Influence of TRP53 Status on FAS Membrane Localization, CFLAR (c-FLIP) Ubiquitinylation, and Sensitivity of GC-2spd (ts) Cells to Undergo FAS-Mediated Apoptosis1

Prominin-1 deletion results in spermatogenic impairment, sperm morphological defects, and infertility in mice

Purpose

Spermatogenesis is a complex process orchestrated by several essential genes. Prominin-1 (Prom1/PROM1) is a gene that is expressed in the testis but with a poorly understood role in spermatogenesis.

Methods

We used Prom1 knockout (Prom1 KO) mice to assess the role of Prom1 in spermatogenesis. To this end, we performed immunohistochemistry, immunofluorescence, western blotting, β-galactosidase staining, and apoptosis assay. Additionally, we analyzed the morphology of sperm and assessed litter sizes.

Results

We observed that PROM1 is localized to the dividing spermatocytes in seminiferous epithelial cells, sperm, and columnar epithelium in the epididymis. In the Prom1 KO testis, an aberrant increase in apoptotic cells and a decrease in proliferating seminiferous epithelial cells were observed. Cellular FLICE-like inhibitory protein (c-FLIP) and extracellular signal-regulated kinase 1/2 (ERK1/2) expression were also significantly decreased in Prom1 KO testis. In addition, a significantly increased number of epididymal spermatozoa with abnormal morphology and less motility was found in Prom1 KO mice.

Conclusions

PROM1 maintains spermatogenic cell proliferation and survival via c-FLIP expression in the testis. It is also involved in sperm motility and fertilization potential. The mechanism underlying the effect of Prom1 on sperm morphology and motility remains to be identified.

Different Approaches for the Profiling of Cancer Pathway-Related Genes in Glioblastoma Cells

Deregulation of signalling pathways that regulate cell growth, survival, metabolism, and migration can frequently lead to the progression of cancer. Brain tumours are a large group of malignancies characterised by inter- and intratumoral heterogeneity, with glioblastoma (GBM) being the most aggressive and fatal. The present study aimed to characterise the expression of cancer pathway-related genes (n = 84) in glial tumour cell lines (A172, SW1088, and T98G). The transcriptomic data obtained by the qRT-PCR method were compared to different control groups, and the most appropriate control for subsequent interpretation of the obtained results was chosen. We analysed three widely used control groups (non-glioma cells) in glioblastoma research: Human Dermal Fibroblasts (HDFa), Normal Human Astrocytes (NHA), and commercially available mRNAs extracted from healthy human brain tissues (hRNA). The gene expression profiles of individual glioblastoma cell lines may vary due to the selection of a different control group to correlate with. Moreover, we present the original multicriterial decision making (MCDM) for the possible characterization of gene expression profiles. We observed deregulation of 75 genes out of 78 tested in the A172 cell line, while T98G and SW1088 cells exhibited changes in 72 genes. By comparing the delta cycle threshold value of the tumour groups to the mean value of the three controls, only changes in the expression of 26 genes belonging to the following pathways were identified: angiogenesis FGF2; apoptosis APAF1, CFLAR, XIAP; cellular senescence BM1, ETS2, IGFBP5, IGFBP7, SOD1, TBX2; DNA damage and repair ERCC5, PPP1R15A; epithelial to mesenchymal transition SNAI3, SOX10; hypoxia ADM, ARNT, LDHA; metabolism ATP5A1, COX5A, CPT2, PFKL, UQCRFS1; telomeres and telomerase PINX1, TINF2, TNKS, and TNKS2. We identified a human astrocyte cell line and normal human brain tissue as the appropriate control group for an in vitro model, despite the small sample size. A different method of assessing gene expression levels produced the same disparities, highlighting the need for caution when interpreting the accuracy of tumorigenesis markers.

Regulation of extrinsic apoptotic signaling by c-FLIP: towards targeting cancer networks

The extrinsic pathway is mediated by death receptors (DRs), including CD95 (APO-1/Fas) or TRAILR-1/2. Defects in apoptosis regulation lead to cancer and other malignancies. The master regulator of the DR networks is the cellular FLICE inhibitory protein (c-FLIP). In addition to its key role in apoptosis, c-FLIP may exert other cellular functions, including control of necroptosis, pyroptosis, nuclear factor κB (NF-κB) activation, and tumorigenesis. To gain further insight into the molecular mechanisms of c-FLIP action in cancer networks, we focus on the structure, isoforms, interactions, and post-translational modifications of c-FLIP. We also discuss various avenues to target c-FLIP in cancer cells for therapeutic benefit.

FAIM Is a Non-redundant Defender of Cellular Viability in the Face of Heat and Oxidative Stress and Interferes With Accumulation of Stress-Induced Protein Aggregates

A key element of cellular homeostasis lies in the way in which misfolded and dysfunctional proteins are handled. Cellular pathways that include proteasomal destruction and autophagic disposal are components of normal proteostasis. Here we report a novel molecule that plays a non-redundant role in maintaining homeostasis, Fas Apoptosis Inhibitory Molecule (FAIM). FAIM is highly conserved throughout evolution and bears no homology to any other protein. We found that FAIM counteracts heat and oxidative stress-induced loss of cell viability. FAIM is recruited to ubiquitinated proteins induced by cellular stress and the levels of stress-induced protein aggregates are much greater in FAIM-deficient cell lines. Primary fibroblasts from FAIM-deficient mice showed the same proteostasis deficits as cell lines. Administration of a mediator of oxidative stress to FAIM-deficient animals induced more ubiquitinated protein aggregates and more organ damage as compared to wild type mice. These results identify a completely new actor that protects cells against stress-induced loss of viability by preventing protein aggregation.

YTHDF2 promotes spermagonial adhesion through modulating MMPs decay via m6A/mRNA pathway

As the foundation of male fertility, spermatogenesis is a complicated and highly controlled process. YTHDF2 plays regulatory roles in biological processes through accelerating the degradation of target mRNAs. However, the function of YTHDF2 in spermatogenesis remains elusive. Here, we knocked out Ythdf2 in mouse spermatogonia via CRISPR/Cas9, and found that depletion of Ythdf2 mainly downregulated the expression of matrix metallopeptidase (MMPs), thus affecting cell adhesion and proliferation. m⁶A-IP-PCR and RIP-PCR analysis showed that Mmp3, Mmp13, Adamts1 and Adamts9 were modified with m⁶A and simultaneously interacted with YTHDF2. Moreover, inhibition of Mmp13 partially rescued the phenotypes in Ythdf2-KO cells. Taken together, YTHDF2 regulates cell-matrix adhesion and proliferation through modulating the expression of Mmps by the m⁶A/mRNA degradation pathway.

Dysregulated signaling, proliferation and apoptosis impact on the pathogenesis of TCRγδ+ T cell large granular lymphocyte leukemia

TCRγδ+ T-LGL leukemia is a rare form of chronic mature T cell disorders in elderly, which is generally characterized by a persistently enlarged CD3+CD57+TCRγδ+ large granular lymphocyte population in the peripheral blood with a monoclonal phenotype. Clinically, the disease is heterogeneous, most patients being largely asymptomatic, although neutropenia, fatigue and B symptoms and underlying diseases such as autoimmune diseases or malignancies are also often observed. The etiology of TCRγδ+ T-LGL proliferations is largely unknown. Here, we aimed to investigate underlying molecular mechanisms of these rare proliferations by performing gene expression profiling of TCRγδ+ T-LGL versus normal TCRγδ+ T cell subsets. From our initial microarray dataset we observed that TCRγδ+ T-LGL leukemia forms a separate group when compared with different healthy control TCRγδ+ T cell subsets, correlating best with the healthy TemRA subset. The lowest correlation was seen with the naive subset. Based on specific comparison between healthy control cells and TCRγδ+ T-LGL leukemia cells we observed up-regulation of survival, proliferation and hematopoietic system related genes, with a remarkable down-regulation of apoptotic pathway genes. RQ-PCR validation of important genes representative for the dataset, including apoptosis (XIAP, CASP1, BCLAF1 and CFLAR), proliferation/development (ID3) and inflammation (CD28, CCR7, CX3CR1 and IFNG) processes largely confirmed the dysregulation in proliferation and apoptosis. Based on these expression data we conclude that TCRγδ+ T-LGL leukemia is likely the result of an underlying aberrant molecular mechanisms leading to increased proliferation and reduced apoptosis.

A Testis-Specific Long Non-Coding RNA, lncRNA-Tcam1, Regulates Immune-Related Genes in Mouse Male Germ Cells

Spermatogenesis is precisely controlled by hormones from the hypothalamus-pituitary-gonadal axis and testis-specific genes, but the regulatory mechanism is not fully understood. Recently, a large number of long non-coding RNAs (lncRNAs) are found to be transcribed at each stage of meiosis of male germ cells, and their functions in spermatogenesis have yet to be fully investigated. lncRNA-testicular cell adhesion molecule 1 (lncRNA-Tcam1) is a nuclear lncRNA which is specifically expressed in mouse male germ cells and presumed to play a role in gene regulation during meiosis. Here, we present the identification of potential target genes of lncRNA-Tcam1 using spermatocyte-derived GC-2spd(ts) cells. Initially, 55 target gene candidates were detected by RNA-sequencing of two GC-2spd(ts) cell clones that were stably transfected with transgenes to express lncRNA-Tcam1 at different levels. Expression of 21 genes of the candidates was found to be correlated with lncRNA-Tcam1 at 7-14 postnatal days, when lncRNA-Tcam1 expression was elevated. Subsequently, we examined expression levels of the 21 genes in other two GC-2spd(ts) clones, and 11 genes exhibited the correlation with lncRNA-Tcam1. Induction of lncRNA-Tcam1 transcription using the Tet-off system verified that six genes, Trim30a, Ifit3, Tgtp2, Ifi47, Oas1g, and Gbp3, were upregulated in GC-2spd(ts) cells, indicating that lncRNA-Tcam1 is responsible for the regulation of gene expression of the six genes. In addition, five of the six genes, namely, Ifit3, Tgtp2, Ifi47, Oas1g, and Gbp3, are immune response genes, and Trim30a is a negative regulator of immune response. Altogether, the present study suggests that lncRNA-Tcam1 is responsible for gene regulation for the immune response during spermatogenesis.

MiR-122 partly mediates the ochratoxin A-induced GC-2 cell apoptosis

Ochratoxin A (OTA) is a mycotoxin which has been shown to be nephrotoxic, hepatotoxic, and immunotoxic to animals, and mainly exists in the mildew grain. MicroRNAs (miRNAs) regulate a wide variety of cellular processes. However, the toxic effects of OTA on the germ cell and whether miRNAs mediate the effects of OTA-induced GC-2 cell apoptosis are still not clear. In the present study, OTA treatment resulted in a dose-dependent increase apoptosis in GC-2 cells. MiR-122 was increased in the OTA-treated GC-2 cells. It showed that Bcl-w was down-regulated after OTA treatment, and caspase-3 was obviously activated. Cyclin G1 (CCNG1) was significantly decreased, and inversely the expression of p53 was increased. Inhibition of miR-122 partly relieved the OTA-induced GC-2 cell apoptosis. These results indicate that OTA induces GC-2 cell apoptosis by causing the increase of caspase-3 activity and that miR-122 partly mediates the OTA-induced cell apoptosis.

Decreased expression of SAM68 in human testes with spermatogenic defects

OBJECTIVE

To assess the expression patterns of SAM68 in the testes of azoospermic patients with normal and abnormal spermatogenesis.

DESIGN

Retrospective study and in vitro study.

SETTING

University hospital.

PATIENT(S)

Testicular biopsies of azoospermic men with normal spermatogenesis (OAZ; n=20), with maturation arrest at the spermatocyte stage (MA; n=20), and with Sertoli cell-only syndrome (SCOS; n=10).

INTERVENTION(S)

No interventions with patients. Knockdown of Sam68 was performed in the GC-2spd(ts) cell line.

MAIN OUTCOME MEASURE(S)

SAM68 expression was analyzed using quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, and immunohistochemistry analysis in tissues. Moreover, Sam68 was knocked down in GC-2spd(ts) cells. Cell viability was measured using the MTT assay, and the apoptosis rate was detected using flow cytometry with the Annexin V-FITC kit.

RESULT(S)

Using qRT-PCR, the expression level of testicular SAM68 mRNA in MA and SCOS patients was statistically reduced compared with in OAZ patients. In addition, using qRT-PCR, Western blot, and immunohistochemistry analyses, mRNA and protein expressions of SAM68 were absent or barely detectable in testicular tissues in 45% (9 of 20) of patients with MA and in all patients with SCOS. Furthermore, decreased expression of Sam68 suppressed germ cell proliferation and induced apoptosis in transfected GC-2spd(ts) cells.

CONCLUSION(S)

Deficient SAM68 expression was observed in the human testis with MA at the spermatocyte stage and SCOS. These results may offer new perspectives on the molecular basis of abnormal spermatogenesis.

Poor antibody validation is a challenge in biomedical research: a case study for detection of c-FLIP

Successful translation of findings derived from preclinical studies into effective therapies is critical in biomedical research. Lack of robustness and reproducibility of the preclinical data, due to insufficient number of repeats, inadequate cell-based and mouse models contribute to the poor success rate. Antibodies are widely used in preclinical research, notably to determine the expression of potential therapeutic targets in tissues of interest, including tumors, but also to identify disease and/or treatment response biomarkers. We sought to determine whether the current antibody characterization standards in preclinical research are sufficient to ensure reliability of the data found in peer-reviewed publications. To address this issue, we used detection of the protein c-FLIP, a major factor of resistance to apoptosis, as a proof of concept. Accurate detection of endogenous c-FLIP levels in the preclinical settings is imperative since it is considered as a potential theranostic biomarker. Several sources of c-FLIP antibodies validated by their manufacturer and recommended for western blotting were therefore rigorously tested. We found a wide divergence in immune recognition properties. While these antibodies have been used in many publications, our results show that several of them failed to detect endogenous c-FLIP protein by Western blotting. Our results suggest that antibody validation standards are inadequate, and that systematic use of genetic knockdowns and/or knockouts to establish proof of specificity is critical, even for antibodies previously used in the scientific literature. Because antibodies are fundamental tools in both preclinical and clinical research, ensuring their specificity is crucial.

Targeting the Anti-Apoptotic Protein c-FLIP for Cancer Therapy

Cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) is a major resistance factor and critical anti-apoptotic regulator that inhibits tumor necrosis factor-alpha (TNF-alpha), Fas-L, and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis as well as chemotherapy-triggered apoptosis in malignant cells. c-FLIP is expressed as long (c-FLIP(L)), short (c-FLIP(S)), and c-FLIP(R) splice variants in human cells. c-FLIP binds to FADD and/or caspase-8 or -10 in a ligand-dependent and-independent fashion, which in turn prevents death-inducing signaling complex (DISC) formation and subsequent activation of the caspase cascade. Moreover, c-FLIP(L) and c-FLIP(S) are known to have multifunctional roles in various signaling pathways, as well as activating and/or upregulating several cytoprotective signaling molecules. Upregulation of c-FLIP has been found in various tumor types, and its downregulation has been shown to restore apoptosis triggered by cytokines and various chemotherapeutic agents. Hence, c-FLIP is an important target for cancer therapy. For example, small interfering RNAs (siRNAs) that specifically knockdown the expression of c-FLIP(L) in diverse human cancer cell lines augmented TRAIL-induced DISC recruitment and increased the efficacy of chemotherapeutic agents, thereby enhancing effector caspase stimulation and apoptosis. Moreover, small molecules causing degradation of c-FLIP as well as decreasing mRNA and protein levels of c-FLIP(L) and c-FLIP(S) splice variants have been found, and efforts are underway to develop other c-FLIP-targeted cancer therapies. This review focuses on (1) the functional role of c-FLIP splice variants in preventing apoptosis and inducing cytokine and drug resistance; (2) the molecular mechanisms that regulate c-FLIP expression; and (3) strategies to inhibit c-FLIP expression and function.

FLIP: a flop for execution signals

Resistance to apoptosis is one of the established hallmarks of cancer cells. This is a function of an imbalance between the proteins that facilitate death execution and those that inhibit apoptosis or promote cell proliferation. The anti-apoptotic protein, FLICE inhibitory protein (FLIP), first identified as a viral protein, is over-expressed in a variety of human pathologies. Initial observations linked FLIP expression to inhibition of death receptor induced apoptosis, due to its structural homology to the cysteine protease, caspase-8. FLIP impedes full processing of pro-caspase-8 to its active form and its release to the cytosol, and by doing so blocks apoptotic signaling downstream of the membrane death initiating signaling complex (DISC). Recent observations have highlighted the complex regulation of this protein and its cross talk with diverse signaling networks and metabolic processes. As FLIP expression is directly associated with chemotherapy resistance, a better understanding of its genomic organization, gene transcription, as well as post-transcriptional regulation could yield novel targets with potential therapeutic implications against drug refractory cancers. In this short review, we provide a brief overview of the structural and functional biology of this somewhat complex protein with direct relevance to carcinogenesis.

MicroRNA-34c enhances murine male germ cell apoptosis through targeting ATF1

Background

MicroRNAs (miRNAs) play vital regulatory roles in many cellular processes. The expression of miRNA (miR)-34c is highly enriched in adult mouse testis, but its roles and underlying mechanisms of action are not well understood.

Methodology/Principal Findings

In the present study, we show that miR-34c is detected in mouse pachytene spermatocytes and continues to be highly expressed in spermatids. To explore the specific functions of miR-34c, we have established an in vivo model by transfecting miR-34c inhibitors into primary spermatocytes to study the loss-of-function of miR-34c. The results show that silencing of miR-34c significantly increases the Bcl-2/Bax ratio and prevents germ cell from apoptosis induced by deprivation of testosterone. Moreover, ectopic expression of the miR-34c in GC-2 cell trigger the cell apoptosis with a decreased Bcl-2/Bax ratio and miR-34c inhibition lead to a low spontaneous apoptotic ratio and an increased Bcl-2/Bax ratio. Furthermore, ectopic expression of miR-34c reduces ATF1 protein expression without affecting ATF1 mRNA level via directly binding to ATF1's 3′UTR, indicating that ATF1 is one of miR-34c's target genes. Meanwhile, the knockdown of ATF1 significantly decreases the Bcl-2/Bax ratio and triggers GC-2 cell apoptosis. Inhibition of miR-34c does not decrease the GC-2 cell apoptosis ratio in ATF1 knockdown cells.

Conclusions/Significance

Our study shows for the first time that miR-34c functions, at least partially, by targeting the ATF1 gene in germ cell apoptosis, providing a novel mechanism with involvement of miRNA in the regulation of germ cell apoptosis.

Transient protection from heat-stress induced apoptotic stimulation by metastasis-associated protein 1 in pachytene spermatocytes

BACKGROUND

Deregulated thermal factors have been frequently implicated in the pathogenesis of male infertility, but the molecular basis through which certain responses are directed remain largely unknown. We previously reported that overexpression of exogenous Metastasis-associated protein 1 (MTA1) protects spermatogenic tumor cells GC-2spd (ts) against heat-induced apoptosis. To further dissect the underlying mechanism, we addressed here the fine coordination between MTA1 and p53 in pachytene spermatocytes upon hyperthermal stimulation.

METHODOLOGY/PRINCIPAL FINDINGS

High level of MTA1 expression sustained for 1.5 h in primary spermatocytes after heat stress before a notable decrease was detected conversely correlated to the gradual increase of acetylation status of p53 and of p21 level. Knockdown of the endogenous MTA1 in GC-2spd (ts) elevated the acetylation of p53 by diminishing the recruitment of HDAC2 and thereafter led to a dramatic increase of apoptosis after heat treatment. Consistent with this, in vivo interference of MTA1 expression in the testes of C57BL/6 mice also urged an impairment of the differentiation of spermatocytes and a disruption of Sertoli cell function due to the elevated apoptotic rate after heat stress. Finally, attenuated expression of MTA1 of pachytene spermatocytes was observed in arrested testes (at the round spermatid level) of human varicocele patients.

CONCLUSIONS

These data underscore a transient protective effect of this histone modifier in primary spermatocytes against heat-stress, which may operate as a negative coregulator of p53 in maintenance of apoptotic balance during early phase after hyperthermal stress.

FasL gene-deficient mice display a limited disruption in spermatogenesis and inhibition of mono-(2-ethylhexyl) phthalate-induced germ cell apoptosis

FasL (TNFSF6, CD95L) is hypothesized to trigger testicular germ cell apoptosis that normally occurs during a distinct peripubertal period as well as in response to toxicant-induced Sertoli cell injury. To test this hypothesis, we evaluated the testis of FasL gene–deficient mice (FasL^−/−) at two distinct developmental ages (postnatal day [PND] 28 and 44) and after toxicant-induced Sertoli cell injury. Testicular cross sections from peripubertal (PND 28) FasL^−/− mice showed significant increases in the basal germ cell apoptotic index (AI; 20.58 ± 4.59) as compared to the testis of C57BL/6J wild-type mice (5.16 ± 0.08) and closely correlated with increased expression of TRAIL protein in the testis of FasL^−/− mice. A limited, but significant, number of seminiferous tubules in the testis of PND 28 FasL^−/− mice showed a severe loss of germ cells with only Sertoli cells present. In contrast, no apparent gross histological changes were observed in the testis of adult (PND 44) FasL^−/− mice. However, PND 44 FasL^−/− mice did show a 51% reduction in homogenization-resistant elongate spermatids as compared to age-matched C57BL/6J mice. Exposure of PND 28 FasL^−/− mice to mono-(2-ethylhexyl) phthalate (MEHP), a well-described Sertoli cell toxicant, unexpectedly caused a rapid decrease in the germ cell AI that paralleled increased levels of the CFLAR (c-FLIP) protein, a known inhibitor of death receptor signaling. In contrast, MEHP treatment did not decrease c-FLIP levels in PND 28 C57BL/6J mice. Taken together, these findings indicate that FasL protein expression is required during the peripubertal period for the proper regulation of germ cell apoptosis that occurs normally during this period. The influence of FasL on the cellular regulation of c-FLIP protein levels appears to be a unique mechanism for modulating germ cell apoptosis after toxicant-induced Sertoli cell injury.

Pretreatment with ascorbic acid prevents lethal gastrointestinal syndrome in mice receiving a massive amount of radiation

While bone marrow or stem cell transplantation can rescue bone marrow aplasia in patients accidentally exposed to a lethal radiation dose, radiation-induced irreversible gastrointestinal damage (GI syndrome) is fatal. We investigated the effects of ascorbic acid on radiation-induced GI syndrome in mice. Ascorbic acid (150 mg/kg/day) was orally administered to mice for 3 days, and then the mice underwent whole body irradiation (WBI). Bone marrow transplantation (BMT) 24 h after irradiation rescued mice receiving a WBI dose of less than 12 Gy. No mice receiving 14 Gy-WBI survived, because of radiation-induced GI syndrome, even if they received BMT. However, pretreatment with ascorbic acid significantly suppressed radiation-induced DNA damage in the crypt cells and prevented denudation of intestinal mucosa; therefore, ascorbic acid in combination with BMT rescued mice after 14 Gy-WBI. DNA microarray analysis demonstrated that irradiation up-regulated expressions of apoptosis-related genes in the small intestine, including those related to the caspase-9-mediated intrinsic pathway as well as the caspase-8-mediated extrinsic pathway, and down-regulated expressions of these genes in ascorbic acid-pretreated mice. Thus, pretreatment with ascorbic acid may effectively prevent radiation-induced GI syndrome.

Akt promotes chemoresistance in human ovarian cancer cells by modulating cisplatin-induced, p53-dependent ubiquitination of FLICE-like inhibitory protein

Although Akt is a determinant of cisplatin (cis-diaminedichloroplatinum (CDDP)) resistance in ovarian cancer cells, which is related in part to its inhibitory action on p53 activation, precisely how Akt confers CDDP resistance is unclear. In this study, we show that CDDP induced p53-dependent Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE)-like inhibitory protein (FLIP) degradation in chemosensitive ovarian cancer cells but not their resistant counterparts. CDDP induced FLIP-p53-Itch interaction, colocalization and FLIP ubiquitination in chemosensitive but not chemoresistant ovarian cancer cells. Moreover, although activated Akt inhibited CDDP-induced FLIP degradation and apoptosis in sensitive cells, these responses were facilitated by dominant-negative Akt expression in chemoresistant cells. Inhibition of Akt function also facilitated p53-FLIP interaction and FLIP ubiquitination, which were attenuated by p53 silencing. These results suggest that Akt confers resistance, in part, by modulating CDDP-induced, p53-dependent FLIP ubiquitination. Understanding the precise etiology of chemoresistance may improve treatment for ovarian cancer.

B-cell-activating factor inhibits CD20-mediated and B-cell receptor-mediated apoptosis in human B cells

B-cell-activating factor (BAFF) is a survival and maturation factor for B cells belonging to the tumour necrosis factor superfamily. Among three identified functional receptors, the BAFF receptor (BAFF-R) is thought to be responsible for the effect of BAFF on B cells though details of how remain unclear. We determined that a hairy-cell leukaemia line, MLMA, expressed a relatively high level of BAFF-R and was susceptible to apoptosis mediated by either CD20 or B-cell antigen receptor (BCR). Using MLMA cells as an in vitro model of mature B cells, we found that treatment with BAFF could inhibit apoptosis mediated by both CD20 and BCR. We also observed, using immunoblot analysis and microarray analysis, that BAFF treatment induced activation of nuclear factor-kappaB2 following elevation of the expression level of Bcl-2, which may be involved in the molecular mechanism of BAFF-mediated inhibition of apoptosis. Interestingly, BAFF treatment was also found to induce the expression of a series of genes, such as that for CD40, related to cell survival, suggesting the involvement of a multiple mechanism in the BAFF-mediated anti-apoptotic effect. MLMA cells should provide a model for investigating the molecular basis of the effect of BAFF on B cells in vitro and will help to elucidate how B cells survive in the immune system in which BAFF-mediated signalling is involved.

Cellular FLICE-like inhibitory protein (C-FLIP): a novel target for cancer therapy

Cellular FLICE-like inhibitory protein (c-FLIP) has been identified as a protease-dead, procaspase-8-like regulator of death ligand-induced apoptosis, based on observations that c-FLIP impedes tumor necrosis factor-alpha (TNF-alpha), Fas-L, and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis by binding to FADD and/or caspase-8 or -10 in a ligand-dependent fashion, which in turn prevents death-inducing signaling complex (DISC) formation and subsequent activation of the caspase cascade. c-FLIP is a family of alternatively spliced variants, and primarily exists as long (c-FLIP(L)) and short (c-FLIP(S)) splice variants in human cells. Although c-FLIP has apoptogenic activity in some cell contexts, which is currently attributed to heterodimerization with caspase-8 at the DISC, accumulating evidence indicates an anti-apoptotic role for c-FLIP in various types of human cancers. For example, small interfering RNAs (siRNAs) that specifically knocked down expression of c-FLIP(L) in diverse human cancer cell lines, e.g., lung and cervical cancer cells, augmented TRAIL-induced DISC recruitment, and thereby enhanced effector caspase stimulation and apoptosis. Therefore, the outlook for the therapeutic index of c-FLIP-targeted drugs appears excellent, not only from the efficacy observed in experimental models of cancer therapy, but also because the current understanding of dual c-FLIP action in normal tissues supports the notion that c-FLIP-targeted cancer therapy will be well tolerated. Interestingly, Taxol, TRAIL, as well as several classes of small molecules induce c-FLIP downregulation in neoplastic cells. Efforts are underway to develop small-molecule drugs that induce c-FLIP downregulation and other c-FLIP-targeted cancer therapies. In this review, we assess the outlook for improving cancer therapy through c-FLIP-targeted therapeutics.

Uncoupling protein 2 protects testicular germ cells from hyperthermia-induced apoptosis

The mRNA of the mitochondrial uncoupling protein 2 (UCP2) was up-regulated by cryptorchidism, a testicular hyperthermic condition under which germ cells undergo severe apoptosis. We investigated whether UCP2 was able to protect germ cells from hyperthermia-induced apoptosis. UCP2 was predominantly present in elongate spermatids under normal conditions, and was detected in all germ cells with its level significantly increased if the testes were exposed to 43 degrees C for 5 min. Such a short heat exposure was non-lethal and enabled the preconditioned cells to be resistant to apoptosis induced by a longer hyperthermic treatment (15 min). While hyperthermia resulted in oxidative stress in mouse testes, it did not change the total anti-oxidative capacity. Indeed, overexpression of UCP2 in the GC-2 germ cell line protected the cells from radical oxygen species (ROS)-induced apoptosis. Taken together, we propose that UCP2 may represent an effective weaponry used by germ cells to combat ROS-induced apoptosis.

Testicular germ cell sensitivity to TRAIL-induced apoptosis is dependent upon p53 expression and is synergistically enhanced by DR5 agonistic antibody treatment

The ability of the TRAIL/DR5 signaling pathway to induce apoptosis has generally been limited to tumor cells. Here we report that in primary testis explants, addition of TRAIL (0.5 mug/ml) caused a three-fold increase in germ cell apoptosis. Furthermore, exposure of C57BL/6 mice to the testicular toxicant, mono-(2-ethylhexyl) phthalate (MEHP), caused an increased p53 stability and elevated DR5 mRNA levels coincident with increases in the levels of apoptosis in spermatocytes. To further assess the mechanisms responsible for the sensitivity of germ cells to undergo TRAIL/DR5-mediated apoptosis, we used the germ cell lines GC-1spg and GC-2spd(ts) (a temperature sensitive spermatocyte-like cell line that allows for p53 nuclear localization at 32 degrees C but not 37 degrees C). Addition of TRAIL and the anti-DR5 monoclonal antibody, MD5-1, triggered a robust synergistic increase of apoptosis in p53 permissive GC-2 cells (32 degrees C) but not in GC-1 cells. In addition, DR5 levels on the plasma membrane of permissive cells were considerably enhanced concomitant with p53 expression and after MD5-1 treatment. These data represent the first indication that testicular germ cells, specifically spermatocytes, can undergo TRAIL-mediated apoptosis and the clinically relevant observation that pretreatment with a DR5 monoclonal antibody can greatly sensitize their apoptotic response to TRAIL.

Up-regulation of CD95 (Apo-1/Fas) is associated with spermatocyte apoptosis during the first round of spermatogenesis in the rat

Apoptosis plays a major role in controlling both the rate of sperm production and chromosomal abnormalities in adult male testes. However, little is known on the mechanisms controlling induction and execution of apoptosis under physiological conditions. In this work we have uncovered a major role for the cell death receptor Fas in both the extrinsic and intrinsic pathways in normal germ cell apoptosis. We show here that Fas levels increased significantly in a group of germ cell in 25 d old rats, which were identified as spermatocytes and only a few spermatogonia. In addition, we show that isolated spermatocytes expressing high levels of Fas display activation of caspase-8, -9, -3, -6 and -2, as well as increased levels of intracellular calcium and decreased pH, which coincides with stabilization of p53, and transcriptional activation of PUMA and Fas. Therefore, our data strongly suggests that transcriptional up regulation of Fas could predispose a group of spermatocytes to Fas ligand triggering apoptosis by the extrinsic and intrinsic pathway.

Transcriptional regulation of FasL expression and participation of sTNF-alpha in response to sertoli cell injury

The Fas/FasL signaling pathway has previously been demonstrated to be critical for triggering germ cell apoptosis in response to mono-(2-ethylhexyl)phthalate (MEHP)-induced Sertoli cell injury. Although Sertoli cells ubiquitously express the FasL protein, MEHP-induced germ cell apoptosis appears to tightly correlate with increased levels of Sertoli cell FasL. Here we characterize the transcriptional regulation of the murine FasL gene in Sertoli cells after MEHP exposure. A serial deletion strategy for 1.5 kb of the 5'-upstream activating sequence of the FasL promoter was used to determine transcriptional activity in response to MEHP. Luciferase activity of the FasL promoter in the rat Sertoli cell line ASC-17D revealed that two regions, -500 to -324 and -1250 to -1000, were necessary to drive the inducible transcription of FasL. Sequence analysis of these two regions revealed two cis-regulatory elements, NF-kappaB and Sp-1. By site-directed mutagenesis, electrophoretic mobility shift and chromatin immunoprecipitation assays, it was confirmed that MEHP-induced FasL expression is enhanced through the transcriptional regulation of both NF-kappaB and Sp-1. Experiments performed both in vitro and in vivo revealed that MEHP exposure results in an increased production of sTNF-alpha and that sTNF-alpha-mediated NF-kappaB activation causes robust increases in FasL levels in both the ASC-17D Sertoli cell line and in primary rat Sertoli cell/germ cell co-cultures. In the seminiferous epithelium, Sertoli cells express TNFR1, whereas germ cells produce TNF-alpha. Therefore, sTNF-alpha released by germ cells after MEHP-induced Sertoli cell injury acts upon Sertoli cell TNFR1 and activates NF-kappaB and Sp-1 that consequently causes a robust induction of FasL expression. These novel findings point to a potential "feed-forward" signaling mechanism by which germ cells prompt Sertoli cells to trigger their apoptotic elimination.

Differential apoptotic signaling in primary glial cells infected with herpes simplex virus 1

Microglial cells and astrocytes are glial cell types that perform distinct functions and generate innate immune responses to counter invading pathogens. Herpes simplex virus 1 (HSV-1) is a neurotropic virus that is capable of causing severe, necrotizing encephalitis. HSV-1 infects both of these glial cell types. Microglial cells undergo an abortive infection, yet respond to viral infection by inducing a burst of proinflammatory cytokine and chemokine production. Following this cytokine burst, they rapidly succumb to cell death. In contrast, astrocytes do permit productive viral replication, but do not generate these same innate immune mediators. Although apoptosis has been implicated in a number of acute and chronic neurological disorders, little is known about apoptosis during viral encephalitis. In the present study, the authors investigated the effect of HSV-1 infection on cell survival and studied the mechanisms of cell-death in virus-infected, primary murine glial cells. The authors report that although apoptosis occurred rapidly in microglia, it was delayed during productive infection of astrocytes. Furthermore, microarray studies revealed significant variations in the expression of apoptotic genes between these two types of glial cells, indicating crucial differences in signaling pathways. Intrinsic as well as extrinsic pathways of apoptosis were found to be activated in both glial cell types. Specifically, genes involved in the tumor necrosis factor (TNF) signaling pathway were predominantly up-regulated in microglia, whereas genes of the Fas pathway were induced during HSV infection of astrocytes.