Biomedical subjects

Kouichiro Goto

Publications and source records attributed to Kouichiro Goto.

6 recordsLinked to original sources

PubMed2007

Ki26894, a novel transforming growth factor-beta type I receptor kinase inhibitor, inhibits in vitro invasion and in vivo bone metastasis of a human breast cancer cell line.

Transforming growth factor (TGF)-beta signaling has been shown to promote tumor growth and metastasis in advanced cancer. Use of inhibitors of TGF-beta signaling may thus be a novel strategy for treatment of patients with such cancers. In this study, we investigated the effects of a novel TGF-beta type I receptor (TbetaR-I) kinase inhibitor, Ki26894, on bone metastasis of a highly bone-metastatic variant of human breast cancer MDA-MB-231 cells, termed MDA-MB-231-5a-D (MDA-231-D). Ki26894 blocked TGF-beta signaling in MDA-231-D cells, as detected by suppression of phosphorylation of Smad2 and inhibition of TGF-beta-responsive reporter activity. Moreover, Ki26894 decreased the motility and the invasion of MDA-231-D cells induced by TGF-beta in vitro. Ki26894 also suppressed transcription of plasminogen activator inhibitor-1 (PAI-1), parathyroid hormone-related protein (PTHrP), and interleukin-11 (IL-11) mRNA of MDA-231-D cells, which were stimulated by TGF-beta. X-ray radiography revealed that systemic Ki26894 treatment initiated 1 day before the inoculation of MDA-231-D cells into the left ventricle of BALB/cnu/nu female mice resulted in decreased bone metastasis of breast cancer cells. Moreover, Ki26894 prolonged the survival of mice inoculated with MDA-231-D cells compared to vehicle-treated mice. These findings suggest that TbetaR-I kinase inhibitors such as Ki26894 may be useful for blocking the progression of advanced cancers.

Activin Receptors, Type I↗

PubMed2006

Nuclear and cytoplasmic c-Ski differently modulate cellular functions.

c-Ski is a proto-oncogene product that induces morphologic transformation, anchorage independence, and myogenic differentiation when it is over-expressed in mesenchymal cells. c-Ski also inhibits signaling of transforming growth factor-beta (TGF-beta) superfamily members through interaction with Smad proteins. Although c-Ski is predominantly localized in the nucleus, aberrant cytoplasmic localization of it has also been reported in some tumor tissues and cell lines. In the present study, we identified the nuclear localization signal (NLS) in c-Ski. By introducing a mutation to abolish NLS activity, we examined the function of cytoplasmic c-Ski. Although cytoplasmic c-Ski suppressed TGF-beta superfamily-induced Smad signaling through sequestration of activated Smad complex to the cytoplasm, it failed to exhibit some of the activities that require nuclear localization of c-Ski, including suppression of basal transcription of the Smad7 gene. These findings indicate that subcellular localization of c-Ski affects its biologic activities. We also found that c-Ski accumulated in the cytoplasm when proteasome activity was inhibited. Mapping of the regions required for cytoplasmic accumulation by proteasome inhibitors suggests that subcellular localization of c-Ski may be regulated by proteasome-sensitive processes through amino acid residues 94-210 and 491-548.

Amino Acid Motifs↗

PubMed2005

NEDD4-2 (neural precursor cell expressed, developmentally down-regulated 4-2) negatively regulates TGF-beta (transforming growth factor-beta) signalling by inducing ubiquitin-mediated degradation of Smad2 and TGF-beta type I receptor.

Inhibitory Smad, Smad7, is a potent inhibitor of TGF-beta (transforming growth factor-beta) superfamily signalling. By binding to activated type I receptors, it prevents the activation of R-Smads (receptor-regulated Smads). To identify new components of the Smad pathway, we performed yeast two-hybrid screening using Smad7 as bait, and identified NEDD4-2 (neural precursor cell expressed, developmentally down-regulated 4-2) as a direct binding partner of Smad7. NEDD4-2 is structurally similar to Smurfs (Smad ubiquitin regulatory factors) 1 and 2, which were identified previously as E3 ubiquitin ligases for R-Smads and TGF-beta superfamily receptors. NEDD4-2 functions like Smurfs 1 and 2 in that it associates with TGF-beta type I receptor via Smad7, and induces its ubiquitin-dependent degradation. Moreover, NEDD4-2 bound to TGF-beta-specific R-Smads, Smads 2 and 3, in a ligand-dependent manner, and induced degradation of Smad2, but not Smad3. However, in contrast with Smurf2, NEDD4-2 failed to induce ubiquitination of SnoN (Ski-related novel protein N), although NEDD4-2 bound to SnoN via Smad2 more strongly than Smurf2. We showed further that overexpressed NEDD4-2 prevents transcriptional activity induced by TGF-beta and BMP, whereas silencing of the NEDD4-2 gene by siRNA (small interfering RNA) resulted in enhancement of the responsiveness to TGF-beta superfamily cytokines. These data suggest that NEDD4-2 is a member of the Smurf-like C2-WW-HECT (WW is Trp-Trp and HECT is homologous to the E6-accessory protein) type E3 ubiquitin ligases, which negatively regulate TGF-beta superfamily signalling through similar, but not identical, mechanisms to those used by Smurfs.

Activin Receptors, Type I↗

PubMed2004

Activation of c-Met (hepatocyte growth factor receptor) in human gastric cancer tissue.

c-Met is a high-affinity receptor for hepatocyte growth factor (HGF) and plays a crucial role in embryonic development, as well as in the process of tissue repair. Overexpression and amplification of c-Met are often observed in various cancer tissues, especially in gastric carcinoma. It has, however, been unclear whether the overexpression leads to activation of the c-Met receptor. To address this point, we prepared an antibody (anti-phospho-Met) which specifically recognizes c-Met that is phosphorylated at Y1235, a major phosphorylation site of c-Met. Normal as well as cancerous gastric tissue was positive for anti-total-Met staining, whereas only cancerous tissue was strongly positive for anti-phospho-Met staining; cells near the basal layer were moderately positive, and the proliferative zone in normal tissue was only weakly positive. Among cancerous tissues from seven patients examined in the present study, those from six patients were strongly positive for phospho-Met staining. These results indicate that c-Met is actually activated in gastric carcinoma tissue, and may trigger proliferation/anti-apoptotic signals.

Adenocarcinoma↗

PubMed2003

Arkadia amplifies TGF-beta superfamily signalling through degradation of Smad7.

Arkadia was originally identified as a protein that enhances signalling activity of Nodal and induces mammalian nodes during early embryogenesis; however, the mechanisms by which Arkadia affects transforming growth factor-beta (TGF-beta) superfamily signalling have not been determined. Here we show that Arkadia is widely expressed in mammalian tissues, and that it enhances both TGF-beta and bone morphogenetic protein (BMP) signalling. Arkadia physically interacts with inhibitory Smad, Smad7, and induces its poly-ubiquitination and degradation. In contrast to Smurf1, which interacts with TGF-beta receptor complexes through Smad7 and degrades them, Arkadia fails to associate with TGF-beta receptors. In contrast to Smad7, expression of Arkadia is down-regulated by TGF-beta. Silencing of the Arkadia gene resulted in repression of transcriptional activities induced by TGF-beta and BMP, and accumulation of the Smad7 protein. Arkadia may thus play an important role as an amplifier of TGF-beta superfamily signalling under both physiological and pathological conditions.

Animals↗

PubMed2003

Chromosomal region maintenance 1 (CRM1)-dependent nuclear export of Smad ubiquitin regulatory factor 1 (Smurf1) is essential for negative regulation of transforming growth factor-beta signaling by Smad7.

Smad ubiquitin regulatory factor 1 (Smurf1), a HECT type E3 ubiquitin ligase, interacts with inhibitory Smad7 and induces translocation of Smad7 to the cytoplasm. Smurf1 then associates with the transforming growth factor (TGF)-beta type I receptor, TbetaR-I, enhancing turnover. However, the mechanism of nuclear export of Smad7 by Smurf1 has not been elucidated. Here we identified a functional nuclear export signal (NES) in a C-terminal region of Smurf1. In transfected cells, the Smurf1-Smad7 complex was accumulated in the cytoplasm by the nuclear export receptor, CRM1; this action was prevented by treatment with leptomycin B, a specific inactivator of CRM1 function. A green fluorescence protein fusion protein containing the C-terminal NES motif of Smurf1, located in the cytoplasm, accumulated in the nucleus following treatment with leptomycin B. Moreover, Smurf1 was shown to bind physically to CRM1 through NES, and nuclear export of the Smurf1-Smad7 complex was prevented by mutations of Smurf1 within the NES. Finally, the Smurf1 NES mutant reduced inhibition by Smad7 of the transcriptional activation induced by TGF-beta. These results thus suggest that CRM1-dependent nuclear export of Smurf1 is essential for the negative regulation of TGF-beta signaling by Smad7.

Active Transport, Cell Nucleus↗