Down-regulation of NF-kappa B activity and NF-kappa B p65 subunit expression by ras and polyoma middle T oncogenes in human colonic Caco-2 cells

The products of ras and src proto-oncogenes are frequently activated in a constitutive state in human colorectal cancer, In this study we attempted to establish whether the tumorigenic progression induced by oncogenic activation of p21(ras) or pp60(c-src) in human colonic cells is associated with alterations of the activity and expression of nuclear factor kappa B (NF-kappa B), a transcription factor suspected to participate in the development of cancer, To this end, we used Caco-2 cells made highly tumorigenic by transfection with an activated Val-12 human Ha-ras gene or with the polyoma middle T (PyMT) oncogene, a constitutive activator of pp60(c-src) tyrosine kinase activity, Compared with control vector-transfected Caco-2 cells, both oncogene-transfected cell lines exhibited: (i) decreased constitutive NF-kappa B DNA-binding activity and NF-kappa B-mediated reporter gene expression, without alteration of their response to TNF-alpha for activation of these parameters; (ii) reduced NF-kappa B cytosolic stores along with a decreased p65 expression due, at least in part, to destabilization of p65 mRNA; (iii) a decrease in adhesion to extracellular matrix component-coated substrata which was partially corrected when stimulating NF-kappa B transcriptional activity with TNF-alpha. These results indicate that the tumorigenic progression induced by oncogenic p21(ras) or PyMT/pp60(c-src) in human colonic Caco-2 cells is associated with a down-regulation of p65 expression and NF-kappa B activity which could be responsible for the reduced adhesive properties of these cells after oncogene transfection.