Role of stem cell factor and c-kit signaling in regulation of fetal intestinal epithelial cell adhesion to fibronectin

Tandutinib inhibits the Akt/mTOR signaling pathway to inhibit colon cancer growth

The c-Kit receptor can activate distinct signaling pathways including phosphoinositide 3-kinase (PI3K)/Akt and mTOR. Aberrant c-Kit activation protects cells from apoptosis and enhances invasion of colon carcinoma cells. Tandutinib is a novel quinazoline-based inhibitor of the type III receptor tyrosine kinases including c-Kit. We determined the effect of tandutinib on colon cancer growth and identified a mechanism of action. Tandutinib inhibited phosphorylation of c-Kit, Akt, mTOR, and p70S6 kinase. In addition, tandutinib significantly inhibited the proliferation and colony formation ability of colon cancer cell lines but did not affect normal colonic epithelial cells. There were increased levels of activated caspase-3 and Bax/Bcl2 ratio, coupled with a reduction in cyclin D1, suggesting apoptosis. There was also a downregulation of COX-2, VEGF, and interleukin-8 expression, suggesting effects on cancer-promoting genes. In addition, overexpressing constitutively active Akt partially suppressed tandutinib-mediated colon cancer cell growth. In vivo, intraperitoneal administration of tandutinib significantly suppressed growth of colon cancer tumor xenografts. There was a reduction in CD31-positive blood vessels, suggesting that there was an effect on angiogenesis. Tandutinib treatment also inhibited the expression of cancer-promoting genes COX-2 and VEGF and suppressed the activation of Akt/mTOR signaling proteins in the xenograft tissues. Together, these data suggest that tandutinib is a novel potent therapeutic agent that can target the Akt/mTOR/p70S6K signaling pathway to inhibit tumor growth and angiogenesis.

Normal mouse intestinal epithelial cells as a model for the in vitro invasion of Trichinella spiralis infective larvae

It has been known for many years that Trichinella spiralis initiates infection by penetrating the columnar epithelium of the small intestine; however, the mechanisms used by the parasite in the establishment of its intramulticellular niche in the intestine are unknown. Although the previous observations indicated that invasion also occurs in vitro when the infective larvae are inoculated onto cultures of intestinal epithelial cells (e.g., human colonic carcinoma cell line Caco-2, HCT-8), a normal readily manipulated in vitro model has not been established because of difficulties in the culture of primary intestinal epithelial cells (IECs). In this study, we described a normal intestinal epithelial model in which T. spiralis infective larvae were shown to invade the monolayers of normal mouse IECs in vitro. The IECs derived from intestinal crypts of fetal mouse small intestine had the ability to proliferate continuously and express specific cytokeratins as well as intestinal functional cell markers. Furthermore, they were susceptible to invasion by T. spiralis. When inoculated onto the IEC monolayer, infective larvae penetrated cells and migrated through them, leaving trails of damaged cells heavily loaded with T. spiralis larval excretory-secretory (ES) antigens which were recognized by rabbit immune sera on immunofluorescence test. The normal intestinal epithelial model of invasion mimicking the natural environment in vivo will help us to further investigate the process as well as the mechanisms by which T. spiralis establishes its intestinal niche.

Imatinib inhibits colorectal cancer cell growth and suppresses stromal-induced growth stimulation, MT1-MMP expression and pro-MMP2 activation

Tumor progress depends on the proliferation of cancer cells, their interactions with stroma and the proteolytic action of enzymes. Colon cancer is c-kit positive and responsive to the specific tyrosine kinase inhibitor imatinib. We investigated the effect of imatinib on the proliferation of a panel of epithelial colon cancer cell lines in presence and absence of the antimetabolite 5-FU, and the effect of conditioned media (CM) derived from colon stromal fibroblasts with and without previous exposure to imatinib. The effects of imatinib on gene expression of MMPs and TIMPs were also studied. Imatinib effectively inhibited the proliferation of all cell lines, showing IC(50) from 0.3 to 3 microM. Its combination with 5-FU significantly enhances the growth inhibition of the highly tumourigenic HT-29 cells. CM derived from stromal fibroblasts induced the proliferation of the HT-29 cells; this stimulatory effect was abolished upon treatment with CM obtained after exposure of fibroblasts to imatinib. Gene expression of MT1-, MT2-MMP and MMP-7 was also inhibited depending on the cell line, whereas that of TIMP-2 was not affected. CM stimulated MT1-MMP protein expression by HT-29; this stimulatory effect was suppressed in the presence of imatinib. Activation of pro-MMP2 to MMP2 in culture medium of HT-29 treated with CM was increased and this activity was inhibited in presence of imatinib. The obtained data showed that imatinib is a powerful inhibitor of human colon cancer cell growth and effectively suppresses the stromal-induced stimulation of cancer cell growth and activation of proMMP2. Further studies are warranted to evaluate the in vivo effects.

Co-expression of c-kit and stem cell factor in primary and metastatic nasopharyngeal carcinomas and nasopharyngeal epithelium

Expression of c-kit has been demonstrated in 33% of adult nasopharyngeal carcinomas (NPCs) and in 88% of paediatric NPCs. Patients with tumours expressing c-kit tend to exhibit better survival, but a paracrine/autocrine function for the stem cell factor (SCF)/c-kit system in nasopharyngeal carcinomas has not been reported. This study evaluated the expression of c-kit and SCF by immunohistochemical staining of nasopharyngeal epithelium (NPE) and of primary and metastatic NPCs. In addition, c-kit and SCF expression were studied in HONE-1 NPC cells by immunoprecipitation and western blotting. Expression of c-kit and SCF was detected in 75% and 57% of NPE, respectively, and there was 48% co-expression. In primary NPCs, 86% expressed c-kit, 69% had SCF expression, and there was 67% co-expression. In metastatic NPCs, 76% expressed c-kit, 72% expressed SCF and there was 68% co-expression. Co-expression of c-kit and SCF with tyrosine autophosphorylation of p145(c - kit) was demonstrated in HONE-1 NPC cells. In addition, the expression level of c-kit and its autophosphorylation status was not obviously influenced by the transient co-expression of Epstein-Barr nuclear antigen 1 (EBNA1) and latent membrane protein 1 (LMP1). Co-expression of c-kit and SCF is therefore commonly found in nasopharyngeal epithelium and NPCs, and in HONE-1 NPC cells with autoactivation possibly independent of the co-expression of EBNA1 and LMP1. All of these findings suggest that autoactivation of SCF/c-kit signalling may be a potent regulator of the nasopharyngeal epithelial barrier and of immune function at the nasopharyngeal mucosa surface, and may contribute to the carcinogenesis and progression of NPC. Further molecular analysis is required to evaluate the possibility of treatment with tyrosine kinase inhibitors in NPC, analogous to the treatment of gastrointestinal stromal tumours with STI571.

Using gene expression profiling to identify the molecular basis of the synergistic actions of hepatocyte growth factor and vascular endothelial growth factor in human endothelial cells

Hepatocyte growth factor (HGF) and vascular endothelial cell growth factor (VEGF) are two potent endothelial mitogens with demonstrated angiogenic activities in animal models of therapeutic angiogenesis. Several recent studies suggest that these growth factors may act synergistically, although the mechanism of this interaction is not understood. Changes in the gene expression profile of human umbilical vein endothelial cells treated with HGF, VEGF or the combination of the two were analyzed with high-density oligonucleotide arrays, representing approximately 22000 genes. Notably, the genes significantly up- and downregulated by VEGF versus HGF exhibited very little overlap, indicating distinct signal transduction pathways. The combination of HGF and VEGF markedly increased the number of significantly up- and downregulated genes. At 4 h, the combination of the two growth factors induced a number of chemokine and cytokines and their receptors (IL-8, IL-6, IL-11, CCR6, CXCR1,CXC1 and IL17RC), numerous genes involved in growth factor signal transduction (egr-1, fosB, grb10, grb14,MAP2K3,MAP3K8, MAPKAP2,MPK3, DUSP4 and DUSP6), as well as a number of other growth factors (PDGFA, BMP2, Hb-EGF, FGF16, heuregulin beta 1, c-kit ligand, angiopoietin 2 and angiopoietin 4 and VEGFC). In addition, the VEGF receptors neuropilin-1 and flt-1 were also upregulated. At 24 h, a clear 'cell cycle' signature is noted, with the upregulated expression of various cell cycle control proteins and gene involved in the regulation of mitosis and mitotic spindle assembly. The receptor for HGF, c-met, is also upregulated. These data are consistent with the hypothesis that the combination of HGF and VEGF results in the cooperative upregulation of a number of different molecular pathways leading to a more robust proliferative response, that is, growth factor(s), receptors, molecules involved in growth factor signal transduction, as well as, at later time points, upregulation of the necessary cellular proteins required for cells to escape cell cycle arrest and enter the cell cycle.