The proapoptotic effects of sulindac, sulindac sulfone and indomethacin are mediated by nucleolar translocation of the RelA(p65) subunit of NF-kappaB.

Understanding the mechanisms that underlie the antitumour activity of non-steroidal anti-inflammatory drugs (NSAIDs) against colorectal cancer will allow the development of more effective and specific chemopreventative agents. Modulation of the NF-kappaB pathway has been implicated as a key effector of the antitumour effect of aspirin, but the effects of non-aspirin NSAIDs on this pathway have yet to be fully defined. Here, we demonstrate that sulindac, sulindac sulfone and indomethacin activate the NF-kappaB pathway in colorectal cancer cells, as determined by western blot analysis of cytoplasmic levels of IkappaBalpha and immunocytochemical analysis of nuclear NF-kappaB/RelA. Furthermore, we show that all of these NSAIDs induce nucleolar translocation of the RelA subunit of NF-kappaB. Using RelA deleted for the previously described nucleolar localization signal, we demonstrate that this response is causally involved in the apoptotic effects of these agents. Finally, we demonstrate that NSAID-mediated nucleolar translocation of RelA is associated with downregulation of NF-kappaB-driven transcription and of the NF-kappaB target gene, ICAM-1. These data identify nucleolar translocation of RelA and the associated repression of the NF-kappaB-driven transcription as a central molecular mechanism of NSAID-mediated growth inhibition and apoptosis. As well as providing new understanding of the molecular determinants of RelA function, these findings also have relevance to the development of novel chemotherapeutic and chemopreventative agents.