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Novel Phosphatase SMP3 Controls Outputs of BMP Signal Transduction
Author(s) -
Shen Tao
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.708.1
Subject(s) - smad , signal transduction , phosphatase , phosphorylation , microbiology and biotechnology , bone morphogenetic protein , biology , bimolecular fluorescence complementation , chemistry , biochemistry , gene
Bone Morphogenetic Proteins (BMPs) and other members of the TGFb superfamily regulate cell growth and differentiation. Abrogation of BMP/TGFb signaling is associated with cancer, cardiovascular, autoimmune and skeletal diseases. The key step of BMP signal transduction is the phosphorylation of transcription factor Smad1, 5 and 8 by BMP receptors. While phosphorylated Smad1/5/8 (P‐Smad1/5/8) activates BMP‐induced gene transcription in the nucleus, protein phosphatases dephosphorylate P‐Smad1/5/8 and consequently terminate BMP signaling. The identity of the Smad phosphatase has been one of the major unanswered questions in BMP/TGFb biology. To identify Smad phosphatases, we generated cDNA encoding all the protein phosphatases in human genome and undertook a genome‐wide screen. Using combined methods of functional genomics and biochemistry, a novel cytoplasm‐localized Smad1/5/8‐specific phosphatase, SMP3 was discovered. The effects of SMP3 on controlling the level of P‐Smad1/5/8 in vivo and in vitro were analyzed by immunofluorescence and western blotting, using a phospho‐specific antibody against P‐Smad1/5/8. In vitro binding, immunoprecipitation, and bimolecular fluorescence complementation assays demonstrated that SMP3 and Smad1 directly interact in the cytoplasm. Consequently, ectopic expression of SMP3 in cells abolished BMP‐induced gene expression as measured by real‐time PCR and transcriptional reporter assays, and loss of SMP3 activity (site‐directed mutagenesis) or expression (RNA interference) greatly enhanced BMP signaling. In conclusion, SMP3 acts as a gatekeeper to prevent excessive BMP signaling through dephosphorylation and subsequent nuclear exclusion of Smad1/5/8. Our results not only gain insights into the important role of BMP signaling in human growth and development, but also are pertinent towards novel therapeutic approaches for the prevention and treatment of human diseases.