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.

Activation of tyrosine kinases is an important factor during cancer development. Axl, one of the receptor tyrosine kinases, binds to the specific ligand growth arrest-specific gene 6 (Gas6), which encodes a vitamin K-dependent gamma-carboxyglutamyl protein. Although many receptor tyrosine kinases and their ligands are involved in gastric carcinogenesis, whether Gas6-Axl signaling is involved in gastric carcinogenesis has not been elucidated. The aim of this study was to investigate the expression of Gas6 and Axl in gastric cancer and also their roles during gastric carcinogenesis. mRNA and protein of Gas6 and Axl were highly expressed in a substantial proportion of human gastric cancer tissue and cell lines, and Gas6 expression was significantly associated with lymph node metastasis. With recombinant Gas6 and a decoy-receptor of Axl in vitro, we demonstrated that Gas6-Axl signaling pathway enhanced cellular survival and invasion and suppressed apoptosis via Akt pathway. Our results suggests that Gas6-Axl signaling plays a role during gastric carcinogenesis, and that targeting Gas6-Axl signaling could be a novel therapeutic for gastric cancer.

Nuclear accumulation of B-catenin is a key event for the development of colorectal cancer. Little is known, however, about the mechanisms underlying translocation of B-catenin from the cytoplasm or the membrane to the nucleus. The present study examined whether signal transducers and activators of transcription 3 (STAT3) activation is involved in the nuclear accumulation of B-catenin in colorectal cancer cells. Of the 90 primary colorectal cancer tissues, 40 (44.4%) were positive for nuclear staining of p-STAT3 and 63 (70.0%) were positive for nuclear staining of B-catenin. The nuclear staining of both p-STAT3 and B-catenin were observed predominantly in the periphery of the cancer tissues. Importantly, of the 40 tumors with p-STAT3 nuclear staining, 37 (92.5%) were also positive for nuclear B-catenin staining and there was a significant correlation between p-STAT3 and B-catenin nuclear staining (P < 0.01). Coexpression of nuclear p-STAT3 and B-catenin was associated with lower patient survival (P < 0.01). In an in vitro study using a human colon cancer cell line, SW480, inhibition of STAT3 by dominant negative STAT3 or the Janus kinase inhibitor, AG490, induced translocation of B-catenin from the nucleus to the cytoplasm or membrane. Luciferase assays revealed that STAT3 inhibition resulted in significant suppression of B-catenin/T-cell factor transcription in association with significant inhibition of cell proliferation (P < 0.05). These findings suggest that in colorectal cancer, STAT3 activation is involved in the nuclear accumulation of B-catenin, resulting in poor patient survival.

Cyclooxygenase-2 (COX-2) plays important roles in tumor development. Especially in the early-stage colorectal tumors, COX-2 expression is often observed in the tumor stroma. However, the mechanism regulating such stromal expression of COX-2 remains unknown. In the present study, we simulated the indirect interaction between epithelial cells and stromal cells in the process of colorectal tumor development using an in vitro co-culture model in which NIH3T3 fibroblasts were co-cultured with 'sparsely' or 'densely' populated intestinal epithelial cells, Intestine-407 as a model of premalignant or benign intestinal epithelial cells, and DLD-1 and Caco-2 as models of malignant epithelial cells. COX-2 expression in NIH3T3 fibroblasts was upregulated when co-cultured with the 'dense' epithelial cells regardless of their character. Interestingly, there was pericellular hypoxia in the vicinity of NIH3T3 fibroblasts when cocultured with 'dense' epithelial cells, and the recovery of the partial pressure of oxygen level resulted in the reduction of enhanced COX-2 expression only in NIH3T3 fibroblasts co-cultured with 'dense' Intestine-407 cells. Furthermore, COX-2 expression was also reduced by the inhibition of transcription factor AP-1. Thus, pericellular hypoxia of the stromal cells caused by densely populated epithelial cells may be one of the potent COX-2 enhancers before completion of malignant transformation during intestinal tumor development.

The inhibitory effects of azelastine hydrochloride on PAF-induced and fMLP-induced Ca2+ influx, actin polymerization and calcium ionophore A23187-induced and aggregated IgG-induced release of eosinophil cationic protein (ECP) of an eosinophilic leukaemia cell line, EoL-1, were examined. EoL-1 cells cultured with 0.2 mM dibutyryladenosine-cyclic monophosphate for 48 hours showed an increase in intracellular free Ca2+ concentration ([Ca2+]i) and actin polymerization when stimulated by PAF and fMLP. Azelastine hydrochloride inhibited PAF-induced and fMLP-induced Ca2+ influx ([Ca2+]i) in a dose-dependent manner with an IC50 of 1 x 10(-8) M and 1 x 10(-7) M, respectively. It also inhibited PAF-induced and fMLP-induced actin polymerization in a dose-dependent manner up to 40% and 30%, respectively. EoL-1 cells were differentiated to contain ECP in their eosinophilic granules when cultured for 9 days with supernatants of a human adult T cell leukaemia cell line, HIL-3 (HIL-3 sup). Calcium ionophore A23187 and aggregated IgG induced the secretion of ECP by EoL-1 cells. Azelastine hydrochloride inhibited the secretion of ECP in a dose-dependent manner. These inhibitory effects were seen even at therapeutic concentrations of 10(-8) M to 10(-9) M. These results indicate that the therapeutic effects of azelastine hydrochloride as an anti-allergic agent may include inhibition of the accumulation of eosinophils into the locus of allergic inflammation and of the release of cytotoxic granules from eosinophils.