Abstract
BackgroundThe PTEN phosphatase acts on phosphatidylinositol 3,4,5-triphosphates resulting from phosphatidylinositol 3-kinase (PI3K) activation. PTEN expression has been shown to be decreased in colorectal cancer. Little is known however as to the specific cellular role of PTEN in human intestinal epithelial cells. The aim of this study was to investigate the role of PTEN in human colorectal cancer cells.Methodology/Principal FindingsCaco-2/15, HCT116 and CT26 cells were infected with recombinant lentiviruses expressing a shRNA specifically designed to knock-down PTEN. The impact of PTEN downregulation was analyzed on cell polarization and differentiation, intercellular junction integrity (expression of cell-cell adhesion proteins, barrier function), migration (wound assay), invasion (matrigel-coated transwells) and on tumor and metastasis formation in mice. Electron microscopy analysis showed that lentiviral infection of PTEN shRNA significantly inhibited Caco-2/15 cell polarization, functional differentiation and brush border development. A strong reduction in claudin 1, 3, 4 and 8 was also observed as well as a decrease in transepithelial resistance. Loss of PTEN expression increased the spreading, migration and invasion capacities of colorectal cancer cells in vitro. PTEN downregulation also increased tumor size following subcutaneous injection of colorectal cancer cells in nude mice. Finally, loss of PTEN expression in HCT116 and CT26, but not in Caco-2/15, led to an increase in their metastatic potential following tail-vein injections in mice.Conclusions/SignificanceAltogether, these results indicate that PTEN controls cellular polarity, establishment of cell-cell junctions, paracellular permeability, migration and tumorigenic/metastatic potential of human colorectal cancer cells.
Highlights
Colorectal cancer (CRC) is the second leading cause of cancerrelated death in Western countries
To investigate the impact of PTEN loss of expression on differentiation and polarization of colorectal cancer cells, recombinant lentiviruses encoding short hairpin RNAs were first developed in order to stably suppress PTEN mRNA levels in Caco-2/15 cells
Caco-2/15 cells were infected with shPTEN lentiviruses or with irrelevant shGFP lentiviruses or lentiviruses expressing a shPTEN with 3 mismatch nucleotides as negative controls
Summary
Colorectal cancer (CRC) is the second leading cause of cancerrelated death in Western countries. Cell-cell adhesion and apical-basal polarity are maintained through the formation of several intercellular adhesion systems such as tight junctions (TJs). As reviewed by Martin and Jiang [4], the expression of many tight junction proteins is disregulated in colorectal cancers. The expression pattern of hDlg and hScribble, known to control the establishment of apical-basal polarity in epithelial cells [7], markedly changes during colorectal tumor progression with down-regulation of both proteins being associated with lack of epithelial cell polarity and disorganized tissue architecture [8]. Little is known as to the specific cellular role of PTEN in human intestinal epithelial cells. The aim of this study was to investigate the role of PTEN in human colorectal cancer cells
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