The epigenetic EZH2/H3K27me3 axis modulates lactotroph tumor cell proliferation.

Interest in epigenetics has gained substantial momentum as a result of their identified role in the regulation of tumor progression as well as their ability to pharmacologically target genes. Pituitary neuroendocrine tumors (PitNETs) tend to be inactivated via epigenetic modification, and although emerging evidence has suggested a role for epigenetic factors in PitNET tumorigenesis, the degree to which these factors may be targeted by new therapeutic strategies still remains poorly understood. The objective of the present study was to examine the participation of the EZH2/H3K27me3 axis in the proliferation of lactotroph tumor cells. We demonstrated that the levels of EZH2 and H3K27me3 were increased in murine experimental prolactin (PRL) tumors with respect to a control pituitary, in contrast with the low p21 mRNA levels encountered, with an H3K27me3 enrichment being observed in its promoter region in a GH3 tumor cell. Furthermore, specific EZH2/H3K27me3 axis inhibition blocked the proliferation of primary tumor cell culture and GH3 cells, thereby making it an attractive therapeutic target for PRL PitNETs.

17ß-oestradiol acts as a negative modulator of insulin-induced lactotroph cell proliferation through oestrogen receptor α, via nitric oxide/guanylyl cyclase/cGMP.

OBJECTIVES: 17ß-oestradiol interacts with growth factors to modulate lactotroph cell population. However, contribution of isoforms of the oestrogen receptor in these activities is not fully understood. In the present study, we have established participation of α and ß oestrogen receptors in effects of 17ß-oestradiol on lactotroph proliferation induced by insulin and shown involvement of the NO/sGC/cGMP pathway. MATERIALS AND METHODS: Cell cultures were prepared from anterior pituitaries of female rats to evaluate lactotroph cell proliferation using bromodeoxyuridine (BrdUrd) detection, protein expression by western blotting and cGMP by enzyme immunoassay. RESULTS: In serum-free conditions, 17ß-oestradiol and α and ß oestrogen receptor agonists (PPT and DPN) failed to increase numbers of lactotroph cells undergoing mitosis. Co-incubation of 17ß-oestradiol/insulin and PPT/insulin significantly decreased lactotroph mitogenic activity promoted by insulin alone. Both ICI 182780 and NOS inhibitors (L-NMMA and L-NAME) induced reversal of the anti-proliferative effect promoted by 17ß-oestradiol/insulin and PPT/insulin. Moreover, 17ß-oestradiol, PPT and insulin increased sGC α1 protein expression and inhibited ß1, whereas co-incubation of 17ß-oestradiol/insulin or PPT/insulin induced increases of the two isoforms α1 and ß1. 17ß-oestradiol and insulin reduced cGMP production, while 17ß-oestradiol/insulin co-incubation increased this cyclic nucleotide. CONCLUSIONS: Our results suggest that 17ß-oestradiol is capable of arresting lactotroph proliferation induced by insulin through ER α with participation of the signalling NO/sGC/cGMP pathway.