Estrogen-like effects of thyroid hormone on the regulation of tumor suppressor proteins, p53 and retinoblastoma, in breast cancer cells

Abstract

T47D cells represent an estrogen-responsive human ductal carcinoma cell line which expresses detectable levels of estrogen receptor (ER). We have previously shown that estradiol (E 2 ) treatment of T47D cells causes an increase in the level of p53 and a concomitant phosphorylation of retinoblastoma protein (pRb). In the present study, we have analysed the expression of p53 and phosphorylation state of pRb and compared the eects of E 2 and triiodothyronine (T 3 ) on these phenomena. Cells were grown in a medium containing charcoal-treated serum to deplete the levels of endogenous steroids. Upon con¯uency, the cells were treated with T 3 (10 712 to 10 77 M) for 24 h and the presence of p53 and pRb was detected by Western analysis. E 2 treatment of cells caused a 2 ± 3-fold increase in the level of p53. Presence of T 3 in the medium caused a gradual increase in the level of p53 in a concentration-dependent manner. Under the above conditions, pRb was phosphorylated (detected as an upshift during SDS ± PAGE) in the presence of E 2 and T 3 . Supplementation of growth medium with T 3 (1 mM) caused an increase in the rate of proliferation of T47D cells and induced hyperphosphorylation of pRb within 4 h; this eect was maintained for up to 12 h. When ICI 164 384 (ICI) (1 mM), an ER antagonist, was combined with E 2 (1 nM) or T 3 (1 mM), eects of hormones on cell proliferation and hyperphosphorylation of pRb were blocked. Western analysis of p53 was supplemented with its cytolocalization by immuno-labeling using laser scanning confocal uorescence microscopy, which revealed an ICI-sensitive increase in the abundance of p53 in hormone-treated cells. Steroid binding analysis revealed lack of competition by T 3 for the [ 3 H]E 2 binding. These results indicate that T 3 regulates T47D cell cycle progression and proliferation raising the p53 level and causing hyperphosphorylation of pRb by a common mechanism involving ER and T 3 receptor (T 3 R)-mediated pathways.

Profile of thyroid hormones in breast cancer patients

“…Alternatively, thyroid hormones might stimulate the transcription of ERß-dependent genes through a combination of ERß-TRα1, as suggested by Vasudevan et al (5). Dinda et al (17) postulated that the estrogen-like effects of T 3 were mediated by TR interaction with ER response element. Therefore, another possibility is that T 3 bound to the T 3 receptor, independently of ER, stimulates ER response element function, promoting transcription of target genes that lead to cellular proliferation.…”

“…On the other hand, physiological concentrations of T 3 , the more active form of thyroid hormone, significantly enhance estradiol growth stimulation of a number of human breast carcinoma cell lines (16). In T47D breast cancer cells, E 2 and T 3 similarly regulate cell cycle progression and proliferation raising the p53 level and causing hyperphosphorylation of pRb (17).…”

Antithyroid peroxidase antibody positivity is associated with lower incidence of metastasis in breast cancer

“…However, despite extensive population studies, the results as a whole have been inconsistent. In preclinical models, it has been found that T3 may sustain serum-free proliferation of several cell lines, including breast cancer; in addition, rodent mammary gland development and physiology have been found to be sensitive to T3 (9)(10)(11).…”

Perfil dos hormônios da tireoide em pacientes com câncer de mama em estado de menopausa

“…Por outro lado, HTs podem alterar a transcrição de genes ERdependentes, através da ligação ERTR, como sugerido por Vasude van e cols. (36) ou ainda ocorrer interação entre TR e elementos responsivos do ER (37). De qualquer for ma, essas interações indicam que, em estado de pós menopausa com níveis baixos de E2, os HTs podem levar ao crescimento tumoral estimulando vias de ação pertencentes aos hormônios estrogênicos.…”