A nuclear protein tyrosine phosphatase TC-PTP is a potential negative regulator of the PRL-mediated signaling pathway: dephosphorylation and deactivation of signal transducer and activator of transcription 5a and 5b by TC-PTP in nucleus.
In the present study we examined involvement of nuclear protein tyrosine phosphatase TC-PTP in PRL-mediated signaling. TC-PTP could dephosphorylate signal transducer and activator of transcription 5a (STAT5a) and STAT5b, but the apparent dephosphorylation activity of TC-PTP was weaker than that of cytosolic PTP1B 30 min after PRL stimulation in transfected COS-7 cells, whereas both STAT5a and STAT5b were dephosphorylated to the same extent by recombinant TC-PTP and PTP1B in vitro. Tyrosine-phosphorylated STAT5 was coimmunoprecipitated with substrate trapping mutants of TC-PTP, suggesting that STAT5 is a specific substrate of TC-PTP. These observations were further extended in mammary epithelial COMMA-1D cells stably expressing TC-PTP. A time-course study revealed that dephosphorylation of STAT5 by TC-PTP was delayed compared with that by cytosolic PTP1B due to nuclear localization of TC-PTP throughout PRL stimulation in mammary epithelial cells. Endogenous beta-casein gene expression and beta-casein gene promoter activation in COS-7 cells were largely suppressed by TC-PTP wild type as well as catalytically inactive mutants, suggesting that stable complexes formed between STAT5 and TC-PTP in the nucleus. Taken together, we conclude that TC-PTP is catalytically competent with respect to dephosphorylation and deactivation of PRL-activated STAT5 in the nucleus.
Aoki
Naohito
N
Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. naoki@agr.nagoya-u.ac.jp
Matsuda
Tsukasa
T
D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism; D008894:Milk Proteins; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011388:Prolactin / Q000378:metabolism*; D021381:Protein Transport; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011993:Recombinant Fusion Proteins; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D011388:Prolactin; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2; D017027:Protein Tyrosine Phosphatases