoxic stress. It is believed that p53 regulates the cell cycle by activating the G1 checkpoint after exposure to agents like ionizing radiation, ultraviolet (UV) radiation, or genotoxic chemicals. Recently, it is conjectured that p53 may have additional functions in DNA repair and apoptosis. Previously, we demonstrated that p53-transgenic mice that carry mutant alleles of a p53 gene developed twice as many skin tumors as control mice after UV exposure. To elucidate the molecular mechanisms of mutant p53 in skin cancers, we studied DNA repair efficiency and the rate of apoptosis in murine keratinocytes after UV irradiation. In this report, we show that mutant p53-transgenic mouse skin has reduced repair of UV-induced DNA damage in both in vivo and in vitro radioimmunoassays. In control mice, DNA repair is associated with increased amounts of wild-type P53 protein. Unexpectedly, mutant p53-transgenic mice had slightly increased apoptosis after UV irradiation, suggesting that the wild-type p53 protein in the cells still functions in inducing apoptosis, or that this cell death results from p53-independent mechanisms. These results suggest that mutant p53 interferes with wild-type p53 in the repair of UV-induced DNA damage but not in apoptosis.

Animals↗
PubMed1996

Immunodetection of apoptosis-regulating proteins in lymphomas from patients with and without human immunodeficiency virus infection.

The expression of the apoptosis-regulating genes Bcl-2, Bcl-x, Bax, Mcl-1, and p53 analyzed in 4 cases of human immunodeficiency virus (HIV)-associated Hodgkin's disease, in 36 cases of HIV-related non-Hodgkin's lymphomas (NHLs), and in 109 cases of non-HIV-related NHLs by using immunohistochemistry. HIV-associated Hodgkin's disease samples were positive for all markers. For the HIV-related NHL samples, 36, 66, 88, 100, and 94% of the cases were Bcl-2, Bcl-x, Bax, Mcl-1, and p53 were found to be expressed in 69, 65, 82, 83, and 42%, respectively. No significant differences were observed in Bax and Mcl-1 staining between HIV-unrelated NHLs of B cell and T cell types. In contrast, Bcl-2 was positive in 66/79 (83%) and 10/30 (33%) of B cell and T cell HIV-unrelated NHLs, respectively (P2 < 0.001). Peculiar patterns were observed for hairy cell leukemia (Bax+, Bcl-2+, Mcl-1-) and for anaplastic large cell lymphoma (Bax+, Mcl-1+, Bcl-2-) in HIV-unrelated NHLs. Of interest, all cases with a positive expression of Bax were also found to express either Mcl-1 and/or Bcl-2, suggesting that Mcl-1 and Bcl-2 may counteract the pro-apoptosis function of Bax in vivo by protein-protein interaction within the tumor cell, as demonstrated previously in vitro. These results suggest that apoptosis regulation may have a role in the pathogenesis of some HIV-related and HIV-unrelated NHLs.

Apoptosis↗
PubMed1996

Intracellular metabolism of Ara-C and resulting DNA fragmentation and apoptosis of human AML HL-60 cells possessing disparate levels of Bcl-2 protein.

We examined the effects of high intracellular levels of Bcl-2 on the metabolism and DNA incorporation of high-dose Ara-C (HIDAC) as well as on Ara-C-induced DNA strand breaks and apoptosis of human AML HL-60 cells. HL-60/Bcl-2 and HL-60/neo cells were created by retrovirally transfecting the human AML HL-60 cells with the pZip-bcl-2 and pZip-neo plasmids, respectively. As compared to HL-60/neo, HL-60/Bcl-2 cells contained significantly higher (approximately 10-fold) p26Bcl-2, but equivalent levels of Bax and undetectable levels of Bcl-xL. HIDAC (10 or 100 microM for 4 h) produced the kilobase size and internucleosomal DNA fragmentation associated with apoptosis in HL-60/neo but not in HL-60/Bcl-2 cells. Significantly greater loss of survival (by MTT assay) and flowcytometric and morphologically recognizable apoptosis were observed in HL-60/neo cells. HIDAC did not affect Bcl-2 levels in either cell type. The intracellular accumulation of Ara-CTP relative to dCTP, Ara-C DNA incorporation and Ara-C-induced early DNA damage in the form of strand breaks (detected by alkaline elution assay) were not significantly different between HL-60/Bcl-2 and HL-60/neo cells. In addition, HIDAC treatment caused similar DNA synthesis inhibition in the two cell types. These results indicate that high intracellular levels of Bcl-2 operate distally to inhibit the final apototic cell death pathway by preventing the conversion of HIDAC-induced early DNA damage into lethal DNA fragmentation associated with apoptosis.

Antimetabolites, Antineoplastic↗
PubMed1996

Immunohistochemical analysis of Bcl-2 family proteins in adenocarcinomas of the stomach.

The apoptosis-regulating proteins Bcl-2, Bax, Bcl-X, Bak, and Mcl-1 were examined by immunohistochemical methods in 48 archival specimens of adenocarcinoma of the stomach, and the results were correlated with tumor histology (intestinal versus diffuse pattern) and clinical stage (early- versus late-stage disease, ie, stages I and II versus stage III). Tumor cells containing immunostaining for the anti-apoptotic proteins Bcl-2, Bcl-X, and Mcl-1 were present in 26 (54%), 41 (85%), and 36 (75%) of the 48 cases evaluated, respectively, whereas immunopositivity for the pro-apoptotic proteins Bax and Bak was found in 44 (92%) and 42 (88%) specimens Comparisons of these immunostaining results with tumor histology revealed statistically significant differences for Bax (P = 0.03), Bcl-X (P = 0.003), and Mcl-1 (P = 0.005), which were all more frequently immunopositive for tumors with an intestinal than a diffuse histological pattern (chi 2 analysis). In addition, the percentage of immunopositive tumor cells was significantly higher for Bcl-X (62 +/- 6% versus 45 +/- 6%, mean +/- SE, P = 0.01) and for Mcl-1 (48 +/- 6% versus 30 +/- 6%; P = 0.04) in tumors with intestinal versus diffuse histology (unpaired t-test). In contrast, the percentage of Bcl-2-immunopositive tumor cells was higher in tumors with diffuse histology compared with intestinal (32 +/- 5% versus 12 +/- 5%; P = 0.01), whereas the percentages of Bax- and Bak-immunopositive tumor cells were not significantly different between these two histological types. In 34 specimens, residual normal gastric epithelial cells (foveolar cells) were present for direct comparisons of immunointensity with tumor cells. The immunointensity for the Bcl-2, Bcl-X, and Mcl-1 proteins was stronger in tumor cells compared with normal foveolar cells in 7 (21%), 15 (44%), and 8 (2.1%) of 34 cases, respectively, whereas the immunointensity of the proapoptotic proteins Bax and Bak was reduced compared with normal cells in 8 (24%) and 24 (71%) cases. Immunointensity, however, did not correlate with histology. clinical stage was not significantly associated with the presence or absence of immunopositive tumor cells, the percentage of immunopositive cells, or immunointensity. Taken together, these results establish for the first time that several Bcl-2 family proteins are expressed in gastric adenocarcinomas and suggest that the repertoire of these proteins may differ depending on the histological type. The findings therefore support the notion that the intestinal and diffuse types of gastric cancer arise at least in part through different mechanisms.

Adenocarcinoma↗
PubMed1996

Structure-function analysis of Bcl-2 family proteins. Regulators of programmed cell death.

The Bcl-2 protein blocks a distal step in an evolutionarily conserved pathway for programmed cell death and apoptosis. To gain better understanding of how this protein functions, we have undertaken a structure-function analysis of this protein, focusing on domains within Bcl-2 that are required for function and for interactions with other proteins. Four conserved domains are present in Bcl-2 and several of its homologs: BH1 (residues 136-155), BH2 (187-202), BH3 (93-107) and BH4 (10-30). Deletion of the BH1, BH2, or BH4 domains of Bcl-2 abolishes its ability to suppress cell death in mammalian cells and prevents homodimerization of these mutant proteins, though these mutants can still bind to the wild-type Bcl-2 protein. These mutants also fail to bind to BAG-1 and Raf-1, two proteins that we have shown can associate with protein complexes containing Bcl-2 and which cooperate with Bcl-2 to suppress cell death. Deletion of either BH1 or BH2 nullifies the ability of Bcl-2 to: (a) suppress death in mammalian cells: (b) block Bax-induced lethality in yeast; and (c) heterodimerize with Bax. In contrast, deletion of the BH4 domain of Bcl-2 nullifies anti-apoptotic function and homodimerization, but does not impair binding to the pro-apoptotic protein Bax. Taken together, the data suggest the possibility that both Bcl-2/Bcl-2 homodimerization and Bcl-2/Bax heterodimerization are necessary but insufficient for the anti-apoptotic function of the Bcl-2 protein. Homodimerization of Bcl-2 with itself involves a head-to-tail interaction, in which an N-terminal domain where BH4 resides interacts with the more distal region of Bcl-2 where BH1, BH2, and BH3 are located. In contrast, Bcl-2/Bax heterodimerization involves a tail-to-tail interaction, that requires the portion of Bcl-2 where BH1, BH2, and BH3 reside and a central region in Bax where the BH3 domain is located. The BH3 domain of Bax is also required for Bax/Bax homodimerization and pro-apoptotic function in both yeast and mammalian cells. Thus, Bcl-2 may suppress cell death at least in part by binding to Bax via the BH3 domain and thereby preventing formation of Bax/Bax homodimers. Further studies however are required to delineate the full significance of Bcl-2/Bcl-2, Bcl-2/Bax, and Bax/Bax dimers and the biochemical mechanisms by which Bcl-2 family proteins ultimately control cell life and death.

Animals↗
PubMed1996

Mechanisms of Bcl-2 family protein function and dysfunction in health and disease.

The Bcl-2 protein blocks a distal step in an evolutionarily conserved pathway for programmed cell death and apoptosis. The gene encoding this protein was first discovered because of its involvement in the t(14;18) chromosomal translocations commonly found in B-cell lymphomas, where it contributes to neoplastic cell expansion by preventing cell turnover due to programmed cell death. Overexpression of BCL-2 also occurs in many other types of human tumors, including cancers of the prostate, colon, and lung, and has been associated with chemoresistance and radioresistance in some types of malignancy. Conversely, expression of BCL-2 is frequently reduced in the circulating lymphocytes of persons infected with Human Immunodeficiency Virus (HIV), which are prone to apoptotic cell death. Since the discovery of Bcl-2 a decade ago, several other cellular and viral genes encoding homologous proteins have been identified, some of which suppress cell death akin to Bcl-2 (Bcl-XL, Mcl-1, A1/Bfl-1, Nr13, Ced-9, BHRF-1) and others which promote apoptosis (Bax, Bcl-Xs, Bak, Bik, Bad). Several of these Bcl-2 family proteins are capable of physically interacting with each other through a complex network of homo- and heterodimers. The expression of some of these other BCL-2 family genes becomes altered in human cancers, as well as in the setting of ischemia and some other pathological conditions, suggesting a potentially important role for these Bcl-2 homologs in human diseases characterized by either insufficient or excessive cell death. Despite intensive investigation, the mechanisms by which Bcl-2 and its homologs control cell life and death largely remain enigmatic. Knowledge about the specific domains in Bcl-2 family proteins that are required for interactions with other proteins and for function however is beginning to provide insights into the molecular mechanisms through which these proteins regulate the programmed cell death pathway in normalcy and disease.

Animals↗
PubMed1996

Modulation of apoptosis-associated genes bcl-2, bcl-x, and bax during rat liver regeneration.

Liver regeneration (LR) after 70% partial hepatectomy (PH) represents a unique in vivo model of cell cycle and gene regulation. This study was conducted to characterize apoptosis-associated gene expression during LR. The results indicated that transcripts for both bcl-x and bcl-2 exhibited similar patterns of expression during LR with peaks at 6 h post-PH. In contrast, the major 1.1-kb bax transcript exhibited peaks at 18 (P < 0.05) and 72 h (P < 0.001) post-PH. Nuclear run-on analyses for all three genes indicated no detectable transcription rate changes during LR. At 6 h post-PH, when bcl-x mRNA levels were increased by 25-fold (P < 0.001), bcl-x mRNA half-life was elevated 4-fold (P < 0.001). Similarly, bax transcript half-life increased from 2.8 h at 0 h to 4.3 h at 24 h (P < 0.001) and > 8 h at 40 h (P < 0.001) post-PH, coincident with increases in steady-state levels of mRNA. Western blot analyses of Bcl-2 and Bcl-x proteins showed no significant change through 96 h of LR, whereas Bax protein levels cycled in parallel with its mRNA. Interestingly, novel Bax- and Bcl-2-cross-reactive proteins of 31 and 32 kDa, respectively, were detected in nuclei isolated from quiescent liver. When liver growth was induced by the peroxisome proliferator clofibrate, transcript and protein levels were coupled for bcl-x but not for bax. In conclusion, the apoptosis-associated genes bcl-2, bcl-x and bax are modulated at the transcript and protein levels during LR, suggesting a role for these gene products in normal liver growth. The alterations in transcript levels occur posttranscriptionally and involve changes in mRNA stability. Furthermore, unlike bax, steady-state protein and transcript levels are uncoupled for both bcl-2 and bcl-x, suggesting a role for translational regulation during LR after PH.

Animals↗
PubMed1996

Expression of bcl-2 and the progression of human and rodent prostatic cancers.

The frequency of bcl-2 protein expression was evaluated using immunocytochemical staining during the progression of human and rat prostate cancer from an androgen-sensitive nonmetastatic to an androgen-independent metastatic phenotype. Previous studies (A. S. Shabaik et al., J. Urol. Pathol., 3: 17-27, 1995) demonstrated that 0 of 20 high-grade prostatic intraepithelial neoplasias and only 3 (7%) of 41 pathologically localized stage B human prostatic cancers had detectable bcl-2 staining. In the present study, 5 (17%) of 30 lymph node metastases from pathologically disseminated D1 disease and 14 (52%) of 27 bone metastases from pathologically disseminated D2 disease expressed detectable bcl-2 protein. These data demonstrate that there is a statistically significant (P < 0.05) association between expression of bcl-2 and the progression of human prostatic cancer cells to a metastatic phenotype. Such bcl-2 expression is not absolutely required, however, for either androgen independence or metastatic ability by human prostatic cancer cells. Likewise, within a series of eight distinct Dunning R3327 rat prostatic cancer sublines, which differ widely in their progressional state, there is also a significant association (P < 0. 05) between bcl-2 expression and progression (four of six androgen-independent rat sublines expressed bcl-2 protein). Again in this rodent system, bcl-2 expression is not an absolute requirement for either androgen independence or metastatic ability. For example, the androgen-independent highly metastatic Dunning AT-3 subline, while expressing bax protein, does not express bcl-2 protein. If such AT-3 cells are genetically engineered to express bcl-2, these expressing cells are now cross-resistant to a variety of mechanistically diverse noxious insults (e.g., viral infection or exposure to antimetabolites, alkylating agents, or agents which elevate the intracellular free Ca2+). The ability of bcl-2 to inhibit the programmed death of AT-3 cells induced by these agents involves a late step in the death process, since the early induction of expression of a series of genes associated with apoptosis is not impaired by bcl-2 expression. These data demonstrate that the development of androgen independence and/or metastatic ability can be associated with the expression of bcl-2 protein but that bcl-2-independent mechanisms also exist for such progression.

Animals↗
PubMed1995

Activin A-induced apoptosis is suppressed by BCL-2.

Activin A, a member of TGF beta superfamily has various activities including induction of apoptosis in mammalian cells. However, it remains unknown how activin A induces cell death. To clarify this, we investigated the expression of BCL-2 and BAX, and the effect of BCL-2 overexpression on activin A-induced apoptosis in B cell hybridoma cell lines. The activin A-sensitive cell lines expressed BAX but not BCL-2 and that activin A did not increase BAX levels. Overexpression of human BCL-2 suppressed activin A-induced apoptosis in these cells. Thus, activin A has been shown to induce apoptosis by a BCL-2-inhibitable mechanism without activating BAX.

Activins↗