Blockade of irradiation-induced autophagosome formation impairs proliferation but does not enhance cell death in HCT-116 human colorectal carcinoma cells.

This work was undertaken to gain further information on the molecular mechanisms underlying autophagosome formation and its relation with tumor cell survival in response to radiation in colon cancer. A human colon cancer cell line, HCT-116, was examined with respect to cell survival after blockade of irradiation-induced autophagosome formation by pharmacological interference. Autophagosome formation was confirmed using a kinetic study with incorporated bovine serum albumin gold-conjugate (BSA-Au) analyzed by electron microscopy and an autophagosome-associated LC3B antibody measured by immunofluorescence and Western blotting. Annexin V/PI double staining was used to monitor cell death by apoptosis, and cell cycle profiles by flow cytometry. Ionizing radiation (IR) promoted autophagosome formation in the HCT-116 IR-surviving cells. Pharmacological interference showed that PI3K/Akt and Src were involved in early stages of autophagosome formation. IR alone decreased cell proliferation by arresting cells in the G2/M phase, and pharmacological interference of autophagosome formation decreased proliferation, but did not affect cell survival. Also, our data suggest that decreased proliferation caused by PI3K and Src inhibitors could be through S phase cell cycle delay. Our results clearly indicate that blockade of IR-induced autophagosome formation impairs proliferation but does not enhance cell death in colon cancer cells.

PI3K/Akt and GSK-3ß prevents in a differential fashion the malignant phenotype of colorectal cancer cells.

PURPOSE: During colorectal cancer progression, the loss of differentiation and cell-cell adhesion as well as a higher migratory potential are well-defined features; however, the signaling mechanism governing these events is not fully elucidated. The aim of this study was to investigate the role that PI3K and downstream effectors play in controlling colon cancer malignant phenotypes. METHODS: HCT-116 cells, a human model of colon cancer, which are highly metastatic and undifferentiated, were treated with LY294002, a specific inhibitor of PI3K. Cell differentiation and apical junctional complex (AJC) formation were monitored using alkaline phosphatase and electron microscopy analysis. Immunofluorescence and Western blotting were used to accompany the subcellular localization of AJC proteins. PI3K downstream molecules were analyzed by western blotting, and proliferation, wound healing, and colony formation techniques to determine malignant phenotype alterations. RESULTS: PI3K inhibition increased alkaline phosphatase activity, led to an enterocyte-like growth and formed a functional AJC. LY294002 treatment was able to recruit E-cadherin, ß-catenin, claudin-3, and ZO-1 to the cell-cell contact region, and this effect was essential for AJC assembly and association of these proteins to the cytoskeleton. Furthermore, we provided evidence that PI3K inhibition leads to a decrease in p-Akt and p-GSK-3ß and increased p-ß-catenin levels, which in turn controlled cell proliferation, motility, and colony formation. CONCLUSION: Our results demonstrate that PI3K/Akt and GSK-3ß prevents in a differential fashion the malignant phenotype of HCT-116 colorectal cancer cells, which could constitute a potential therapeutic target for treatment of this cancer type.