Par-4 inducible apoptosis in prostate cancer cells

Development of a novel prostate apoptosis response-4 (Par-4) protein entity with an extended duration of action for therapeutic treatment of cancer

Prostate apoptosis response-4 (Par-4) is a tumor suppressor which protects against neoplastic transformation. Remarkably, Par-4 is capable of inducing apoptosis selectively in cancer cells without affecting the normal cells. In this study, we found that recombinant Par-4 protein had limited serum persistence in mice that may diminish its anti-tumor activity in vivo. To improve the in vivo performance of the short-lived Par-4 protein, we aimed to develop a novel, long-lasting form of Par-4 with extended sequence, denoted as Par-4Ex, without affecting the desirable molecular function of the natural Par-4. We demonstrate that the Par-4Ex protein entity, produced by using the Escherichia coli expression system suitable for large-scale production, fully retains the desirable pro-apoptotic activity of Par-4 protein, but with ~7-fold improved biological half-life. Further in vivo tests confirmed that, due to the prolonged biological half-life, the Par-4Ex protein is indeed more potent in suppressing metastatic tumor growth in mice.

Prostate apoptosis response 4 (PAR4) expression modulates WNT signaling pathways in MCF7 breast cancer cells: A possible mechanism underlying PAR4-mediated docetaxel chemosensitivity

Docetaxel is an effective drug for the treatment of metastatic breast cancer. However, the exact mechanisms and/or markers associated with chemosensitivity or resistance to docetaxel remain unclear. We previously showed that the expression of prostate apoptosis response 4 (PAR4) inhibits the growth of MCF7 breast cancer cells and increases their sensitivity to docetaxel. Using cDNA microarray analysis, we evaluated transcriptome changes in MCF7 cells expressing increased levels of PAR4 and control cells before and after docetaxel treatment. Some of the top gene networks generated from the differentially expressed genes were related to the wingless‑type MMTV integration 1 (WNT) canonical (WNT/β-catenin) and non‑canonical (β‑catenin‑independent) pathways. The Human WNT signaling pathway RT2 profiler™ PCR array was used to validate the effects of PAR4 on the expression pattern of genes involved in the WNT pathway. CACNAD2A3, GDF5 and IL6 were upregulated and NANOG was downregulated in the MCF7 breast cancer cells expressing increased levels of PAR4 after treatment with docetaxel, likely indicating inactivation of the WNT/β-catenin pathway. Upregulation of FGF7, LEF1 and TWIST1 indicated activation of the WNT/β‑catenin pathway. Although preliminary, our findings could be of particular interest for understanding the action of PAR4 in chemosensitivity, particularly to increase the specificity and effectiveness of drug treatment and overcome resistance to chemotherapy. Further studies are needed to better understand the biological roles of PAR4 in the regulation of WNT pathways in breast cancer cells in response to docetaxel and other chemotherapeutic agents.

A journey beyond apoptosis: new enigma of controlling metastasis by pro-apoptotic Par-4

Prostate apoptotic response 4 (Par-4) is coined as a therapeutic protein since owing to its diverse physiologically relevant properties, especially in the cancer perspective. Albeit, Par-4 expression is not restricted to any specific tissue/organ, apart from cell death promotion (due to challenging threats), the other biological role of Par-4 is convincingly emerging. In the recent years, several laboratories have intended to dissect the signaling or mechanisms involved in Par-4 activation to augment apoptosis cascades but new developments in Par-4 research have widened its therapeutic potential. One of these important avenues is the prevention of metastasis by pro-apoptotic Par-4. In this review, we will focus on the therapeutic perspective of Par-4 with a special reference to its (Par-4) virgin prospect of devastating metastasis control.

Plant-derived SAC domain of PAR-4 (Prostate Apoptosis Response 4) exhibits growth inhibitory effects in prostate cancer cells

The gene Par-4 (Prostate Apoptosis Response 4) was originally identified in prostate cancer cells undergoing apoptosis and its product Par-4 showed cancer specific pro-apoptotic activity. Particularly, the SAC domain of Par-4 (SAC-Par-4) selectively kills cancer cells leaving normal cells unaffected. The therapeutic significance of bioactive SAC-Par-4 is enormous in cancer biology; however, its large scale production is still a matter of concern. Here we report the production of SAC-Par-4-GFP fusion protein coupled to translational enhancer sequence (5' AMV) and apoplast signal peptide (aTP) in transgenic Nicotiana tabacum cv. Samsun NN plants under the control of a unique recombinant promoter M24. Transgene integration was confirmed by genomic DNA PCR, Southern and Northern blotting, Real-time PCR, and Nuclear run-on assays. Results of Western blot analysis and ELISA confirmed expression of recombinant SAC-Par-4-GFP protein and it was as high as 0.15% of total soluble protein. In addition, we found that targeting of plant recombinant SAC-Par-4-GFP to the apoplast and endoplasmic reticulum (ER) was essential for the stability of plant recombinant protein in comparison to the bacterial derived SAC-Par-4. Deglycosylation analysis demonstrated that ER-targeted SAC-Par-4-GFP-SEKDEL undergoes O-linked glycosylation unlike apoplast-targeted SAC-Par-4-GFP. Furthermore, various in vitro studies like mammalian cells proliferation assay (MTT), apoptosis induction assays, and NF-κB suppression suggested the cytotoxic and apoptotic properties of plant-derived SAC-Par-4-GFP against multiple prostate cancer cell lines. Additionally, pre-treatment of MAT-LyLu prostate cancer cells with purified SAC-Par-4-GFP significantly delayed the onset of tumor in a syngeneic rat prostate cancer model. Taken altogether, we proclaim that plant made SAC-Par-4 may become a useful alternate therapy for effectively alleviating cancer in the new era.

Regulation of the proapoptotic functions of prostate apoptosis response-4 (Par-4) by casein kinase 2 in prostate cancer cells

The proapoptotic protein, prostate apoptosis response-4 (Par-4), acts as a tumor suppressor in prostate cancer cells. The serine/threonine kinase casein kinase 2 (CK2) has a well-reported role in prostate cancer resistance to apoptotic agents or anticancer drugs. However, the mechanistic understanding on how CK2 supports survival is far from complete. In this work, we demonstrate both in rat and humans that (i) Par-4 is a new substrate of the survival kinase CK2 and (ii) phosphorylation by CK2 impairs Par-4 proapoptotic functions. We also unravel different levels of CK2-dependent regulation of Par-4 between species. In rats, the phosphorylation by CK2 at the major site, S124, prevents caspase-mediated Par-4 cleavage (D123) and consequently impairs the proapoptotic function of Par-4. In humans, CK2 strongly impairs the apoptotic properties of Par-4, independently of the caspase-mediated cleavage of Par-4 (D131), by triggering the phosphorylation at residue S231. Furthermore, we show that human Par-4 residue S231 is highly phosphorylated in prostate cancer cells as compared with their normal counterparts. Finally, the sensitivity of prostate cancer cells to apoptosis by CK2 knockdown is significantly reversed by parallel knockdown of Par-4. Thus, Par-4 seems a critical target of CK2 that could be exploited for the development of new anticancer drugs.

Prostate apoptosis response-4 is involved in the apoptosis response to docetaxel in MCF-7 breast cancer cells

Experimental evidence indicates that prostate apoptosis response-4 (Par-4, also known as PAWR) is a key regulator of cancer cell survival and may be a target for cancer-selective targeted therapeutics. Par-4 was first identified in prostate cancer cells undergoing apoptosis. Both intracellular and extracellular Par-4 have been implicated in apoptosis. Relatively little is known about the role of Par-4 in breast cancer cell apoptosis. In this study, we sought to investigate the effects of Par-4 expression on cell proliferation, apoptosis and drug sensitivity in breast cancer cells. MCF-7 cells were stably transfected with expression vectors for Par-4, or transiently transfected with siRNA for Par-4 knockdown. Cell proliferation assays were performed using MTT and apoptosis was evaluated using acridine orange staining, fluorescence microscopy and flow cytometry. Par-4 overexpression reduced MCF-7 proliferation rates. Conversely, Par-4 knockdown led to increased MCF-7 proliferation. Par-4 downregulation also led to increased BCL-2 and reduced BID expression. Par-4 overexpression did not affect the cell cycle profile. However, MCF-7 cells with increased Par-4 expression showed reduced ERK phosphorylation, suggesting that the inhibition of cell proliferation promoted by Par-4 may be mediated by the MAPK/ERK1/2 pathway. MCF-7 cells with increased Par-4 expression showed a marginal increase in early apoptotic cells. Importantly, we found that Par-4 expression modulates apoptosis in response to docetaxel in MCF7 breast cancer cells. Par-4 exerts growth inhibitory effects on breast cancer cells and chemosensitizes them to docetaxel.

Changes in the gene expression programs of renal mesangial cells during diabetic nephropathy

Background

Diabetic nephropathy is the leading cause of end stage renal disease. All three cell types of the glomerulus, podocytes, endothelial cells and mesangial cells, play important roles in diabetic nephropathy. In this report we used Meis1-GFP transgenic mice to purify mesangial cells from normal mice and from db/db mice, which suffer diabetic nephropathy. The purpose of the study is to better define the unique character of normal mesangial cells, and to characterize their pathogenic and protective responses during diabetic nephropathy.

Methods

Comprehensive gene expression states of the normal and diseased mesangial cells were defined with microarrays. By comparing the gene expression profiles of mesangial cells with those of multiple other renal cell types, including podocytes, endothelial cells and renal vesicles, it was possible to better define their exceptional nature, which includes smooth muscle, phagocytic and neuronal traits.

Results

The complete set of mesangial cell expressed transcription factors, growth factors and receptors were identified. In addition, the analysis of the mesangial cells from diabetic nephropathy mice characterized their changes in gene expression. Molecular functions and biological processes specific to diseased mesangial cells were characterized, identifying genes involved in extracellular matrix, cell division, vasculogenesis, and growth factor modulation. Selected gene changes considered of particular importance to the disease process were validated and localized within the glomuerulus by immunostaining. For example, thrombospondin, a key mediator of TGFβ signaling, was upregulated in the diabetic nephropathy mesangial cells, likely contributing to fibrosis. On the other hand the decorin gene was also upregulated, and expression of this gene has been strongly implicated in the reduction of TGFβ induced fibrosis.

Conclusions

The results provide an important complement to previous studies examining mesangial cells grown in culture. The remarkable qualities of the mesangial cell are more fully defined in both the normal and diabetic nephropathy diseased state. New gene expression changes and biological pathways are discovered, yielding a deeper understanding of the diabetic nephropathy pathogenic process, and identifying candidate targets for the development of novel therapies.

Expression Pattern of the Pro-apoptotic Gene PAR-4 During the Morphogenesis of MCF-10A Human Mammary Epithelial Cells

The histological organization of the mammary gland involves a spatial interaction of epithelial and myoepithelial cells with the specialized basement membrane (BM), composed of extra-cellular matrix (ECM) proteins, which is disrupted during the tumorigenic process. The interactions between mammary epithelial cells and ECM components play a major role in mammary gland branching morphogenesis. Critical signals for mammary epithelial cell proliferation, differentiation, and survival are provided by the ECM proteins. Three-dimensional (3D) cell culture was developed to establish a system that simulates several features of the breast epithelium in vivo; 3D cell culture of the spontaneously immortalized cell line, MCF10A, is a well-established model system to study breast epithelial cell biology and morphogenesis. Mammary epithelial cells grown in 3D form spheroids, acquire apicobasal polarization, and form lumens that resemble acini structures, processes that involve cell death. Using this system, we evaluated the expression of the pro-apoptotic gene PAWR (PKC apoptosis WT1 regulator; also named PAR-4, prostate apoptosis response-4) by immunofluorescence and quantitative real time PCR (qPCR). A time-dependent increase in PAR-4 mRNA expression was found during the process of MCF10A acinar morphogenesis. Confocal microscopy analysis also showed that PAR-4 protein was highly expressed in the MCF10A cells inside the acini structure. During the morphogenesis of MCF10A cells in 3D cell culture, the cells within the lumen showed caspase-3 activation, indicating apoptotic activity. PAR-4 was only partially co-expressed with activated caspase-3 on these cells. Our results provide evidence, for the first time, that PAR-4 is differentially expressed during the process of MCF10A acinar morphogenesis.

PAR-4 as a possible new target for pancreatic cancer therapy

IMPORTANCE OF THE FIELD

Pancreatic cancer (PC) is a deadly disease that is intractable to currently available treatment regimens. Although well described in different tumors types, the importance of apoptosis inducer prostate apoptosis response-4 (Par-4) in PC has not been appreciated. PC is an oncogenic kras driven disease, which is known to downregulate Par-4. Therefore, this review highlights its significance and builds a strong case supporting the role of Par-4 as a possible therapeutic target in PC.

AREAS COVERED IN THIS REVIEW

Literature-based evidence spanning the last 15 years on Par-4 and its significance in PC.

WHAT THE READER WILL GAIN

This review provides comprehensive knowledge of the significance of Par-4 and its association with kras status in PC, along with the crosstalk with crucial resistance and survival molecules NF-kappaB and Bcl-2 that ultimately are responsible for the overall poor outcome of different therapeutic approaches in this disease.

TAKE HOME MESSAGE

Par-4 holds promise as a potential therapeutic target that can be induced by chemopreventive agents and small-molecule inhibitors either alone or in combination with standard chemotherapeutics leading to selective apoptosis in PC cells. It also acts as a chemosensitizer and therefore warrants further clinical investigations in this disease.

Transcriptional regulation of pro-apoptotic Par-4 by NF-kappaB/p65 and its function in controlling cell kinetics during early events in endometrial tumourigenesis

Prostatic apoptosis response-4 (Par-4) was first identified in prostatic cancer cells that were induced to undergo apoptosis. Recently, Par-4 has been suggested to be a tumour suppressor gene that plays a role in the development of endometrial carcinomas (ECs), but the exact mechanism remains to be clarified. Here we examined gene activation signalling cascades and influence on cell kinetics during endometrial tumourigenesis. In normal endometrium, constitutively high levels of Par-4 expression were observed in epithelial cells through the menstrual cycle, in contrast to the transient up-regulation in stromal components in the menstrual stage, correlated positively with the phospho-p65 (pp65) status and apoptosis. In contrast, most ECs exhibited significant down-regulation as compared to normal endometrium, with positive links only to pp65 expression. In EC cell lines, transfection of the NF-kappaB subunit p65 led to transactivation of Par-4 through specific binding to its promoter region, in contrast to the suppression by active Akt, suggesting that the balance between the two signals may be important to determine Par-4 expression levels. In addition, transient overexpression of Par-4 resulted in the induction of not only apoptosis but also senescence, through changes in the expression of bcl-2 and p21$;{{\rm WAF1}}$, respectively. Together, these findings suggest that a signalling cascade involving sequential activation of NF-kappaB/p65 and Par-4 may participate in relatively early events of endometrial tumourigenesis, leading to modulation of cell kinetics including apoptosis and cell cycle progression.

Expression of prostate apoptosis response (Par-4) is associated with progesterone receptor in breast cancer

BACKGROUND

The prostate apoptosis response (Par-4) gene encodes a proapoptotic protein that selectively induces apoptosis in cancer cells after diverse apoptotic stimuli. Par-4 expression and its association with other biomarkers have not been reported in breast cancer. The purpose of this study was to determine Par-4 expression in breast cancer samples and its association with other biomarkers and clinical factors (T-stage, age, nodal status).

METHODS

Paraffin-embedded section samples of breast cancer were evaluated by immunohistochemical analysis to determine Par-4, estrogen receptor (ER), progesterone receptor (PgR), c-erbB2, Ki67, p53 and bcl-2 expression. The correlation between Par-4 and the other biomarkers and clinical factors was determined by multivariate analysis.

RESULTS

Thirty five percent (n=21) of samples were PAR-4 positive and 64.4% (n=38) were negative. The hormonal status was 64% ER positive (n=38), 35% ER-negative (n=21) and 40.7% PgR positive (n=24), 59.3% PgR negative (n=35). The majority (90%) of the samples presented clear cytoplasmic localization and a small portion (10%) was cytoplasmic and nuclear. Univariate analysis indicates that the Par-4 expression has a significant inverse association (p=0.04) only with expression of PgR and not with the other variables analyzed. Normal breast tissue analyzed was negative for Par-4 immunostaining.

CONCLUSIONS

Our results suggest that, in breast cancer, Par-4 plays a similar tumor suppressor gene role as reported in endometrial carcinoma.

aPKClambda/iota promotes growth of prostate cancer cells in an autocrine manner through transcriptional activation of interleukin-6

Understanding the mechanism by which hormone refractory prostate cancer (HRPC) develops remains a major issue. Alterations in HRPC include androgen receptor (AR) changes. In addition, the AR is activated by cytokines such as interleukin-6 (IL-6). Atypical protein kinase C (aPKClambda/iota) has been implicated in the progression of several cancers. Herein, we provide evidence that aPKClambda/iota expression correlates with prostate cancer recurrence. Experiments in vitro and in vivo revealed aPKClambda/iota to be involved in prostate cancer cell growth through secretion of IL-6. Further, aPKClambda/iota activates transcription of the IL-6 gene through NFkappaB and AP-1. We conclude that aPKClambda/iota promotes the growth of hormone independent prostate cancer cells by stimulating IL-6 production in an autocrine manner. Our findings not only explain the link between aPKClambda/iota and IL-6, implicated in the progression a variety of cancers, but also establish a molecular change involved in the development of HRPC. Further, aPKClambda/iota expression might be a biomarker for prostate cancer progression.

Intrinsic disorder and coiled-coil formation in prostate apoptosis response factor 4

Prostate apoptosis response factor-4 (Par-4) is an ubiquitously expressed pro-apoptotic and tumour suppressive protein that can both activate cell-death mechanisms and inhibit pro-survival factors. Par-4 contains a highly conserved coiled-coil region that serves as the primary recognition domain for a large number of binding partners. Par-4 is also tightly regulated by the aforementioned binding partners and by post-translational modifications. Biophysical data obtained in the present study indicate that Par-4 primarily comprises an intrinsically disordered protein. Bioinformatic analysis of the highly conserved Par-4 reveals low sequence complexity and enrichment in polar and charged amino acids. The high proteolytic susceptibility and an increased hydrodynamic radius are consistent with a largely extended structure in solution. Spectroscopic measurements using CD and NMR also reveal characteristic features of intrinsic disorder. Under physiological conditions, the data obtained show that Par-4 self-associates via the C-terminal domain, forming a coiled-coil. Interruption of self-association by urea also resulted in loss of secondary structure. These results are consistent with the stabilization of the coiled-coil motif through an intramolecular association.

EBV LMP-1 negatively regulates expression and pro-apoptotic activity of Par-4 in nasopharyngeal carcinoma cells

Latent membrane protein-1 (LMP-1) of the Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), and in this study we sought to determine whether the pro-apoptotic activity of prostate apoptosis response-4 (Par-4) is modulated by LMP-1 in NPC cells. We found that LMP-1 diminished the pro-apoptotic activity of Par-4 and negatively regulated Par-4 protein by de novo synthesis; moreover, although LMP-1 accelerated a Par-4 activator, PKA, we demonstrated that LMP-1 also activated the PI3K/Akt pathway and increased Bcl-2 expression to suppress the activity of Par-4. Consequently, our results revealed a novel negative action of LMP-1 on the pro-apoptosis protein Par-4 by the coordination of multiple signaling pathways.

Apoptosis induced by capsaicin in prostate PC-3 cells involves ceramide accumulation, neutral sphingomyelinase, and JNK activation

Numerous studies have recently focused on the anticarcinogenic, antimutagenic, or chemopreventive activities of the main pungent component of red pepper, capsaicin (N-vanillyl-8-methyl-1-nonenamide). We have previously shown that, in the androgen-independent prostate cancer PC-3 cells, capsaicin inhibits cell growth and induces apoptosis through reactive oxygen species (ROS) generation [Apoptosis 11 (2006) 89-99]. In the present study, we investigated the signaling pathways involved in the antiproliferative effect of capsaicin. Here, we report that capsaicin apoptotic effect was mediated by ceramide generation which occurred by sphingomyelin hydrolysis. Using siRNA, we demonstrated that N-SMase expression is required for the effect of capsaicin on prostate cell viability. We then investigated the role of MAP kinase cascades, extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, in the antiproliferative effect of capsaicin, and we confirmed that capsaicin could activate ERK and JNK but not p38 MAPK. Pharmacological inhibition of JNK kinase, as well as inhibition of ROS by the reducing agent N-acetylcysteine, prevented ceramide accumulation and capsaicin-induced cell death. However, inhibition of ceramide accumulation by the SMase inhibitor D609 did not modify JNK activation. These data reveal JNK as an upstream regulator of ceramide production. Capsaicin-promoted activation of ERK was prevented with all the inhibitors tested. We conclude that capsaicin induces apoptosis in PC-3 cells via ROS generation, JNK activation, ceramide accumulation, and second, ERK activation.

Protein expression and intracellular localization of prostate apoptosis response-4 (Par-4) are associated with apoptosis induction in nasopharyngeal carcinoma cell lines

Prostate apoptosis response-4 (Par-4) is a proapoptotic gene that selectively induces cell death in most cancer cells. In addition to the increased percentage of apoptotic cells, caspase-3 activity, and poly (ADP-ribose) polymerase (PARP) cleavage, we demonstrate that elevated expression of Par-4 and nuclear entry resulted in apoptosis of nasopharyngeal carcinoma (NPC) cell lines either in serum deprivation or by ectopic overexpression of Par-4. Moreover, disassociation from the Par-4/Akt complex was correlated with the induced proapoptotic ability of Par-4. Therefore, our data suggest that the cytoplasmic localization and expression level of endogenous Par-4 in NPC cells are not sufficient to augment apoptosis.

Inactivation of the candidate tumor suppressor par-4 in endometrial cancer

Recently, it has been shown that mice deficient in the proapoptotic protein prostate apoptosis response 4 (Par-4) are specifically prone to develop endometrial carcinomas. Based on this, we have examined here the possible role of Par-4 as a tumor suppressor gene in human endometrial cancer. Using cDNA arrays, quantitative reverse transcription-PCR, and immunohistochemistry, we detected Par-4 down-regulation in approximately 40% of endometrial carcinomas. This alteration was not associated with phosphatase and tensin homologue (PTEN), K-RAS, or beta-catenin mutations, but was more frequent among tumors showing microsatellite instability (MSI) or among tumors that were estrogen receptor positive. Mutational analysis of the complete coding sequence of Par-4 in endometrial cancer cell lines (n = 6) and carcinomas (n = 69) detected a mutation in a single carcinoma, which was localized in exon 3 [Arg (CGA) 189 (TGA) Stop]. Interestingly, Par-4 promoter hypermethylation was detected in 32% of the tumors in association with low levels of Par-4 protein and was more common in MSI-positive carcinomas. Par-4 promoter hypermethylation and silencing was also detected in endometrial cancer cell lines SKUT1B and AN3CA, and reexpression was achieved by treatment with the demethylating agent 5'-aza-2'-deoxycytidine. Together, these data show that Par-4 is a relevant tumor suppressor gene in human endometrial carcinogenesis.

Unraveling the molecular targets pertinent to junction restructuring events during spermatogenesis using the Adjudin-induced germ cell depletion model

During spermatogenesis, extensive restructuring takes place at the Sertoli-Sertoli and Sertoli-germ cell interface, which is regulated via intriguing interactions among cytokines, proteases, protease inhibitors, kinases, phosphatases, and transcription factors. This in turn determines the steady-state levels of integral membrane proteins at the cell junctions. We sought to further expand these observations using the Adjudin model. Adjudin is a potential male contraceptive that targets Sertoli-germ cell adhesion, causing exfoliation of spermatids and spermatocytes, but not spermatogonia, from the seminiferous epithelium. This model thus provides the means to identify crucial regulatory molecules and signaling pathways pertinent to junction restructuring events during spermatogenesis. In this study, genome-wide expression profiling of rat testes after treatment with Adjudin at the time of extensive junction restructuring was performed. Differentially regulated genes, such as cytokines, proteases, protease inhibitors, cell junction-associated proteins, and transcription factors pertinent to junction restructuring were identified. These data were consistent with earlier findings; however, much new information was obtained which has been deposited at the Gene Expression Omnibus data repository website: http://www.ncbi.nih.gov/geo/ with Accession number: GSE5131. The primary signaling events pertinent to junction restructuring in the testis induced by Adjudin were also delineated using bioinformatics. These findings were also consistent with recently published reports. The identified molecular signatures or targets pertinent to junction dynamics in the testis as reported herein, many of which have not been investigated, thus offer a framework upon which the regulation of junction restructuring events at the Sertoli-Sertoli and Sertoli-germ cell interface pertinent to spermatogenesis can be further studied.

Structural basis for protein recognition by B30.2/SPRY domains

B30.2/SPRY domains are found in numerous proteins that cover a wide spectrum of biological functions, including regulation of cytokine signaling and innate retroviral restriction. Herein, we report the crystal structure of the B30.2/SPRY domain of a SPRY domain-containing SOCS box (SSB) protein, GUSTAVUS, complexed with a 20 amino acid peptide derived from the RNA helicase VASA, revealing how these domains recognize target proteins. The peptide-binding site is conformationally rigid and has a preformed pocket. The interaction between the pocket and the Asp-Ile-Asn-Asn-Asn-Asn sequence within the peptide accounts for the high-affinity binding between GUSTAVUS and VASA. This observation led to a facile identification of the Glu-Leu-Asn-Asn-Asn-Leu sequence as the recognition motif in a proapoptotic protein Par-4 for its interaction with a GUSTAVUS homolog, SSB-1. Ensuing analyses indicated that many B30.2/SPRY domains have a similar preformed pocket, which would allow them to bind multiple targets.

A novel isoform of prostate apoptosis response 4 (PAR-4) that co-distributes with F-actin and prevents apoptosis in neural stem cells

The elevated expression of prostate apoptosis response-4 (PAR-4) induces apoptosis in differentiating mouse embryonic stem (ES) cells. In embryoid body (EB) cells and the E15.5 stage of embryonic mouse brain, PAR-4 is expressed as two isoforms (38 and 33 kDa). Using mouse EB-derived RNA as a template we have cloned and characterized a novel isoform of PAR-4 (PAR-4/p33) that lacks exon 3 and shows a bona fide splice junction of exons 2 and 4. The molecular mass for PAR-4/p33 is estimated to be 33 kDa, corresponding to the short form found in the EB cells and E15.5 mouse brain. The fluorescent fusion protein of PAR-4/p33 is mainly found in the cytosol and is co-distributed with F-actin filaments, while that of the 38 kDa full length PAR-4/p38 is predominantly translocated to the nucleus. In contrast to the full length PAR-4 (PAR-4/p38), ectopic expression of PAR-4/p33 does not result in the activation of caspase 3 and the induction of apoptosis. PAR-4/p33 forms a complex with PAR-4/p38, which inhibits its nuclear translocation and the induction of apoptosis. PAR-4/p33 is suggested to be a dominant negative isoform of PAR-4/p38 and may regulate PAR-4-dependent apoptosis.

Dynamics of the SPRY domain-containing SOCS box protein 2: flexibility of key functional loops

The SPRY domain was identified originally as a sequence repeat in the dual-specificity kinase splA and ryanodine receptors and subsequently found in many other distinct proteins, including more than 70 encoded in the human genome. It is a subdomain of the B30.2/SPRY domain and is believed to function as a protein-protein interaction module. Three-dimensional structures of several B30.2/SPRY domain-containing proteins have been reported recently: murine SSB-2 in solution by NMR spectroscopy, a Drosophila SSB (GUSTAVUS), and human PRYSPRY protein by X-ray crystallography. The three structures share a core of two antiparallel beta-sheets for the B30.2/SPRY domain but show differences located mainly at one end of the beta-sandwich. Analysis of SSB-2 residues required for interactions with its intracellular ligands has provided insights into B30.2/SPRY binding specificity and identified loop residues critical for the function of this domain. We have investigated the backbone dynamics of SSB-2 by means of Modelfree analysis of its backbone (15)N relaxation parameters and carried out coarse-grained dynamics simulation of B30.2/SPRY domain-containing proteins using normal mode analysis. Translational self-diffusion coefficients of SSB-2 measured using pulsed field gradient NMR were used to confirm the monomeric state of SSB-2 in solution. These results, together with previously reported amide exchange data, highlight the underlying flexibility of the loop regions of B30.2/SPRY domain-containing proteins that have been shown to be important for protein-protein interactions. The underlying flexibility of certain regions of the B30.2/SPRY domain-containing proteins may also contribute to some apparent structural differences observed between GUSTAVUS or PRYSPRY and SSB-2.

Regulation of cancer cell survival by Par-4

Prostate apoptosis response-4 (Par-4) is a unique pro-apoptotic protein that selectively induces apoptosis in cancer cells. Moreover, Par-4 sensitizes cells to the action of diverse apoptotic stimuli and causes tumor regression. This review discusses the prominent structural and functional features of Par-4 and the multiple levels of regulation of its apoptotic function, all of which can be utilized to develop targeted cancer therapy.

Systematic discovery of the grammar of translational inhibition by RNA hairpins

Recent discovery of gene expression mechanisms has propelled molecular genetics to a state of rapid development, a state likely to persist due to continuing advances in understanding control systems of fundamental cellular processes. An algorithm for that advancement starts in this paper with a gene of interest and a characteristic function of that gene. The set of all genes with counteracting function is identified by pathway searches. Also associated with the first gene is the set of the genes which byproducts of its transcription might downregulate, identified relative to searches involving sequence alignments. Our focus is the intersection of the counteracting gene set and the downregulated gene set. The result is hypothesis generation. Examples of and predictions from this approach are given in the context of apoptosis. Also discussed is application of the algorithm to rational drug design from a new development platform.

The SPRY domain of SSB-2 adopts a novel fold that presents conserved Par-4-binding residues

The four mammalian SPRY domain-containing SOCS box proteins (SSB-1 to SSB-4) are characterized by a C-terminal SOCS box and a central SPRY domain. We have determined the first SPRY-domain structure, as part of SSB-2, by NMR. This domain adopts a novel fold consisting of a beta-sandwich structure formed by two four-stranded antiparallel beta-sheets with a unique topology. We demonstrate that SSB-1, SSB-2 and SSB-4, but not SSB-3, bind prostate apoptosis response protein-4 (Par-4). Mutational analysis of SSB-2 loop regions identified conserved structural determinants for its interaction with Par-4 and the hepatocyte growth factor receptor, c-Met. Mutations in analogous loop regions of pyrin and midline-1 SPRY domains have been shown to cause Mediterranean fever and Opitz syndrome, respectively. Our findings provide a template for SPRY-domain structure and an insight into the mechanism of SPRY-protein interaction.

Tumour-suppression activity of the proapoptotic regulator Par4

The proapoptotic protein encoded by Par4 (prostate apoptosis response 4) has been implicated in tumour suppression, particularly in the prostate. We report here that Par4-null mice are prone to develop tumours, both spontaneously and on carcinogenic treatment. The endometrium and prostate of Par4-null mice were particularly sensitive to the development of proliferative lesions. Most (80%) Par4-null females presented endometrial hyperplasia by 9 months of age, and a significant proportion (36%) developed endometrial adenocarcinomas after 1 year of age. Similarly, Par4-null males showed a high incidence of prostate hyperplasia and prostatic intraepithelial neoplasias, and were extraordinarily sensitive to testosterone-induced prostate hyperplasia. Finally, the uterus and prostate of young Par4-null mice have increased levels of the apoptosis inhibitor XIAP (X-chromosome-linked inhibitor of apoptosis), supporting the previously proposed function of Par4 as an inhibitor of the (zeta)PKC (atypical protein kinase)-NF-(kappa)B (nuclear factor-(kappa)B)-XIAP pathway. These data show that Par4 has an important role in tumour suppression, with a particular relevance in the endometrium and prostate.

Selective apoptosis of pluripotent mouse and human stem cells by novel ceramide analogues prevents teratoma formation and enriches for neural precursors in ES cell-derived neural transplants

The formation of stem cell-derived tumors (teratomas) is observed when engrafting undifferentiated embryonic stem (ES) cells, embryoid body-derived cells (EBCs), or mammalian embryos and is a significant obstacle to stem cell therapy. We show that in tumors formed after engraftment of EBCs into mouse brain, expression of the pluripotency marker Oct-4 colocalized with that of prostate apoptosis response-4 (PAR-4), a protein mediating ceramide-induced apoptosis during neural differentiation of ES cells. We tested the ability of the novel ceramide analogue N-oleoyl serinol (S18) to eliminate mouse and human Oct-4(+)/PAR-4(+) cells and to increase the proportion of nestin(+) neuroprogenitors in EBC-derived cell cultures and grafts. S18-treated EBCs persisted in the hippocampal area and showed neuronal lineage differentiation as indicated by the expression of beta-tubulin III. However, untreated cells formed numerous teratomas that contained derivatives of endoderm, mesoderm, and ectoderm. Our results show for the first time that ceramide-induced apoptosis eliminates residual, pluripotent EBCs, prevents teratoma formation, and enriches the EBCs for cells that undergo neural differentiation after transplantation.