MicroRNA profile indicates downregulation of the TGFβ pathway in sporadic non-functioning pituitary adenomas

MicroRNAs (miRs) are small, 16-29 nucleotide long, non-coding RNA molecules which regulate the stability or translational efficiency of targeted mRNAs via RNA interference. MiRs participate in the control of cell proliferation, cell differentiation, signal transduction, cell death, and they play a role in carcinogenesis. The aims of our study were to analyse the expression profile of miRs in sporadic clinically non-functioning pituitary adenomas (NFPA) and in normal pituitary tissues, and to identify biological pathways altered in these pituitary tumors. MiR expression profiles of 12 pituitary tissue specimens (8 NFPA and 4 normal pituitary tissues) were determined using miR array based on quantitative real-time PCR with 678 different primers. Five overexpressed miRs and mRNA expression of Smads (Smad1-9), MEG and DLK1 genes were evaluated with individual Taqman assays in 10 NFPA and 10 normal pituitary tissues. Pathway analysis was performed by the DIANA-mirPath tool. Complex bioinformatical analysis by multiple algorithms and association studies between miRs, Smad3 and tumor size was performed. Of the 457 miRs expressed in both NFPA and normal tissues, 162 were significantly under- or overexpressed in NFPA compared to normal pituitary tissues Expression of Smad3, Smad6, Smad9, MEG and DLK1 was significantly lower in NFPA than in normal tissues. Pathway analysis together with in silico target prediction analysis indicated possible downregulation of the TGF beta signaling pathway in NFPA by a specific subset of miRs. Five miRs predicted to target Smad3 (miR-135a, miR-140-5p, miR-582-3p, miR-582-5p and miR-938) were overexpressed. Correlation was observed between the expression of seven overexpressed miRs and tumor size. Downregulation of the TGF beta signaling through Smad3 via miRs may have a possible role in the complex regulation of signaling pathways involved in the tumorigenesis process of NFPA.