Protein kinase C-dependent activation of NF-kappaB in enterocytes is independent of IkappaB degradation.

Abstract

Nuclear translocation of the NF-kappaB family of transcription factors is a proximal step in the signal transduction of a pleiotropic group of proinflammatory genes. Activation of RelA is under the negative control of IkappaB, a family of proteins degraded in response to immunologic and oxidant stimuli. The aim of this study was to examine this mechanism of NF-kappaB activation in intestinal epithelial cells. DLD-1 cell monolayers stimulated by interleukin (IL)-1beta or phorbol myristate acetate (PMA) were assayed for the nuclear translocation of NF-kappaB and immunoreactivity of various IkappaB isoforms that regulate NF-kappaB1/RelA activation. NF-kappaB activation triggered by PMA was not associated with the disappearance of immunoreactive IkappaBalpha, IkappaBbeta, IkappaBgamma, or IkappaBepsilon or with the dissociation of intact IkappaB from RelA. NF-kappaB activation induced by PMA was blocked by the protein kinase C inhibitor staurosporine but not by the proteasomal inhibitor N-acetyl-leucine leucine norleucinal (ALLN). In contrast, IL-1beta-induced NF-kappaB activation was associated with the disappearance of IkappaBalpha and was inhibited by ALLN but not staurosporine. Our data imply the existence of a novel pathway of NF-kappaB activation mediated by protein kinase C that does not require proteosomal degradation or the loss of IkappaB.