Role of circCCDC138 in early malignant transformation of human lung epithelial cells induced by carbon black nanoparticles

Background With the large-scale production and application of carbon black nanoparticles (CBNPs), occupational and general exposure is obviously increasing. Related studies have shown that exposure to CBNPs can induce oxidative stress, inflammation, and DNA damage.

Objective To establish a CBNPs-induced malignant transformation (C-BEAS-2B) model of human lung epithelial cells (BEAS-2B) and explore the role and mechanism of circCCDC138 in the malignant transformation process.

Methods At 0, 10, 20, 40 and 80 μg·mL⁻¹ CBNPs concentrations, cell viability was detected by CCK8 assay. BEAS-2B cells were exposed to 20 mg·mL⁻¹ CBNPs for three months, and a malignant transformation model of BEAS-2B induced by CBNPs was constructed. The migration and invasion abilities of the cells were detected by cell scratch and Transwell assays. The expressions of circ-CCDC138 in BEAS-2B and C-BEAS-2B were detected by qRT-PCR, and its stability was verified by a digestive resistance test. A cell model with interference or overexpression of circCCDC138 was constructed, and the expression of circCCDC138 in the cells was detected by quantitative reverse transcription-PCR. The cell cycle and apoptosis were determined by flow cytometry. Western blot was used to analyze the expression of p53 protein.

Results The CBNPs used in the experiment were spherical particles with a chain-like structure. In the 20 μg·mL⁻¹ CBNPs group, the reduction in the viability of BEAS-2B cells was relatively small (10%). Compared with the control cells, the 20 μg·mL⁻¹ CBNPs group showed more obvious cell migration and invasion at 24 h and 48 h, indicating that the exposure to CBNPs induced early malignant transformation of BEAS-2B cells (P<0.01). The circCCDC138 expression in C-BEAS-2B was upregulated in a time-dependent manner after exposure to CBNPs. Compared with the C-BEAS-2B cells, the C-BEAS-2B cells over-expressing circCCDC138 exhibited arrested S phase progression (36.9%) and apoptosis resistance (P<0.01), along with down regulation of p53 protein expression in the cells (P<0.01), while the C-BEAS-2B cells interfering with circCCDC138 showed the opposite results (P<0.01).

Conclusion BEAS-2B cells exposed to CBNPs (20 μg·mL⁻¹) have significantly enhanced migration and invasion abilities, showing early malignant transformation characteristics. In addition, circCCDC138 is highly expressed in C-BEAS-2B cells with RNase R digestive resistance and increases in a time-dependent manner with CBNPs exposure. More importantly, circCCDC138 may promote the induction of malignant transformation of cells by inhibiting p53 protein expression.