Post-transcriptional and post-translational regulation of PTEN by transforming growth factor-beta1.
PTEN is a critical tumor suppressor gene mutated frequently in various human cancers. Previous studies have showed that PTEN mRNA expression is down-regulated by TGF-beta1 in various cell lines. In present study, we have found that TGF-beta1 down-regulates PTEN mRNA and protein expression in a dose- and time-dependent manner in hepatocarcinoma cell line SMMC-7721. Based on the PTEN promoter dual-luciferase report assay, we have found that PTEN transcription is not affected by TGF-beta1. By using transcriptional inhibitor actinomycin D (Act D), the turnover rate of PTEN transcripts appeared to be accelerated during TGF-beta1 stimulation, which indicated that down-regulation of PTEN by TGF-beta1 was post-transcriptional. What interested us was that transfection of PTEN coding sequence increased TGF-beta1-induced degradation of PTEN mRNA, suggesting that PTEN coding region was account for TGF-beta1-mediated down-regulation of PTEN. In addition, TGF-beta1 down-regulated PTEN expression was blocked by the TbetaIR inhibitor SB431542 and the p38 inhibitor SB203580, suggesting Smad and p38 MAPK signal pathways played crucial roles in PTEN down-regulation via TGF-beta1 stimulation. In this study, we also found TGF-beta1 accelerated down-regulation of PTEN through the ubiquitin-proteasome pathway. Collectively, our data clearly demonstrated that TGF-beta1-mediated down-regulation of PTEN was post-transcriptional and post-translational, depending on its coding sequence, Smad and p38-MAPK signal pathways were involved in this down-regulation.
Yang
Yong
Y
Department of Biochemistry and Molecular Biology, Shanghai Medical College, Fudan University, Shanghai 200032, China.
Zhou
Feng
F
Fang
Zengyu
Z
Wang
Liying
L
Li
Zengxia
Z
Sun
Lidong
L
Wang
Can
C
Yao
Wantong
W
Cai
Xiumei
X
Jin
Jiawei
J
Zha
Xiliang
X
D000818:Animals; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008113:Liver Neoplasms; D051059:PTEN Phosphohydrolase / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human