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Deregulation of hexose transporter expression in Caco-2 cells by ras and polyoma middle T oncogenes
S Baron-Delage1, L Mahraoui, A Cadoret
1Laboratoire de Biologie Cellulaire, Institut National de la Santé et de la Recherche Médicale Unité 402, Faculté de Médicine Saint-Antoine, Paris, France.
Abstract:
We investigated whether the oncogenic activation of p21ras or pp60c-src, which is frequently observed in colorectal cancers, induced alterations of sugar uptake in human colonic cells. We therefore examined hexose transporter expression and/or activity in Caco-2 cells transfected either with an activated human (Val-12) Ha-ras gene or with the polyoma middle T (PyMT) oncogene, a constitutive activator of pp60c-src tyrosine kinase activity. Experiments were performed at day 20 of culture, when Caco-2 cells express enterocyte-specific GLUT-2, GLUT-5, and SGLT-1 transporters in addition to GLUT-1 and GLUT-3. Along with increased glucose consumption rates, both oncogene-transfected cells exhibited increased levels of GLUT-1 and GLUT-3 mRNAs and/or immunoreactive proteins compared with control vector Caco-2 cells. In contrast, oncogene-transfected cells lost GLUT-2, GLUT-5, and SGLT-1 expression as determined by Northern and/or Western blot analyses and/or specific transport assays. The oncogene-induced repressive effect on these enterocyte-specific hexose transporters extended to brush-border hydrolases and villin but not to tight junctional protein ZO-1. In conclusion, oncogenic p21ras and PyMT/pp60c-src induce severe deregulation of hexose transporter expression in Caco-2 cells, which is manifested by 1) increased GLUT-1 and GLUT-3 expression and 2) repression of GLUT-2, GLUT-5, and SGLT-1, which parallels repression of some markers of the enterocyte-like differentiated phenotype of Caco-2 cells.
Insights
Oncogenic activation of p21ras and pp60c-src in colon cells increases glucose transporters GLUT-1 and GLUT-3 while decreasing enterocyte-specific transporters GLUT-2, GLUT-5, and SGLT-1.
Area of Science:
- Cell biology
- Molecular oncology
- Gastroenterology
Background:
- Colorectal cancers frequently exhibit oncogenic activation of p21ras and pp60c-src.
- Altered sugar metabolism is a hallmark of cancer cells.
- Understanding sugar transporter regulation in colon cancer is crucial.
Purpose of the Study:
- To investigate the impact of oncogenic p21ras and pp60c-src activation on sugar uptake in human colonic cells.
- To examine hexose transporter expression and activity in response to oncogene transfection.
- To determine if oncogene-induced changes affect differentiated enterocyte markers.
Main Methods:
- Caco-2 cells were transfected with activated human Ha-ras or polyoma middle T (PyMT) oncogene.
- Hexose transporter expression was analyzed using Northern and Western blot analyses.
- Hexose transporter activity was assessed via specific transport assays.
- Expression of enterocyte-specific markers and tight junction proteins was evaluated.
Main Results:
- Oncogene-transfected cells showed increased glucose consumption.
- Levels of GLUT-1 and GLUT-3 mRNAs and proteins were elevated.
- Expression of enterocyte-specific transporters GLUT-2, GLUT-5, and SGLT-1 was lost.
- Repression of these transporters paralleled the loss of other enterocyte differentiation markers.
Conclusions:
- Oncogenic p21ras and PyMT/pp60c-src significantly deregulate hexose transporter expression in Caco-2 cells.
- This deregulation involves increased GLUT-1/GLUT-3 and repressed GLUT-2/GLUT-5/SGLT-1 expression.
- The observed changes correlate with a loss of the differentiated enterocyte phenotype.