Endocrine Abstracts

Introduction: The last World Health Organization (WHO) 2016 classification of Pituitary Tumours recommends the determination of transcription factors. During the last few years, silent variants of the main pituitary tumours (PTs) have been described. The mechanisms of silencing of these tumors are still unknown. POU1F1 (Pit1) encodes a member of the POU family of transcription factors that has a relevant role in the differentiation, proliferation and survival of three pituitary cell types: somatotroph, lactotroph and thyrotroph lineage. It regulates the expression of GH, PRL and TSH-beta in the anterior pituitary gland.

Aim: To analyze the gene expression of POU1F1 in a series of lactotroph and thyrotrophtumours, both functioning and silent, in order to observe if there are differences between the functioning and silent variants in both subtypes.

Material and methods: We selected 24 samples of PTs (seven functioning lactotropinomas (FLT), five silent lactotropinomas (SLT), three functioning thyrotropinomas (FTT) and nine silent thyrotropinomas (STT)) from our collection of 258 PTs. The tumours were previously molecularly identified on the basis of the expression of gene expression. Silent tumours were defined when the gene expression of PRL or TSHβ in the correspondent subtypes were similar to the respective functioning tumours, but without symptoms. The gene expression of POU1F1 was performed using qRT-PCR with TaqMan probes. The data are expressed as the mean and S.D. of the Fold Change (FC). The ANOVA test was used to analyze differences between functioning and silent tumours in both subtypes.

Results: There were no significant differences in the expression of POU1F1 between LT and TT subtypes in the overall series (2.87±2.11 vs 2.00±1.11, P=0.266) and between their respective silent or functioning tumours (1.39±1.45 vs 1.91±1.26, P=0.797; 3.94±1.89 vs 2.27±0.48, P=0.267). FLT but not FTT expressed more POU1F1 than their silent variants (FLT vs SLT:3.94±1.89 vs 1.39±1.45, P=0.036); FTT vs STT (2.27±0.48 vs 1.91±1.26, P=0.983).

Conclusions: The lower expression of POU1F1 in the silent variant of functioning lacto and thyrotropinomas could contribute to the silencing of these tumours. The absence of statistical significance in TT could be attributed to the short number of analyzed tumours.