The mechanisms by which angiotensin II (Ang II) promotes renal fibrosis remain incompletely understood. Ang II both stimulates TGFb signaling and activates the EGF receptor (EGFR), but the relative contribution of these pathways to renal fibrogenesis is unknown. Using a murine model with EGFRdeficient proximal tubules, we demonstrate that upstream activation of EGFR-dependent ERK signaling is critical for mediating sustained TGFb expression in renal fibrosis. Persistent activation of the Ang II receptor stimulated ROS-dependent phosphorylation of Src, leading to sustained EGFRdependent signaling for TGFb expression. Either genetic or pharmacologic inhibition of EGFR significantly decreased TGFb-mediated fibrogenesis. We conclude that TGFb-mediated tissue fibrosis relies on a persistent feed-forward mechanism of EGFR/ERK activation through an unexpected signaling pathway, highlighting EGFR as a potential therapeutic target for modulating tissue fibrogenesis.

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The metabolic syndrome was associated with kidney disease even in subjects without major classical risk factors for chronic kidney disease.

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-

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