Loss of MEG3 promotes migration and invasion of nickel-transformed cells, partially via upregulation of RUNX2.

Nickel is a transition metal that is widely distributed in the environment. Nickel compounds are classified as Group 1 carcinogens (human carcinogens) by the International Agency for Research on Cancer (IARC). Despite extensive studies, the molecular mechanisms underlying nickel-induced carcinogenesis remain incompletely understood. Maternally Expressed Gene 3 (MEG3) is the first long non-coding RNA (lncRNA) identified as a tumor suppressor. Previous studies have shown that downregulation of MEG3 increases HIF-1α expression in human bronchial epithelial BEAS-2B cells chronically exposed to nickel. In the present study, we observed that MEG3 expression is markedly reduced in nickel-transformed cells. Dysregulation of Runt-Related Transcription Factor 2 (RUNX2) has also been implicated in multiple cancer types. Previous studies have demonstrated that RUNX2 is upregulated in nickel-induced malignantly transformed BEAS-2B cells. Consistent with these findings, we observed that chronic exposure of BEAS-2B cells to low-dose nickel increases both RUNX2 mRNA and protein expression, accompanied by elevated expression of mesenchymal markers and enhanced migratory and invasive capacities. Overexpression of MEG3 in nickel-transformed cells reduces RUNX2 protein levels and reverses the alterations of epithelial-mesenchymal transition (EMT) markers, resulting in decreased cell migration and invasion in nickel-transformed cells. Similarly, silencing RUNX2 reverses the expression of EMT markers and suppresses the migratory and invasive capacities of nickel-transformed cells. Notably, shRNA-mediated RUNX2 knockdown increases MEG3 expression, indicating reciprocal regulation between MEG3 and RUNX2 in nickel-transformed cells. Collectively, our findings demonstrate that MEG3 and RUNX2 form a reciprocally regulated signaling axis that contributes to EMT, thereby promoting migration and invasion in nickel-transformed cells. These results identify MEG3 and RUNX2 as interconnected biomarkers and potential therapeutic targets for cancer prevention and treatment, warranting further mechanistic investigation.