Protein phosphatase 5 modulates SMAD3 function in the transforming growth factor-β pathway.
Protein phosphatases play a key role in balancing the cellular responses to the transforming growth factor-β (TGFβ) signals. Several protein phosphatases have been attributed roles in the regulation of the TGFβ pathway. Among these, PPM1A is the only phosphatase reported to dephosphorylate SMAD2/3 in the nucleus. However we observed PPM1A exclusively in the cytoplasmic fractions independently of TGFβ treatment in all cells tested. These observations imply that a bona fide nuclear SMAD2/3 phosphatase remains elusive. In this study, we report a role for protein phosphatase 5 (PP5) in the TGFβ pathway. We identified PP5 as an interactor of SMAD2/3. Interestingly, in mouse embryonic fibroblast cells derived from PP5-null mice, TGFβ-induced transcriptional responses were significantly enhanced. Rather surprisingly, this enhancement is due to the increased levels of SMAD3 protein observed in PP5-null MEFs compared to the wild type. No differences in the levels of SMAD3 transcripts were observed between the wild-type and PP5-null MEFs. While PP5 is capable of dephosphorylating SMAD3-tail in overexpression assays, we demonstrate that its activity is essential in controlling SMAD3 protein levels in MEFs. We propose that PP5 regulates the TGFβ pathway in MEFs by regulating the expression of SMAD3 protein levels.
MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, UK.
David L
DL
Bruce
Thomas
T
Macartney
Weidong
W
Yong
Weinian
W
Shou
Gopal P
GP
Sapkota
D000818:Animals; D002460:Cell Line; D057809:HEK293 Cells; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D000071636:Protein Phosphatase 2C; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D009687:Nuclear Proteins; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; C000607456:PPM1A protein, human; D010749:Phosphoprotein Phosphatases; C000607466:Ppm1a protein, mouse; D000071636:Protein Phosphatase 2C; C089641:protein phosphatase 5