Molecular mechanisms of mutation enhancement by serum factors from pancreatic cancer patients and purification of the factors.

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The molecular mechanisms that regulate mutability of human cells are intriguing biological problems. The present study revealed that mutability of human RS cell strain was enhanced by serum factors From pancreatic cancer patients and conditioned medium from cultures of a human pancreatic cancer cell line. RS cells, established from human fetal fibroblasts, are highly sensitive to far-rultraviolet light (UV) mutagenicity. Preculture of human RS cells with the serum factors or the medium prior to irradiation with UV resulted in an increase in the frequency of ouabain resistance (Oua^R) mutations, compared with cells irradiated but not treated with either the serum factors or the medium. Decreases in expression levels of the molecular chaperone GRP78/Bip mRNA and protein were observed in the medium-treated RSa cells. Studies using antisense oligonucleotides for GRF78/Bip mRNA showed that the antisense oligonucieotide-treated RSb cells were more susceptible to UV-induced K-ras codon 12 base substitution mutations than mock-treated cells, as determined by PCR and differential dot-blot hybridization. Thus, down-regulation of GRP78/Bip was suggested to be involved in the enhancement of mutability of human cells.