CAP43, A NOVEL GENE SPECIFICALLY INDUCED BY NI2+ COMPOUNDS

To better understand the molecular mechanism(s) involved in the essent iality, toxicity, and/or carcinogenicity of nickel compounds, a mRNA d ifferential display technique was used to identify gene(s) that were s pecifically induced by these carcinogens. Differential expression of s everal genes was observed in human lung A549 cells exposed to nickel s ubsulfide. One gene, Cap43 which expressed a 3.0-kb mRNA encoding a M- r 43,000 protein, was found to be induced within 4-6 h by either Ni3S2 or NiCl2 in A549 cells and attained a level as high as 30-fold within 24-36 h of treatment. Twelve other tested metal compounds failed to i nduce Cap43 expression, leading to the conclusion that, with regard to metals, the induction of this gene was nickel-specific. Oxidative str ess that is often caused by metals and heat shock did not induce Cap43 further, suggesting a specific nature in the signaling pathway involv ed in Cap43 induction. Activation of signaling pathways with vanadate did not induce Cap43 nor did trifluoperazine block its induction by ni ckel; however, okadaic acid, a serine/threonine phosphatase inhibitor, induced Cap43 to a greater extent than any nickel compound tested. Ho mocysteine did not induce Cap43 in a number of cell lines, with the ex ception of human endothelial cells. The Cap43 gene was found to be ind uced by nickel not only in all tested human and rodent cell lines in v itro but also in several rat organs after oral exposure to NiCl2. We h ave found that the primary signal for Cap43 induction was an elevation of free intracellular Ca2+ caused by Ni2+ exposure because Cap43 was induced by calcium ionophores and its induction was attenuated by bis- (O-aminophenyl)-ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) -ester, a chelator of intracellular Ca2+. We found that the Cap43 gene was evolutionarily conserved and similarly regulated in humans, mice, and rats. Recent studies have shown that Cap43 is expressed at lower levels in colon cancer. Further studies of Cap43 regulation by Ca2+ sh ould enhance our understanding of the role of Cap43 in cell function a nd cancer pathogenesis.