Nickel may contribute to EGFR mutation and synergistically promotes tumor invasion in EGFR-mutated lung cancer via nickel-induced microRNA-21 expression

We recently reported that nickel accumulation in lung tissues may be associated with an increased in p53 mutation risk via reduced DNA repair activity. Here, we hypothesized that nickel accumulation in lung tissues could contribute to EGFR mutations in never-smokers with lung cancer. We enrolled 76 never-smoking patients to evaluate nickel level in adjacent normal lung tissues by ICP-MS. The prevalence of EGFR mutations was significantly higher in the high-nickel subgroup than in the low-nickel subgroup. Intriguingly, the OR for the occurrence of EGFR mutations in female, adenocarcinoma, and female adenocarcinoma patients was higher than that of all patients. Mechanistically, SPRY2 and RECK expressions were decreased by nickel-induced miR-21 via activation of the EGFR/NF-κB signaling pathway, which promoted invasiveness in lung cancer cells, and particularly in the cells with EGFR L858R expression vector transfection. The patients' nickel levels were associated with miR-21 expression levels. Kaplan-Meier analysis revealed poorer overall survival (OS) and shorter relapse free survival (RFS) in the high-nickel subgroup than in low-nickel subgroup. The high-nickel/high-miR-21 subgroup had shorter OS and RFS periods when compared to the low-nickel/low-miR-21 subgroup. Our findings support previous epidemiological studies indicating that nickel exposure may not only contribute to cancer incidence but also promote tumor invasion in lung cancer.