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 i n a constitutive state in human colorectal cancer, In this study we at tempted to establish whether the tumorigenic progression induced by on cogenic activation of p21(ras) or pp60(c-src) in human colonic cells i s associated with alterations of the activity and expression of nuclea r factor kappa B (NF-kappa B), a transcription factor suspected to par ticipate in the development of cancer, To this end, we used Caco-2 cel ls made highly tumorigenic by transfection with an activated Val-12 hu man Ha-ras gene or with the polyoma middle T (PyMT) oncogene, a consti tutive activator of pp60(c-src) tyrosine kinase activity, Compared wit h control vector-transfected Caco-2 cells, both oncogene-transfected c ell lines exhibited: (i) decreased constitutive NF-kappa B DNA-binding activity and NF-kappa B-mediated reporter gene expression, without al teration of their response to TNF-alpha for activation of these parame ters; (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 tr anscriptional 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-regulatio n of p65 expression and NF-kappa B activity which could be responsible for the reduced adhesive properties of these cells after oncogene tra nsfection.