Cadmium induces carcinogenesis in BEAS-2B cells through ROS-dependent activation of PI3K/AKT/GSK-3β/β-catenin signaling

Abstract

Cadmium has been widely used in industry and is known to be carcinogenic to humans. Although it is widely accepted that chronic exposure to cadmium increases the incidence of cancer, the mechanisms underlying cadmium-induced carcinogenesis are unclear. The main aim of this study was to investigate the role of reactive oxygen species (ROS) in cadmium-induced carcinogenesis and the signal transduction pathways involved. Chronic exposure of human bronchial epithelial BEAS-2B cells to cadmium induced cell transformation, as evidenced by anchorage-independent growth in soft agar and clonogenic assays. Chronic cadmium treatment also increased the potential of these cells to invade and migrate. Injection of cadmium-stimulated cells into nude mice resulted in the formation of tumors. In contrast, the cadmium-mediated increases in colony formation, cell invasion and migration were prevented by transfection with catalase, superoxide dismutase-1 (SOD1), or SOD2. In particular, chronic cadmium exposure led to activation of signaling cascades involving PI3K, AKT, GSK-3β, and β-catenin and transfection with each of the above antioxidant enzymes markedly inhibited cadmium-mediated activation of these signaling proteins. Inhibitors specific for AKT or β-catenin almost completely suppressed the cadmium-mediated increase in total and active β-catenin proteins and colony formation. Moreover, there was a marked induction of AKT, GSK-3β, β-catenin, and carcinogenic markers in tumor tissues formed in mice after injection with cadmium-stimulated cells. Collectively, our findings suggest a direct involvement of ROS in cadmium-induced carcinogenesis and implicate a role of AKT/GSK-3β/β-catenin signaling in this process.

Antioncogenic and Oncogenic Properties of Nrf2 in Arsenic-induced Carcinogenesis

“…Plasmids and Transfection-The overexpression of catalase, SOD1, and SOD2 in BEAS-2B cells has been described previously (17). The mCherry-EGFP-LC3B plasmid was purchased from Addgene (Cambridge, MA), and GFP-LC3 plasmid has been described previously (18).…”

Nrf2/p62 Signaling in Apoptosis Resistance and Its Role in Cadmium-induced Carcinogenesis

“…Plasmids and Transfection-The overexpression of catalase, SOD1, and SOD2 in BEAS-2B cells has been described previously (21). The mCherry-EGFP-LC3B plasmid was purchased from Addgene (Cambridge, MA), and GFP-LC3 plasmid has been described previously (24).…”

“…The soft agar assay was performed as described previously (21). Briefly, 3 ml of 0.5% agar in DMEM supplemented with 10% FBS was spread onto each well of a 6-well culture plate.…”

“…The food chain, cigarette smoke, and the cadmium mining industry are the main sources of cadmium exposure to humans (19). Cadmium induces apoptosis or transformation, depending on exposure concentrations and times (20,21). Cadmium also induces autophagy in the mesangial cells (22,23) and in the skin's epidermal cells (24).…”

“…Cadmium also induces autophagy in the mesangial cells (22,23) and in the skin's epidermal cells (24). Interestingly, cadmium-induced apoptosis, autophagy, or transformation is caused by ROS (20,21,24). Although ROS, autophagy, apoptosis, and cell transformation are important players in the mechanism of cadmium carcinogenesis, most studies are focused on the events leading to cell transformation, which can be considered the first stage of cadmium carcinogenesis.…”