MicroRNA-7 inhibits proliferation, migration and invasion of thyroid papillary cancer-cells via targeting CKS2

The purpose of this study was to examine the expression levels of microRNA-7 (miR-7) in human thyroid papillary cancer and its potential role in disease pathogenesis. The expression levels of different miRNAs were detected by miRNA-microarray analysis in ten thyroid papillary cancer specimens and adjacent normal thyroid cancer tissues. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was conducted to determine the expression level of miR-7 in both thyroid papillary cancer tissues and cell lines. To characterize the function of miR-7, MTT assay, colony formation assay, cell migration assay, cell invasion assay, cell cycle assay and cell apoptosis assay were used. Luciferase reporter assays were performed to validate the regulation of a putative target of miR-7, in corroboration with western blot assays. Finally, MTT assay, cell migration assay, cell invasion assay and cell cycle assay were used to indicate the roles of endogenous cyclin-dependent kinase regulatory subunit 2 (CKS2) in thyroid papillary cancer cells. Our results reveal that miR-7 expression was relatively decreased in thyroid papillary cancer specimens and cell lines compared with adjacent normal tissues and normal thyroid cells. Overexpression of miR-7 inhibited cellular proliferation, suppressed cellular migration and invasion, caused a G0/G1 arrest in vitro. Dual-luciferase reporter assays showed that miR-7 binds the 3'-untranslated region (3'-UTR) of CKS2. Western blotting showed that miR-7 negatively regulated CKS2 protein expression. As its downstream genes, cyclin B1 (G2/mitotic-specific cyclin-B1) and cdk1 (cyclin-dependent kinase 1) were regulated by miR-7 and CKS2 axis. Knockdown of CKS2 expression by CKS2-siRNA in TPC1 and K1 cells also significantly suppressed cell proliferation, cell migration and invasion. Our results demonstrated for the first time that miR-7 functions as a tumor suppressor and plays an important role in inhibiting the tumorigenesis through targeting CKS2 in thyroid papillary cancer cells.