The TGF-β superfamily comprises pleiotropic cytokines that regulate SMAD and non-SMAD signaling. TGF-β-SMAD signal transduction is known to be involved in tissue fibrosis, including renal fibrosis. Here, we found that 1,25-dihydroxyvitamin D 3 -bound [1,25(OH) 2 D 3 -bound] vitamin D receptor (VDR) specifically inhibits TGF-β-SMAD signal transduction through direct interaction with SMAD3. In mouse models of tissue fibrosis, 1,25(OH) 2 D 3 treatment prevented renal fibrosis through the suppression of TGF-β-SMAD signal transduction. Based on the structure of the VDR-ligand complex, we generated 2 synthetic ligands. These ligands selectively inhibited TGF-β-SMAD signal transduction without activating VDR-mediated transcription and significantly attenuated renal fibrosis in mice. These results indicate that 1,25(OH) 2 D 3 -dependent suppression of TGF-β-SMAD signal transduction is independent of VDR-mediated transcriptional activity. In addition, these ligands did not cause hypercalcemia resulting from stimulation of the transcriptional activity of the VDR. Thus, our study provides a new strategy for generating chemical compounds that specifically inhibit TGF-β-SMAD signal transduction. Since TGF-β-SMAD signal transduction is reportedly involved in several disorders, our results will aid in the development of new drugs that do not cause detectable adverse effects, such as hypercalcemia.

Novel N-substituted phthalimides (2-substituted 1H-isoindole-1,3-diones) were prepared, and their effects on tumor necrosis factor-alpha (TNF-alpha) production by human leukemia cell line HL-60 stimulated with 12-O-tetradecanoylphorbol 13-acetate (TPA) or okadaic acid (OA) were examined. A structure-activity relationship study of the N-phenylphthalimides and N-benzylphthalimides revealed that their enhancing effect on TPA-induced TNF-alpha production by HL-60 cells and their inhibiting effect on OA-induced TNF-alpha production by HL-60 cells are only partially correlated.

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Human peroxisome proliferator-activated receptors (hPPARs) are ligand-dependent transcription factors that control various biological responses, and there are three subtypes: hPPARα, hPPARδ, and hPPARγ. We report here that α-substituted phenylpropanoic acid-type hPPAR agonists with similar structure bind to the hPPAR ligand binding domain (LBD) in different conformations, depending on the receptor subtype. These results might indicate that hPPAR ligand binding pockets have multiple binding points that can be utilized to accommodate structurally flexible hPPAR ligands.

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