MTMR4 Attenuates Transforming Growth Factor β (TGFβ) Signaling by Dephosphorylating R-Smads in Endosomes

• Published in: The Journal of biological chemistry Vol. 285; no. 11; pp. 8454 - 8462
• Main Authors: Yu, Junjing, Pan, Lei, Qin, Xincheng, Chen, Hua, Xu, Youli, Chen, Yeguang, Tang, Hong
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 12.03.2010; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Aorta - cytology; Cell Nucleus - metabolism; Endosomes; Endosomes - metabolism; Endothelial Cells - cytology; Gene Expression Regulation, Enzymologic - physiology; HeLa Cells; Homeostasis - physiology; Humans; Kidney - cytology; MTMR4; Phosphatase; Phosphorylation - physiology; Protein Structure, Tertiary; Protein Tyrosine Phosphatases, Non-Receptor - chemistry; Protein Tyrosine Phosphatases, Non-Receptor - genetics; Protein Tyrosine Phosphatases, Non-Receptor - metabolism; Signal Transduction; Signal Transduction - physiology; Smad Proteins, Receptor-Regulated - metabolism; SMAD Transcription Factor; Smad2 Protein - metabolism; Smad3 Protein - metabolism; Swine; Transforming Growth Factor beta - metabolism; Transforming Growth Factor β (TGFβ); SMAD Transcription Factor; Signal Transduction; Transforming Growth Factor β (TGFβ); Phosphatase; MTMR4; Endosomes
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.075036

Homeostasis of Smad phosphorylation at its C-terminal SXS motif is essential for transforming growth factor β (TGFβ) signaling. Whereas it is known that TGFβ signaling can be terminated by phosphatases, which dephosphorylate R-Smads in the nucleus, it is unclear whether there are any cytoplasmic phosphatase(s) that can attenuate R-Smad phosphorylation and nuclear translocation. Here we demonstrate that myotubularin-related protein 4 (MTMR4), a FYVE domain-containing dual-specificity protein phosphatase (DSP), attenuates TGFβ signaling by reducing the phosphorylation level of R-Smads in early endosomes. Co-immunoprecipitation experiments showed that endogenous MTMR4 interacts with phosphorylated R-Smads, and that this interaction is correlated with dephosphorylation of R-Smads. Further analysis showed that overexpression of MTMR4 resulted in the sequestration of activated Smad3 in the early endosomes, thus reducing its nuclear translocation. However, both point mutations at the conserved catalytic site of the phosphatase (MTMR4-C407S) and small interference RNA of endogenous Mtmr4 expression led to sustained Smad3 activation. This work therefore suggests that MTMR4 plays an important role in preventing the overactivation of TGFβ signaling by dephosphorylating activated R-Smads that have been trafficked to early endosomes.