Endocrine Abstracts

Molecular mechanisms involved in lactotrophs cell proliferation that led to prolactinoma development are not fully understood. Cyclin-dependant kinase (CDK) p27^Kip1 is a key cell cycle regulator, and it is regulated by Menin. The transgenic mice model MEN1^+/-, as the p27 ^-/- knock-out mice, develop pituitary adenomas and other neuroendocrine tumours. Menin can also interfere with phosphorylated AKT (pAKT) function, known for its stimulatory action on cell proliferation. Additionally, PTEN is an inhibitor of AKT activation/phosphorylation. For better understanding, we studied these regulatory mechanisms in a mice model of prolactinoma that overexpress the human chorionic gonadotrophic hormone β-subunit (hCGβ), in which the transgenic female (hCGβ+), but not the transgenic male, develops lactotroph hyperplasia from 3-month of age onwards. We used 6 months old mice, and we analysed pituitary gene expression by Real-Time PCR and lactotroph protein expression by double indirect immunofluorescence detection (PRL+ protein+), comparing transgenic mice (hCGβ+) and wild-types (WT). We observed higher levels of MEN1 gene expression in males vs females, without genotype differences. Male pituitaries presented similar levels of p27 gene expression as WT females, without genotype differences. However, hCGβ+ females showed lower levels of p27 compared to WTs. In addition, p27 protein expression was found to decrease in lactotrophs (PRL+) from hCGβ+ female pituitaries vs WTs. When Menin protein expression was analysed in female pituitaries, although no genotype differences were observed in the percentage of lactotrophs expressing Menin, important changes in its subcellular localization was observed: in lactotrophs from WT females Menin was expressed in cytoplasm and nuclei, while in hCGβ+ lactotrophs Menin was expressed mostly in cytoplasm. WT female lactotrophs showed low pAKT expression and it was most prevalent in cytoplasm while its expression was found increased in cytoplasm and nuclei in lactotrophs from hCGβ+ females. Additionally, lower levels of PTEN gene expression was observed in hCGβ+ pituitaries vs WTs. Pituitary PTEN gene expression was higher in males than females without genotype differences. We conclude that lower Menin expression in nulcei from hCGβ+ lactotrophs concomitant with lower PTEN expression could contribute to the decreased p27 and increased pAKT levels in transgenic females leading to tumour development. On the other hand, the higher levels of pituitary MEN1 and PTEN observed in males could help to control the cell proliferation rate in this sex.