Orphan nuclear receptor small heterodimer partner inhibits transforming growth factor-beta signaling by repressing SMAD3 transactivation.
Orphan nuclear receptor small heterodimer partner (SHP) is an atypical member of the nuclear receptor superfamily; SHP regulates the nuclear receptor-mediated transcription of target genes but lacks a conventional DNA binding domain. In this study, we demonstrate that SHP represses transforming growth factor-beta (TGF-beta)-induced gene expression through a direct interaction with Smad, a transducer of TGF-beta signaling. Transient transfection studies demonstrate that SHP represses Smad3-induced transcription. In vivo and in vitro protein interaction assays revealed that SHP directly interacts with Smad2 and Smad3 but not with Smad4. Mapping of domains mediating the interaction between SHP and Smad3 showed that the entire N-terminal domain (1-159 amino acids) of SHP and the linker domain of Smad3 are involved in this interaction. In vitro glutathione S-transferase pulldown competition experiments revealed the SHP-mediated repression of Smad3 transactivation through competition with its co-activator p300. SHP also inhibits the activation of endogenous TGF-beta-responsive gene promoters, the p21, Smad7, and plasminogen activator inhibitor-1 (PAI-1) promoters. Moreover, adenovirus-mediated overexpression of SHP decreases PAI-1 mRNA levels, and down-regulation of SHP by a small interfering RNA increases both the transactivation of Smad3 and the PAI-1 mRNA levels. Finally, the PAI-1 gene is expressed in SHP(-/-) mouse hepatocytes at a higher level than in normal hepatocytes. Taken together, these data indicate that SHP is a novel co-regulator of Smad3, and this study provides new insights into regulation of TGF-beta signaling.
Suh
Ji Ho
JH
Hormone Research Center, School of Biological Science and Technology, Chonnam National University, Kwangju 500-757, Republic of Korea.
Huang
Jiansheng
J
Park
Yun-Yong
YY
Seong
Hyun-A
HA
Kim
Dongwook
D
Shong
Minho
M
Ha
Hyunjung
H
Lee
In-Kyu
IK
Lee
Keesook
K
Wang
Li
L
Choi
Hueng-Sik
HS
D000818:Animals; D005786:Gene Expression Regulation; D006367:HeLa Cells; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D051900:Smad3 Protein / Q000502:physiology*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D017395:Plasminogen Activator Inhibitor 1; D018160:Receptors, Cytoplasmic and Nuclear; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; C099713:nuclear receptor subfamily 0, group B, member 2