Correlation of alternative splicing of the D2 dopamine receptor mRNA and estrogen receptor mRNA in the prolactinomas and gonadotrope tumors

Estrogen inhibits D2S receptor-regulated Gi3 and Gs protein interactions to stimulate prolactin production and cell proliferation in lactotropic cells

The neurotransmitter dopamine (DA) is known to inhibit prolactin (PRL) secretion and the proliferation of lactotropes in the pituitary gland. Dopamine-2 (D2) receptor short (D2S) isoform is expressed in a reduced level while the D2 receptor long (D2L) isoform is expressed in an elevated level during estradiol (E(2))-induced PRL production and cell proliferation in lactotropes. To evaluate the role of these D2 receptor isoforms in E(2)-regulated lactotropic cell function, we compared E(2) effects on the level of PRL, cell proliferation, and G proteins in enriched lactotropes and lactotrope-derived PR1 cells containing only D2S isoform (D2S cells), D2L isoform (D2L cells), or no D2 receptor (V cells). Additionally, we determined the effects of G protein blockade on the E(2)-induced PRL production and cell proliferation in these cells. We here show that E(2) actions on G proteins, PRL production, and cell proliferation were maximally achieved in D2S cells, oppositely or marginally achieved in D2L cells, and absent in V cells. We also show that the DA and pertussis toxin modulations of E(2) actions on PRL, G proteins, and cell proliferation were maximally achieved in D2S cells compared with in D2L or V cells. Furthermore, we provide evidence for the existence of an inhibitory action of Gi3 on Gs that is under the control of the D2S receptor and is inhibited by E(2). These results suggest that the suppression of D2S-regulated Gi3 inhibition of Gs protein may be one of the mechanisms controlling E(2)-activated PRL synthesis and cell proliferation in lactotropes.

Expression of estrogen receptor α and growth factors in human prolactinoma and its correlation with clinical features and gender

BACKGROUND

Many studies demonstrate that growth factors play an important role in the pathogenesis of prolactinoma induced by estrogen. The effects of estrogen are mainly mediated through its nuclear receptor (ERα); however, expression of ERα and growth factors in prolactinoma and healthy pituitary and their relationship remain obscure.

AIM

To obtain new insights regarding the expression differences of these factors and their relationship and to investigate the correlation between gender and clinical features in patients with prolactinoma.

SUBJECTS AND METHODS

A total of 21 human prolactinomas and 6 healthy human pituitaries were examined for mRNA expression of ERα, basic fibroblast growth factor (bFGF), transforming growth factor α (TGFα), TGFβ1, TGFβ3, and TGFβ receptor type II (TGFβRII) by means of real-time PCR. Patient clinical data was also analyzed.

RESULTS

Both PRL level and tumor volume of the male patient group were higher than that of the female patient group. There was a significant correlation between PRL level and tumor volume in the total patient group. Expression of ERα, bFGF, TGFα, and TGFβ3 mRNA levels of the patient group were significantly different from that of the control group. A significant correlation between ERα mRNA levels and PRL levels, tumor volume, TGFβ1 mRNA levels in the total patient group were found.

CONCLUSIONS

PRL level and tumor volume have a significant difference between genders in prolactinoma patients. ERα and some growth factors may be involved in the tumorigenesis of prolactinoma. ERα could potentially be an effective therapy target for treating prolactinoma.