Pin1 Down-regulates Transforming Growth Factor-β (TGF-β) Signaling by Inducing Degradation of Smad Proteins

Abstract

Transforming growth factor-␤ (TGF-␤) is crucial in numerous cellular processes, such as proliferation, differentiation, migration, and apoptosis. TGF-␤ signaling is transduced by intracellular Smad proteins that are regulated by the ubiquitinproteasome system. Smad ubiquitin regulatory factor 2 (Smurf2) prevents TGF-␤ and bone morphogenetic protein signaling by interacting with Smads and inducing their ubiquitinmediated degradation. Here we identified Pin1, a peptidylprolyl cis-trans isomerase, as a novel protein binding Smads. Pin1 interacted with Smad2 and Smad3 but not Smad4; this interaction was enhanced by the phosphorylation of (S/T)P motifs in the Smad linker region. (S/T)P motif phosphorylation also enhanced the interaction of Smad2/3 with Smurf2. Pin1 reduced Smad2/3 protein levels in a manner dependent on its peptidyl-prolyl cis-trans isomerase activity. Knockdown of Pin1 increased the protein levels of endogenous Smad2/3. In addition, Pin1 both enhanced the interaction of Smurf2 with Smads and enhanced Smad ubiquitination. Pin1 inhibited TGF-␤-induced transcription and gene expression, suggesting that Pin1 negatively regulates TGF-␤ signaling by down-regulating Smad2/3 protein levels via induction of Smurf2-mediated ubiquitin-proteasomal degradation.

Pin1 Protein Regulates Smad Protein Signaling and Pulmonary Fibrosis

“…Previous studies in transformed human keratinocytes or prostate cancer cell lines have revealed TGF-␤1-induced interactions between Pin1 and phosphorylated Thr 179 -Pro 180 in the linker region of Smad3 (28,29). In addition, Pin1 knockdown had no effect on TGF-␤1-responsive genes in transformed keratinocytes but did suppress the migration and invasion of prostate cancer cell lines (29).…”

“…R-Smad linkers are also phosphorylated at Ser-Pro and Thr-Pro sites by MAPKs. In tumor cells, these sites in Smad3 are targets for Pin1, although the physiologic consequences or occurrence in normal cells remains unclear (28,29). To test this, lysates from primary Fb were immunoprecipitated with anti-Pin1 followed by immunoblot with anti-Smads.…”

Inactivation of the Carney Complex Gene 1 (Protein Kinase A Regulatory Subunit 1A) Inhibits SMAD3 Expression and TGFβ-Stimulated Apoptosis in Adrenocortical Cells

“…This study shows in vitro as well as in vivo the inhibition of SMAD3 by cAMP and ACTH in the adrenal cortex. This differs from the gonads and reprogrammed tumor cells from pluripotent adrenocortical stem/progenitors adopting a gonad-like differentiation after inhibin a inactivation (39,40). This difference also underlines the tissue-specific effect of cAMP pathway dysregulation in tumorigenesis.…”

Definition of Smad3 Phosphorylation Events That Affect Malignant and Metastatic Behaviors in Breast Cancer Cells

“…Although repression of TGFb signaling by Smad linker phosphorylation was attributed to inhibition of nuclear translocation of Smad2 and Smad3 (10), and proteasomal degradation of Smad3 through poly-ubiquitination (31,32), mice with targeted-disruption of Smurf2 allele have now unveiled Smurf2 binding to the phosphorylated Smad3 linker regions in vivo and subsequent induction of multiple mono-ubiquitination at the MH2 domain, leading to a negative regulation of TGFb signaling by inhibiting the formation of Smad3 complexes acting on target genes (33). This provides a molecular mechanism by which the EPSM has increased transcriptional activity.…”