Cytokinins are a class of plant hormones that are central to the regulation of cell division and differentiation in plants. It has been proposed that they are detected by a two-component system, because overexpression of the histidine kinase gene CKI1 induces typical cytokinin responses and genes for a set of response regulators of two-component systems can be induced by cytokinins. Two-component systems use a histidine kinase as an environmental sensor and rely on a phosphorelay for signal transduction. They are common in microorganisms, and are also emerging as important signal detection routes in plants. Here we report the identification of a cytokinin receptor. We identified Arabidopsis cre1 (cytokinin response 1) mutants, which exhibited reduced responses to cytokinins. The mutated gene CRE1 encodes a histidine kinase. CRE1 expression conferred a cytokinin-dependent growth phenotype on a yeast mutant that lacked the endogenous histidine kinase SLN1 (ref. 10), providing direct evidence that CRE1 is a cytokinin receptor. We also provide evidence that cytokinins can activate CRE1 to initiate phosphorelay signalling.

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Epithelial-mesenchymal transition (EMT) is an important mechanism for phenotypic conversion in normal development and disease states such as tissue fibrosis and metastasis. While this conversion of epithelia is under tight transcriptional control, few of the key transcriptional proteins are known. Fibroblasts produced by EMT express a gene encoding fibroblast-specific protein 1 (FSP1), which is regulated by a proximal cisacting promoter element called fibroblast transcription site-1 (FTS-1). In mass spectrometry, chromatin immunoprecipitation, and siRNA studies, we used FTS-1 as a unique probe for mediators of EMT and identified a complex of 2 proteins, CArG box-binding factor-A (CBF-A) and KRAB-associated protein 1 (KAP-1), that bind this site. Epithelial cells engineered to conditionally express recombinant CBF-A (rCBF-A) activate the transcription of FSP1 and undergo EMT. The FTS-1 response element also exists in the promoters modulating a broader EMT transcriptome, including Twist, and Snail, as well as E-cadherin, β-catenin, ZO 1, vimentin, α1(I) collagen, and α-smooth muscle actin, and the induction of rCBF-A appropriately alters their expression as well. We believe formation of the CBF-A/KAP-1/FTS-1 complex is sufficient for the induction of FSP1 and a novel proximal activator of EMT. IntroductionThe mechanisms governing molecular signals for epithelialmesenchymal transition (EMT) are increasingly more complex (1, 2). Fibrogenesis during wound healing or following organ inflammation depends on the formation and proliferation of new fibroblasts by EMT. We previously described a gene encoding fibroblast-specific protein 1 (FSP1) that activates in epithelia during EMT and is constitutively and selectively present in newly formed fibroblasts thereafter; FSP1, also known as S100A4 in the cancer literature, is an intracellular calcium-binding protein whose appearance is linked to EMT (3-7), tissue fibrosis (4, 8), pulmonary vascular disease (9), increased tumor cell motility and invasiveness (10), and metastatic tumor development (11-16). FSP1 helps epithelia transition to new morphology and motility based on its ability to influence levels of intracellular calcium and actin disassembly when transfected into cultured cells. The important role of FSP1 in EMT is underscored by findings that induction of EMT in vitro by epithelial growth factor (EGF) and TGF-β is blocked by antisense oligomers against mRNA encoding FSP1 (6) and that levels of mRNA encoding E-cadherin are inversely correlated with FSP1 expression in invasive lines of squamous cell carcinoma (17).The transcriptional control of EMT diversifies the lineage specification of epithelia during development (18), lineage com-

Connective tissue growth factor (CTGF) is one of the candidate factors that are thought to mediate the downstream profibrotic action of TGF-␤. However, its precise role in renal interstitial fibrogenesis has not yet been clarified. It was demonstrated previously that CTGF was expressed in tubular epithelial cells that had been engulfed by interstitial fibrosis in the remnant kidney of the subtotal nephrectomy (SNx) model. In the present study, co-cultures of tubular epithelial cells (mProx24) and tubulointerstitial fibroblasts (TFB) that mimic the subepithelial mesenchyme in the kidney were used to study the profibrotic effects of TGF-␤1-induced CTGF. In these co-cultures, TGF-␤1 treatment resulted in significantly increased mRNA levels of type I collagen and fibronectin in the TFB. These effects were both direct and indirect, with the latter being mediated by CTGF derived from the co-cultured mProx24. C onnective tissue growth factor (CTGF) is a 38-kD cysteine-rich peptide that belongs to the emerging CCN (CTGF, cyr 61/cef 10, nov) family of multifunctional growth factors (1-4). Murine CTGF, which is also called fisp-12, promotes chemotaxis, migration, adhesion, proliferation, and differentiation or formation of the extracellular matrix (ECM), depending on whether the target cell is a fibroblast, chondrocyte, or vascular endothelial cell (2). CTGF is induced exclusively by TGF-␤ and is thought to mediate the latter's profibrotic effects by modulating fibroblast cell growth and ECM protein synthesis (1,4). CTGF expression has been shown to increase in a variety of human diseases and experimental disease models that are characterized by fibrosis, including those that affect the kidney, skin, blood vessels, lung, and liver (1,2). In the case of the kidney, CTGF mRNA was shown to be expressed primarily in glomerular mesangial, epithelial, and endothelial cells in IgA nephropathy, focal and segmental glomerulosclerosis, and diabetic nephropathy (5,6). Moreover, CTGF mRNA overexpression was found in tubular epithelial cells and interstitial cells at sites of chronic interstitial damage (5,6). In the remnant kidney of the subtotal nephrectomy (SNx) model and in the kidneys with ureteral obstruction, tubular CTGF was shown to be expressed in response to renal interstitial fibrosis (7,8). These findings strongly suggest that renal interstitial fibrogenesis is mediated by CTGF that is expressed in the tubular epithelial cells. However, whether CTGF plays a direct role in vivo in renal interstitial fibrogenesis remains to be elucidated. In the present study, we demonstrated, using neutralization protocols, that tubular CTGF directly and significantly contributed to TGF-␤1-dependent renal interstitial fibrogenesis. Materials and Methods CTGF Antisense OligodeoxynucleotidesPhosphorothioate-capped oligodeoxynucleotides (ODN) were synthesized by an automated synthesizer. After deprotection, ODN were dissolved in water, extracted with phenol/chloroform/isoamyl alco-

We investigated the mechanism of the anti-fibrotic effects of hepatocyte growth factor (HGF) in the kidney, with respect to its effect on connective tissue growth factor (CTGF), a down-stream, profibrotic mediator of transforming growth factor-beta1 (TGF-beta1). In wild-type (WT) mice with 5/6 nephrectomy (Nx), HGF and TGF-beta1 mRNAs increased transiently in the remnant kidney by week 1 after the Nx, returned to baseline levels, and increased again at weeks 4 to 12. In contrast, CTGF and alpha1(I) procollagen (COLI) mRNAs increased in parallel with HGF and TGF-beta1 during the early stage, but did not re-increase during the late stage. In the case of TGF-beta1 transgenic (TG) mice with 5/6 Nx, excess TGF-beta1 derived from the transgene enhanced CTGF expression significantly in the remnant kidney, accordingly accelerating renal fibrogenesis. Administration of dHGF (5.0 mg/kg/day) to TG mice with 5/6 Nx for 4 weeks from weeks 2 to 6 suppressed CTGF expression in the remnant kidney, attenuating renal fibrosis and improving the survival rate. In an experiment in vitro, renal tubulointerstitial fibroblasts (TFB) were co-cultured with proximal tubular epithelial cells (PTEC). Pretreatment with HGF reduced significantly CTGF induction in PTEC by TGF-beta1, consequently suppressing COLI synthesis in TFB. In conclusion, HGF can block, at least partially, renal fibrogenesis promoted by TGF-beta1 in the remnant kidney, via attenuation of CTGF induction.

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