Antiestrogens Induce Growth Inhibition by Sequential Activation of p38 Mitogen-Activated Protein Kinase and Transforming Growth Factor-β Pathways in Human Breast Cancer Cells

Abstract

Antiestrogens are successfully used in the treatment of breast cancer. The purpose of this study was to investigate the role of different signal transduction pathways in antiestrogen-induced growth inhibition to gain insights into mechanisms of antiestrogen resistance. We used specific MAPK inhibitors and MCF-7 carcinoma cells as a model to demonstrate that p38 MAPK is an important mediator of antiestrogen growth inhibition in breast cancer. A kinase assay showed that antiestrogens (4-hydroxytamoxifen and ICI 182.780) rapidly induce p38 activity. Overexpression of kinase-deficient mutants of p38 reduced the antiestrogen suppression of Cyclin A transcription. TGFbeta, a negative regulator of breast cancer cell growth, is induced by antiestrogens; therefore, activation of p38 could have been mediated by TGFbeta. We used a TGFbeta and antiestrogen-sensitive reporter gene assay to show that p38 activation precedes TGFbeta activation. These results were further confirmed by quantitative RT-PCR analysis of the antiestrogen-induced transcription of TGFbeta2 and TGFbeta receptor II. Inhibition of p38 reduced the induction of both genes. Finally, Western blot analysis shows that antiestrogens induce phosphorylation of Smad (mothers against decapentaplegic homolog) 2 via p38. Promoter assays with the Smad-dependent reporter p6SBE confirm participation of Smad3 and Smad4 in antiestrogen action. Taken together, our data delineate an antiestrogen signal transduction pathway involving sequential activation of p38 and TGFbeta pathways to mediate growth inhibition.

KAI1/CD82 is a novel target of estrogen receptor‐mediated gene repression and downregulated in primary human breast cancer

“…22,23 In line with previous reports, fulvestrant effectively inhibited proliferation of ER-positive breast cancer cells. 37,38 Moreover, fulvestrant reduced the migratory activity of ER-positive MCF-7 cells, thus confirming previously reported results. 33 Importantly, we observed that fulvestrant also induced a significant upregulation of KAI1 in ERpositive but not ER-negative breast cancer cells in vitro.…”

“…5a-d). 37,38 Fulvestrant also affected the migration of ER-positive MCF-7 breast cancer cells, thus confirming previously reported results (Fig. 5e).…”

Estrogen receptor α attenuates transforming growth factor-β signaling in breast cancer cells independent from agonistic and antagonistic ligands

“…We additionally confirmed this putative crosstalk with a vice versa approach using a model system of ER-negative cancer cells, transfected to transiently overexpress the ER isoform ERa or ERb. These transfected MDA-MB-435 cells were completely sensitive to agonist and antagonist treatment and maximal effects on ligand-dependent receptor activation or inactivation were achieved in concentration ranges similar to those determined in prior stimulation experiments using ER-positive MCF-7 breast cancer cells [13,26]. Interestingly, these concentrations (10 -11 M E2, 10 -9 M ICI) also maximized the effects on growth induction or growth inhibition of untransfected MCF-7 cells [27,28].…”

“…Previous studies of our group emphasized the crucial role of TGF-b signaling in antiestrogen therapy and in the progression of breast cancer in general [6,[10][11][12][13]. By KaplanMeier analysis, we identified a correlation between the expression of TGF-b receptor II and a highly reduced overall survival in ER-negative breast cancer patients [14].…”

KAI1/CD82 is a novel target of estrogen receptor‐mediated gene repression and downregulated in primary human breast cancer (Int J Cancer 123: 2239–2246, 2008)

“…The authors acknowledge that those experiments confirm previously published observations by other research groups. [4][5][6][7] It seems that Christgen et al's only original and novel contribution is the finding that KAI1 is upregulated by fulvestrant in 2 ER-positive breast cancer cell lines.…”