Suppression of TGF-beta signaling by conophylline via upregulation of c-Jun expression.
In the course of screening for inhibitors of transforming-growth factor-beta (TGF-beta) functions we found that conophylline, a vinca alkaloid, inhibited TGF-beta-induced apoptosis in rat hepatoma cells. Because conophylline also inhibited TGF-b-induced promoter activity in mink lung cells, we studied the mechanism of the inhibition in this cell line. Conophylline did not inhibit nuclear translocation of Smad2. Instead, we found that conophylline increased the expression of c-Jun, which had been earlier shown to interact with the corepressor TGIF to suppress the transcriptional activity dependent on Smad2. Conophylline attenuated the interaction between the Smad2 complex and p300 but enhanced that between the Smad2 complex and TGIF. In cells overexpressing c-Jun, suppression of promoter activity induced by TGF-beta and the enhancement of the association of the Smad2 complex with TGIF were also observed. Thus, our data suggest that inhibition of TGF-beta-induced promoter activity by conophylline can be attributed to its potency in modulating the interaction of downstream transcriptional factors via upregulation of c-Jun expression.
Atsumi
S
S
Microbial Chemistry Research Center, 3-14-23 Kamioosaki, Shinagawa-ku, Tokyo 141-0021, Japan. atsumi@bikaken.or.jp
Nagasawa
A
A
Koyano
T
T
Kowithayakornd
T
T
Umezawa
K
K
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D016758:Genes, jun; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011401:Promoter Regions, Genetic; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D051899:Smad2 Protein; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors*; D015854:Up-Regulation; D014748:Vinca Alkaloids / Q000494:pharmacology*
D004268:DNA-Binding Proteins; D051899:Smad2 Protein; C497784:Smad2 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D014748:Vinca Alkaloids; C099167:conophylline; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases