Endocrine Abstracts

MicroRNA (miRNAs) are small non-coding RNA molecules that significantly impacted the understanding of cell biology in the last decade. They regulate the expression of 10–30% of all protein-coding gene, thus playing a crucial role in a wide range of biological and pathological processes. Consistently, aberrant miRNA expression has been implicated in numerous human diseases, including pituitary tumours. Different studies analysed the entire miRNA transcriptoma, by microarray and RT-PCR, in normal and neoplastic pituitary tissues, and several aberrant expression patterns of miRNAs in pituitary tumours as compared to normal pituitary have been identified to date. A different miRNA signature has revealed miRNAs to be useful for discrimination of the different pituitary adenoma sub-types, for distinguishing pharmacological treated pituitary adenomas, as well as for differentiation of microadenomas from macroadenomas and carcinomas from adenomas. This is particularly important in the still unsolved issue of distinguishing benign from malignant pituitary tumours prior to metastasis. Based on their differential expression, it is possible to infer the likely role of certain miRNAs in tumor development. In this way a number of studies identified miRNAs controlling pituitary cell proliferation, apoptosis and invasion. Also by identifying the putative or confirmed target of the aberrantly expressed miRNAs has been possible to get significant insight into the role of miRNAs in pituitary tumorigenesis. This is the case of a group of miRNAs, all downregulated in a wide range of pituitary adenomas compared to normal pituitary tissue, which are able to inhibit pituitary cell growth by targeting HMGA proteins in pituitary cells. Indeed, overexpression of HMGA genes is a common feature of human pituitary tumours and it causes pituitary cell cycle dysregulation and development of pituitary adenomas in transgenic mice, thus suggesting that HMGA genes might be considered as specific oncogenes for pituitary cell transformation. Therefore, the restoration of miRNAs targeting HMGA genes or other pituitary oncogenes may represent a new promising therapeutic approach for pituitary adenomas.