ß-Catenin triggers nuclear factor ?B-dependent up-regulation of hepatocyte inducible nitric oxide synthase

Disruption of cell-to-cell contacts, as observed in many pathophysiological conditions, prime hepatocytes for compensatory hyperplastic response that involves induction of several genes, including proto-oncogenes and other gene targets of ß-catenin signaling pathway. By using cultured hepatocytes and experimental models of adherens junction disruption we have investigated changes in ß-catenin subcellular localization and their relationships with inducible nitric oxide synthase (iNOS) expression. Two experimental models were employed: (a) rat hepatocytes obtained by collagenase liver perfusion within the first 48 h of culture; (b) 48-h old cultured hepatocytes, transiently transfected or not with a plasmid encoding for dominant/negative inhibitory kappa B-a, exposed to ethylene glycol-bis-(2-aminoethylether)-N,N,N',N'-tetraacetic acid/LiCl treatment. ß-Catenin signaling and cellular localization, iNOS expression and nuclear factor ?B involvement, were investigated using morphological, cell and molecular biology techniques. E-cadherin-mediated disruption of cell-to-cell contacts induces early ß-catenin translocation from membrane to cytoplasm and nuclear compartments, events that are followed by up-regulation of c-myc, cyclin D1 and ß-transducin repeat-containing protein expression. This, in turn, resulted eventually in iNOS induction that was mechanistically related to nuclear factor ?B activation, as unequivocally shown in cells expressing dominant negative inhibitory kappa B-a. Our data indicate that E-cadherin disassembly and concomitant inactivation of glycogen synthase kinase-3ß result in nuclear factor ?B-dependent induction of iNOS in hepatocytes.