Smads in human trophoblast cells: expression, regulation and role in TGF-beta-induced transcriptional activity.
Smad proteins have recently been shown to be downstream signaling molecules that transduce TGF-beta signals from cell surface to the nucleus. To determine the mechanisms of TGF-beta action in human trophoblast cells, we investigated the expression and regulation of Smad2,3,4, and 7 mRNAs in a normal trophoblast cell line, NPC, and a cell line derived from choriocarcinoma, JEG-3. Messenger RNAs for Smad2,3,4 and 7 were detected in both NPC and JEG-3 cells. TGF-beta1 induced modest increases in Smad2 and Smad4 mRNA levels without affecting Smad3 mRNA expression in both cell lines. Significant increases in Smad7 mRNA levels in both NPC and JEG-3 cells following TGF-beta1 treatment were observed. TGF-beta1 also induced promoter activity of the Smad7 gene, indicating a direct effect at the level of gene transcription. The transcriptional activity of TGF-beta was examined in JEG-3 cells using two TGF-beta responsive reporter constructs, p3TP-Lux and pAR3-Lux. We found that Smad3 and to a lesser extent, Smad2 and Smad4, enhanced, while Smad7 inhibited, TGF-beta1-induced transcriptional activities. The basal and TGF-beta1-induced transcription can be blocked by overexpression of a dominant negative TGF-beta type II receptor. Taken together, these findings demonstrate that in human trophoblast cell lines, the Smad pathway involved in TGF-beta signal transduction is functional and that TGF-beta plays an autocrine role in regulating gene expression.
Wu
D
D
Department of Biology, York University, 4700 Keele Street, Toronto, M3J 1P3, Ontario, Canada.
Luo
S
S
Wang
Y
Y
Zhuang
L
L
Chen
Y
Y
Peng
C
C
D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D005786:Gene Expression Regulation; D006801:Humans; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D012333:RNA, Messenger; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; C497806:SMAD7 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta