miR-138-1* regulates aflatoxin B1-induced malignant transformation of BEAS-2B cells by targeting PDK1

Environmental carcinogens-induced lung cancer and potential mechanisms have attracted widespread attention. Currently, microRNAs (miRNAs) have been recognized as key players in development of cancer, among which guide strand of miRNA has been well documented rather than its passenger strand (miRNA*). Our previous study showed that treatment of 0.1 nM AFB1 for 50 passages could induce malignant transformation of immortalized human bronchial epithelial cells stably expressing CYP2A13 (P50 B-2A13 cells). However, the role of miRNAs in this carcinogenic proceeding is still unclear. In present study, 36 upregulated and 27 downregulated miRNAs in P50 B-2A13 cells were first identified by miRNA microarray, and miR-138-1* was selected as a candidate miRNA by RT-qPCR and pilot experiments. Functional studies revealed that miR-138-1* could inhibit proliferation, colony formation, migration and invasion of P50 B-2A13 cells. Further, target analysis and dual-luciferase reporter gene assay identified that miR-138-1(*) was consequentially paired with 3'-UTR of 3-phosphoinositide-dependent protein kinase-1 (PDK1) and decreased the luciferase activity. miR-138-1* could decrease the expressions of PDK1 and its downstream proteins in PI3K/PDK/Akt pathway but not vice versa, indicating that miR-138-1* might affect AFB1-induced malignant transformation through targeting PDK1. As predicted, interference of PDK1 showed the similar effects to miR-138-1* in the proliferation, colony formation, migration and invasion of P50 B-2A13 cells. Our study demonstrated that miR-138-1* played a critical role in AFB-induced malignant transformation of B-2A13 cells by targeting PDK1. Still, the study provides a novel insight into the roles of miRNA* during carcinogenesis, particularly airborne carcinogens-induced lung cancer.