title: K-ras 4A and 4B mRNA levels correlate with superoxide in lung adenocarcinoma cells, while at the protein level, only mutant K-ras 4A protein correlates with superoxide.
abstract: The K-ras gene is frequently mutated in lung and other cancers. K-ras protein includes two splice variants, K-ras 4A and 4B. While K-ras 4B is more widely expressed, recent evidence implicates K-ras 4A in lung tumorigenesis. We found that K-ras 4A protein has a wide range of expression in a large panel of human lung adenocarcinoma cell lines. In cell lines with mutant K-ras, but not those with wildtype K-ras, the K-ras 4A protein had a strong positive correlation with levels of cellular superoxide. We investigated whether K-ras 4A protein was involved in superoxide production, or alternatively was modulated by elevated superoxide. Experiments with small interfering RNA targeting K-ras 4A did not confirm its role in superoxide generation. However, decreasing cellular superoxide with the scavenger Tiron tended to reduce levels of K-ras 4A protein. K-ras 4A and 4B mRNA were also quantified in a number of NSCLC cell lines. 4A mRNA correlated with 4A protein only in K-ras-mutant cells. K-ras 4A mRNA also correlated with superoxide, but with no difference between cell lines with mutant or wildtype K-ras. K-ras 4B mRNA correlated with 4A mRNA and with superoxide, in both K-ras mutant and wildtype cells. The results are consistent with superoxide directly or indirectly up-regulating expression of all K-ras genes, and also increasing the stability of K-ras 4A mutant protein selectively.
authors.affiliation: U.S. Food and Drug Administration, MOD-1 Laboratory, 8301 Muirkirk Road, Laurel, MD 20708, USA. richard.calvert@fda.hhs.gov
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Calvert
authors.forename: Meghana
authors.initials: M
authors.lastname: Gupta
authors.forename: Anna
authors.initials: A
authors.lastname: Maciag
authors.forename: Yih-Horng
authors.initials: YH
authors.lastname: Shiao
authors.forename: Lucy M
authors.initials: LM
authors.lastname: Anderson
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D000077192:Adenocarcinoma of Lung; D063646:Carcinogenesis / Q000235:genetics*; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D013481:Superoxides / Q000378:metabolism*
chemical_list: C117307:KRAS protein, human; D050505:Mutant Proteins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D013481:Superoxides; D016283:Proto-Oncogene Proteins p21(ras)