MEKK1 activation of human estrogen receptor α and stimulation of the agonistic activity of 4-hydroxytamoxifen in endometrial and ovarian cancer cells
MEKK1 activation of human estrogen receptor α and stimulation of the agonistic activity of 4-hydroxytamoxifen in endometrial and ovarian cancer cells
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DOI：
10.1210/me.14.11.1882
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发表时间：
2000-11-01
影响因子：
--
通讯作者：
Bai, WL
中科院分区：
文献类型：
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作者：
Lee, H;Jiang, F;Bai, WL
雌激素是刺激正常和转化的女性生殖系统上皮细胞生长的有丝分裂原。雌激素的作用是通过雌激素受体介导的，雌激素受体是受配体调节的转录因子。他莫昔芬是一种选择性雌激素受体调节剂，在乳房作为雌激素受体拮抗剂，在子宫作为激动剂。在目前的研究中，我们表明，在子宫内膜癌细胞和卵巢癌细胞中，共表达具有结构性活性的MEKK1，而不是RAF或MEKK2，显著增加了该受体的转录活性。野生型MEKK1和MEKK1上游的活性Rad的表达也增加了受体的活性，而显性负性MEKK1的共同表达则阻断了Rad的诱导，表明内源性MEKK1能够激活受体。进一步的实验表明，MEKK1诱导的激活是通过Jun N-末端激酶和p38/Hog1两种途径介导的，并且不依赖于受体p38上的已知磷酸化位点，而不是Jun N-末端激酶，在免疫复合酶检测中有效地使该受体磷酸化，这表明这两种激酶在受体激活中的参与程度不同。更重要的是，MEKK1的表达增加了4-羟基他莫昔芬的激动剂活性，使其激动剂活性达到与雌二醇相当的水平，并完全阻断了其拮抗作用。这些发现表明，他莫昔芬化合物的子宫特异性激动剂活性可能由作用于MEKK1下游的激酶的状态决定。
Estrogens are mitogens that stimulate the growth of both normal and transformed epithelial cells of the female reproductive system. The effect of estrogens is mediated through the estrogen receptors, which are ligand-regulated transcription factors. Tamoxifen, a selective estrogen receptor modulator, functions as an estrogen receptor antagonist in breast but an agonist in uterus. In the current study, we show that coexpression of a constitutively active MEKK1, but not RAF or MEKK2, significantly increases the transcriptional activity of the receptor in endometrial and ovarian cancer cells. The expression of wild-type MEKK1 and an active Rad, which functions upstream of MEKK1, also increased the activity of the receptor while coexpression of dominant negative MEKK1 blocked the Rad induction, indicating that endogenous MEKK1 is capable of activating the receptor. Additional experiments demonstrated that the MEKK1-induced activation was mediated through both Jun N-terminal kinases and p38/Hog1 and was independent of the known phosphorylation sites on the receptor, p38, but not Jun N-terminal kinases, efficiently phosphorylated the receptor in immunocomplex kinase assays, suggesting a differential involvement of the two kinases in the receptor activation. More importantly, the expression of the constitutively active MEKK1 increased the agonistic activity of 4-hydroxytamoxifen to a level comparable to that of lira-estradiol and fully blocked its antagonistic activity. These findings suggest that the uterine-specific agonistic activity of the tamoxifen compound may be determined by the status of kinases acting downstream of MEKK1.