Tissue distribution of Diablo/Smac revealed by monoclonal antibodies

Spermatogenesis in mammals: proteomic insights

Spermatogenesis is a highly sophisticated process involved in the transmission of genetic heritage. It includes halving ploidy, repackaging of the chromatin for transport, and the equipment of developing spermatids and eventually spermatozoa with the advanced apparatus (e.g., tightly packed mitochondrial sheat in the mid piece, elongating of the tail, reduction of cytoplasmic volume) to elicit motility once they reach the epididymis. Mammalian spermatogenesis is divided into three phases. In the first the primitive germ cells or spermatogonia undergo a series of mitotic divisions. In the second the spermatocytes undergo two consecutive divisions in meiosis to produce haploid spermatids. In the third the spermatids differentiate into spermatozoa in a process called spermiogenesis. Paracrine, autocrine, juxtacrine, and endocrine pathways all contribute to the regulation of the process. The array of structural elements and chemical factors modulating somatic and germ cell activity is such that the network linking the various cellular activities during spermatogenesis is unimaginably complex. Over the past two decades, advances in genomics have greatly improved our knowledge of spermatogenesis, by identifying numerous genes essential for the development of functional male gametes. Large-scale analyses of testicular function have deepened our insight into normal and pathological spermatogenesis. Progress in genome sequencing and microarray technology have been exploited for genome-wide expression studies, leading to the identification of hundreds of genes differentially expressed within the testis. However, although proteomics has now come of age, the proteomics-based investigation of spermatogenesis remains in its infancy. Here, we review the state-of-the-art of large-scale proteomic analyses of spermatogenesis, from germ cell development during sex determination to spermatogenesis in the adult. Indeed, a few laboratories have undertaken differential protein profiling expression studies and/or systematic analyses of testicular proteomes in entire organs or isolated cells from various species. We consider the pros and cons of proteomics for studying the testicular germ cell gene expression program. Finally, we address the use of protein datasets, through integrative genomics (i.e., combining genomics, transcriptomics, and proteomics), bioinformatics, and modelling.

Signaling Pathways for Germ Cell Death in Adult Cynomolgus Monkeys (Macaca fascicularis) Induced by Mild Testicular Hyperthermia and Exogenous Testosterone Treatment1

Male contraception has focused, to a great extent, on approaches that induce azoospermia or severe oligospermia through accelerated germ cell apoptosis. Understanding the specific steps in the germ cell apoptotic pathways that are affected by male contraceptives will allow more specific targeting in future contraceptive development. In this study, we have used a nonhuman primate model to characterize the key apoptotic pathway(s) in germ cell death after mild testicular hyperthermia, hormonal deprivation, or combined interventions. Groups of 8 adult (7- to 10-year-old) cynomolgus monkeys (Macaca fascicularis) received one of the following treatments: 1) two empty silastic implants; 2) two 5.5-cm testosterone (T) implants; 3) daily exposure of testes to heat (43 degrees C for 30 min) for 2 consecutive days; and 4) two T implants plus testicular heat exposure for two consecutive days. Testicular biopsies were performed before and at Days 3, 8, and 28 of treatment. Treatment with T, heat, or both led to sustained activation of both mitogen-activated protein kinase (MAPK) 1/3 and MAPK14. Activation of MAPK1/3 and MAPK14 were accompanied by an increase in B-cell leukemia/lymphoma (BCL) 2 levels in both cytosolic and mitochondrial fractions of testicular lysates (BAX levels remained unaffected) and cytochrome c and DIABLO release from mitochondria. These treatments also resulted in inactivation of BCL2 through phosphorylation at serine 70, thereby favoring the death pathway. We conclude that the serine phosphorylation of BCL2 and activation of the MAPK14-mediated mitochondria-dependent pathway are critical for male germ cell death in monkeys.

Two-Dimensional Fluorescence Difference Gel Electrophoresis Analysis of Spermatogenesis in the Rat

The molecular mechanisms underlying normal and pathological spermatogenesis remain poorly understood. We compared protein concentrations in different germ cell types to identify those proteins specifically or preferentially expressed at each stage of rat spermatogenesis. Crude cytosolic protein extracts and reversed-phase HPLC prefractionated cytosolic extracts from spermatogonia, pachytene spermatocytes, and early spermatids were subjected to two-dimensional difference gel electrophoresis (2-D DIGE). By comparing gels and carrying out statistical analyses, we were able to identify 1274 protein spots with relative abundances differing significantly between the three cell types. We found that 265 of these spots displaying highly differential expression (ratio > or = 2.5 between two cell types), identified by mass fingerprinting, corresponded to 123 nonredundant proteins. The proteins clustered into three clades, corresponding to mitotic, meiotic, and post-meiotic cell types. The differentially expressed proteins identified by 2-D DIGE were confirmed and validated by western blotting and immunohistochemistry, in the few cases in which antibodies were available. 2-D DIGE appears a relevant proteomics approach for studying rat germ cell differentiation, allowing the establishment of the precise expression profiles for a relatively large number of proteins during normal spermatogenesis.

Synthetic Smac peptide enhances the effect of etoposide-induced apoptosis in human glioblastoma cell lines

Smac/DIABLO is a mitochondrial protein released into cytosol during the progression of apoptosis. Smac/DIABLO promotes apoptosis by neutralizing the inhibitory effect of the inhibitor of apoptosis proteins (IAPs) on the processing and activity of the effecter of caspase. Here, we generated synthetic Smac peptide which possesses an IAP-binding domain and Drosophila antennapaedia penetration sequence, and examined whether it enhances the effect of the chemotherapeutic agent etoposide in the human glioblastoma cell line. Cellular uptake of Smac peptide in several glioma cell lines was most prominent at 6-12 h after addition. Caspase activity assay showed that our peptide successfully increased the activity of caspase-3 and caspase-9 in etoposide-induced apoptosis. In addition, Smac peptide increased the amount of cleaved PARP (poly ADP-ribose polymerase), but control peptides did not. Moreover, the addition of z-VAD-fmk, a caspase inhibitor, counterbalanced the effect of Smac peptide. Finally, we demonstrated that Smac peptide could enhance the growth inhibition effect of etoposide compared with control peptides. These results suggest that synthetic Smac peptide may be a new molecular targeting anti-tumor therapy for human glioblastoma.

Nuclear Factor-κB Represses Hypoxia-Induced Mitochondrial Defects and Cell Death of Ventricular Myocytes

Background— Oxygen deprivation for prolonged periods of time provokes cardiac cell death and ventricular dysfunction. Preventing inappropriate cardiac cell death in patients with ischemic heart disease would be of significant therapeutic value as a means to improve ventricular performance. In the present study, we wished to ascertain whether activation of the cellular factor nuclear factor (NF)-κB suppresses mitochondrial defects and cell death of ventricular myocytes during hypoxic injury.

Methods and Results— In contrast to normoxic control cells, ventricular myocytes subjected to hypoxia displayed a 9.1-fold increase ( P <0.05) in cell death, as determined by Hoechst 33258 nuclear staining and vital dyes. Mitochondrial defects consistent with permeability transition pore opening, loss of mitochondrial membrane potential (ΔΨm), and Smac release were observed in cells subjected to hypoxia. An increase in postmitochondrial caspase 9 and caspase 3 activity was observed in hypoxic myocytes. Adenovirus-mediated delivery of wild-type IKKβ (IKKβwt) resulted in a significant increase in NF-κB-dependent DNA binding and gene transcription in ventricular myocytes. Interestingly, subcellular fractionation of myocytes revealed that the p65 subunit of NF-κB was localized to mitochondria. Hypoxia-induced mitochondrial defects and cell death were suppressed in cells expressing IKKβwt but not in cells expressing the kinase-defective IKKβ mutant.

Conclusions— To the best of our knowledge, the data provide the first direct evidence that activation of the NF-κB signaling pathways is sufficient to suppress cell death of ventricular myocytes during hypoxia. Moreover, our data further suggest that NF-κB averts cell death through a mechanism that prevents perturbations to the mitochondrion during hypoxic injury.

SMAC is expressed de novo in a subset of cervical cancer tumors

Background

Smac/Diablo is a recently identified protein that is released from mitochondria after apoptotic stimuli. It binds IAPs, allowing caspase activation and cell death. In view of its activity it might participate in carcinogenesis. In the present study, we analyzed Smac expression in a panel of cervical cancer patients.

Methods

We performed semi quantitative RT-PCR on 41 cervical tumor and 6 normal tissue samples. The study included 8 stage I cases; 16 stage II; 17 stage III; and a control group of 6 samples of normal cervical squamous epithelial tissue.

Results

Smac mRNA expression was below the detection limit in the normal cervical tissue samples. In contrast, 13 (31.7%) of the 41 cervical cancer biopsies showed detectable levels of this transcript. The samples expressing Smac were distributed equally among the stages (5 in stage I, 4 in stage II and 4 in stage III) with similar expression levels. We found no correlation between the presence of Smac mRNA and histology, menopause, WHO stage or disease status.

Conclusions

Smac is expressed de novo in a subset of cervical cancer patients, reflecting a possible heterogeneity in the pathways leading to cervical cancer. There was no correlation with any clinical variable.

Mitochondria-Dependent Pathway Is Involved in Heat-Induced Male Germ Cell Death: Lessons from Mutant Mice1

The signaling events leading to apoptosis can be divided into two major pathways, involving either mitochondria (intrinsic) or death receptors (extrinsic). In a recent study, we have shown the involvement of the mitochondria-dependent apoptotic pathway in heat-induced male germ cell apoptosis in the rat. In additional studies, using the gld (generalized lymphoproliferation disease) and lprcg (lymphoproliferation complementing gld) mice, which harbor loss-of-function mutations in Fas L and Fas, respectively, we have shown that heat-induced germ cell apoptosis is not blocked, thus providing evidence that the Fas signaling system is not required for heat-induced germ cell apoptosis in the testis. In the present study, we have found that the initiation of apoptosis in wild-type mice was preceded by a redistribution of Bax from a cytoplasmic to paranuclear localization in heat-susceptible germ cells. The relocation of Bax is accompanied by sequestration of ultracondensed mitochondria into paranuclear areas of apoptotic germ cells, cytosolic translocation of mitochondrial cytochrome c and DIABLO, and is associated with activation of the initiator caspase 9 and the executioner caspase 3. Similar events were also noted in both gld and lprcg mice. Taken together, these results indicate that the mitochondria-dependent pathway is the key apoptotic pathway for heat-induced male germ cell death in mice.

Expression of Smac/Diablo in tubular epithelial cells and during acute renal failure

BACKGROUND

Apoptosis contributes to tubular cell loss in the course of renal injury. However, the mechanisms regulating tubular cell apoptosis are not well understood. Smac/Diablo is a mitochondrial protein that is released to the cytosol during apoptosis, where it blocks the antiapoptotic activity of inhibitor of apoptosis proteins (IAPs).

METHODS

We have studied the regulation of Smac/Diablo mRNA and protein expression in murine toxic acute tubular necrosis, and in cultured tubular epithelial cells exposed to the lethal cytokine tumor necrosis factor (TNF).

RESULTS

Folic acid-induced acute renal failure was associated with tubular cell apoptosis. Smac/Diablo mRNA and protein levels increased by 50% at 24 hours. TNF, a cytokine whose renal expression increases in folic acid nephropathy, induced apoptosis in cultured tubular epithelial cells in a time-dependent manner. In addition, TNF increased the mRNA and protein expression of Smac/Diablo.

CONCLUSION

These findings support the concept that regulation of Smac/Diablo mRNA and protein expression is a mechanism by which lethal stimuli amplify their lethal potential in renal cells.

Mammalian mitochondrial IAP binding proteins

Four mitochondrial proteins have been identified that immunoprecipitate with the mammalian inhibitor of apoptosis (IAP) protein XIAP. Each of them interacts via a processed amino terminus that resembles those of the insect pro-apoptotic IAP binding proteins Grim, HID, Reaper, and Sickle. Two, Diablo/Smac and HrtA2/Omi, have been extensively characterized. Both Diablo and HtrA2 can bind to IAPs and promote apoptosis when over-expressed in transfected cells, but unlike the insect IAP antagonists, to date there is scant evidence that they are important regulators of apoptosis in more physiological circumstances.