Deregulation of hexose transporter expression in Caco-2 cells by ras and polyoma middle T oncogenes

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.