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Biomedical subjects

L H Boise

Publications and source records attributed to L H Boise.

At least 19 recordsLinked to original sources
PubMed2001

Induction of a TRAIL-mediated suicide program by interferon alpha in primary effusion lymphoma.

Gammaherpes viruses are often detected in lymphomas arising in immunocompromised patients. We have found that Azidothymidine (AZT) alone induces apoptosis in Epstein Barr Virus (EBV) positive Burkitt's lymphoma (BL) cells but requires interferon alpha (IFN-alpha) to induce apoptosis in Human Herpes Virus Type 8 (HHV-8) positive Primary Effusion Lymphomas (PEL). Our analysis of a series of AIDS lymphomas revealed that IFN-alpha selectively induced very high levels of the Death Receptor (DR) tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in HHV-8 positive PEL lines and primary tumor cells whereas little or no induction was observed in primary EBV+ AIDS lymphomas and EBV-Burkitt's lines. AZT and IFN-alpha mediated apoptosis in PEL was blocked by stable overexpression of dominant negative Fas Associated Death Domain (FADD), decoy receptor 2 (DcR2), soluble TRAIL receptor fusion proteins (DR-4 and DR-5) and thymidine. Trimeric TRAIL (in place of IFN-alpha) similarly synergized with AZT to induce apoptosis in HHV-8 positive PEL cells. This is the first demonstration that IFN-alpha induces functional TRAIL in a malignancy that can be exploited to effect a suicide program. This novel antiviral approach to Primary Effusion lymphomas is targeted and may represent a highly effective and relatively non-toxic therapy.

Antimetabolites, Antineoplastic↗
PubMed2001

Ascorbic acid enhances arsenic trioxide-induced cytotoxicity in multiple myeloma cells.

Multiple myeloma (MM) is a clonal B-cell malignancy characterized by slow-growing plasma cells in the bone marrow (BM). Patients with MM typically respond to initial chemotherapies; however, essentially all progress to a chemoresistant state. Factors that contribute to the chemorefractory phenotype include modulation of free radical scavenging, increased expression of drug efflux pumps, and changes in gene expression that allow escape from apoptotic signaling. Recent data indicate that arsenic trioxide (As(2)O(3)) induces remission of refractory acute promyelocytic leukemia and apoptosis of cell lines overexpressing Bcl-2 family members; therefore, it was hypothesized that chemorefractory MM cells would be sensitive to As(2)O(3). As(2)O(3) induced apoptosis in 4 human MM cell lines: 8226/S, 8226/Dox40, U266, and U266/Bcl-x(L). The addition of interleukin-6 had no effect on cell death. Glutathione (GSH) has been implicated as an inhibitor of As(2)O(3)-induced cell death either through conjugating As(2)O(3) or by sequestering reactive oxygen induced by As(2)O(3). Consistent with this possibility, increasing GSH levels with N-acetylcysteine attenuated As(2)O(3) cytotoxicity. Decreases in GSH have been associated with ascorbic acid (AA) metabolism. Clinically relevant doses of AA decreased GSH levels and potentiated As(2)O(3)-mediated cell death of all 4 MM cell lines. Similar results were obtained in freshly isolated human MM cells. In contrast, normal BM cells displayed little sensitivity to As(2)O(3) alone or in combination with AA. Together, these data suggest that As(2)O(3) and AA may be effective antineoplastic agents in refractory MM and that AA might be a useful adjuvant in GSH-sensitive therapies. (Blood. 2001;98:805-813)

Acetylcysteine↗
PubMed2001

Salmonella-induced cell death: apoptosis, necrosis or programmed cell death?

Over the past several years, it has become apparent that enteropathogens activate cell death programs. For Salmonella and Shigella species, the induction of cell death is required for pathogenesis, and the mechanisms by which these bacteria induce cell death is an area of intense investigation. Although initial studies suggested that Salmonella induce cell death through an apoptotic pathway, recent studies demonstrate that cell death occurs through a unique caspase 1-dependent mechanism.

Animals↗
PubMed2001

Mitochondria as targets for established and novel anti-cancer agents.

Chemoresistant cells have acquired the ability to evade the action of multiple classes of anti-neoplastic compounds. One mechanism by which tumor cells survive in the presence of chemotherapy is by increasing their apoptotic threshold. Since mitochondria are central players in drug-induced apoptosis, recent efforts to eradicate chemorefractory cells have focused on the identification of compounds that directly affect mitochondrial function. A number of reports indicate that mitochondria are direct targets for multiple classes of experimental compounds. A few clinically available anticancer agents like DNA damaging compounds and anti-microtubule agents are also reported to act directly on mitochondria. The purpose of this mini-review is to discuss recent advances in the interactions between anti-cancer agents and mitochondria, and highlight potential mitochondrial targets for novel chemotherapeutic interventions.

Animals↗
PubMed2000

Epidermal growth factor receptor-dependent control of keratinocyte survival and Bcl-xL expression through a MEK-dependent pathway.

Previous work has shown that the epidermal growth factor receptor (EGFR) tyrosine kinase moiety provides protection to normal human keratinocytes against apoptosis. This protection is, at least in part, due to EGFR-dependent expression of the antiapoptotic Bcl-2 family member, Bcl-x(L). Here we focused on intracellular signaling pathways relevant to keratinocyte survival and/or Bcl-x(L) expression. By using pharmacological inhibitors and dominant negative expression constructs, we observed that phosphatidylinositol 3-kinase/AKT and phospholipase C gamma/protein kinase C alpha activation were required for keratinocyte survival independently of EGFR activation or Bcl-x(L) expression. By contrast, MEK activity required EGFR activation and, as shown by use of the MEK inhibitor PD98059 and a dominant negative MEK construct, was necessary for Bcl-x(L) expression and survival. Consistent with an earlier study, blocking SRC kinase activities similarly led to down-regulation of Bcl-x(L) protein expression and impaired keratinocyte survival. In conclusion, our results demonstrate that EGFR-dependent MEK activity contributes to both Bcl-x(L) expression and survival of normal keratinocytes. Other signaling pathways (i.e. phosphatidylinositol 3-kinase/AKT and phospholipase C gamma/protein kinase C alpha) are obligatory to keratinocyte survival but not to Bcl-x(L) expression, and control of these pathways by EGFR activation is not rate-limiting to normal keratinocyte survival.

Cell Line↗
PubMed2000

Potentiation of 1-beta-D-arabinofuranosylcytosine-mediated mitochondrial damage and apoptosis in human leukemia cells (U937) overexpressing bcl-2 by the kinase inhibitor 7-hydroxystaurosporine (UCN-01).

Antileukemic interactions between the nucleoside analog 1-beta-D-arabinofuranosylcytosine (ara-C) and the kinase inhibitor 7-hydroxystaurosporine (UCN-01) have been examined in relation to Bcl-2 expression/phosphorylation, mitochondrial damage, caspase activation, and loss of clonogenic potential. Subsequent exposure of ara-C-pretreated U937 cells (1 microM; 6 hr) to UCN-01 (300 nM; 24 hr) resulted in marked potentiation of pro-caspase-3 and -9 cleavage/activation, poly(ADP-ribose)polymerase degradation, diminished mitochondrial membrane potential (Deltapsi(m)), enhanced cytochrome c release, reduction in the S-phase fraction, and induction of classic apoptotic morphologic features. Enforced expression of full-length Bcl-2 significantly protected cells (at 24 hr) from ara-C/UCN-01-induced caspase activation and apoptosis, but was ineffective in preventing loss of Deltapsi(m) and cytochrome c release. Ectopic expression of a Bcl-2 N-terminal phosphorylation loop-deleted protein (Bcl-2Delta(32-80)) was more potent than its full-length counterpart in blocking drug-induced loss of Deltapsi(m, ) caspase activation, and apoptotic morphology, but not cytochrome c release. Examination of cells at later intervals revealed that ectopic expression of Bcl-2 or Bcl-2Delta(32-80) could only delay, but not prevent, mitochondrial damage, caspase activation, and cell death induced by ara-C/UCN-01 treatment. Despite their initial ability to inhibit apoptosis, neither full-length nor truncated Bcl-2 protein restored clonogenic potential to drug-treated cells. These findings indicate that subsequent exposure of ara-C-pretreated human leukemia cells to UCN-01 potently triggers mitochondrial damage and apoptosis, and that these events are postponed but not prevented by ectopic expression of Bcl-2 or its phosphorylation loop-deleted counterpart.

Alkaloids↗
PubMed2000

CD30 signals integrate expression of cytotoxic effector molecules, lymphocyte trafficking signals, and signals for proliferation and apoptosis.

Although CD30 has long been recognized as an important marker on many lymphomas of diverse origin and as activation molecule on B cells and T cells, its primary function has remained obscure. We now report that CD30 signals may serve to inhibit effector cell activity by integrating gene expression changes of several pathways important for cytotoxic NK and T cell effector function. In the large granular lymphoma line YT, CD30 signals down-regulate the expression of cytotoxic effector molecules, Fas ligand, perforin, granzyme B, and abrogate cytotoxicity. c-myc, a regulator of proliferation and an upstream regulator of Fas ligand expression, is completely suppressed by CD30. Furthermore, CD30 signals strongly induce CCR7, suggesting a role for CD30 signals in the homing of lymphocytes to lymph nodes. The up-regulation of Fas, death receptor 3, and TNF-related apoptosis-inducing ligand by CD30 indicates an increase in susceptibility to apoptotic signals whereas up-regulation of TNFR-associated factor 1 and cellular inhibitor of apoptosis 2 protect cells from certain types of apoptosis. Using gene microarrays, 750 gene products were induced and 90 gene products were suppressed >2-fold by CD30 signals. Signals emanating from CD30 use both TNFR-associated factor 2-dependent and -independent pathways. The integration of CD30 signals in a lymphoma line suggests that CD30 can down-modulate lymphocyte effector function and proliferation while directing the cells to lymph nodes and increasing their susceptibility to certain apoptotic signals. These studies may provide a molecular mechanism for the recently observed CD30-mediated suppression of CTL activity in vivo in a diabetes model.

Apoptosis↗
PubMed2000

Bcl-xL inhibits cytochrome c release but not mitochondrial depolarization during the activation of multiple death pathways by tumor necrosis factor-alpha.

Cells can respond differently to anti-CD95 antibody treatment. Type I cells show strong activation of caspase-8 and directly activate caspase-3. Type II cells weakly activate caspase-8 and must amplify their death signal through the mitochondria. These cells can be rescued by Bcl-x(L). Here we show that tumor necrosis factor-alpha induces both Type I and II pathways, which can be inhibited by benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-fmk) and Bcl-x(L) in a cooperative fashion. Death induced in the presence of Z-VAD-fmk was associated with a partial inhibition of caspase-8, whereas no effects on cytochrome c release, DEVDase activity, and intranucleosomal DNA cleavage were observed. Thus, Z-VAD-fmk is likely weakening the death-inducing signaling complex-mediated activation of caspase-8 and diverting cells to a Type II pathway. Bcl-x(L) cooperates with Z-VAD-fmk by blocking the Type II pathway at the level of cytochrome c release. Surprisingly, although Bcl-x(L) was able to block cytochrome c release, it was unable to block mitochondrial depolarization, suggesting that these are separate events. This suggests that mitochondria occupy two places in apoptotic signaling, as initiators of apoptosis through the release of cytochrome c as well as a target for effector caspases.

Amino Acid Chloromethyl Ketones↗
PubMed2000

Regulation of Bcl-xL: a little bit of this and a little bit of STAT.

The Bcl-2 family of proteins are key regulators of apoptosis. Bcl-xL, is an anti-apoptotic protein with a high degree of homology to Bcl-2; however, the signals that regulate Bcl-xL and Bcl-2 appear to be different. Levels of Bcl-xL, but not Bcl-2, are increased in response to various survival signals. Furthermore, an inverse correlation between the levels of Bcl-2 and Bcl-xL has been reported for a number of cancers. Although the precise molecules that control Bcl-xL activity are unclear, the STAT, Rel/NF-kappaB, and Ets transcription factor families have recently been reported to directly regulate the bcl-x gene. Activated Ras, integrin, vitronectin, and hepatocyte growth factor signaling cascades have also been linked to changes in Bcl-xL expression. Bcl-xL can also be affected by post-translational mechanisms. Here we review recent advances in identifying the signaling pathways and factors involved in regulation of the bcl-x gene.

Animals↗
PubMed1999

Azidothymidine and interferon-alpha induce apoptosis in herpesvirus-associated lymphomas.

Lymphoproliferative diseases that occur in immunocompromised patients are frequently associated with herpesviruses. These patients often fare poorly after treatment with conventional chemotherapy. We reported previously that patients with AIDS-related Burkitt's lymphoma (BL) responded to parenteral azidothymidine (AZT) and IFN-alpha. We found that EBV-positive lymphoma cells derived from these patients cultured with AZT express CD95 and undergo apoptosis. AZT-mediated apoptosis was caspase dependent and occurred despite Fas receptor blockade. In contrast, EBV-negative lymphomas were resistant to AZT-induced apoptosis, as were EBV-positive lymphomas that expressed high levels of bcl-2. Primary effusion lymphoma (PEL) cell lines infected with human herpesvirus type 8 required IFN-alpha to potentiate AZT-induced apoptosis. IFN-alpha did not up-regulate CD95 in BL or PEL but did induce expression of the death receptor ligand, CD95 ligand. AZT-sensitive lymphomas also accumulated significantly higher intracellular AZT monophosphate than did resistant lymphomas. Our data demonstrated distinct apoptotic responses to AZT and IFN-alpha in herpesvirus-associated lymphomas. EBV-positive BL cells that expressed low BCL-2 levels were sensitive to AZT alone; PEL cells required the addition of IFN-alpha to enhance apoptosis, and EBV-negative lymphomas were insensitive to both agents. AZT-sensitive BL cells transfected with BCL-2 became resistant. Susceptibility to antivirus-mediated apoptosis may be exploited to improve the therapy of certain herpesvirus-associated lymphomas.

Apoptosis↗
PubMed1999

Bcl-2 and caspase inhibition cooperate to inhibit tumor necrosis factor-alpha-induced cell death in a Bcl-2 cleavage-independent fashion.

The ability of proteins of the Bcl-2 family to either induce or inhibit apoptosis is dependent on both cell type and the apoptotic stimulus. We have shown in the murine pro-B cell line FL5.12 that Bcl-2 is incapable of inhibiting tumor necrosis factor alpha (TNFalpha)-induced cell death and is cleaved during this process. One potential explanation for this observation is that caspase activation directly or indirectly inhibits Bcl-2 function. It has been suggested that caspase cleavage of Bcl-2 is responsible for its inability to block certain cell deaths. Consistent with Bcl-2 cleavage being a caspase-mediated event, this cleavage is inhibitable by 50 microM CBZ-Val-Ala-Asp-fluoromethylketone (zVAD-fmk). Furthermore, Bcl-2 can cooperate with the caspase inhibitor zVAD-fmk in a dose-dependent manner to block TNFalpha-induced cell death. Overexpression of Bcl-2 results in a 10-fold decrease in the amount of zVAD-fmk required to inhibit TNFalpha-induced apoptosis. However, cleavage-defective mutants (D31A and D34A) show no enhanced viability relative to wild-type Bcl-2 in response to TNFalpha-induced cell death and also show the same cooperativity with zVAD-fmk. These results suggest that Bcl-2 cleavage is not important for the inhibition of TNFalpha-induced cell death but do not preclude an involvement in a post-commitment phase of apoptosis.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Bryostatin 1 enhances paclitaxel-induced mitochondrial dysfunction and apoptosis in human leukemia cells (U937) ectopically expressing Bcl-xL.

The effects of the protein kinase C (PKC) activator and down-regulator bryostatin 1 were examined with respect to paclitaxel-induced apoptosis and antiproliferative activity in human myeloid leukemia cells (U937) displaying enforced expression of the anti-apoptotic protein Bcl-xL. Overexpression of Bcl-xL blocked various aspects of paclitaxel-mediated apoptosis, including caspase-3 activation, degradation of poly(ADP-ribose) polymerase (PARP), loss of mitochondrial membrane potential (Delta Psim), and release of cytochrome c. However, subsequent (but not prior) exposure of paclitaxel-treated U937/Bcl-xL cells (500 nM; 6 h) to bryostatin 1 (10 nM; 15 h) restored the extent of apoptosis, caspase activation, and mitochondrial damage to levels approximating those in paclitaxel-treated empty-vector control cells (U937/Neo). Potentiation of paclitaxel-induced apoptosis by bryostatin 1 in U937/Bcl-xL cells occurred primarily in the G2M cell population, and was associated with alterations in Bcl-xL gel mobility and a reduction in paclitaxel-mediated stimulation of CDK1 activity. Enhancement of paclitaxel-induced apoptosis by bryostatin 1 in Bcl-xL overexpressors was accompanied by a corresponding reduction in clonogenic potential. In contrast to its effects on apoptosis, bryostatin 1 failed to restore paclitaxel-mediated increases in free Bax levels in U937/Bcl-xL cells. Lastly, the actions of bryostatin 1 were mimicked by a pharmacologic inhibitor of the MEK1/MAP kinase pathway (PD98059), but not by SB203580, an inhibitor of p 38 MAP kinase. Moreover, sequential exposure of both U937/Neo or/Bcl-xL cells to paclitaxel followed by bryostatin 1 or PD98059 was associated with a net reduction in MAP kinase activity. Collectively, these findings indicate that protection against paclitaxel-mediated mitochondrial dysfunction and apoptosis in human U937 leukemia cells conferred by Bcl-xL overexpression can be substantially overcome by bryostatin 1 and possibly other agents that interrupt the MAP kinase signal transduction pathway.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1997

Bcl-x(L) can inhibit apoptosis in cells that have undergone Fas-induced protease activation.

Programmed cell death or apoptosis provides an irreversible mechanism for the elimination of excess or damaged cells. Several recent studies have implicated the activation of the interleukin 1beta-converting enzyme/Ced-3 (ICE/Ced-3) family of proteases as the "point of no return" in apoptotic cell death, while others have suggested that loss of mitochondrial membrane potential (delta psi(m)) is the ultimate determinant of cell death. The temporal relationship of these two events during apoptosis and the role of Bcl-2 proteins in inhibiting these steps has not been defined. To examine these issues, control and Bcl-x(L)-transfected Jurkat T cells were treated with Fas antibodies in the presence and absence of the ICE protease inhibitor zVAD-FMK. ICE/Ced-3 protease activity was monitored by following the cleavage of poly(ADP-ribose) polymerase (PARP) and delta psi(m) was followed by rhodamine 123 fluorescence. Although Bcl-x(L) expression did not block Fas-induced protease activation, it substantially inhibited the subsequent loss of delta psi(m) and cell death in Fas-treated cells. In contrast, zVAD-FMK blocked PARP cleavage as well as loss of delta psi(m) and cell death. Together these data demonstrate that Bcl-x(L) can maintain cell viability by preventing the loss of mitochondrial membrane potential that occurs as a consequence of ICE/Ced-3 protease activation.

Apoptosis↗
PubMed1997

Impaired induction of the apoptosis-protective protein Bcl-xL in activated PBMC from asymptomatic HIV-infected individuals.

Progression to AIDS in asymptomatic HIV-infected individuals is characterized by a gradual but progressive loss of CD4+ T cells. While the mechanisms underlying this decline are currently unknown, recent evidence suggests that these cells are abnormally sensitive to apoptosis in response to activation signals. Recent work has implicated downregulation of Bcl-2 with the increased spontaneous apoptosis in lymphocytes from HIV-infected patients. We have evaluated the roles of the apoptosis-protective proteins Bcl-2 and Bcl-x in stimulated PBMC from asymptomatic HIV-infected and HIV-uninfected individuals. We found that Bcl-2 was constitutively expressed in PBMC from both HIV-infected and uninfected samples. However, Bcl-x induction was delayed and responses were decreased in stimulated HIV-infected samples. Additionally, single-cell intracellular staining of Bcl-x revealed a significant inverse correlation between PWM-induced Bcl-x expression and apoptosis (r = -0.695, P = 0.05). This was confirmed at the single-cell level in direct experiments when stimulated cells were sorted based on Bcl-x induction and then measured for apoptosis. Furthermore, low Bcl-x expression was not due to reduced lymphocyte activation following PWM stimulation. Our data indicate that the induction of Bcl-x is markedly impaired in asymptomatic HIV-infected patients and that stimuli which induce inadequate expression of Bcl-x are associated with increased levels of apoptosis in these cells.

Antigens, CD↗
PubMed1997

Modulation of the expression of Bcl-2 and related proteins in human leukemia cells by protein kinase C activators: relationship to effects on 1-[beta-D-arabinofuranosyl]cytosine-induced apoptosis.

We have previously reported that pretreatment of HL-60 human promyelocytic leukemia cells with the non-tumor-promoting protein kinase C (PKC) activator bryostatin 1 potentiates induction of apoptosis by the antimetabolite 1-[beta-D-arabinofuranosyl]cytosine (ara-C) (Biochem Pharmacol 47:839,1994). To determine whether this phenomenon results from altered expression of Bcl-2 or related proteins, Northern and Western analysis was employed to assess the effects of bryostatin 1 and other PKC activators on steady-state levels of Bcl-2, Bax, Bcl-x, and Mcl-1 mRNA and protein. Pretreatment of cells for 24 h with 10 nM bryostatin 1, or, to a lesser extent, the stage-1 tumor-promoter phorbol dibutyrate (PDB) significantly potentiated apoptosis induced by ara-C (100 microM; 6 h); in contrast, equivalent exposure to the stage-2 tumor promoter, mezerein (MZN), which, unlike bryostatin 1, is a potent inducer of differentiation in this cell line, failed to modify ara-C-related cell death. Neither bryostatin 1 nor PDB altered expression of bcl-2/Bcl-2 over this time frame. In contrast, MZN down-regulated bcl-2 mRNA levels, but this effect was not accompanied by altered expression of Bcl-2 protein. None of the PKC activators modified expression of Bax or Bcl-x(L) mRNA or protein; levels of Bcl-x(S) were undetectable in both treated and untreated cells. However, expression of Mcl-1 mRNA and protein increased modestly after treatment with either bryostatin 1 or PDB, and to a greater extent following exposure to MZN. Combined treatment of cells with bryostatin 1 and MZN resulted in undiminished potentiation of ara-C-mediated apoptosis and by antagonism of cellular maturation. These effects were accompanied by unaltered expression of Bcl-2, Bax, and Bcl-x(L), and by a further increase in Mcl-1 protein levels. When cells were co-incubated with bryostatin 1 and calcium ionophore (A23187), an identical pattern of expression of Bcl-2 family members was observed, despite the loss of bryostatin 1's capacity to potentiate apoptosis, and the restoration of its ability to induce differentiation. Finally, treatment of cells with bryostatin 1+/-ara-C (but not ara-C alone) resulted in a diffuse broadening of the Bcl-2 protein band, whereas exposure of cells to taxol (250 nM, 6 h) led to the appearance of a distinct Bcl-2 species with reduced mobility, phenomena compatible with protein phosphorylation. Together, these findings indicate that the ability of bryostatin 1 to facilitate drug-induced apoptosis in human myeloid leukemia cells involves factors other than quantitative changes in the expression of Bcl-2 family members, and raise the possibility that qualitative alterations in the Bcl-2 protein, such as phosphorylation status, may contribute to this capacity. They also suggest that increased expression of Mcl-1 occurs early in the pre-commitment stage of myeloid cell differentiation, and that this event does not protect cells from drug-induced apoptosis.

Journal Article↗
PubMed1997

Elevated expression of Bcl-2 and Bcl-x by intestinal intraepithelial lymphocytes: resistance to apoptosis by glucocorticoids and irradiation.

Administration of glucocorticoids or exposure to ionizing radiation in vivo results in a rapid cell death of thymocytes. We report that murine small intestinal intraepithelial lymphocytes (IEL) are resistant to both steroid- and radiation-induced deletion. This is due to resistance to apoptosis, as evidenced by the absence of detectable apoptotic IEL nuclei in situ after in vivo glucocorticoid treatment. IEL express normal levels of glucocorticoid receptors and these receptors bind [3H]dexamethasone to equivalent levels as other lymphocyte populations. Thus, their survival is due to post-receptor signaling mechanisms. Many IEL express high levels of Bcl-2 and that of these Bcl-2high IEL are largely TCR gamma delta +. Those IEL that do express high levels of Bcl-2 are CD8 alpha + beta - CD4-. In addition, IEL express Bcl-x, another protein shown to be involved in the protection of cells from apoptotic signals. IEL represent the first lymphocyte population in vivo shown to have high levels of expression of both molecules, that otherwise occur only in activated lymphocytes in vitro. These data suggest that the Bcl-2+Bcl-x+ IEL are activated cells and not an effete population of cells necessarily destined to die. Also, the high levels of Bcl-2 and Bcl-x in this in vivo activated population supports the in vitro correlate of protection from activation-induced cell death.

Animals↗
PubMed1996

The apoptosis-associated gamma-ray response of BCL-X(L) depends on normal p53 function.

We have investigated the effect of DNA damage on the expression of BCL-X, a member of the BCL-2 family. BCL-X mRNA levels were found to increase upon exposure human cells to ionizing radiation (IR). The Bcl-X(L) protein, but not Bcl-X(S), was identified to be induced by IR. Like BAX, another member of the BCL-2 family and a p53-regulated gene, the induction of BCL-X(L) was dependent on normal p53 function and required that cells have an apoptosis-susceptible phenotype. The induction of BCL-X(L) was rapid, transient and dose-dependent. The mRNA level peaked at 4 h and returned to baseline by 24 h post-irradiation. In agreement with the increased transcript level, Bcl-X(L) protein level was also observed to increase in cells with wild-type p53 where IR triggered apoptosis. In addition, a survey of the BCL-X(L) mRNA basal levels in human cells with known apoptotic responses showed that low basal levels of BCL-X(L) mRNA in cells were highly correlated with a strong ability of cells to undergo IR-induced apoptosis. On the other hand, high levels of basal BCL-X(L) were correlated with the resistance of cells to IR-induced apoptosis regardless of p53 status. These results indicate that BCL-2 and BCL-X(L) behave differently in response to DNA damage treatment even though they both are able to protect cells from p53-mediated apoptosis; along with down-regulation of BCL-2, BCL-X(L) was up-regulated by IR in human cells with wild-type p53 and susceptibility to IR-induced apoptosis. We speculate that the physiological function of increased BCL-X(L) protein would be expected to probably limit the severity and length of BAX effect in order to maintain a proper threshold for apoptosis and to complete cell cycle arrest activated by p53.

Apoptosis↗