Opposite roles of DMRT1 and its W-linked paralogue, DM-W, in sexual dimorphism of Xenopus laevis: implications of a ZZ/ZW-type sex-determining system.

A Y-linked gene, DMY/dmrt1bY, in teleost fish medka and a Z-linked gene, DMRT1, in chicken are both required for male sex determination. We recently isolated a W-linked gene, DM-W, as a paralogue of DMRT1 in Xenopus laevis, which has a ZZ/ZW-type sex-determining system. The DNA-binding domain of DM-W shows high sequence identity with that of DMRT1, but DM-W has no significant sequence similarity with the transactivation domain of DMRT1. Here, we first show colocalization of DM-W and DMRT1 in the somatic cells surrounding primordial germ cells in ZW gonad during sex determination. We next examined characteristics of DM-W and DMRT1 as a transcription factor in vitro. DM-W and DMRT1 shared a DNA-binding sequence. Importantly, DM-W dose-dependently antagonized the transcriptional activity of DMRT1 on a DMRT1-driven luciferase reporter system in 293 cells. We also examined roles of DM-W or DMRT1 in gonadal formation. Some transgenic ZW tadpoles bearing a DM-W knockdown vector had gonads with a testicular structure, and two developed into frogs with testicular gonads. Ectopic DMRT1 induced primary testicular development in some ZW individuals. These observations indicated that DM-W and DMRT1 could have opposite functions in the sex determination. Our findings support a novel model for a ZZ/ZW-type system in which DM-W directs female sex as a sex-determining gene, by antagonizing DMRT1. Additionally, they suggest that DM-W diverged from DMRT1 as a dominant-negative type gene, i.e. as a ;neofunctionalization' gene for the ZZ/ZW-type system. Finally, we discuss a conserved role of DMRT1 in testis formation during vertebrate evolution.

Tumor necrosis factor-related apoptosis-inducing ligand 1 (TRAIL1) enhances the transition of red blood cells from the larval to adult type during metamorphosis in Xenopus.

The transition of red blood cells (RBCs) from primitive to definitive erythropoiesis is conserved across vertebrates. In anuran amphibians, the larval RBCs from primitive erythropoiesis are replaced by adult RBCs from definitive erythropoiesis during metamorphosis. The molecular mechanisms by which the primitive (larval) blood cells are specifically removed from circulation are not yet understood. In this study, we identified Xenopus tumor necrosis factor-related apoptosis-inducing ligand 1 (xTRAIL1) and xTRAIL2 as ligands of Xenopus death receptor-Ms (xDR-Ms) and investigated whether TRAIL signaling could be involved in this transition. The Trail and xDR-M genes were highly expressed in the liver and RBCs, respectively, during metamorphosis. Interestingly, xTRAIL1 enhanced the transition of the RBCs, and a dominant-negative form of the xTRAIL1 receptor attenuated it, when injected into tadpoles. Moreover, xTRAIL1 induced apoptosis in larval RBCs, but had little effect on adult RBCs in vitro. We also found that adult RBCs treated with staurosporine, a protein kinase C (PKC) inhibitor, were sensitized to xTRAIL1. The mRNAs for PKC isoforms were up-regulated in RBCs during metamorphosis. These results suggest that xTRAIL1 can cause apoptosis, probably mediated through xDR-Ms, in larval RBCs, but may not kill adult RBCs, presumably owing to PKC activation, as part of the mechanism for RBC switching.

JNK-binding protein 1 regulates NF-kappaB activation through TRAF2 and TAK1.

The mitogen-activated protein kinase (MAPK) cascades, including c-Jun N-terminal kinase (JNK), are composed of a MAPK, MAPK kinase (MAPKK), and MAPKK kinase (MAPKKK). Previously, we reported that JNK-binding protein 1 (JNKBP1) enhances JNK activation induced by the TGF-beta-activated kinase1 (TAK1) MAPKKK in transfected cells. We have investigated whether JNKBP1 functions as an adaptor protein for nuclear factor (NF)-kappaB activation mediated by TAK1 in COS-7 cells. Co-expression experiments showed that JNKBP1 interacted with not only TAK1, but also with its upstream regulators, TNF-receptor associated factors 2 and 6 (TRAF2 and TRAF6). An endogenous interaction between JNKBP1 and TRAF2 or TAK1 was confirmed by immunoprecipitation analysis. We also found that JNKBP1 could enhance the NF-kappaB activation induced by TAK1 and TRAF2, and could promote TRAF2 polyubiquitination. These results suggest a scaffolding role for JNKBP1 in the TRAF2-TAK1-NF-kappaB signaling pathway.

Tumor necrosis factor-alpha attenuates thyroid hormone-induced apoptosis in vascular endothelial cell line XLgoo established from Xenopus tadpole tails.

Amphibian metamorphosis induced by T(3) involves programmed cell death and the differentiation of various types of cells in degenerated and reconstructed tissues. However, the signaling pathway that directs the T(3)-dependent cell-fate determinations remains unclear. TNF-alpha is a pleiotropic cytokine that affects diverse cellular responses. Engagement of TNF-alpha with its receptor (TNFR1) causes intracellular apoptotic and/or survival signaling. To investigate TNF signaling functions during anuran metamorphosis, we first identified Xenopus laevis orthologs of TNF (xTNF)-alpha and its receptor. We found that xTNF-alpha activated nuclear factor-kappaB in X. laevis A6 cells through the Fas-associated death domain and receptor-interacting protein 1. Interestingly, xTNF-alpha mRNA in blood cells showed prominent expression at prometamorphosis during metamorphosis. Next, to elucidate the apoptotic and/or survival signaling induced by xTNF-alpha in an in vitro model of metamorphosis, we established a vascular endothelial cell line, XLgoo, from X. laevis tadpole tail. XLgoo cells formed actin stress fibers and elongated in response to xTNF-alpha. T(3) induced apoptosis in these cells, but the addition of xTNF-alpha blocked the T(3)-induced apoptosis. In addition, treatment of the cells with T(3) for 2 d induced the expression of thyroid hormone receptor-beta and caspase-3, and this thyroid hormone receptor-beta induction was drastically repressed by xTNF-alpha. Furthermore, in organ culture of the tail, xTNF-alpha significantly attenuated the tail degeneration induced by T(3). These findings suggested that xTNF-alpha could protect vascular endothelial cells from apoptotic cell death induced by T(3) during metamorphosis and thereby participate in the regulation of cell fate.

Mammalian Sox15 gene: promoter analysis and implications for placental evolution.

Sox15 belongs to the Sox (Sry-type HMG box) protein family, which is involved in placental development and muscle regeneration. Previously, we showed that the Sox15 gene is highly expressed in the trophoblast giant cells of the mouse placenta. To elucidate the molecular mechanisms of the tissue-dependent transcription of the gene, we isolated approximately 2.2 kb of the 5'-flanking sequence upstream of the transcription initiation site and used it to construct luciferase reporter plasmids. A variety of cell lines, including trophoblast stem (TS) cells, placenta-derived Rcho-1 cells, and myoblast C2C12 cells, required the same 5'-flanking sequence, from -109 to -8, for basal promoter activity. In contrast, the sequences from -297 to -149 and from -148 to -110 were required for cell-type-specific promoter activity in myoblast-derived C2C12 cells and placenta-derived Rcho-1 and TS cells, respectively. These results suggest that the region from -297 to -8 of the Sox15 gene contains three distinct cis-elements that respectively control placenta-specific, myoblast-specific, and common basal expression. We also searched for Sox15 ortholog(s) in the genome databases of various vertebrate species. The results indicated that the three regulatory promoter sequences of the Sox15 genes were conserved among eutherian mammals during vertebrate evolution. Interestingly, the marsupial opossum gene that is closest to Sox15 appeared to be a pseudogene. These findings indicate that Sox15 may have been involved in placental evolution.

A W-linked DM-domain gene, DM-W, participates in primary ovary development in Xenopus laevis.

In the XX/XY sex-determining system, the Y-linked SRY genes of most mammals and the DMY/Dmrt1bY genes of the teleost fish medaka have been characterized as sex-determining genes that trigger formation of the testis. However, the molecular mechanism of the ZZ/ZW-type system in vertebrates, including the clawed frog Xenopus laevis, is unknown. Here, we isolated an X. laevis female genome-specific DM-domain gene, DM-W, and obtained molecular evidence of a W-chromosome in this species. The DNA-binding domain of DM-W showed a strikingly high identity (89%) with that of DMRT1, but it had no significant sequence similarity with the transactivation domain of DMRT1. In nonmammalian vertebrates, DMRT1 expression is connected to testis formation. We found DMRT1 or DM-W to be expressed exclusively in the primordial gonads of both ZZ and ZW or ZW tadpoles, respectively. Although DMRT1 showed continued expression after sex determination, DM-W was expressed transiently during sex determination. Interestingly, DM-W mRNA was more abundant than DMRT1 mRNA in the primordial gonads of ZW tadpoles early in sex determination. To assess the role of DM-W, we produced transgenic tadpoles carrying a DM-W expression vector driven by approximately 3 kb of the 5'-flanking sequence of DM-W or by the cytomegalovirus promoter. Importantly, some developing gonads of ZZ transgenic tadpoles showed ovarian cavities and primary oocytes with both drivers, suggesting that DM-W is crucial for primary ovary formation. Taken together, these results suggest that DM-W is a likely sex (ovary)-determining gene in X. laevis.

USF is involved in the transcriptional regulation of the chipmunk HP-25 gene.

The hibernation-specific HP-25 gene is expressed specifically in the liver of the chipmunk, a hibernating species of the squirrel family, and exists as a pseudogene in the tree squirrel, a nonhibernating species. Our previous studies have revealed two positively acting transcriptional regulatory regions in the 5'-flanking region of the chipmunk HP-25 gene, one from -260 to -80 and another from -80 to -59, and a pivotal role for hepatocyte nuclear factor-4 (HNF-4), which binds to the proximal regulatory region, in HP-25's liver-specific transcription. A database search for transcription factor binding sites in the distal regulatory region indicated the presence of two potential binding sites for upstream stimulatory factor (USF): one between -161 and -156 and the other between -143 and -138. In an electrophoretic mobility shift assay (EMSA), in vitro-translated USF bound only to the sequence from -143 to -138. USF did not bind the corresponding sequence of the tree squirrel HP-25 gene, which has two base substitutions. Transient transfection studies in COS-7 cells showed that USF could activate the transcription of the chipmunk HP-25 gene, and that tree squirrel-type base substitutions in the USF-binding site aborted the transactivation by USF. By chromatin immunoprecipitation (ChIP) analysis, we confirmed that USF bound to the promoter region of the HP-25 gene in the chipmunk liver, and not in the kidney or heart. These results indicate that USF is involved in the transcriptional regulation of the chipmunk HP-25 gene in the liver, and that the base substitutions in the USF-binding site contribute to the lack of HP-25 gene expression in the tree squirrel.

Expression and promoter analysis of Xenopus DMRT1 and functional characterization of the transactivation property of its protein.

The doublesex and mab-3-related transcription factor 1 (DMRT1) is involved in testis formation in a variety of vertebrates. In the teleost fish, Medaka, DMY/DMRT1Y on the Y chromosome, a duplicate of the autosomal DMRT1 gene, is characterized as a sex-determining gene. We report here the characterization of the Xenopus DMRT1 genes. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that X. laevis DMRT1 was expressed throughout the embryo during early development and was restricted to the primordial gonads after embryogenesis. Whole-mount in situ hybridization analysis of the gene confirmed its specific expression in the primordial gonads. To study the transcriptional control of DMRT1 gene expression, we isolated the predicted promoter region of X. tropicalis DMRT1 using databases for this species. Analysis of transgenic tadpoles with a green fluorescence protein (GFP) reporter showed that approximately 3 kb of the 5'-flanking sequence of the DMRT1 gene was implicated in DMRT1 expression in the primordial gonads. We also showed that the C-terminal region of DMRT1 functioned as a transactivation domain in cultured cells, by a luciferase reporter assay using fusion proteins with the DNA-binding domain of GAL4. These findings suggest that DMRT1 functions as an activator of one or more genes involved in sex determination or gonadal differentiation.

Isolation and characterization of recombinant Drosophila Copia aspartic proteinase.

The wild type Copia Gag precursor protein of Drosophila melanogaster expressed in Escherichia coli was shown to be processed autocatalytically to generate two daughter proteins with molecular masses of 33 and 23 kDa on SDS/PAGE. The active-site motif of aspartic proteinases, Asp-Ser-Gly, was present in the 23 kDa protein corresponding to the C-terminal half of the precursor protein. The coding region of this daughter protein (152 residues) in the copia gag gene was expressed in E. coli to produce the recombinant enzyme protein as inclusion bodies, which was then purified and refolded to create the active enzyme. Using the peptide substrate His-Gly-Ile-Ala-Phe-Met-Val-Lys-Glu-Val-Asn (cleavage site: Phe-Met) designed on the basis of the sequence of the cleavage-site region of the precursor protein, the enzymatic properties of the proteinase were investigated. The optimum pH and temperature of the proteinase toward the synthetic peptide were 4.0 and 70 degrees C respectively. The proteolytic activity was increased with increasing NaCl concentration in the reaction mixture, the optimum concentration being 2 M. Pepstatin A strongly inhibited the enzyme, with a Ki value of 15 nM at pH 4.0. On the other hand, the active-site residue mutant, in which the putative catalytic aspartic acid residue was mutated to an alanine residue, had no activity. These results show that the Copia proteinase belongs to the family of aspartic proteinases including HIV proteinase. The B-chain of oxidized bovine insulin was hydrolysed at the Leu15-Tyr16 bond fairly selectively. Thus the recombinant Copia proteinase partially resembles HIV proteinase, but is significantly different from it in certain aspects.

Sox15 enhances trophoblast giant cell differentiation induced by Hand1 in mouse placenta.

Some members of the Sry-type HMG box (Sox) protein family play important roles in embryogenesis as transcription factors. Here, we report that Sox15 transcripts were much more abundant in mouse placenta than in the fetus, the yolk sac, or several adult tissues. In situ hybridization analysis of the mouse E8.0 conceptus indicated that Sox15 mRNA was predominantly expressed in the trophoblast giant cells of the placenta. We also observed that the amount of Sox15 mRNA dramatically increased during the differentiation of mouse trophoblast stem cells. Ectopic expression of Sox15 in Rat choriocarcinoma cells enhanced the giant cell differentiation induced by a bHLH transcription factor, Hand1. Binding experiments in cotransfected 293 T cells and in vitro revealed that Sox15 interacted with Hand1. We next examined the effects of this interaction on the transcriptional activity of Hand1 and Sox15 using the luciferase reporter assay. Overexpression of Hand1 repressed the Sox15-driven reporter expression, but Sox15 enhanced the Hand1-driven transcription. This enhancement required both the Hand1-binding region and the transactivation domain of Sox15. These results may suggest that the increased transcriptional activity of Hand1 caused by Sox15 might promote the transcription of the target gene resulting in the trophoblast giant cell differentiation in the mouse placenta.

Xenopus death-domain-containing proteins FADD and RIP1 synergistically activate JNK and NF-kappaB.

BACKGROUND INFORMATION: Death receptors (DRs) induce intracellular signalling upon engagement of their cognate ligands, leading to apoptosis, cell survival or pro-inflammatory responses. In mammals, DR signalling is mediated by the recruitment of several DD (death domain)-containing molecules, such as FADD (Fas-associated DD) and RIP1 (receptor-interacting protein 1). RESULTS: To elucidate the molecular mechanisms of intracellular DR signalling in Xenopus, we have isolated cDNAs encoding xFADD (Xenopus FADD), and xRIP1 and its short isoform xRIP1beta, which is produced by alternative splicing of the xRIP1 gene. These DD-containing proteins interacted with Xenopus DR members xDR-M1 and xDR-M2 through their DDs in co-transfected HEK-293T cells. Overexpression of xFADD activated not only xCaspase 8, but also AP-1 (activator protein 1), which reflects activation of JNK (c-Jun N-terminal kinase) and NF-kappaB (nuclear factor kappaB). A comparative analysis of xRIP1, a kinase-dead mutant of xRIP1 and xRIP1beta indicated that the kinase activity of xRIP1 was required for the activation of AP-1 and NF-kappaB. Interestingly, xFADD and xRIP1 interacted with each other via their DDs, and the expression of a mutant xRIP1 containing only the DD (xRIP1-DD) repressed the xFADD-induced activation of NF-kappaB and AP-1. xFADD and xRIP1 synergistically induced the activation of AP-1 and NF-kappaB, both of which were partially mediated by TRAF2 (tumour-necrosis-factor-receptor-associated factor 2) and TAK1 (transforming-growth-factor-beta-activated kinase 1). We also found that the activation pathways of NF-kappaB induced by xDR-M2 were inhibited by xRIP1-DD. CONCLUSIONS: Xenopus FADD, RIP1 and its splice variant RIP1beta have been characterized. Interaction of xFADD and xRIP1 induced synergistic activation of JNK and NF-kappaB. In addition, the NF-kappaB activation induced by xDR-M2 was partially mediated by xRIP1.

Transcriptional regulation of the rainbow trout CYP19a gene by FTZ-F1 homologue.

In rainbow trout, there are at least two CYP19 genes (CYP19a and CYP19b). They encode distinct P450arom isozymes that are differentially expressed in the ovary and brain. To understand the transcriptional regulation of the rainbow trout CYP19a (rtCYP19a) gene in the ovary, we isolated its 5'-flanking region. The presence of potential FTZ-F1-binding sites prompted us to isolate the cDNA encoding a rainbow trout FTZ-F1 homologue (rtFTZ-F1) and analyze its effect on the rtCYP19a gene transcriptional activity. RT-PCR analysis showed overlapping expression of the rtCYP19a and rtFTZ-F1 genes in the ovary. Transient transfection studies in Chinese hamster ovary-derived CHO-K1 cells revealed that the region from -247 to -105, which contains three potential FTZ-F1-binding sites, was required for rtFTZ-F1-mediated transcriptional activation of the rtCYP19a gene. Among the three potential binding sites, the two from -150 to -142 and from -118 to -110 showed strong affinities for rtFTZ-F1 in gel shift assays, and base substitutions in either site almost abolished the transcriptional activation by rtFTZ-F1. Taken together, these results demonstrate that rtFTZ-F1 plays an important role in the transcriptional regulation of the rtCYP19a gene in the ovary.

CpG methylation at the USF-binding site is important for the liver-specific transcription of the chipmunk HP-27 gene.

The chipmunk hibernation-specific HP-27 gene is expressed specifically in the liver and has a CpG-poor promoter. To reveal how the liver-specific transcription of the HP-27 gene is regulated, we performed yeast one-hybrid screening of a chipmunk liver cDNA library. A 5'-flanking sequence of the HP-27 gene, extending from -170 to -140 and containing an E-box (5'-CACGTG-3'), is essential for the liver-specific transcription of HP-27. We used this sequence as bait and found that a ubiquitously expressed transcription factor, USF (upstream stimulatory factor), bound to the E-box. In COS-7 cells, USF activated transcription from the HP-27 gene promoter. We then used bisulphite genomic sequencing to analyse the methylation status of the four CpG dinucleotides that lie in the 5'-flanking sequence of the HP-27 gene up to -450, to investigate how the ubiquitously expressed USF activates transcription of the HP-27 gene only in the liver, while its transcription is repressed elsewhere. The only difference in methylation in the tissues tested was in the CpG dinucleotide in the USF-binding site, which was hypomethylated in the liver, but highly methylated in the kidney and heart. The specific methylation of the CpG dinucleotide at the USF-binding site impeded both the binding of USF and its transcriptional activation of the HP-27 gene. Chromatin immunoprecipitation using anti-USF antibodies revealed that USF bound to the HP-27 gene promoter in the liver, but not in the kidney or heart. Thus CpG methylation at the USF-binding site functions in establishing and maintaining tissue-specific transcription from the CpG-poor HP-27 gene promoter.

Promoter activity of sea lamprey proopiocortin and proopiomelanotropin genes in AtT-20/D16v cells.

Adrenocorticotropic hormone (ACTH) and melanophore-stimulating hormone (MSH) are produced in the pars distalis and pars intermedia, respectively, throughout vertebrates. These hormones together with beta-endorphin are encoded on a single gene proopiomelanocortin (POMC) in gnathostomes, but in the sea lamprey, an agnathan, ACTH and MSH are encoded on two separate genes, proopiocortin (POC) and proopiomelanotropin (POM), respectively. Moreover, the nucleotide sequences of 5'-flanking regions of the POC and POM genes are significantly different from each other. To investigate the potential promoter activities of the POC and POM genes, we constructed promoter reporter plasmids by fusing the 5' flanking sequences (nucleotides -1151 to +31 and -2510 to +51, respectively) to a firefly luciferase gene. Transient transfection studies in AtT-20/D16v cells, which derived from a mouse pituitary tumor cell line, revealed that the 5'-flanking sequence of the POC gene did not exhibit promoter activity, whereas that of the POM gene showed the activity at high levels nearly equivalent to SV40 promoter. Analysis of a series of the 5'-deleted reporter for the POM gene in the AtT-20/D16v cells demonstrated that the 422 bp 5'-flanking sequence was sufficient for promoter activity, while the sequence from -853 to -574 may contain negatively acting regulatory elements. Because the POC and POM genes are supposed to have differentiated from a common ancestor, during evolution, the POC gene may lack essential element(s) for expression in the AtT-20/D16v cells.

The complete genomic sequence of Nocardia farcinica IFM 10152.

We determined the genomic sequence of Nocardia farcinica IFM 10152, a clinical isolate, and revealed the molecular basis of its versatility. The genome consists of a single circular chromosome of 6,021,225 bp with an average G+C content of 70.8% and two plasmids of 184,027 (pNF1) and 87,093 (pNF2) bp with average G+C contents of 67.2% and 68.4%, respectively. The chromosome encoded 5,674 putative protein-coding sequences, including many candidate genes for virulence and multidrug resistance as well as secondary metabolism. Analyses of paralogous protein families suggest that gene duplications have resulted in a bacterium that can survive not only in soil environments but also in animal tissues, resulting in disease.

HNF-1 regulates the promoter activity of the HP-27 gene.

The hibernation-specific HP-27 gene is expressed specifically in the liver of the chipmunk, a hibernating species of the squirrel family, and exists as a pseudogene in the tree squirrel, a nonhibernating species. In the promoter region, the chipmunk gene has a potential HNF-1 binding site, and the tree squirrel gene has two base substitutions in the corresponding sequence. In this paper, we investigated the role of HNF-1 in the HP-27 gene promoter activity. Gel retardation assays with in vitro-translated HNF-1 and super-shift assays using HepG2 nuclear extracts and an anti-HNF-1 antibody revealed that HNF-1 bound to the chipmunk gene sequence. HNF-1 also bound to the tree squirrel sequence, but with much lower affinity. In HepG2 cells, HNF-1 activated transcription from the chipmunk HP-27 gene, but not from the tree squirrel gene. In addition, the tree squirrel-type base substitutions in the HNF-1 binding site greatly reduced the promoter activity of the chipmunk HP-27 gene. These results indicate that HNF-1 is required for the promoter activity of the chipmunk HP-27 gene, and that the base substitutions in the HNF-1 binding site are involved in the lack of HP-27 gene expression in the tree squirrel.

Analysis of gene structures and promoter activities of the chipmunk alpha(1)-antitrypsin-like genes.

The chipmunk hibernation-specific protein HP-55 is a component of a 140-kDa complex whose levels are drastically decreased in the blood during hibernation. It is highly homologous to alpha(1)-antitrypsin (AT). In the chipmunk, several alpha(1)-AT-like genes in addition to HP-55 (or CM55-ML) are expressed in the liver and have distinct patterns of regulation during hibernation: in hibernating chipmunks, the level of CM55-ML gene expression is greatly reduced, that of the CM55-MS gene is slightly increased, and the expression of the CM55-MM gene is hardly affected. As a first step towards understanding the hibernation-associated gene regulation of these chipmunk alpha(1)-AT-like genes, we isolated genomic clones for the CM55-ML, CM55-MM, and CM55-MS genes, and analyzed their promoter activities. These alpha(1)-AT-like genes are composed of five exons, and show a similar gene structure to that of the human alpha(1)-AT gene, suggesting that they were generated by the duplication of an ancestral alpha(1)-AT gene. Transient transfection studies using HepG2 and COS-7 cells revealed that for all three alpha(1)-AT-like genes, approximately 150-bp 5' flanking sequences were sufficient for the liver-specific promoter activity, and that the binding of HNF-1 to the promoter region could transactivate transcription. In addition, analysis of the activity of chimeric promoters composed of CM55-ML and CM55-MS gene sequences indicated that the lack of a TATA box-like sequence in the CM55-MS gene is responsible for its weak promoter activity.

Xenopus death receptor-M1 and -M2, new members of the tumor necrosis factor receptor superfamily, trigger apoptotic signaling by differential mechanisms.

Signaling through the tumor necrosis factor receptor (TNFR) superfamily can lead to apoptosis or promote cell survival, proliferation, and differentiation. A subset of this family, including TNFR1 and Fas, signals cell death via an intracellular death domain and therefore is termed the death receptor (DR) family. In this study, we identified new members of the DR family, designated xDR-M1 and xDR-M2, in Xenopus laevis. The two proteins, which show high homology (71.7% identity), have characteristics of the DR family, that is, three cysteine-rich domains, a transmembrane domain, and a death domain. To elucidate how members of xDR-M subfamily regulate cell death and survival, we examined the intracellular signaling mediated by these receptors in 293T and A6 cells. Overexpression of xDR-M2 induced apoptosis and activated caspase-8, c-Jun N-terminal kinase, and nuclear factor-kappaB, although its death domain to a greater extent than did that of xDR-M1 in 293T cells. A caspase-8 inhibitor potently blocked this apoptosis induced by xDR-M2. In contrast, xDR-M1 showed a greater ability to induce apoptosis through its death domain than did xDR-M2 in A6 cells. Interestingly, a general serine protease inhibitor, but not the caspase-8 inhibitor, blocked the xDR-M1-induced apoptosis. These results imply that activation of caspase-8 or serine protease(s) may be required for the xDR-M2- or xDR-M1-induced apoptosis, respectively. Although xDR-M1 and xDR-M2 are very similar to each other, the difference in their death domains may result in diverse signaling, suggesting distinct roles of xDR-M1 and xDR-M2 in cell death or survival.

Caspase-mediated cleavage of JNK during stress-induced apoptosis.

The c-Jun N-terminal kinases (JNKs) are a subfamily of the mitogen-activated protein kinases (MAPKs). The JNKs are encoded by three separate genes (jnk1, jnk2, and jnk3), which are spliced alternatively to create 10 JNK isoforms that are either p46 or p54 in size. In this study, we found that the p52 form of JNK emerged in human leukemia MOLT-4 or U937 cells following X-irradiation or heat treatment. The accumulation of p52 coincided with the reduction of p54 JNK. On the other hand, the amounts of p46 JNK did not change by X-irradiation. Induction of the p52 form of JNK also paralleled the appearance of the active form of caspase-3 and was suppressed by a caspase-specific inhibitor, Ac-DEVD-CHO, but not by Ac-YVAD-CHO. In vitro cleavage assays indicated that recombinant human JNK1beta2 and JNK2beta2 were cleaved by caspase-3, and that the mutation of aspartic acid at position 413 of JNK1beta2 or 410 of JNK2beta2 to alanine abolished the cleavage. Altogether, our results demonstrated that p54 JNKs, at least JNK1beta2 and JNK2beta2, were new selective targets of caspases in JNK splicing variants, and suggested that the p52 form could serve as a marker of apoptosis.

Amplification, up-regulation and over-expression of DVL-1, the human counterpart of the Drosophila disheveled gene, in primary breast cancers.

Wnt proteins form a family of highly conserved, secreted signaling molecules that regulate cell-to-cell interactions during embryogenesis. Wnt genes and Wnt signaling are also implicated in cancer. It has been shown that Wnt proteins bind to receptors of the frizzled family on the cell surface. Through several cytoplasmic relay components including DVL-1, the human counterpart of the Drosophila disheveled gene, the signal is transduced to beta-catenin, which then enters the nucleus and forms a complex with T-cell factor (TCF) to activate transcription of Wnt target genes. We describe here the amplification of DVL-1 in 13 of 24 primary breast cancers examined, and increased expression of this gene in 11 of those tumors in comparison to corresponding non-cancerous breast tissues. Immunohistochemical staining demonstrated that DVL-1 protein was prominent in the cytoplasm of cancer cells, but not in normal epithelial cells of the mammary duct or in myoepithelial cells. These data indicate that amplification and increased expression of the DVL-1 gene may play some role in human breast carcinogenesis through derangement of the Wnt signaling pathway.