Involvement of MAP kinase cascades in Smad7 transcriptional regulation

Smad7 transcription is known to be regulated by TGF-beta to form a negative -feedback loop of TGF-beta -mediated biological responses. In this study, w e sought to determine whether other signaling cascades, especially mitogen- activated protein (MAP) kinases, might be involved in the transcriptional r egulation of Smad7. Hyperosmolarity (500 mOsm/kg H2O) or anisomycin (10 mug /ml) potentiated TGF-beta -induced increases of Smad7 mRNA abundance in nor mal rat kidney fibroblasts. SB203580 (10 muM) treatment had no effect on ba sal and TGF-beta -induced Smad7 mRNA abundance, and the overexpression of k inase-negative ATF2 had no effect on Smad7 promoter activity. On the other hand, overexpression of dominant-negative JNK and dominant-negative c-Jun s ignificantly attenuated the TGF-beta -induced increases of Smad7 mRNA abund ance and promoter activity, respectively. Mutations of the AP-1 element nea r the Smad-binding element in the rat Smad7 promoter also completely abolis hed TGF-beta -induced Smad7 promoter activity. These results suggested that the JNK cascade, not p38 kinase, cooperated with the Small signaling to in duce Smad7 transcription through the AP-1 element. Serum treatment (10%) at tenuated the TGF-beta -induced Smad7 mRNA increase, and PD98059 (30 muM) tr eatment increased the basal and TGF-beta -induced Smad7 promoter activity. Gel shift analysis revealed that serum treatment decreased the amount of nu clear Smad complex that PD98059 treatment was shown to restore. These resul ts indicated that ERK activation negatively regulated Smad7 transcription p ossibly by inhibiting translocation of Smad complex to nuclei. In conclusio n, JNK cascade and ERK cascade are important positive and negative regulato rs of Smad7 transcription, respectively. (C) 2001 Elsevier Science.