Gap junction-mediated transfer of miR-145-5p from microvascular endothelial cells to colon cancer cells inhibits angiogenesis.

IF 5.008International audienceGap junctional communication between cancer cells and blood capillary cells is crucial to tumor growth and invasion. Gap junctions may transfer microRNAs (miRs) among cells. Here, we explore the impact of such a transfer in co-culture assays, using the antitumor miR-145 as an example. The SW480 colon carcinoma cells form functional gap junction composed of connexin-43 (Cx43) with human microvascular endothelial cells (HMEC). When HMEC are loaded with miR-145-5p mimics, the miR-145 level drastically increases in SW480. The functional inhibition of gap junctions, using either a gap channel blocker or siRNA targeting Cx43, prevents this increase. The transfer of miR-145 also occurs from SW480 to HMEC but not in non-contact co-cultures, excluding the involvement of soluble exosomes. The miR-145 transfer to SW480 up-regulates their Cx43 expression and inhibits their ability to promote angiogenesis. Our results indicate that the gap junctional communication can inhibit tumor growth by transferring miRs from one endothelial cell to neighboring tumor cells. This "bystander" effect could find application in cancer therapy

Contribution of the cyclin-dependent kinase inhibitor p27KIP1 to the confluence-dependent resistance of HT29 human colon carcinoma cells

International audienceWe have previously shown that growth of HT29 human colorectal cancer cells at confluence increased their resistance to the cytotoxic agent cisplatin. This study further explores the mechanisms of this resistance phenotype. DNA platination induced by cisplatin exposure is slightly reduced by confluence. However, at an equivalent DNA platination level, non-confluent cells accumulate in the G2/M phase of the cell cycle, demonstrate aberrant mitotic figures and die by apoptosis, while confluent cells progress slowly through the cell cycle, do not reach mitosis and are more resistant to drug-induced cell death. At a molecular level, cisplatin enhances cyclin B and p34cdc2 levels and histone H1 kinase activity in non-confluent, but not in confluent, cells. Furthermore, when HT29 cells reach confluence, expression of the cyclin-dependent kinase inhibitor p27Kip1 increases and cells accumulate in the G0/G1 phase of the cell cycle. Transfection-mediated over-expression of p27Kip1 in non-confluent HT29 cells decreases the cytotoxic activity of cisplatin as well as its ability to trigger apoptosis. Non-confluent HT29 cells over-expressing p27Kip1 are also more resistant to doxorubicin, etoposide and 5-fluorouracil. Our results suggest that p27Kip1 contributes to the confluence-dependent resistance phenotype

Transfer of functional microRNAs between glioblastoma and microvascular endothelial cells through gap junctions

IF 5.008International audienceExtensive invasion and angiogenesis are hallmark features of malignant glioblastomas. Here, we co-cultured U87 human glioblastoma cells and human microvascular endothelial cells (HMEC) to demonstrate the exchange of microRNAs that initially involve the formation of gap junction communications between the two cell types. The functional inhibition of gap junctions by carbenoxolone blocks the transfer of the anti-tumor miR-145-5p from HMEC to U87, and the transfer of the pro-invasive miR-5096 from U87 to HMEC. These two microRNAs exert opposite effects on angiogenesis in vitro. MiR-5096 was observed to promote HMEC tubulogenesis, initially by increasing Cx43 expression and the formation of heterocellular gap junctions, and secondarily through a gap-junction independent pathway. Our results highlight the importance of microRNA exchanges between tumor and endothelial cells that in part involves the formation of functional gap junctions between the two cell types

Influence of the nitric oxide donor glyceryl trinitrate on apoptotic pathways in human colon cancer cells

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