Intracellular Progesterone Receptor Mediates the Increase in Glioblastoma Growth Induced by Progesterone in the Rat Brain

BACKGROUND AND AIMS

Progesterone (P) is a steroid hormone involved in the development of several types of cancer including astrocytomas, the most common and malignant brain tumors. We undertook this study to investigate the effects of P on the growth and infiltration of a tumor caused by the xenotransplant of U87 cells derived from a human astrocytoma grade IV (glioblastoma) in the cerebral cortex of male rats and the participation of intracellular progesterone receptor (PR) on these effects.

METHODS

Eight weeks after the implantation of U87 cells in the cerebral cortex, we administered phosphorothioated antisense oligodeoxynucleotides (ODNs) to silence the expression of PR. This treatment lasted 15 days and was administered at the site of glioblastoma cells implantation using Alzet osmotic pumps. Vehicle (propylene glycol) or P₄ (400 μg/100 g) was subcutaneously injected for 14 days starting 1 day after the beginning of ODN administration.

RESULTS

We observed that P significantly increased glioblastoma tumor area and infiltration length as compared with vehicle, whereas PR antisense ODNs blocked these effects.

CONCLUSION

P, through the interaction with PR, increases the area and infiltration of a brain tumor formed from the xenotransplant of human glioblastoma-derived U87 cells in the cerebral cortex of the rat.

Growth factors and kinases in glioblastoma growth

<p>Glioblastoma multiforme (GBM) is the most aggressive type of brain cancer, having the highest invasion, migration, proliferation, and angiogenesis rates. Several signaling pathways are involved in the regulation of these processes including growth factors and their tyrosine kinase receptors, such as vascular endothelial growth factor (VEGF), transforming growth factor beta (TGFβ), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), and insulin-like growth factor–I (IGF–I). Different kinases and regulators also participate in signaling pathways initiated by growth factors, such as mitogen-activated kinases (MAPK), protein kinases C (PKC), phosphatidylinositol-3 kinases (PI3K), protein kinase B (PKB or Akt), glycogen synthase kinase 3β (GSK3β), the mTOR complex, and Bcl-2. In this review, we will focus on the role of these proteins as possible therapeutic targets in GBM.</p>

Expression and hormonal regulation of membrane progesterone receptors in human astrocytoma cells

Progesterone (P) participates in the regulation of the growth of several tumors, including astrocytomas, the most common and malignant human brain tumors. It has been reported that P induces astrocytomas growth in part by its interaction with its intracellular receptors (PR). Recently, it has been reported that membrane progesterone receptors (mPRs) are expressed in ovarian and breast cancer cells, and that P could exert some actions through these receptors, however, it is unknown whether mPRs are expressed in astrocytomas. In this work, U251 and U87 cell lines derived from human astrocytomas grade IV were used to study the expression, localization and hormonal regulation of three mPRs subtypes. Using RT-qPCR and Western blot techniques, we found that mPRα and mPRβ are clearly expressed at mRNA and protein levels in astrocytoma cells whereas mPRγ was barely expressed in these cells. Immunofluorescence staining showed that mPRα and mPRβ were mainly located in the cell surface. Flow cytometry assays demonstrated that in U251 and U87 cells, mPRβ is expressed by a higher percentage of both permeabilized and non-permeabilized cells as compared with mPRα. The percentage of cells expressing mPRγ was very low. P and estradiol (E) (10, 100 nM and 1 μM) decreased mPRα protein content at 12 h. In contrast, both P (100 nM and 1 μM) and E (10 and 100 nM) increased mPRβ content. Finally, by in silico analysis, we identified that mPRα, mPRβ and mPRγ promoters contain several progesterone and estrogen response elements. Our results indicate that mPRs are expressed in human astrocytoma cells, exhibiting a differential regulation by E and P. These data suggest that some P actions in astrocytoma cells may be mediated by mPRs.

Changes in the content of sex steroid hormone receptors in the growing and regressing ovaries of Gallus domesticus during development

Sex steroids participate in the regulation of reproduction in female chickens. In this work, we determined the content of androgen receptor (AR), intracellular progesterone receptor isoforms (PR-A and PR-B), membrane progesterone receptor γ (mPRγ) and estrogen receptor α (ER-α) in the left growing and right regressing ovaries of Gallus domesticus from 13-day-old chicken embryos to 1-month-old chickens by western blot analysis. A marked difference in the morphological characteristics of the left and the right ovaries during development was observed. Results show a higher content of AR in the left ovary than in the right one in all ages. In the left ovary, the highest content of AR was observed on day 13 of embryonic development, and diminished with age. In the right ovary, AR was expressed from day 13 of embryonic development to 1-day-old, and became undetectable at 1-week and 1-month-old. In the left ovary, PR isoforms were not detected on day 13 of embryonic development, but they presented a marked expression after hatching. In the right ovary, the highest expression of both PR isoforms was found on 1-day-old, and significantly decreased with age. PR-B was the predominant isoform on 1-day and 1-month old in the left ovary, whereas PR-A was the predominant one on day 13 of embryonic development in the right ovary. Interestingly, mPRγ was detected at 1-week and 1-month-old in the left ovary meanwhile in the right ovary, it was detected from day 13 of embryonic development to 1-day-old. ER-α was only detected in the left ovary from day 13 to 1-week-old, while in 1-month-old chickens, it was expressed in both ovaries. In the left ovary, ER-α content was lower from 1-day to 1-month-old as compared with day 13 of embryonic development. Our results demonstrate a differential expression of sex steroid hormone receptors between the left growing and the right regressing ovary, and throughout chickens' age; and this is the first report about mPR expression in birds.