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 kB (NF-kB), 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 vectortransfected Caco-2 cells, both oncogene-transfected cell lines exhibited: (i) decreased constitutive NF-kB DNAbinding activity and NF-kB-mediated reporter gene expression, without alteration of their response to TNF-a for activation of these parameters; (ii) reduced NF-kB 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-kB transcriptional activity with TNF-a. 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-kB activity which could be responsible for the reduced adhesive properties of these cells after oncogene transfection.

We identified a candidate Interferon-Stimulated Response Element (ISRE), overlapping with an Interferon Regulatory Factors binding motif (IRF-E) in the promoter region of SMN and SMNc genes. Both ISRE and IRF-E motifs are involved in mediating transcriptional induction of interferon-stimulated gene expression. We, therefore, investigated whether SMN and SMNc genes were regulated by interferons (IFN). Here we show that both IFN-beta and IFN-gamma rapidly induced SMN and SMNc mRNA and protein expression in various cell lines. The transcription factor IRF-1 bound to the candidate ISRE/IRF-E sequence of SMN and SMNc genes in vitro and overexpression of IRF-1 induced expression of both genes in transfection assays. IRF-1 is, therefore, at least in part responsible for the induction of SMN and SMNc by IFNs. In primary culture of fibroblasts from SMA patients, IFN-beta and IFN-gamma induced SMNc gene expression and restored protein defect.

Summary 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'as and pp6Ocsrc in human colonic Caco-2 cells is associated with specific alterations of syndecan-1, a membrane-anchored proteoglycan playing a role in cell-matrix interaction and neoplastic growth control. 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 (Py-MT) oncogene, a constitutive activator of pp6Oc-src tyrosine kinase activity. Compared with control vector-transfected Caco-2 cells, both oncogene-transfected cell lines (1) contained smaller amounts of membrane-anchored PGs; (2) exhibited decreased syndecan-1 expression at the protein but not the mRNA level; (3) synthesised 35S-labelled syndecan-1 with decreased specific activity; (4) produced a syndecan-1 ectodomain with a lower molecular mass and reduced GAG chain size and sulphation; and (5) expressed heparanase degradative activity. These results show that the dramatic activation of the tumorigenic potential induced by oncogenic p2l" or Py-MT/pp60csrc in Caco-2 cells is associated with marked alterations of syndecan-1 expression at the translational and posttranslational levels.

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