Bcl-2 maintains B cell memory

Lipid metabolism associated crosstalk: the bidirectional interaction between cancer cells and immune/stromal cells within the tumor microenvironment for prognostic insight

Cancer is closely related to lipid metabolism, with the tumor microenvironment (TME) containing numerous lipid metabolic interactions. Cancer cells can bidirectionally interact with immune and stromal cells, the major components of the TME. This interaction is primarily mediated by fatty acids (FAs), cholesterol, and phospholipids. These interactions can lead to various physiological changes, including immune suppression, cancer cell proliferation, dissemination, and anti-apoptotic effects on cancer cells. The physiological modulation resulting from this lipid metabolism-associated crosstalk between cancer cells and immune/stromal cells provides valuable insights into cancer prognosis. A comprehensive literature review was conducted to examine the function of the bidirectional lipid metabolism interactions between cancer cells and immune/stromal cells within the TME, particularly how these interactions influence cancer prognosis. A novel autophagy-extracellular vesicle (EV) pathway has been proposed as a mediator of lipid metabolism interactions between cancer cells and immune cells/stromal cells, impacting cancer prognosis. As a result, different forms of lipid metabolism interactions have been described as being linked to cancer prognosis, including those mediated by the autophagy-EV pathway. In conclusion, understanding the bidirectional lipid metabolism interactions between cancer cells and stromal/immune cells in the TME can help develop more advanced prognostic approaches for cancer patients.

Heterologous booster vaccination enhances antibody responses to SARS-CoV-2 by improving Tfh function and increasing B-cell clonotype SHM frequency

Heterologous prime-boost has broken the protective immune response bottleneck of the COVID-19 vaccines. however, the underlying mechanisms have not been fully elucidated. Here, we investigated antibody responses and explored the response of germinal center (GC) to priming with inactivated vaccines and boosting with heterologous adenoviral-vectored vaccines or homologous inactivated vaccines in mice. Antibody responses were dramatically enhanced by both boosting regimens. Heterologous immunization induced more robust GC activation, characterized by increased Tfh cell populations and enhanced helper function. Additionally, increased B-cell activation and antibody production were observed in a heterologous regimen. Libra-seq was used to compare the differences of S1-, S2- and NTD-specific B cells between homologous and heterologous vaccination, respectively. S2-specific CD19+ B cells presented increased somatic hypermutations (SHMs), which were mainly enriched in plasma cells. Moreover, a heterologous booster dose promoted the clonal expansion of B cells specific to S2 and NTD regions. In conclusion, the functional role of Tfh and B cells following SARS-CoV-2 heterologous vaccination may be important for modulating antibody responses. These findings provide new insights for the development of SARS-CoV-2 vaccines that induce more robust antibody response.

Insights into Canine Infertility: Apoptosis in Chronic Asymptomatic Orchitis

Chronic asymptomatic orchitis (CAO) is a common cause of acquired non-obstructive azoospermia in dogs. To understand the impact and mode of action of apoptosis, we investigated TUNEL, Bax, Bcl-2, Fas/Fas ligand, and caspase 3/8/9 in testicular biopsies of CAO-affected dogs and compared the results to undisturbed spermatogenesis in healthy males (CG). TUNEL⁺ cells were significantly increased in CAO, correlating with the disturbance of spermatogenesis. Bcl-2, Bax (p < 0.01 each), caspase 9 (p < 0.05), Fas, caspase 8 (p < 0.01 each), and caspase 3 (p < 0.05) were significantly increased at the mRNA level, whereas FasL expression was downregulated. Cleaved caspase 3 staining was sporadic in CAO but not in CG. Sertoli cells, some peritubular (CAO/CG) and interstitial immune cells (CAO) stained Bcl-2⁺, with significantly more immunopositive cells in both compartments in CAO compared to CG. Bcl-2 and CD20 co-expressing B lymphocytes were encountered interstitially and in CAO occasionally also found intratubally, underlining their contribution to the maintenance of CAO. Our results support the crucial role of the intrinsic and extrinsic apoptotic pathways in the pathophysiology of canine CAO. Autoprotective Bcl-2 expression in Sertoli cells and B lymphocytes seems to be functional, however, thereby also maintaining and promoting the disease by immune cell activation.

Follicular lymphoma dynamics

Follicular lymphoma (FL) is an indolent yet challenging disease. Despite a generally favorable response to immunochemotherapy regimens, a fraction of patients does not respond or relapses early with unfavorable prognosis. For the vast majority of those who initially respond, relapses will repeatedly occur with increasing refractoriness to available treatments. Addressing the clinical challenges in FL warrants deep understanding of the nature of treatment-resistant FL cells seeding relapses, and of the biological basis of early disease progression. Great progress has been made in the last decade in the description and interrogation of the (epi)genomic landscape of FL cells, of their major dependency to the tumor microenvironment (TME), and of the stepwise lymphomagenesis process, from healthy to subclinical disease and to overt FL. A new picture is emerging, in which an ever-evolving tumor-TME duo sparks a complex and multilayered clonal and functional heterogeneity, blurring the discovery of prognostic biomarkers, patient stratification and reliable designs of risk-adapted treatments. Novel technological approaches allowing to decipher both tumor and TME heterogeneity at the single-cell level are beginning to unravel unsuspected cell dynamics and plasticity of FL cells. The upcoming drawing of a comprehensive functional picture of FL within its ecosystem holds great promise to address the unmet medical needs of this complex lymphoma.

AMPKα1 in B Cells Dampens Primary Antibody Responses yet Promotes Mitochondrial Homeostasis and Persistence of B Cell Memory

Emerging evidence indicates that metabolic programs regulate B cell activation and Ab responses. However, the metabolic mediators that support the durability of the memory B cell and long-lived plasma cell populations are not fully elucidated. Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionary conserved serine/threonine kinase that integrates cellular energy status and nutrient availability to intracellular signaling and metabolic pathways. In this study, we use genetic mouse models to show that loss of ΑMPKα1 in B cells led to a weakened recall Ab response associated with a decline in the population of memory-phenotype B cells. AMPKα1-deficient memory B lymphocytes exhibited aberrant mitochondrial activity, decreased mitophagy, and increased lipid peroxidation. Moreover, loss of AMPKα1 in B lymphoblasts was associated with decreased mitochondrial spare respiratory capacity. Of note, AMPKα1 in B cells was dispensable for stability of the bone marrow-resident, long-lived plasma cell population, yet absence of this kinase led to increased rates of Ig production and elevated serum Ab concentrations elicited by primary immunization. Collectively, our findings fit a model in which AMPKα1 in B cells supports recall function of the memory B cell compartment by promoting mitochondrial homeostasis and longevity but restrains rates of Ig production.

Overview of BCL-2 Family Proteins and Therapeutic Potentials

BCL-2 family proteins interact in a network that regulates apoptosis. The BH3 amino acid sequence motif serves to bind together this conglomerate protein family, both literally and figuratively. BH3 motifs are present in antiapoptotic and proapoptotic BCL-2 homologs, and in a separate group of unrelated BH3-only proteins often appended to the BCL-2 family. BH3-containing helices mediate many of their physical interactions to determine cell death versus survival, leading to the development of BH3 mimetics as therapeutics. Here we provide an overview of BCL-2 family interactions, their relevance in health and disease, and the progress toward regulating their interactions therapeutically.

Genetic Architecture of Adaptive Immune System Identifies Key Immune Regulators

The immune system is highly diverse, but characterization of its genetic architecture has lagged behind the vast progress made by genome-wide association studies (GWASs) of emergent diseases. Our GWAS for 54 functionally relevant phenotypes of the adaptive immune system in 489 healthy individuals identifies eight genome-wide significant associations explaining 6%-20% of variance. Coding and splicing variants in PTPRC and COMMD10 are involved in memory T cell differentiation. Genetic variation controlling disease-relevant T helper cell subsets includes RICTOR and STON2 associated with Th2 and Th17, respectively, and the interferon-lambda locus controlling regulatory T cell proliferation. Early and memory B cell differentiation stages are associated with variation in LARP1B and SP4. Finally, the latrophilin family member ADGRL2 correlates with baseline pro-inflammatory interleukin-6 levels. Suggestive associations reveal mechanisms of autoimmune disease associations, in particular related to pro-inflammatory cytokine production. Pinpointing these key human immune regulators offers attractive therapeutic perspectives.

Regulation of B cell fate, survival, and function by mitochondria and autophagy

B cells are responsible for protective antibody production after differentiation into antibody-secreting cells during humoral immune responses. From early B cell development in the bone marrow, to their maturation in the periphery, activation in the germinal center, and differentiation into plasma cells or memory B cells, B cells display ever-changing functions and properties. Autophagy and mitochondria play important roles in B cell development, activation, and differentiation to accommodate the phenotypic and environmental changes encountered over the lifetime of the cell. Among their many functions, mitochondria and autophagy generate energy, mediate cell survival, and produce/eliminate reactive oxygen species that can serve as signal molecules to regulate differentiation. As B cells mature and differentiate into plasma or memory cells, both autophagic and mitochondrial functions undergo significant changes. In this review, we aim to provide an overview of the role of the autophagosome and mitochondria in regulating B cell fate, survival, and function. Moreover, we will discuss the interplay between these two highly metabolic organelles during B cell development, maturation, and differentiation.

Maintenance of the HIV Reservoir Is Antagonized by Selective BCL2 Inhibition

Decay of the HIV reservoir is slowed over time in part by expansion of the pool of HIV-infected cells. This expansion reflects homeostatic proliferation of infected cells by interleukin-7 (IL-7) or antigenic stimulation, as well as new rounds of infection of susceptible target cells. As novel therapies are being developed to accelerate the decay of the latent HIV reservoir, it will be important to identify interventions that prevent expansion and/or repopulation of the latent HIV reservoir. Our previous studies showed that HIV protease cleaves the host protein procaspase 8 to generate Casp8p41, which can bind and activate Bak to induce apoptosis of infected cells. In circumstances where expression of the anti-apoptotic protein BCL2 is high, Casp8p41 instead binds BCL2, and cell death does not occur. This effect can be overcome by treating cells with the clinically approved BCL2 antagonist venetoclax, which prevents Casp8p41 from binding BCL2, thereby allowing Casp8p41 to bind Bak and kill the infected cell. Here we assess whether the events that maintain the HIV reservoir are also antagonized by venetoclax. Using the J-Lat 10.6 model of persistent infection, we demonstrate that proliferation and HIV expression are countered by the use of venetoclax, which causes preferential killing of the HIV-expressing cells. Similarly, during new rounds of infection of primary CD4 T cells, venetoclax causes selective killing of HIV-infected cells, resulting in decreased numbers of HIV DNA-containing cells.IMPORTANCE Cure of HIV infection requires an intervention that reduces the HIV reservoir size. A variety of approaches are being tested for their ability to impact HIV reservoir size. Even if successful, however, these approaches will need to be combined with additional complementary approaches that prevent replenishment or repopulation of the HIV reservoir. Our previous studies have shown that the FDA-approved BCL2 antagonist venetoclax has a beneficial effect on the HIV reservoir size following HIV reactivation. Here we demonstrate that venetoclax also has a beneficial effect on HIV reservoir size in a model of homeostatic proliferation of HIV as well as in acute spreading infection of HIV in primary CD4 T cells. These results suggest that venetoclax, either alone or in combination with other approaches to reducing HIV reservoir size, is a compound worthy of further study for its effects on HIV reservoir size.

Biophysical changes reduce energetic demand in growth factor-deprived lymphocytes

Cytokine regulation of lymphocyte growth and proliferation is essential for matching nutrient consumption with cell state. Here, we examine how cellular biophysical changes that occur immediately after growth factor depletion promote adaptation to reduced nutrient uptake. After growth factor withdrawal, nutrient uptake decreases, leading to apoptosis. Bcl-xL expression prevents cell death, with autophagy facilitating long-term cell survival. However, autophagy induction is slow relative to the reduction of nutrient uptake, suggesting that cells must engage additional adaptive mechanisms to respond initially to growth factor depletion. We describe an acute biophysical response to growth factor withdrawal, characterized by a simultaneous decrease in cell volume and increase in cell density, which occurs before autophagy initiation and is observed in both FL5.12 Bcl-xL cells depleted of IL-3 and primary CD8(+) T cells depleted of IL-2 that are differentiating toward memory cells. The response reduces cell surface area to minimize energy expenditure while conserving biomass, suggesting that the biophysical properties of cells can be regulated to promote survival under conditions of nutrient stress.

Lymphocytes shrink to stay fit

Researchers describe how immune cells quickly adapt to cytokine withdrawal and nutrient stress.

Follicular lymphoma: too many reminders for a memory B cell

Memory B cells are a dynamic subset of the mature B cell population that in some cases can reenter germinal centers (GCs) in response to iterative infections. Such a reactivation can lead to accumulation of genetic lesions in these cells, potentially from repetitive activation of the B cell mutator enzyme AID. Normal memory B cells do not survive repeated reentries into GCs. In this issue, Sungalee et al. demonstrate that memory B cells harboring the oncogenic BCL2:IGH translocation, which results in constitutive BCL2 expression, survive multiple GC entries upon repetitive immunization. Through these multiple GC reentries, the hallmark BCL2:IGH translocation enables AID-induced hypermutation and propagates clonal evolution toward malignant follicular lymphoma.

Germinal center reentries of BCL2-overexpressing B cells drive follicular lymphoma progression

It has recently been demonstrated that memory B cells can reenter and reengage germinal center (GC) reactions, opening the possibility that multi-hit lymphomagenesis gradually occurs throughout life during successive immunological challenges. Here, we investigated this scenario in follicular lymphoma (FL), an indolent GC-derived malignancy. We developed a mouse model that recapitulates the FL hallmark t(14;18) translocation, which results in constitutive activation of antiapoptotic protein B cell lymphoma 2 (BCL2) in a subset of B cells, and applied a combination of molecular and immunofluorescence approaches to track normal and t(14;18)(+) memory B cells in human and BCL2-overexpressing B cells in murine lymphoid tissues. BCL2-overexpressing B cells required multiple GC transits before acquiring FL-associated developmental arrest and presenting as GC B cells with constitutive activation-induced cytidine deaminase (AID) mutator activity. Moreover, multiple reentries into the GC were necessary for the progression to advanced precursor stages of FL. Together, our results demonstrate that protracted subversion of immune dynamics contributes to early dissemination and progression of t(14;18)(+) precursors and shapes the systemic presentation of FL patients.

Getting away with murder: how does the BCL-2 family of proteins kill with immunity?

The adult human body produces approximately one million white blood cells every second. However, only a small fraction of the cells will survive because the majority is eliminated through a genetically controlled form of cell death known as apoptosis. This review places into perspective recent studies pertaining to the BCL-2 family of proteins as critical regulators of the development and function of the immune system, with particular attention on B cell and T cell biology. Here we discuss how elegant murine model systems have revealed the major contributions of the BCL-2 family in establishing an effective immune system. Moreover, we highlight some key regulatory pathways that influence the expression, function, and stability of individual BCL-2 family members, and discuss their role in immunity. From lethal mechanisms to more gentle ones, the final portion of the review discusses the nonapoptotic functions of the BCL-2 family and how they pertain to the control of immunity.

Early steps of follicular lymphoma pathogenesis

Follicular lymphoma (FL) pathogenesis is a complex and fascinating multi-hit process, escalating along successive derailments of the distinctive molecular and cellular mechanisms paving B-cell differentiation and activation. This progressive subversion of B-cell receptor diversification mechanisms and B-cell homeostasis likely occurs during a protracted preclinical phase of asymptomatic growth, in which premalignant clones already disseminate and establish "niches" in secondary lymphoid organs. Following FL diagnosis, a parallel indolent behavior is observed in most patients, slowly progressing over a period of many years, to eventually generate a highly refractory (and in some case transform into an aggressive subtype of) lymphoma. Novel insights in human germinal center B-cell biology recently allowed a more comprehensive understanding of the various illegitimate events sequentially involved in the premalignant progression phases. In this review, we will discuss how these new data have modified our perception of early FL pathogenesis, the new questions and challenges it opened up, and how this knowledge could impact on innovative programs of early detection, follow-up, and patient management.

Reduced association of anti-apoptotic protein Mcl-1 with E3 ligase Mule increases the stability of Mcl-1 in breast cancer cells

Background:

Mechanisms that increase resistance to apoptosis help promote cellular transformation. Cancer cells have deregulated apoptotic pathways, where increased expression and stability of anti-apoptotic proteins Mcl-1 and Bcl-2 increases resistance to apoptosis. Pathways that increase the stability of proteins in cancer cells remain poorly understood.

Methods:

Using human mammary epithelial and established breast cancer cell lines, we assessed the mechanisms that increase the stability of anti-apoptotic proteins in breast cancer cells by caspase assay, western blot, small-inhibitory RNA treatment and immunoprecipitation.

Results:

While breast cancer cells were resistant to de novo inhibition of protein synthesis, a rapid proteosome-mediated degradation of Mcl-1 and Bcl-2 induced apoptosis in mammary epithelial cells. Although Mule, an E3 ligase that targets Mcl-1 for degradation was expressed in mammary epithelial and breast cancer cell lines, rapid increase of polyubiquitinated Mcl-1 and Bcl-2 was detected only in mammary epithelial cells. Only transient formation of the Mule–Mcl-1 complex was detected in breast cancer cells. Downregulation of pERK1/2 in breast cancer cells reduced Mcl-1 levels and increased Mcl-1/Mule complex.

Conclusion:

Our findings suggest that reduced Mule/Mcl-1 complex has a significant role in increasing the stability of Mcl-1 in breast cancer cells and increased resistance to apoptosis.

Enforced expression of the apoptosis inhibitor Bcl-2 ablates tolerance induction in DNA-reactive B cells through a novel mechanism

How self tolerance is maintained during B cell development in the bone marrow has been a focal area of study in immunology. Receptor editing, anergy and clonal deletion all play important roles in the regulation of autoimmunity in the immature population. The mechanisms of tolerance induction in the periphery, however, are less well characterized. Overexpression of the apoptosis inhibitor Bcl-2 rescues autoreactive B cells from deletion and can contribute to the development of autoimmune disease in certain genetic backgrounds. Using a peptide-induced autoimmunity model, we recently identified a peripheral tolerance checkpoint in antigen-activated B cells that have undergone class switching and somatic hypermutation. At this checkpoint, receptor editing, induced by antigen engagement, dampened the autoantibody response. In this study, we show that receptor editing fails to be induced in antigen-activated DNA-reactive B cells that overexpress Bcl-2 (Bcl-2 Tg). The failure to induce RAG and receptor editing is likely due, at least partially, to the lack of self antigen. First, the levels of circulating DNA and of apoptotic bodies in the spleen of Bcl-2 Tg mice are significantly lower than in control mice. Second, in Bcl-2 Tg mice, RAG can be induced in a population of antigen-activated B cells by providing exogenous soluble antigen. These data suggest that, in addition to its anti-apoptotic activity, Bcl-2 may indirectly inhibit tolerance induction in B cells acquiring anti-nuclear antigen reactivity after peripheral activation by limiting the availability of self antigen.

B-cell overexpression of Bcl-2 cooperates with p21 deficiency for the induction of autoimmunity and lymphomas

Genetic abnormalities predisposing to autoimmunity generally act in a cooperative manner affecting one or several mechanisms regulating immunological tolerance. In addition, many of these genetic abnormalities are also involved in the development of lymphoproliferative diseases. In the present study, we have determined the possible cooperation between deficiencies in members of the Cip/Kip family of cell cycle regulators (p21(WAF1/Cip1) or p27(kip1)) and the overexpression of human Bcl-2 in B lymphocytes in the induction of autoimmune and lymphoproliferative diseases in non-autoimmune C57BL/6 (B6) mice. Unlike single mutant mice, B6.p21(-/-) mice transgenic for human Bcl-2 in B cells developed a lethal autoimmune syndrome characterized by the production of autoantibodies, the prominent expansion of memory B and CD4(+) T cells and the development of severe glomerular lesions resembling IgA nephropathy. Furthermore, these mice presented a high incidence of B-cell lymphoproliferative disorders. Such genetic cooperation in the induction of autoimmunity was not observed in B6.p27(-/-) mice transgenic for human Bcl-2 in B cells. Altogether, what we have demonstrated here is the existence of preferential interactions among particular regulators of the G(1)/S transition of the cell cycle and B-cell survival in the induction of systemic autoimmune and lymphoproliferative diseases.

Apoptosis signaling pathways

Cell death is often an active and highly choreographed process of cell suicide known as apoptosis. The molecular signals governing this process have been the subject of intense research in recent years. During apoptosis a profusion of pathways either promote cellular survival or lead to certain death. These pathways engage in constant crosstalk with those that control cell proliferation and other activities, in order to maintain the delicate balance between cell births and deaths. This commentary unit discusses two major pathways, active (antigen-induced) and passive (lymphokine-withdrawal) apoptosis, and provides background for the following unit on flow cytometry of apoptosis.

Effects of fibroblast growth factor-2 on the in vitro culture of caprine preantral follicles

The aims of the present study were to evaluate the effects of fibroblast growth factor-2 (FGF-2) on survival, activation and growth of caprine early-staged (preantral) follicles using histological and ultrastructural studies. Fragments of caprine ovarian cortex were cultured for 1 or 5 days in an enriched minimum essential medium, supplemented or not with different concentrations of FGF-2 (10, 50 or 100 ng/ml). Fragments from non-cultured ovarian tissue (control) and from tissues cultured for 1 or 5 days in a specific medium were processed for transmission electron microscopy (TEM) or classical histology to evaluate the morphological quality of caprine preantral follicles and to calculate the percentages of normal follicles. Additionally, effects of FGF-2 on oocyte and follicle diameter of cultured preantral follicles were investigated. Our results showed that, although the percentages of histologically normal follicles were lower in cultured than in non-cultured ovarian tissue fragments, there were no differences in this regard among treatments, neither on day 1 nor on day 5 of culture. After 1 and 5 days of culture, a significantly higher percentage of growing follicles was observed in the medium supplemented with 50 ng/ml of FGF-2. This FGF-2 treatment furthermore resulted in an increase in diameter of both oocytes and follicles that were cultured for 5 days. TEM showed that the ultrastructural integrity of caprine preantral follicles was maintained during their 5-day culture in the presence of 50 ng/ml FGF-2. In conclusion, this study demonstrated that at a concentration of 50 ng/ml FGF-2 not only maintains the morphological integrity of caprine preantral follicles cultured for 5 days, but also stimulates the activation of primordial follicles and the growth of activated follicles.

Retinoic acid and histone deacetylase inhibitor BML-210 inhibit proliferation of human cervical cancer HeLa cells

Human papillomavirus (HPV) infection is believed to be the central cause of cervical cancer. The viral proteins E6 and E7 from high-risk HPV types prevent cells from differentiating apoptosis and inducing hyperproliferative lesions. Human cervical carcinoma HeLa cells contain integrated human papillomavirus type 18 (HPV-18). Retinoic acid (RA) is a key regulator of epithelial cell differentiation and a growth inhibitor in vitro of HeLa cervical carcinoma cells. Cellular responses to RA are mediated by nuclear retinoic acid receptors (RARs) and retinoid X receptors. On the other hand, histone deacetylase inhibitors have been shown to be chemopreventive agents for the treatment of cancer cells. In this article, we have examined the antiproliferative effect of RA and histone deacetylase inhibitor BML-210 on HeLa cells, and particularly the effects on protein expression that may be involved in the cell cycle control and apoptosis. Our data suggest that a combination of RA and BML-210 leads to cell growth inhibition with subsequent apoptosis in a treatment time-dependent manner. We confirm that BML-210 alone or in combination with RA causes a marked increase in the level of p21. The changes in the p53 level are under the influence of p38 phosphorylation. We also discovered that the histone deacetylase inhibitor BML-210 causes increased levels of anti-apoptotic protein Bcl-2 and phosphorylated p38 MAP Kinase; the latter link in cell cycle arrest with response to extracellular stimuli. Our results suggest that RA and BML-210 are involved in different signaling pathways that regulate cell cycle arrest and lead to apoptosis of HeLa cells.

BCL2 family of apoptosis-related genes: functions and clinical implications in cancer

One of the most effective ways to combat different types of cancer is through early diagnosis and administration of effective treatment, followed by efficient monitoring that will allow physicians to detect relapsing disease and treat it at the earliest possible time. Apoptosis, a normal physiological form of cell death, is critically involved in the regulation of cellular homeostasis. Dysregulation of programmed cell death mechanisms plays an important role in the pathogenesis and progression of cancer as well as in the responses of tumours to therapeutic interventions. Many members of the BCL2 (B-cell CLL/lymphoma 2; Bcl-2) family of apoptosis-related genes have been found to be differentially expressed in various malignancies, and some are useful prognostic cancer biomarkers. We have recently cloned a new member of this family, BCL2L12, which was found to be differentially expressed in many tumours. Most of the BCL2 family genes have been found to play a central regulatory role in apoptosis induction. Results have made it clear that a number of coordinating alterations in the BCL2 family of genes must occur to inhibit apoptosis and provoke carcinogenesis in a wide variety of cancers. However, more research is required to increase our understanding of the extent to which and the mechanisms by which they are involved in cancer development, providing the basis for earlier and more accurate cancer diagnosis, prognosis and therapeutic intervention that targets the apoptosis pathways. In the present review, we describe current knowledge of the function and molecular characteristics of a series of classic but also newly discovered genes of the BCL2 family as well as their implications in cancer development, prognosis and treatment.

B cells expressing Bcl-2 and a signaling-impaired BAFF-specific receptor fail to mature and are deficient in the formation of lymphoid follicles and germinal centers

The TNF family cytokine B cell-activating factor belonging to the TNF family (BAFF) (BLyS) plays a fundamental role in regulating peripheral B cell survival and homeostasis. A BAFF-specific receptor (BAFF-R; BR3) appears to mediate these functions via activation of the NF-kappaB2 pathway. Signaling by the BAFF-R is also required to sustain the germinal center (GC) reaction. Engagement of this receptor results in the induction of Bcl-2, suggesting that this antiapoptotic factor acts downstream of the BAFF-R and NF-kappaB2 pathway to promote peripheral B cell survival during primary and Ag-driven development. To test this idea, we created lines of mice coexpressing a Bcl-2 transgene and a signaling-deficient form of the BAFF-R derived from the B lymphopenic A/WySnJ strain. Surprisingly, although dramatically elevated numbers of B cells accumulate in the periphery of these mice, these B cells exhibit extremely perturbed primary development, formation of lymphoid microenvironments, and GC and IgG responses. Moreover, mice expressing the bcl-2 transgene alone display a loss of marginal zone B cells, an expansion of follicular B cells that appear immature, and alterations of the GC reaction. These results suggest that the BAFF-R and Bcl-2 regulate key and nonoverlapping aspects of peripheral B cell survival and development.

Anti-apoptotic protein Bcl-2 interacts with and destabilizes the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA)

The anti-apoptotic effect of Bcl-2 is well established, but the detailed mechanisms are unknown. In the present study, we show in vitro a direct interaction of Bcl-2 with the rat skeletal muscle SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase), leading to destabilization and inactivation of the protein. Recombinant human Bcl-2D21, a truncated form of Bcl-2 with a deletion of 21 residues at the C-terminal membrane-anchoring region, was expressed and affinity-purified as a glutathione S-transferase fusion protein. Bcl-2D21 co-immunoprecipitated and specifically interacted with SERCA in an in vitro-binding assay. The original level of Bcl-2 in sarcoplasmic reticulum vesicles was very low, i.e. hardly detectable by immunoblotting with specific antibodies. The addition of Bcl-2D21 to the sarcoplasmic reticulum resulted in the inhibition of the Ca2+-ATPase activity dependent on the Bcl-2D21/SERCA molar ratio and incubation time. A complete inactivation of SERCA was observed after 2.5 h of incubation at approx. 2:1 molar ratio of Bcl-2D21 to SERCA. In contrast, Bcl-2D21 did not significantly change the activity of the plasma-membrane Ca2+-ATPase. The redox state of the single Cys158 residue in Bcl-2D21 and the presence of GSH did not affect SERCA inhibition. The interaction of Bcl-2D21 with SERCA resulted in a conformational transition of SERCA, assessed through a Bcl-2-dependent increase in SERCA thiols available for the labelling with a fluorescent reagent. This partial unfolding of SERCA did not lead to a higher sensitivity of SERCA towards oxidative inactivation. Our results suggest that the direct interaction of Bcl-2 with SERCA may be involved in the regulation of apoptotic processes in vivo through modulation of cytoplasmic and/or endoplasmic reticulum calcium levels required for the execution of apoptosis.

The role of Bcl-2 family members in tumorigenesis

The Bcl-2 family consists of about 20 homologues of important pro- and anti-apoptotic regulators of programmed cell death. The established mode of function of the individual members is to either preserve or disturb mitochondrial integrity, thereby inducing or preventing release of apoptogenic factors like Cytochrome c (Cyt c) from mitochondria. Recent findings also indicate further Bcl-2-controlled mitochondria-independent apoptosis pathways. Bcl-2 represents the founding member of the new and growing class of cell death inhibiting oncoproteins. In this review, we try to briefly summarize current models of Bcl-2 family function and to outline the work demonstrating the influence of deregulated Bcl-2 family member expression on tumorigenesis and cancer therapy. Since several Bcl-2 homologues, in addition to influencing apoptotic behaviour, also impinge on cell cycle progression, we discuss possible implications of this additional role for the expression of Bcl-2 family members in tumor cells.

Quantitative analysis of bcl-2 expression in normal and leukemic human B-cell differentiation

Lack of apoptosis has been linked to prolonged survival of malignant B cells expressing bcl-2. The aim of the present study was to analyze the amount of bcl-2 protein expressed along normal human B-cell maturation and to establish the frequency of aberrant bcl-2 expression in B-cell malignancies. In normal bone marrow (n=11), bcl-2 expression obtained by quantitative multiparametric flow cytometry was highly variable: very low in both CD34(+) and CD34(-) B-cell precursors, high in mature B-lymphocytes and very high in plasma cells. Bcl-2 expression of mature B-lymphocytes from peripheral blood (n=10), spleen (n=8) and lymph node (n=5) was significantly higher (P<0.02) in CD23(-) as compared to CD23(+) B cells, independent of the type of tissue analyzed. Upon comparison with normal human B-cell maturation, bcl-2 expression in neoplastic B cells from 144 patients was found to be aberrant in 66% of the cases, usually corresponding to bcl-2 overexpression (63%). Follicular lymphoma (FL) carrying t(14;18) and MALT lymphoma were the only diagnostic groups constantly showing overexpression of bcl-2. Bcl-2 overexpression was also frequently found in precursor B-acute lymphoblastic leukemia (84%), typical (77%) and atypical (75%) B-cell chronic lymphocytic leukemia, prolymphocytic leukemia (two of three cases), mantle cell lymphoma (55%), but not in t(14;18)(-) FL, splenic marginal zone lymphoma, Burkitt lymphoma and multiple myeloma.

The life and death of a B cell

Regulation of apoptosis in the B cell lineage has implications for homeostasis, quality control of the antibody response, and tolerance. In this chapter we examine the different checkpoints that control life and death decisions of B cells during the antigen-independent and antigen-dependent phases of their development. We discuss the cell death mechanism involved in elimination of unwanted B cells at different stages of their development as well as the signals that trigger or repress the apoptotic process. At the steady state, before or after development of an immune response, B cell apoptosis ensures that the antigen receptor (BCR) on newly produced B cells is functional and does not recognize self-antigens with high avidity. It also ensures that the size of the peripheral B cell compartment remains constant in spite of the continuous input of B cells from the bone marrow. All these processes are controlled by the mitochondrial death pathway and are thus perturbed by overexpression of the antiapoptotic members of the bcl-2 gene family. By contrast, the death receptor pathway plays a prominent role during the antigen-dependent phase of B cell development. Three sets of membrane molecules stand as crucial regulators of B cell survival. First, the BCR which plays a central but ambiguous role. On the one hand, it triggers death of B cells that recognize self-antigens or have been exposed to repeated antigenic stimulations. On the other hand, it promotes survival of the peripheral mature B cell pool and protects activated B cells from CD95-induced killing. Second, the death receptor Fas/CD95 which is instrumental in censoring B cells activated in a bystander fashion at the initiation of the response to T-dependent antigens. It also drives elimination of low-affinity and self-reactive B cell clones that arise through the process of somatic mutations during the germinal center reaction. As such, it contributes to the affinity maturation of the antibody response. Finally, three membrane receptors (TACI, BCMA, and BAFF-R) which bind a newly discovered member of the tumor necrosis factor family named BAFF. BAFF acts specifically on peripheral B cells but its cellular targets seem to be restricted to two splenic B cell populations: (i) transitional immature B cells and (ii) marginal zone B cells, known to be responsible for the response to thymus-independent type 2 antigens. This suggests its possible implication in positive selection of peripheral B cells and in the antibacterial B cell responses.

The Bcl-2 protein family: sensors and checkpoints for life-or-death decisions

Members of the Bcl-2 family are crucial integrators of survival and death signals in higher eukaryotes. Although recent studies have provided novel and quite unexpected insights into the mechanisms by which these proteins might issue life permits or death sentences in cells, we are still on the way to fully understand their modes of action. This review provides a snapshot on where we are on this journey and how we may exploit our knowledge on this family of proteins to unveil the mysteries of immune regulation.

Immunoglobulin G3 cardiac myosin autoantibodies correlate with left ventricular dysfunction in patients with dilated cardiomyopathy: immunoglobulin G3 and clinical correlates

BACKGROUND

Effector functions of an aberrant immune response have been implicated in the pathogenesis of idiopathic dilated cardiomyopathy (DCM). The immunologic determinants of myocardial dysfunction, however, remain poorly understood. This study sought to determine the relation of different immunologic responses to hemodynamic dysfunction in DCM.

METHODS

Immunoglobulin (Ig) G class/subclass response ELISA (enzyme-linked immunosorbent assay) against cardiac myosin heavy chain, histologic characteristics (DALLAS criteria), immunohistochemistry, plasma interleukin-4 and plasma interferon gamma (IFN-gamma) were determined in patients (n = 76) with clinically suspected myocarditis or DCM. Patients were prospectively evaluated, both clinically and hemodynamically, on admission (baseline) and at 6-month follow-up.

RESULTS

Indices of hemodynamic dysfunction (by cardiac catheterization and transthoracic echocardiography) correlated significantly with an Ig subclass response. IgG3 levels correlated with left ventricular ejection fraction (P =.02), pulmonary capillary wedge pressure (P <.0001), left ventricular end-systolic volume index (P =.002), left ventricular end-diastolic volume index (P =.033), left ventricular end-diastolic pressure (P =.04), right ventricular end-diastolic pressure (P =.039), and left ventricular end-systolic dimension and left ventricular end-diastolic dimension (P <.05). Patients positive for IgG3 (predominantly male, P =.01) had depressed left ventricular ejection fraction (< or =45%, relative risk 3.0, 95% CI 1.5-5.7, P =.005) at baseline and 6 months. Mitral-septal separation at follow-up improved in patients negative for IgG3 (P =.018), and the number of patients on conventional therapy in this group declined at 6-month follow-up (P <.05). Lymphocyte counts/high-power field; CD2, CD3, CD4, and CD8 (independent of IgG class/subclass response and left ventricular dysfunction) were significantly higher in patients positive for IFN-gamma (25%). A positive IFN-gamma response was higher in patients positive for IgG3. These patients, positive for IgG3 and IFN-gamma (10%), had significantly shorter duration of clinical symptoms: 0.17 years (0.12-2.36 y) versus 1.01 years (0.49-5.35 y, P =.04).

CONCLUSION

IgG3 reactivity correlated with depressed myocardial dysfunction. This may render this subclass Ig a surrogate target for therapeutic intervention in DCM. With IFN-gamma, IgG3 may reflect a more aggressive disease.

A role for calcium in Bcl-2 action?

Changes in the cytosolic Ca(2+) concentration ([Ca(2+)](c)) translate a variety of extracellular signals into widely diverse intracellular effects, ranging from secretion to movement, proliferation and also cell death. As regards the last one, it has long been known that large [Ca(2+)](c) increases lead cells to death. More recently, experimental evidence has been obtained that the oncogene Bcl-2 reduces the state of filling of intracellular Ca(2+) stores and thus affects the Ca(2+) responses induced by physiological and pathological stimuli. In this contribution, we will discuss this effect and its significance for the mechanism of action of Bcl-2, an important checkpoint of the apoptotic process.

Mechanism of BLyS action in B cell immunity

The B lymphocyte stimulator (BLyS), also known as BAFF, THANK, TALL-1 and zTNF4, is the most recent addition to the tumor necrosis factor family (TNF) ligands and has a unique role in B cell immunity. Its requirement for the humoral immune response is evident in mice lacking BlyS, which exhibit profound deficiencies in peripheral B cell development and maturation. It regulates the antibody response, as shown in mice overexpressing BLyS, which develop autoimmune manifestations resulting from peripheral B cell expansion and differentiation. Attenuation of apoptosis appears to underlie BLyS action in B cells. However, elucidation of the mechanism of BLyS has proven to be more challenging, because BLyS binds three different TNF receptors (TACI/BCMA/BAFF-R) and shares overlapping functions with a related TNF ligand, APRIL. The unique role of BLyS in B cell development and differentiation and the pathogenesis of autoimmune diseases, systemic lupus erythematosus (SLE) in particular, makes the study of BLyS and its downstream targets attractive in the development of novel therapies.

A role for secondary V(D)J recombination in oncogenic chromosomal translocations?

Chromosomal translocations are hallmarks of certain lymphoproliferative disorders. Indeed, in many leukemias and lymphomas, translocations are the transforming event that brings about malignancy. Recurrence of the immunoglobulin (Ig) and T-cell receptor (Tcr) loci at the breakpoints of oncogenic chromosomal translocations has led to speculation that the lymphocyte-specific process of V(D)J rearrangement, which is necessary for the generation of functional Ig and TCR antigen receptors on B and T lymphocytes, mediates translocation. Recent studies have led to a fuller understanding of the molecular mechanisms of V(D)J rearrangement and have revealed that the V(D)J recombinase possesses latent transposase activity. These studies have led to plausible models of illegitimate V(D)J recombination producing chromosomal translocations consistent with those present in lymphomas and leukemias. Errors of V(D)J recombination may even generate lymphomas with the phenotypes of mature cells. For example, follicular and Burkitt's lymphomas have been classified by phenotype and somatic genotype as malignant germinal center (GC) B or post-GC B cells. The GC is a site of affinity maturation where B cells undergo V(D)J hypermutation and Ig class switch; in addition, much evidence has accumulated to suggest that GC B cells may also support secondary V(D)J recombination. Interestingly, all three of these elements, genomic plasticity, mutation, and translocation breakpoints near switch sites or recombinational elements, are characteristic of certain lymphomas. The high frequency of lymphomas carrying these GC markers suggests that the GC reaction may play a significant role in lymphomagenesis.

Persistent polyclonal B-cell lymphocytosis is an expansion of functional IgD(+)CD27(+) memory B cells

Persistent polyclonal B-cell lymphocytosis (PPBL) is a rare disorder of unknown aetiology affecting predominantly young to middle-aged women. It is characterized by a polyclonal expansion of B cells, including typical binucleated lymphocytes, and is associated with the presence of the translocation t(14;18), involving the bcl-2 oncogene. The stage of differentiation of the B cells expanded in PPBL is not known. We analysed the immunophenotype of the expanded B-cell subset in five new patients with PPBL and found a large uniform expansion of a recently defined human memory B-cell population, IgD(+)CD27(+) memory B cells. After in vitro stimulation with interleukin 2 (IL-2) and Staphylococcus aureus Cowan strain I, B cells from PPBL patients produced high levels of IgM immunoglobulins, which is a characteristic feature of IgD(+)CD27(+) memory B cells. Using a quantitative real-time polymerase chain reaction method, we found a high frequency of the translocation t(14;18) in the range of 1000-3000 per 106 B cells in PPBL patients. In contrast, a much smaller number of cells with a t(14;18) was found in B cells from healthy individuals. Our finding that PPBL is an accumulation of memory B cells further suggests that chronic antigeneic stimulation plays an important part in the pathogenesis of this disorder. This IgD(+)CD27(+) memory B-cell population might harbour a certain number of 'physiological' t(14;18) translocations that increases as this population expands in PPBL patients and constitutes the majority of peripheral blood lymphocytes.

Rewiring of CD40 is necessary for delivery of rescue signals to B cells in germinal centres and subsequent entry into the memory pool

Memory B-cell development is impaired by in vivo blockade of the CD40-CD40 ligand (CD40L) interaction using human Fc immunoglobulin G1 (IgG1)-mouse CD40 fusion protein (CD40-Ig); however, germinal centre (GC) formation is not. We show here that the block in B-cell differentiation in these mice is at the stage of rescue from apoptosis and exit from the GC. Thus, GC from CD40-Ig-treated mice contain a three- to fourfold higher level of apoptotic cells than found in control mice injected with human IgG1 alone. This increase in apoptosis is not caused by a blockade of the CD40L-mediated rescue signal but is the result of an intrinsic defect of GC B cells in CD40-Ig-treated mice to receive rescue signals via CD40. While anti-CD40 stimulation maintained the viability in culture of GC B cells from control mice, it did not rescue GC B cells from CD40-Ig-treated mice. This data is consistent with the notion that a 'rewiring' of the CD40 molecule is induced by CD40 ligation early in the response and is necessary to allow B-cell rescue from apoptosis when they subsequently enter the GC.

Tissue-specific Bcl-2 protein partners in apoptosis: An ovarian paradigm

Apoptosis is an essential physiological process by which multicellular organisms eliminate superfluous cells. An expanding family of Bcl-2 proteins plays a pivotal role in the decision step of apoptosis, and the differential expression of Bcl-2 members and their binding proteins allows the regulation of apoptosis in a tissue-specific manner mediated by diverse extra- and intracellular signals. The Bcl-2 proteins can be divided into three subgroups: 1) antiapoptotic proteins with multiple Bcl-2 homology (BH) domains and a transmembrane region, 2) proapoptotic proteins with the same structure but missing the BH4 domain, and 3) proapoptotic ligands with only the BH3 domain. In the mammalian ovary, a high rate of follicular cell apoptosis continues during reproductive life. With the use of the yeast two-hybrid system, the characterization of ovarian Bcl-2 genes serves as a paradigm to understand apoptosis regulation in a tissue-specific manner. We identified Mcl-1 as the main ovarian antiapoptotic Bcl-2 protein, the novel Bok (Bcl-2-related ovarian killer) as the proapoptotic protein, as well as BOD (Bcl-2-related ovarian death agonist) and BAD as the proapoptotic ligands. The activity of the proapoptotic ligand BAD is regulated by upstream follicle survival factors through its binding to constitutively expressed 14-3-3 or hormone-induced P11. In contrast, the channel-forming Mcl-1 and Bok regulate cytochrome c release and, together with the recently discovered Diva/Boo, control downstream apoptosis-activating factor (Apaf)-1 homologs and caspases. Elucidation of the role of Bcl-2 members and their interacting proteins in the tissue-specific regulation of apoptosis could facilitate an understanding of normal physiology and allow the development of new therapeutic approaches for pathological states.

Quantification of illegitimate V(D)J recombinase-mediated mutations in lymphocytes of newborns and adults

We used a direct polymerase chain reaction (PCR) method for quantification of HPRT exons 2 + 3 deletions and t(14;18) translocations as a measure of illegitimate V(D)J recombination. We determined the baseline frequencies of these two mutations in mononuclear leukocyte DNA from the umbilical cord blood of newborns and from the peripheral blood of adults. In an initial group of 21 newborns, no t(14;18) translocations were detected (< 0.049 x 10(-7)). The frequency of HPRT exons 2 + 3 deletions was 0.10 x 10(-7) per mononuclear leukocyte, lower than expected based on the T-cell proportion of this cell fraction (55%-70%) and previous results using the T-cell cloning assay (approximately 2-3 x 10(-7) per clonable T-cell). Phytohemagglutinin (PHA), as used in the T-cell cloning assay, was examined for its effect on the frequencies of these mutation events in mononuclear leukocytes from an additional 11 newborns and from 12 adults. There was no significant effect of PHA on t(14;18) translocations which were rare among the newborns (1 detected among 2.7 x 10(8) leukocytes analyzed), and which occurred at frequencies from < 1 x 10(-7) (undetected) to 1.6 x 10(-4) among the adults. The extremely high frequencies of t(14;18)-bearing cells in three adults were due mainly to in vivo expansion of two to six clones. However, PHA appeared to stimulate a modest (although not significant) increase in the frequency of HPRT exons 2 + 3 deletions in the leukocytes of the newborns, from 0.07 x 10(-7) to 0.23 x 10(-7). We show that both the direct PCR assay and the T-cell cloning assay detect similar frequencies of HPRT exons 2 + 3 deletions when calculations are normalized to blood volume, indicating that the apparent discrepancy is probably due to the different population of cells used in the assays. This direct PCR assay may have utility in characterizing the effects of environmental genotoxic agents on this clinically important recombination mechanism.

Spontaneous Apoptosis in Lymphocytes From Patients With Wiskott-Aldrich Syndrome: Correlation of Accelerated Cell Death and Attenuated Bcl-2 Expression

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by thrombocytopenia, eczema, and a progressive deterioration of immune function. WAS is caused by mutations in an intracellular protein, WASP, that is involved in signal transduction and regulation of actin cytoskeleton rearrangement. Because immune dysfunction in WAS may be due to an accelerated destruction of lymphocytes, we examined the susceptibility to apoptosis of resting primary lymphocytes isolated from WAS patients in the absence of exogenous apoptogenic stimulation. We found that unstimulated WAS lymphocytes underwent spontaneous apoptosis at a greater frequency than unstimulated normal lymphocytes. Coincident with increased apoptotic susceptibility, WAS lymphocytes had markedly attenuated Bcl-2 expression, whereas Bax expression did not differ. A negative correlation between the frequency of spontaneous apoptosis and the level of Bcl-2 expression was demonstrated. These data indicate that accelerated lymphocyte destruction by spontaneous induction of apoptosis may be one pathogenic mechanism by which the progressive immunodeficiency in WAS patients develops.

Spontaneous Apoptosis in Lymphocytes From Patients With Wiskott-Aldrich Syndrome: Correlation of Accelerated Cell Death and Attenuated Bcl-2 Expression

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by thrombocytopenia, eczema, and a progressive deterioration of immune function. WAS is caused by mutations in an intracellular protein, WASP, that is involved in signal transduction and regulation of actin cytoskeleton rearrangement. Because immune dysfunction in WAS may be due to an accelerated destruction of lymphocytes, we examined the susceptibility to apoptosis of resting primary lymphocytes isolated from WAS patients in the absence of exogenous apoptogenic stimulation. We found that unstimulated WAS lymphocytes underwent spontaneous apoptosis at a greater frequency than unstimulated normal lymphocytes. Coincident with increased apoptotic susceptibility, WAS lymphocytes had markedly attenuated Bcl-2 expression, whereas Bax expression did not differ. A negative correlation between the frequency of spontaneous apoptosis and the level of Bcl-2 expression was demonstrated. These data indicate that accelerated lymphocyte destruction by spontaneous induction of apoptosis may be one pathogenic mechanism by which the progressive immunodeficiency in WAS patients develops.

Following the development of a CD4 T cell response in vivo: from activation to memory formation

The in vivo differentiation of CD4 T cells from naive to memory cells was followed after their adoptive transfer together with syngeneic dendritic cells into MHC mismatched adoptive hosts lacking lymphocytes and NK cells. Functional and molecular changes were measured as the antigenic stimulus, provided by the cotransferred dendritic cells, disappeared. Memory cells as opposed to effector cells show an inversion in the relative expression of Bcl-2 family members in favor of antiapoptotic molecules, and compared with naive cells they have an increased ratio of bcl-xL to bcl-2. They differ qualitatively from naive T cells, suggesting that accelerated CD4 memory responses can occur without the need for increased frequencies of specific T cells.

The central effectors of cell death in the immune system

The immune system relies on cell death to maintain lymphoid homeostasis and avoid disease. Recent evidence has indicated that the caspase family of cysteine proteases is a central effector in apoptotic cell death and is absolutely responsible for many of the morphological features of apoptosis. Cell death, however, can occur through caspase-independent and caspase-dependent pathways. In the case of cells that are irreversibly neglected or damaged, death occurs even in the absence of caspase activity. In contrast, healthy cells require caspase activation to undergo cell death induced by surface receptors. This review summarizes the current understanding of these two pathways of cell death in the immune system.

Genetic models of abnormal apoptosis in lymphocytes

Apoptosis is a critical mechanism for regulating cell numbers during development, normal responses to hormones and other stimuli, and immune and inflammatory reactions. Recent advances in defining the biochemical mechanisms of cell death, and the development of animal models with isolated defects in cell death pathways, have led to an increasing appreciation of the pathophysiologic importance of lymphocyte apoptosis. In this article, we review our current understanding of the pathways and roles of apoptosis in lymphocytes, with an emphasis on transgenic and knockout models. We also summarize the relevance of these animal models to human diseases.

Protective function of von Hippel-Lindau protein against impaired protein processing in renal carcinoma cells

The absence of functional von Hippel-Lindau (VHL) tumor suppressor gene leads to the development of neoplasias characteristic of VHL disease, including renal cell carcinoma (RCC). Here, we compared the sensitivity of RCC cells lacking VHL gene function with that of RCC cells expressing the wild-type VHL gene (wtVHL) after exposure to various stresses. While the response to most treatments was not affected by the VHL gene status, glucose deprivation was found to be much more cytotoxic for RCC cells lacking VHL gene function than for wtVHL-expressing cells. The heightened sensitivity of VHL-deficient cells was not attributed to dissimilar energy requirements or to differences in glucose uptake, but more likely reflects a lesser ability of VHL-deficient cells to handle abnormally processed proteins arising from impaired glycosylation. In support of this hypothesis, other treatments which act through different mechanisms to interfere with protein processing (i.e., tunicamycin, brefeldin A, and azetidine) were also found to be much more toxic for VHL-deficient cells. Furthermore, ubiquitination of cellular proteins was elevated in VHL-deficient cells, particularly after glucose deprivation, supporting a role for the VHL gene in ubiquitin-mediated proteolysis. Accordingly, the rate of elimination of abnormal proteins was lower in cells lacking a functional VHL gene than in wtVHL-expressing cells. Thus, pVHL appears to participate in the elimination of misprocessed proteins, such as those arising in the cell due to the unavailability of glucose or to other stresses.

Expression and function of Fas and Fas ligand on peripheral blood lymphocytes in normal subjects

We investigated the expression and function of Fas and Fas ligand (FasL) on peripheral blood lymphocytes (PBLs). The cells were stimulated with various cytokines or 12-0-tetradecanoyl phorbol 13-acetate (PMA) plus ionomycin. About 30% of unstimulated PBLs expressed Fas, and the expression was augmented by interleukin-1beta (IL-1beta), IL-2, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), or PMA plus ionomycin. Although only minimal FasL expression was detected on unstimulated PBLs, FasL expression was markedly induced by IL-2 or PMA plus ionomycin, suggesting that Fas and FasL were both expressed on IL-2-stimulated or PMA-plus-ionomycin-stimulated PBLs. Although IL-2-stimulated or PMA-plus-ionomycin-stimulated PBLs were positive for both Fas and FasL, no significant increase in apoptosis was demonstrated in these activated PBLs. In addition, treatment of PBLs with IL-2 or PMA plus ionomycin did not change anti-Fas-induced apoptosis, although these activated PBLs expressed Fas strongly when compared with unstimulated PBLs. Only IL-2-stimulated or PMA-plus-ionomycin-stimulated PBLs killed Fas+ target cells efficiently via the interaction of Fas on target cells with FasL of PBLs. Bcl-2 was constitutively expressed on unstimulated PBLs, but its expression was significantly augmented by IL-2 or PMA plus ionomycin. The expression of Bax was clearly induced only on IL-2-stimulated or PMA-plus-ionomycin-stimulated PBLs and that of other Bcl-2 family proteins such as Bcl-x and Bad could not be detected on human PBLs, including IL-2-stimulated or PMA-plus-ionomycin-stimulated PBLs. Our results suggest that PBLs activated by IL-2 or PMA plus ionomycin express both Fas and FasL and that they kill Fas+ target cells by using FasL on the surface. The resistance of these activated PBLs to Fas-mediated apoptosis may be due to the augmented Bcl-2 expression or the presence of Bcl-2:Bax heterodimers on these cells.

The Bcl-2 gene family and apoptosis

Apoptosis, or programmed cell death, is an essential process for normal embryonic development, maintaining homeostasis in adult tissues, and suppressing carcinogenesis. The bcl-2 protein, discovered in association with follicular lymphoma, plays a prominent role in controlling apoptosis and enhancing cell survival in response to diverse apoptotic stimuli. The evolutionarily conserved bcl-2 protein is now recognized as being a member of a family of related proteins which can be categorized as death agonists or death antagonists. Progress in defining the role of bcl-2 and its family members in regulating apoptosis is rapidly advancing. This review describes, in detail, current bcl-2 family members and the possible mechanisms of function which allow the bcl-2 family of proteins to either promote or suppress cell death.

Bcl-2 obstructs negative selection of autoreactive, hypermutated antibody V regions during memory B cell development

We analyzed the participation of a predominant B cell clonotype in the anti-arsonate immune response of mice in which Bcl-2 expression was enforced in B cells. Many of the antibodies expressed by the arsonate-induced memory compartment of these mice were "dual-reactive," displaying increased affinity acquired via V region somatic hypermutation for both arsonate and the autoantigen DNA. The hypermutated antibodies expressed by the anti-arsonate memory B cell compartment of normal mice have increased affinity for arsonate but lack measurable affinity for DNA. Thus, interference with apoptotic pathways allows developing memory B cells that have acquired autoreactivity to bypass a peripheral tolerance checkpoint. These data demonstrate that both positive and negative selection, working in concert with V gene somatic hypermutation, result in the "specificity maturation" of the antibody response.