Fibronectin is chemotactic for CT 26 colon carcinoma cells: sub-lines selected for increased chemotaxis to fibronectin display decreased tumorigenicity and lung colonization

Methylselenol generated from selenomethionine by methioninase downregulates integrin expression and induces caspase-mediated apoptosis of B16F10 melanoma cells

Melanoma is a highly metastatic cancer resistant to current chemotherapeutic and radiotherapeutic approaches. Several studies have shown that interactions between cancer cells and the extracellular matrix (ECM) are critical for the survival and invasion of metastatic cancer cells. In this study, we examine the effects of methylselenol generated from selenomethionine (SeMet) by methioninase (METase) on cell proliferation, adhesion, and expression of integrins in murine melanoma B16F10 cells, which are metastatic in the lungs of syngeneic C57BL/6J mice. Combined treatment with SeMet-METase decreased the expression of integrins alpha(4), beta(1), alpha(nu), and beta(3), and inhibited melanoma-ECM adhesion. Caspase-mediated apoptosis was induced following loss of cell adherence. Phosphorylation of focal adhesion kinase (FAK) and Akt, related to integrin-mediated survival, were decreased upon treatment with SeMet-METase while phosphorylation of p38, PKC-delta, and IkappaBalpha increased. In the presence of specific inhibitors of p38, PKC-delta, and NF-kappaB, expression of integrins and cell adhesion to ECM were maintained and cell apoptosis was prevented in SeMet-METase-treated melanoma cells. Treatment with caspase inhibitors restored cell viability and blocked poly (ADP-ribose) polymerase (PARP) cleavage, but did not restore integrin expression and cell adhesion to ECMs reduced by SeMet-METase. Based on these results, we propose that combined treatment with SeMet-METase induces caspase-mediated apoptosis in melanoma cells by altering integrin expression and adhesion. Furthermore, activation of p38, PKC-delta, and NF-kappaB is a prerequisite for the down-regulation of integrin expression, followed by detachment-mediated apoptosis.

Studies on MIP-2 and CXCR2 expression in a mouse model of extrahepatic colorectal metastasis

AIMS

The CXC chemokine macrophage inflammatory protein (MIP)-2 has been shown to promote outgrowth of colorectal liver metastasis by enhancing angiogenesis and tumor cell migration. However, the effect of MIP-2 on extrahepatic metastasis is not known yet. With a use of a murine model, we therefore studied cell proliferation and microvascularization of extrahepatic CT26.WT-GFP colorectal tumors after exposure to MIP-2.

METHODS

Green fluorescent protein (GFP)-transfected CT26.WT colorectal cancer cells were implanted in dorsal skinfold chambers of syngeneic BALB/c mice. After 5 days, the tumors were locally exposed to 100 nM MIP-2. Cell proliferation as well as tumor microvascularization and growth were studied during a further 9-day period using intravital fluorescence microscopy, histology and immunohistochemistry. Tumors exposed to PBS served as controls.

RESULTS

MIP-2 induced a marked CXCR2 expression and promoted a distinct tumor cell proliferation. This was associated with a significant increase of tumor size compared to PBS-treated controls. Of interest, MIP-2 did not affect dilation and permeability of the tumor microvessels, which would be indicators for an enhanced VEGF action. Accordingly, the angiogenic response, e.g. the outgrowth of new microvessels, was not affected, and the density of the established tumor microvascular network was even found decreased after MIP-2 exposure when compared to PBS controls.

CONCLUSION

With the use of a murine tumor model, we demonstrate that MIP-2 accelerates growth of experimentally established extrahepatic colorectal metastases by inducing tumor cell proliferation rather than promoting vascularization.

Experimental liver metastasis: standards for local cell implantation to study isolated tumor growth in mice

Experimental hepatic metastasis of colorectal tumors is frequently studied by local intrahepatic tumor cell implantation. However, although a variety of factors of the implantation procedure may markedly influence tumor growth characteristics, standards are not defined yet. Herein, we studied the effect of different modes of cell implantation on tumor growth and angiogenesis by in vivo fluorescence microscopy and histology seven days after grafting colorectal CT26.WT tumor cells into the left liver lobe of syngeneic BALB/c mice. We demonstrate that (i) radial growth of cells implanted within the central area of the lobe is inhibited by a regularly observed fissura which crosses at midline the surface of the lobe; (ii) cells suspended during implantation in RPMI show an uncontrolled overwhelming growth 40-fold of those suspended in PBS; (iii) cell implantation in 100 microl and 20 microl suspension medium is significantly more complicated by rupture of the liver capsule, uncontrolled intraparenchymal cell spread and recoil of the cells through the injection canal compared to cells suspended in 10 microl; (iv) the frequency of metastasis within the injection canal and at the puncture site is significantly reduced using 32G compared to 27G or 29G needles; (v) occlusion of the puncture site by acrylic glue or electric coagulation completely abolishes peritoneal tumor spread compared to no treatment or gentle compression by cotton gauze. We conclude that a standardized growth of isolated metastases is best achieved by implanting CT26.WT cells in a 10 microl PBS blister subcapsularly into the paramedian area of the lower surface of the left liver lobe, using a 32-gauge needle and closing the puncture site with acrylic glue.

Vascular endothelial growth factor is a chemoattractant for trophoblast cells

A role for angiogenic growth factors in trophoblast invasion has been postulated. Directional motility (chemotaxis) is an important function of trophoblast cells. We have previously shown that vascular endothelial growth factor (VEGF) increases the random movement of trophoblast cells although placental growth factor (PlGF) has no effect. Heparin inhibited this effect of VEGF. Motility of trophoblast cells has been proposed to be mediated by a nitric oxide (NO) pathway. We hypothesized that VEGF but not PlGF would be chemotactic for trophoblast cells. Chemotaxis of a first trimester extravillous trophoblast cell line, SGHPL-4, and primary isolates of first trimester and term trophoblast cells was measured using a Boyden chamber. Initial experiments to optimize the time of the experiment and identify a positive control were performed. Subsequent experiments ran for 20 h, used 0.5 per cent FBS or 10 ng/ml PDGF as negative and positive controls and were performed in triplicate. VEGF (1, 10 and 100 ng/ml+/-1 microg/ml heparin or +/-100 microM L-NAME) and PlGF (1, 10, 100 ng/ml) were tested. The chamber was placed in a 5 per cent CO(2) in air, 37 degrees C incubator. The number of cells in the lower chamber were counted. There was a dose dependent increase in chemotactic motility of the SGHPL-4 cell line and term trophoblast cells in response to VEGF. PlGF had no effect on the movement of the first trimester trophoblast cell line but did increase the motility of the term trophoblast cells in a dose dependent manner. Heparin increased the cellular motility of both cell types alone. It also further enhanced the chemoactivity of VEGF on the term trophoblast cells but not the cell line. L-NAME did not affect the VEGF-stimulated motility of the first trimester cell line. However, in the term trophoblast cells L-NAME increased the directional cellular motility in the absence of, or in the presence of low concentrations of VEGF. In conclusion, the first trimester and term trophoblast cells appeared to respond differently to the various factors tested in the present study that may reflect differential cellular function as gestation progresses.

Chemokines induce the cellular migration of MCF-7 human breast carcinoma cells: subpopulations of tumour cells display positive and negative chemotaxis and differential in vivo growth potentials

We previously reported that chemotactic cytokines (chemokines) induce the directional migration of cells derived from the breast carcinoma cell line MCF-7 in vitro, however it was apparent that only a small percentage of cells displayed the ability to migrate upon stimulation. In the present study three sub-lines derived from the parental MCF-7 cell line were selected for their ability to migrate in response to MIP-1alpha, MIP-1beta or RANTES across Transwell filters of 8 microm pore size. The first round selection of migratory cells resulted in sub-populations which demonstrated an increased chemotactic response compared with parental cells. Cells migrating to MIP-1beta were subjected to four further rounds of positive or negative selection, resulting in two sub-lines, MCF-7L4 and MCF-7U4 which displayed an increased and decreased chemotactic response respectively to MIP-1alpha MIP-1beta and RANTES. No difference in chemokine receptor RNA message expression between these sub-lines and the parental MCF-7 line were detected, although increased levels of alpha3, alpha6 and alphav integrin sub-units were shown for MCF-7L4 (positively selected sub-line) compared with MCF-7U4 cells. Moreover, the in vivo growth of cells derived from the two MCF-7 sub-lines was inversely correlated with their chemotactic response. The results of this study depict further the inherent heterogeneity in cancer, suggesting that the chemotactic response may influence the migratory traits of sub-populations within the tumour and potentially contribute to their in vivo behavior, growth and survival.