Arsenic activates STAT3 signaling during the transformation of the human bronchial epithelial cells

Arsenic (As³⁺), a metalloid abundant in environment, is classified as a group I carcinogen associated with several common human cancers, including cancers in lung, skin, bladder, liver, and prostate (Wei et al., 2019). The mechanisms of As³⁺-induced carcinogenesis had been extensively studied, and different mechanisms might be involved in different types of cancer (Wei et al., 2019). Recent studies showed that exposure to a high dose of arsenic is able to induce lung cancer. Meanwhile, prolonged exposure to a low concentration of arsenic can increase the risk of lung cancer also (Liao et al., 2009; Fernández et al., 2012). Emerging evidence indicated that prolonged exposure to arsenic promotes malignant transformation and some of the transformed cells have cancer-stem-like properties (Ngalame et al., 2014). In the present report, we revealed that exposure to As³⁺ for short time period inhibited tyrosine-705 phosphorylation of signal transducer and activator of transcription 3 (pSTAT3^Y705) and induced Src homology region 2 domain-containing phosphatase-1 (SHP-1) in bronchial epithelial cell line, BEAS-2B. In addition, we found that long term exposure of the cells to As³⁺ activates phosphorylation of STAT3 at serine 727 (pSTAT3^S727) as well as pSTAT3^Y705. Moreover, As³⁺ is able to induce the expression of miRNA-21 (miR-21) and decrease the expression of PDCD4. Taken together, our data suggest that activation of STAT3 and induction of miR-21 are important contributing factors to the reduced expression of PDCD4, which may play significant role in As³⁺-induced transformation of BEAS-2B cells.