ASK1 and ASK2 differentially regulate the counteracting roles of apoptosis and inflammation in tumorigenesis.

Apoptosis and inflammation generally exert opposite effects on tumorigenesis: apoptosis serves as a barrier to tumour initiation, whereas inflammation promotes tumorigenesis. Although both events are induced by various common stressors, relatively little is known about the stress-induced signalling pathways regulating these events in tumorigenesis. Here, we show that stress-activated MAP3Ks, ASK1 and ASK2, which are involved in cellular responses to various stressors such as reactive oxygen species, differentially regulate the initiation and promotion of tumorigenesis. ASK2 in cooperation with ASK1 functioned as a tumour suppressor by exerting proapoptotic activity in epithelial cells, which was consistent with the reduction in ASK2 expression in human cancer cells and tissues. In contrast, ASK1-dependent cytokine production in inflammatory cells promoted tumorigenesis. Our findings suggest that ASK1 and ASK2 are critically involved in tumorigenesis by differentially regulating apoptosis and inflammation.

Trps1 functions downstream of Bmp7 in kidney development.

During embryonic development, the mesenchyme of the lungs, gut, kidneys, and other tissues expresses Trps1, an atypical member of the GATA-type family of transcription factors. Our previous work suggested the possibility that Trps1 acts downstream of bone morphogenic protein 7 (Bmp7), which is essential for normal renal development. To examine the role of Trps1 during early renal development, we generated Trps1-deficient mice and examined their renal histology. Compared with wild-type mice, Trps1-deficient newborn mice had fewer tubules and glomeruli, an expanded renal interstitium, and numerous uninduced metanephric mesenchymal cells, which resulted in fewer nephrons. In wild-type kidneys, Trps1 expression was present in ureteric buds, cap mesenchyme, and renal vesicles, whereas Trps1 was virtually absent in Bmp7-deficient kidneys. Furthermore, Trps1-deficient kidneys had low levels of Pax2 and Wt1, which are markers of condensed mesenchymal cells, suggesting that a lack of Trps1 affects the differentiation of cap mesenchyme to renal vesicles. In cultured metanephric mesenchymal cells, Bmp7 induced Trps1 and E-cadherin and downregulated vimentin. Knockdown of Trps1 with small interference RNA inhibited this Bmp7-induced mesenchymal-to-epithelial transition. Last, whole-mount in situ hybridization of Wnt9b and Wnt4 demonstrated prolonged branching of ureteric buds and sparse cap mesenchyme in the kidneys of Trps1-deficient mice. Taken together, these findings suggest that normal formation of nephrons requires Trps1, which mediates mesenchymal-to-epithelial transition and ureteric bud branching during early renal development.

Trps1 plays a pivotal role downstream of Gdf5 signaling in promoting chondrogenesis and apoptosis of ATDC5 cells.

Tricho-rhino-phalangeal syndrome (TRPS) is an autosomal dominant skeletal disorder caused by mutations of TRPS1. Based on the similar expression patterns of Trps1 and Gdf5, we hypothesized a possible functional interaction between these two molecules. Using a chondrogenic cell line (ATDC5), we investigated the association of Gdf5-mediated signaling pathways with Trps1 and the phenotypic changes of ATDC5 cells due to over-expression or suppression of Trps1. Treatment of cells with Gdf5 enhanced Trps1 protein levels and phosphorylation of p38 mitogen-activated protein kinase (MAPK) in a dose-dependent manner. Nuclear translocation of Trps1 was also induced by Gdf5. These effects were blocked by a dominant negative form of activin-linked kinase 6 (dn-Alk6) and by SB203580, an inhibitor of the p38 MAPK pathway. Conversely, Gdf5 expression was suppressed by the over-expression of Trps1. Trps1-overexpressing ATDC5 (O/E) cells differentiated into chondrocytes more quickly than mock-infected control cells, whereas cells transfected with dn-Alk6 showed slower differentiation. On the other hand, O/E cells showed an increase of apoptosis along with the up-regulation of cleaved caspase 3 and down-regulation of Bcl-2, whereas dn-Alk6 cells showed suppression of apoptosis. In conclusion, Trps1 acts downstream of the Gdf5 signaling pathway and promotes the differentiation and apoptosis of ATDC5 cells.

Trps1 deficiency enlarges the proliferative zone of growth plate cartilage by upregulation of Pthrp.

We have reported that elongation of the columnar proliferative zone of long bone growth plates in Trps1-/- mice during the late fetal stage in the previous study [1]. Since expression of Trps1 protein was found to overlap with that of mRNAs for Indian hedgehog (Ihh), PTH/PTHrP receptor (PPR), and PTHrP, we hypothesized that Trps1 may inhibit the hypertrophic differentiation of chondrocytes by interacting with the Ihh/PTHrP feedback loop. To investigate whether Trps1 has a role in this Ihh/PTHrP feedback loop, we compared the growth plates of Trps1-/- mice and wild-type (Trps1+/+) mice. Immunohistochemistry showed that Trps1 protein was strongly expressed in the periarticular and prehypertrophic zones of the fetal growth plate in wild-type mice on embryonic day 18.5 (E18.5). On the other hand, Ihh, PPR, and PTHrP mRNAs were predominantly expressed in the prehypertrophic zone at this stage of development. While expression of Ihh and PPR by prehypertrophic chondrocytes was unaffected in the growth plates of Trps1-/- mice, the range of PTHrP expression was expanded toward the proliferating zone in these mice. Quantitative real-time PCR analysis demonstrated upregulation of PTHrP in the epiphyseal growth plates of Trps1-/- mice. Furthermore, promoter analysis combined with the chromatin immunoprecipitation (ChIP) assay demonstrated that direct binding of Trps1 to the PTHrP promoter suppressed the transcription of PTHrP. Finally, organ culture of E14.5 tibiae in the absence or the presence of Pthrp revealed that the proliferative zone of the tibial growth plate was elongated by culture with Pthrp compared to that of control tibiae. Taken together, these data provide the first genetic evidence that lack of Trps1 leads to overexpression of PTHrP, and that Trps1 is required to maintain the normal organization of chondrocytes in the growth plate.

TNF-alpha deficiency accelerates renal tubular interstitial fibrosis in the late stage of ureteral obstruction.

TNF-alpha and TGF-beta1 have a complementary relationship in fibrogenesis. This study was performed to investigate the role of TNF-alpha in renal tubular interstitial fibrosis. We compared the extent of renal tubular interstitial fibrosis after unilateral ureteral obstruction (UUO) between wild-type and TNF-alpha-deficient mice by using immunohistochemistry, enzyme-linked immunoassay, and the real-time polymerase chain reaction (PCR). In comparison with wild-type mice, there was no significant difference in the extent of renal fibrosis in the TNF-alpha-deficient mice at 2 weeks after UUO. By 4 weeks after UUO, however, fibrosis marked an increase in the TNF-alpha-deficient mice to exceed that in the wild-type mice. Immunohistochemistry, enzyme-linked immunoassay, and real-time PCR demonstrated an increase of extracellular matrix in the kidneys of TNF-alpha-deficient mice that was caused by upregulation of the expression of TGF-beta1 and Snail, which in turn resulted from an increase of infiltrating macrophages. Real-time PCR revealed an increase in expression of the TNF-alpha type 2 receptor at 4 weeks after UUO, which explained the difference in the extent of renal fibrosis between TNF-alpha-deficient and wild-type mice. In the chronic stage of renal fibrosis, TNF-alpha suppresses the infiltration of macrophages by inducing TNF-alpha type 2 receptor expression, resulting in the amelioration of fibrosis.

Apoptosis signal-regulating kinase (ASK) 2 functions as a mitogen-activated protein kinase kinase kinase in a heteromeric complex with ASK1.

Apoptosis signal-regulating kinase (ASK) 1 is a mitogen-activated protein kinase kinase kinase (MAP3K) in the c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase pathways that play multiple important roles in cytokine and stress responses. Here we show that ASK2, a highly related serine/threonine kinase to ASK1, also functions as a MAP3K only in a heteromeric complex with ASK1. We found that endogenous ASK2 was constitutively degraded in ASK1-deficient cells, suggesting that ASK1 is required for the stability of ASK2. ASK2 in a heteromeric complex with a kinase-negative mutant of ASK1 (ASK1-KN) effectively activated MAP2K and was more competent to respond to oxidative stress than ASK2 alone. Knockdown of ASK2 revealed that ASK2 was required for oxidative stress-induced JNK activation. These results suggest that ASK2 forms a functional MAP3K complex with ASK1, in which ASK1 supports the stability and the active configuration of ASK2. Moreover, ASK2 was found to activate ASK1 by direct phosphorylation, suggesting that ASK1 and ASK2 in a heteromeric complex facilitate their activities to each other by distinct mechanisms. Such a formation of functional heteromeric complex between different MAP3Ks may be advantageous for cells to cope with a wide variety of stimuli by fine regulation of cellular responses.