Yoshitaka Konda

STAT3 is constitutively activated and supports cell survival in association with survivin expression in gastric cancer cells

Signal transduction and activator of transcription 3(STAT3) signaling is constitutively activated in various tumors, and is involved in cell survival and proliferation during oncogenesis. There are few reports, however, on the role of STAT3 signaling in gastric cancer. The aim of the present study was to clarify the role of STAT3 signaling in apoptosis and cellular proliferation in gastric cancer. Here we reported that STAT3 was constitutively activated in various human gastric cancer cells and its inhibition by ectopic dominant-negative STAT3 or Janus kinase inhibitor, tyrphostin AG490, induced apoptosis. Furthermore, STAT3 inhibition markedly decreased survivin expression, and forced expression of survivin rescued AGS cells from apoptosis induced by STAT3 inhibition. Although some reports demonstrated that the PI3K/Akt pathway regulates survivin expression, inhibition of the PI3K/Akt pathway did not affect survivin expression in AGS and MKN1 cells. Finally, activated form of STAT3, Tyr-705 phospho-stat3, was found in the nucleus of cancer cells in 11 of 40 (27.5%) human gastric cancer specimens. These findings suggest that constitutively activated STAT3 signaling supports gastric cancer cell survival in association with survivin expression.

Differentiation-inducing factor-1 (DIF-1) inhibits STAT3 activity involved in gastric cancer cell proliferation via MEK-ERK-dependent pathway

Differentiation-inducing factor-1 (DIF-1) is a chlorinated hexaphenone isolated from Dictyostelium. DIF-1 exhibits antitumor activity in several types of mammalian tumor cells, although the underlying mechanisms remain unknown. On the other hand, recent studies indicate that constitutively activated STAT3 acts as an oncogene and could be a target for antitumor drug. In the present study, we examined the effects of DIF-1 on proliferation of gastric cancer cell lines as well as on its signal transduction pathways, focusing mainly on STAT proteins. DIF-1 inhibited proliferation of gastric cancer cells. Western blot analysis and electrophoretic mobility shift assay showed that DIF-1 inhibited STAT3 activity in an MEK-ERK-dependent manner in gastric cancer cell lines, AGS and MKN28. Moreover, blockade of STAT3 activity by ectopic expression of dominant-negative STAT3 or the Janus kinase inhibitor, tyrphostin AG490, inhibited cell growth of AGS cells. These results suggest that STAT3 activity plays an important role for cell growth in AGS cells, and raises the possibility that inhibition of STAT3 activity is one of the mechanisms responsible for the antitumor effect of DIF-1 in these cells.

Expression of the REG IV gene in ulcerative colitis

The regenerating gene (REG) IV gene was isolated from a cDNA library of ulcerative colitis (UC) tissues. However, its role in the pathophysiology of UC and subsequent development of colitic cancer is still unclear. We investigated the expression of the REG IV gene in UC and colitic cancer tissues and examined whether cytokines or growth factors are responsible for REG IV gene expression and whether REG IV gene induction affects cell growth and apoptosis in colon cancer cells. The expressions of REG IV and growth factor genes in UC tissues were analyzed by real time reverse transcription-polymerase chain reaction. The effects of cytokines and growth factors on REG IV gene expression were examined in SW403 cells by Northern blot analysis. The effects of REG IV gene induction on cell growth and H2O2-induced apoptosis were examined in DLD-1 cells by MTT and TUNEL assays, respectively. REG IV mRNA was strongly expressed in inflamed epithelium and in dysplasias and cancerous lesions in UC tissues. The level of REG IV mRNA expression was correlated with that of basic fibroblast growth factor (bFGF) as well as hepatocyte growth factor (HGF) mRNA expression in UC tissues. The REG IV gene expression in SW403 colon cancer cells was enhanced by stimulation with transforming growth factor-α, epidermal growth factor, bFGF, and HGF. REG IV gene induction promoted cell growth and conferred resistance to H2O2-induced apoptosis in DLD-1 cells. The REG IV gene is inducible by growth factors and may function as a growth promoting and/or an antiapoptotic factor in the pathophysiology of UC.

Activation of fibroblast-derived matrix metalloproteinase-2 by colon-cancer cells in non-contact co-cultures

Stromal fibroblasts interact with invading cancer cells by secreting and activating matrix metalloproteinases (MMPs). To elucidate the mechanisms involved in the expression and activation patterns of MMPs, human colon‐cancer cell lines Caco‐2 and LoVo and colon‐fibroblast cell line CCD18‐Co were co‐cultivated in non‐contact and contact conditions which mimic in vivo interaction between cancer cells and fibroblasts before and after cancer invasion respectively. Gelatin zymography disclosed that MMP‐2 was secreted from the fibroblasts but not from the cancer cells. The quantity of fibroblast‐derived MMP‐2 in conditioned medium was not significantly changed in either the contact or the non‐contact co‐cultures when compared with that of individual cultures of CCD18‐Co fibroblasts. Cancer cells in non‐contact co‐cultures, however, enhanced the activation of fibroblast‐derived MMP‐2. Transcripts of membrane‐type matrix metalloproteinase‐1 (MT1‐MMP), which is thought to be present on the cell surface and to work as a candidate activator of MMP‐2, were detected in both cancer cell lines. Plasma membrane extracts of cancer cells also activated MMP‐2 in conditioned media in cell‐free conditions. This activation of MMP‐2 may be caused by MT1‐MMP of the cancer cells, since it was inhibited by a series of MMP inhibitors, including ethylenediaminetetraacetic acid (EDTA), the tissue inhibitor of metalloproteinase‐2 (TIMP‐2), and the MMP inhibitor CGS 27023A, but not by TIMP‐1. Our data demonstrate that in non‐contact co‐cultures colon‐cancer cells activate fibroblast‐derived MMP‐2 on their plasma membranes. These findings should help to elucidate the mechanism involved in the initial destruction of basement membrane by cancer cells. Int. J. Cancer 87:165–171, 2000.

Effect of CYP2C19 polymorphism on the safety and efficacy of omeprazole in Japanese patients with recurrent reflux oesophagitis

Background :u2002The polymorphic enzyme cytochrome P450 2C19 affects omeprazole metabolism. This influence on metabolism might affect serum gastrin levels, and safety, during long‐term treatment of reflux oesophagitis.

Prohormone convertase furin has a role in gastric cancer cell proliferation with parathyroid hormone-related peptide in a reciprocal manner.

We investigated the expression of parathyroid hormone-related peptide (PTHrP) and the relationship between PTHrP and its endoprotease furin in gastric cancer. PTHrP was colocalized with furin in 75% of gastric cancer tissues (six of eight) from patients with high serum PTHrP levels. PTHrP mRNA expression was confirmed in 67% of gastric cancer cell lines (four of six), whereas furin mRNA was detected in all six gastric cancer cell lines. In a cultured gastric cancer cell line, MKN28, mature PTHrP protein expression was markedly increased by transfection of furin cDNA. Furin cDNA-transfected MKN28 cells grew faster than did the mock controls. Moreover, furin mRNA expression in cultured gastric cancer cells was enhanced when PTHrP was added to the culture medium. These results suggest a link between PTHrP and furin in the regulation of gastric cancer cell growth. Furin might be involved not only in the production of the mature form of PTHrP, but also in promoting growth in gastric cancer cells.

Gastrin interferes with the differentiation of gastric pit cells and parietal cells.

Gastrin is known to have stimulatory effects on gastric mucosa; however, long‐term effect of gastrin stimulation is not well known.