Down-regulation of Wee1 kinase by a specific subset of microRNA in human sporadic pituitary adenomas.

CONTEXT: The tumorigenic mechanisms involved in pituitary adenomas, especially of nonfunctional pituitary adenomas (NFAs), remains unclear. Various cell cycle inhibitors have been found to be underexpressed in pituitary tumors; however, Wee1 kinase, a nuclear protein that delays mitosis and was recently recognized as a tumor suppressor gene, has not been previously investigated in pituitary tumors.

OBJECTIVE: Our objective was to examine the expression of Wee1 in pituitary tumors and to identify microRNAs (miRs) that can regulate its expression.

DESIGN: Expression of Wee1 was examined by immunohistochemistry and quantitative real-time PCR (qRT-PCR). Identification of miRs targeting the Wee1 3'-untranslated region was performed by miR array followed by expression analysis of identified miRs using qRT-PCR. Dual-luciferase assay and transient transfection of miRs into Hela cells followed by immunoblot analysis of Wee1 protein and cell proliferation analysis were carried out.

PATIENTS: A total of 57 pituitary tissue samples including 27 NFAs, 15 GH-producing adenomas with or without prolactin overproduction, and 15 normal pituitary glands were analyzed.

RESULTS: Wee1 protein expression was decreased in NFAs and GH-producing tumors with or without prolactin production, but no change in mRNA expression was observed with qRT-PCR. A specific subset of five miRNAs revealed by in silico target prediction was significantly overexpressed in NFA samples; three miRs (miR-128a, miR-155, and miR-516a-3p) targeted the 3'-untranslated region of the Wee1 transcript, and exogenous overexpression of these miRs inhibited Wee1 protein expression and HeLa cell proliferation.

CONCLUSIONS: To our knowledge, this is the first report suggesting that regulation of Wee1 kinase by miRs may be linked to pituitary tumorigenesis.