Department of Nutrition, China Medical University, Taichung, Taiwan, ROC.
J Cell Physiol. 2012 Dec;227(12):3820-7. doi: 10.1002/jcp.24093.
MED28, a mammalian Mediator subunit, exhibits several cellular roles, including a merlin, Grb2, and cytoskeleton-associated protein (magicin), a repressor of smooth muscle cell differentiation, and an endothelial-derived gene (EG-1). Overexpression of MED28 may stimulate cell proliferation which presumably results from the transcriptional activation of the Mediator function. Additionally, several tumors, including breast cancer, highly express MED28. We have found recently that MED28 potentiated epidermal growth factor (EGF)-induced migration in human breast cancer cells. Therefore, the objective of this study is to identify the role of MED28 in the aspect of cellular migration and invasion in human breast cancer cells. Suppression of MED28 blocked cellular migration and invasion with concomitant reduced expression levels of matrix metalloproteinase-2 (MMP2) and mitogen-activated protein kinase kinase 1 (MAP2K1; MEK1); overexpression of MED28 enhanced cellular migration and upregulated MMP2 and MEK1 expression. Moreover, suppression of MEK1, by dominant-negative, kinase-dead MEK1 cDNA construct or MEK1-specific small interfering RNA (siRNA) as well as MEK1 inhibitors, blocked MED28-induced MMP2 activation, cellular migration, and invasion in breast cancer cells. Furthermore, ectopic expression of MEK1 rescued the inhibitory effect of MED28 knockdown on invasion, and exogenous MMP2 recombinant protein recovered the suppression on invasion upon MED28 or MEK1 knockdown. Our data indicate that MED28 regulates cellular migration in a MEK1-dependent manner in human breast cancer cells, reinforcing the important cellular roles of MED28.
MED28 是一种哺乳动物 Mediator 亚基，具有多种细胞功能，包括 Merlin、Grb2 和细胞骨架相关蛋白（magicin），它可以抑制平滑肌细胞分化，同时也是一种内皮细胞来源的基因（EG-1）。MED28 的过表达可能会刺激细胞增殖，这可能是由于 Mediator 功能的转录激活所致。此外，包括乳腺癌在内的几种肿瘤高度表达 MED28。我们最近发现 MED28 增强了人乳腺癌细胞中表皮生长因子（EGF）诱导的迁移。因此，本研究的目的是确定 MED28 在人乳腺癌细胞迁移和侵袭方面的作用。抑制 MED28 会阻断细胞迁移和侵袭，同时降低基质金属蛋白酶-2（MMP2）和丝裂原活化蛋白激酶激酶 1（MAP2K1；MEK1）的表达水平；过表达 MED28 会增强细胞迁移，并上调 MMP2 和 MEK1 的表达。此外，通过显性负性突变体、激酶失活 MEK1 cDNA 构建体或 MEK1 特异性小干扰 RNA（siRNA）以及 MEK1 抑制剂抑制 MEK1，可阻断 MED28 诱导的 MMP2 激活、细胞迁移和乳腺癌细胞侵袭。此外，过表达 MEK1 可挽救 MED28 敲低对侵袭的抑制作用，外源性 MMP2 重组蛋白可恢复 MED28 或 MEK1 敲低对侵袭的抑制作用。我们的数据表明，MED28 通过依赖 MEK1 的方式调节人乳腺癌细胞的细胞迁移，这进一步证实了 MED28 在细胞中的重要作用。
