Manganese-Induced Central Precocious Puberty (MnPP) Increases Hormone Receptor Expression (HR+) in Proliferating Mammary Epithelial Cells in Adult Female Rats
Academic Article
Overview
Research
Identity
Additional Document Info
Other
View All
Overview
abstract
In the developing mammary gland (MG), hormone receptor expressing (HR+) cells very rarely proliferate. The actions of estrogen (E2) and progesterone (P4) on ductal morphogenesis are paracrine and require mediators to stimulate growth of HR adjacent cells. However, in premalignant and invasive human breast lesions, proliferating cells are HR+. Thus, a dramatic change occurs in MG cell fate with a suspected increased sensitivity to steroid mediated growth. Studies have theorized that early pubertal onset alters MG cell fate increasing the risk of breast cancer later in life. Yet, it is not known if early puberty can cause this conversion to HR+ proliferating MG cells and if this phenotype is sustained in the adult gland. We previously demonstrated that manganeseinduced precocious puberty (MnPP) accelerates E2regulated MG development, resulting in sustained proliferation of MG epithelial cells and adult hyperplasia. In the current study, we characterized the normal distribution of HR+ proliferative cells in the MG of prepubertal and adult female rats, determined if MnPP could increase this population and identify cellular proteins that may be involved. Sprague Dawley female rats were exposed daily to 10mg/kg manganese chloride (MnCl2) or saline (control) via gastric gavage from postnatal day (PND) 12 to PND 30. MGs were collected on PNDs 30 and 120. Using dual labeling immunofluorescence (IF), only 2% of total MG epithelial cells coexpress HRs (E2 or P4 receptor) and the proliferative marker PCNA in the prepubertal MG. As expected, MnPP significantly (p<0.01) increased the percentage of proliferating (PCNA+) MG cells. The percentage of proliferating cells coexpressing progesterone receptor (PR+/PCNA+) increased by more than 2fold in MnPP females relative to controls at PND30 (p<0.01). The proportion of proliferating HR+ cells (ER+/PCNA+ or PR+/PCNA+) remained elevated in PND120 glands of MnPP females compared to controls (p<0.001). Western blot analysis revealed a significant switch in expression levels of the cell cycle regulator, p27, and the mitotic stimulator EREG in MGs that corroborated changes in PR+ proliferation between PND 30 and 120. Furthermore, histologically normal human breast tissue adjacent to ductal carcinoma in situ (DCIS) from The Human Protein Atlas show ER and PR expression similar to expression levels observed in our MnPP rat MGs at PND120. Collectively, these data show that MnPP results in persistent HR expression in proliferating MG cells. Thereby possibly sensitizing it to the hormonal milieu and making the MG more responsive to steroid mediated growth.Support or Funding InformationThis work was supported by NIEHS grant ESO13143 awarded to WLD and NIGMS grant 1R25GM100866 awarded to RKD.
