miR-15a and miR-16-1 down-regulation in pituitary adenomas

Micro RNAs (miRs) are small noncoding RNAs, functioning as antisense regulators of other RNAs. miR-15a and miR-16-1 genes are located at chromosome 13q14, a region which is frequently deleted in pituitary tumors. An inverse correlation has been shown in B cell chronic lymphocytic leukemia (B-CLL) between miR-15a and miR-16-1 expression and the expression levels of arginyl-tRNA synthetase (RARS), an enzyme which associates with the cofactor p43 in the aminoacyl-tRNA synthetase complex. When secreted, p43 regulates local inflammatory response and macrophage chemotaxis, and seems to have anti-neoplastic properties in mice. We explored miR-15a and miR-16-1 expression in 10 GH-secreting and in 10 PRL-secreting pituitary macroadenomas by Northern blot, and investigated the possible correlation with in vivo and in vitro characteristics. We found that miR-15a and miR-16-1 are expressed at lower levels in pituitary adenomas as compared to normal pituitary tissue. Moreover, their expression inversely correlates with tumor diameter and with RARS expression (P < 0.05), but directly correlates with p43 secretion (P < 0.02). Therefore, miR15 and miR16 down-regulation in pituitary adenomas correlates with a greater tumor diameter and a lower p43 secretion, suggesting that these genes may, at least in part, influence tumor growth.