title: Small C-terminal domain phosphatases dephosphorylate the regulatory linker regions of Smad2 and Smad3 to enhance transforming growth factor-beta signaling.
abstract: Transforming growth factor-beta (TGF-beta) controls a diverse set of cellular processes, and its canonical signaling is mediated via TGF-beta-induced phosphorylation of receptor-activated Smads (2 and 3) at the C-terminal SXS motif. We recently discovered that PPM1A can dephosphorylate Smad2/3 at the C-terminal SXS motif, implicating a critical role for phosphatases in regulating TGF-beta signaling. Smad2/3 activity is also regulated by phosphorylation in the linker region (and N terminus) by a variety of intracellular kinases, making it a critical platform for cross-talk between TGF-beta and other signaling pathways. Using a functional genomic approach, we identified the small C-terminal domain phosphatase 1 (SCP1) as a specific phosphatase for Smad2/3 dephosphorylation in the linker and N terminus. A catalytically inactive SCP1 mutant (dnSCP1) had no effect on Smad2/3 phosphorylation in vitro or in vivo. Of the other FCP/SCP family members SCP2 and SCP3, but not FCP1, could also dephosphorylate Smad2/3 in the linker/N terminus. Depletion of SCP1/2/3 enhanced Smad2/3 linker phosphorylation. SCP1 increased TGF-beta-induced transcriptional activity in agreement with the idea that phosphorylation in the Smad2/3 linker must be removed for a full transcriptional response. SCP1 overexpression also counteracts the inhibitory effect of epidermal growth factor on TGF-beta-induced p15 expression. Taken together, this work identifies the first example of a Smad2/3 linker phosphatase(s) and reveals an important new substrate for SCPs.
authors.affiliation: Michael E. DeBakey Department of Surgery, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
authors.forename: Katharine H
authors.initials: KH
authors.lastname: Wrighton
authors.forename: Danielle
authors.initials: D
authors.lastname: Willis
authors.forename: Jianyin
authors.initials: J
authors.lastname: Long
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.forename: Xia
authors.initials: X
authors.lastname: Lin
authors.forename: Xin-Hua
authors.initials: XH
authors.lastname: Feng
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004815:Epidermal Growth Factor / Q000378:metabolism; D006801:Humans; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism* / Q000502:physiology; D010766:Phosphorylation; D011485:Protein Binding; D015398:Signal Transduction; D051899:Smad2 Protein / Q000737:chemistry / Q000378:metabolism*; D051900:Smad3 Protein / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D004815:Epidermal Growth Factor; D010744:Phosphoric Monoester Hydrolases