DISRUPTION OF I-KAPPA-B-ALPHA REGULATION BY ANTISENSE RNA EXPRESSION LEADS TO MALIGNANT TRANSFORMATION

NF-kappa B transcription factors regulate the expression of a variety of genes involved in immune regulation and cell growth. In most cell t ypes NF-kappa B proteins are localized in an inactive form in the cyto plasm coupled to the inhibitory I kappa B proteins. Viruses, cytokines , lipopolysaccharides and other stimulating agents promote the dissoci ation of the cytosolic NF-kappa B/I kappa B complexes, via phosphoryla tion and degradation of I kappa B, resulting in the translocation of D NA binding, NF-kappa B complexes to the nucleus. To further understand the association of I kappa B with cell growth regulation, the effect of ectopic expression of sense and antisense I kappa B genes was exami ned in NIH3T3 cells. Overexpression of I kappa B alpha antisense RNA b ut not I kappa B gamma antisense RNA decreased the steady state levels of I kappa B alpha protein, altered NF-kappa B DNA binding and gene a ctivity and, most importantly, induced malignant transformation as mea sured by saturation density, growth in soft agar and tumorigenicity in nude mice. In contrast, overexpression of I kappa B alpha resulted in decreased saturation density, a battened cellular morphology and decr eased NF-kappa B dependent reporter gene activity. These results indic ate that overexpression of an I kappa B alpha antisense RNA may disrup t the NF-kappa B/I kappa B autoregulatory loop, leading to cellular tr ansformation. Our results raise the interesting possibility that I kap pa B alpha represents a potential tumor suppressor activity.