Molecular biology of deregulated gene expression in transformed C3H/10T1/2 mouse embryo cell lines induced by specific insoluble carcinogenic nickel compounds.

In the past, exposure of workers to mixtures of soluble and insoluble nickel compounds by inhalation during nickel refining correlated with increased incidences of lung and nasal cancers. Insoluble nickel subsulfide and nickel oxide (NiO) are carcinogenic in animals by inhalation; soluble nickel sulfate is not. Particles of insoluble nickel compounds were phagocytized by C3H/10T1/2 mouse embryo cells and induced morphological transformation in these cells with the following order of potency: NiO (black) > NiO (green) > nickel subsulfide. Foci induced by black/green NiO and nickel monosulfide developed into anchorage-independent transformed cell lines. Random arbitrarily primed-polymerase chain reaction mRNA differential display showed that nine c-DNA fragments are differentially expressed between nontransformed and nickel compound-transformed 10T1/2 cell lines in 6% of total mRNA; 130 genes would be differentially expressed in 100% of the mRNA. Fragment R3-2 was a sequence in the mouse calnexin gene, fragment R3-1 a portion of the Wdr1 gene, and fragment R2-4 a portion of the ect-2 protooncogene. These three genes were overexpressed in transformed cell lines. Fragment R1-2 was 90% homologous to a fragment of the DRIP/TRAP-80 (vitamin D receptor interacting protein/thyroid hormone receptor-activating protein 80) genes and was expressed in nontransformed but not in nickel-transformed cell lines. Specific insoluble carcinogenic nickel compounds are phagocytized into 10T1/2 cells and likely generate oxygen radicals, which would cause mutations in protooncogenes, and chromosome breakage, and mutations in tumor suppressor genes, inactivating them. These compounds also induce methylation of promoters of tumor suppressor genes, inactivating them. This could lead to permanent overexpresssion of the ect-2, calnexin, and Wdr1 genes and suppression of expression of the DRIP/TRAP-80 gene that we observed, which likely contribute to induction and maintenance of transformed phenotypes.