Efectos de la T4 en la apoptosis y proliferación de tumores de mama

Hypothyroidism is a protective factor against breast cancer but long-term exposure or overdoses of thyroid replacement therapy with thyroxine (T4) may increase breast cancer risk. Objective: to study, in vivo and in vitro, the effects of T4 on the proliferation and apoptosis of mammary tumors of hypo- and euthyroid rats, and the possible mechanisms involved in these effects. Material and Methods: Female Sprague-Dawley rats were treated with a single dose of dimethylbenzathracene (15 mg/rat) at 55 days of age and were divided into three groups: hypothyroidism (HypoT; 0.01% 6-N-propyl-2-thiouracil -PTU- in drinking water, n = 20), hypothyroidism treated with T4 (HypoT + T4; 0.01% PTU in drinking water and 0.25 mg/kg/day T4 via sc; n = 20) and EUT (untreated control, n = 20). At sacrifice, tumor explants from HypoT and EUT rats were obtained and treated either with 10􀀀 10 M T4 in DMEM/F12 without phenol red with 1% Charcoalized Fetal Bovine Serum or DMEM/ F12 only for 15 min to evaluate intracellular signaling pathways associated with T4, and 24 h to evaluate changes in the expression of hormone receptors and proteins related to apoptosis and proliferation by immunohisto-chemistry and Western Blot. Results: In vivo, hypothyroidism retards mammary carcinogenesis but its treatment with T4 reverted the protective effects. In vitro, the proliferative and anti-apoptosis mechanisms of T4 were different regarding the thyroid status. In EUT tumors, the main signaling pathway involved was the cross-talk with other receptors, such as ERα, PgR, and HER2. In HypoT tumors, the non-genomic signaling pathway of T4 was the chief mechanism involved since αvβ3 integrin, HER2, β-catenin and, downstream, PI3K/AKT and ERK signaling pathways were activated. Conclusion: T4 can regulate mammary carcinogenesis by mainly activating its non-genomic signaling pathway and by interacting with other hormone or growth factor pathways endorsing that overdoses of thyroid replacement therapy with T4 can increase the risk of breast cancer.

甲状腺功能减退症可作为一种防御因素抵御乳腺癌，然而，长期暴露或过量使用甲状腺替代疗法中的甲状腺素（T4）可能会增加乳腺癌的风险。研究目的：旨在通过体内和体外实验，探讨T4对甲状腺功能减退及正常甲状腺大鼠乳腺肿瘤的增殖和凋亡的影响，并研究这些影响背后的可能机制。实验材料与方法：选取雌性Sprague-Dawley大鼠，于55日龄时给予单剂量二甲基苯并蒽（15 mg/鼠）处理，并将大鼠分为三组：甲状腺功能减退组（HypoT；饮水添加0.01% 6-丙基-2-硫尿嘧啶-PTU，n = 20）、甲状腺功能减退并接受T4治疗组（HypoT + T4；饮水添加0.01% PTU和经皮注射0.25 mg/kg/天的T4，n = 20）以及未处理对照组（EUT，n = 20）。在处死大鼠后，从HypoT和EUT大鼠中获取肿瘤移植，并将其分别用10^-4 M T4在无酚红的DMEM/F12培养基中添加1%炭化胎牛血清或仅使用DMEM/F12培养基处理15分钟，以评估与T4相关的细胞内信号通路，并处理24小时以通过免疫组化和Western Blot评估激素受体和与凋亡及增殖相关的蛋白表达的变化。结果：在体内实验中，甲状腺功能减退延缓了乳腺肿瘤的发生，但T4治疗逆转了这种保护作用。在体外实验中，T4的增殖和抗凋亡机制在不同甲状腺状态下存在差异。在EUT肿瘤中，主要涉及的信号通路是与ERα、PgR和HER2等其他受体的交叉对话。在HypoT肿瘤中，T4的非基因组信号通路是主要机制，因为αvβ3整合素、HER2、β-连环蛋白以及下游的PI3K/AKT和ERK信号通路被激活。结论：T4可以通过主要激活其非基因组信号通路以及与其他激素或生长因子通路相互作用来调节乳腺肿瘤的发生，从而证实了甲状腺素替代疗法中的T4过量可能增加乳腺癌的风险。