Non-steroidal anti-inflammatory drugs (NSAIDs) are used for the treatment of inflammatory diseases. Recently, NSAIDs have been reported to have a chemopreventive effect on the development of human colorectal cancer. However, some reports indicate that the chemopreventive effect on colon cancer may, in part, be independent of prostaglandin inhibition. In preliminary experiments, NSAIDs (indomethacin & aspirin) treatment of human colon cancer cells as well as breast and lung cancer cells causes the up-regulation of novel gene (name as nrg-1) which we have characterized as member of the TGF-Beta superfamily gene. Although they used different names (PTGFB, MIC-1, PDF, PLAB, and novel TGF-Beta gene), the sequence analysis revealed that the five genes are almost identical to each other and belong to the new TGF-Beta superfamily with unknown biological function. We have now sequenced the entire gene induced by Indo in HCT-116 cells and the sequence is identical to sequences reported. Indo induces nrg-1 gene expression with time and concentration dependent manner with highest expression at 48 hrs and 100mM indo. Indo also induced an increase in expression of nrg-1 in other cell lines, breast cell, prostate, and macrophage. In addition, we tested several inactive precursors or metabolites of NSAIDs, which are devoid of the ability to inhibit Cox-1/2. These inactive chemicals do not induce nrg-1 expression. Since the concentration of NSAID required to induce nrg-1 expression is higher than the concentration required to inhibit Cox-1/2, we suspected that the expression was not related to Cox-1/2 inhibition. Previous reports indicate NSAIDS at the concentrations used in our experiments to be ligands for PPARg. We measured the activation of PPARgamma by a luciferase assay using a system. It appears there is a relationship between activation of PPARg and increased expression of nrg-1. We tested several PPARgamma activators (BRL-troglitazone) and these chemicals were very potent inducers of nrg-1 expression. Moreover, nrg-1 expression in response to PPARg activators was very rapid compared to the NSAID response. Since both NSAIDs and troglitazone reduce several cancers in animals, one could hypothesize a common mechanism via the increased expression of nrg-1. Preliminary studies with cells in culture indicate NSAIDs and troglitazone are inducing apoptosis and some data suggests that nrg-1 may play an important role preventing tumor growth. - Prostaglandin H synhase, TGFBeta, NSAIDs, apoptosis, PPAR, colorectal cancer
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