Lenferink A E, Busse D, Flanagan W M, Yakes F M, Arteaga C L
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Cancer Res. 2001 Sep 1;61(17):6583-91.
It is well established that ErbB1 and ErbB2 can cooperate in mammary epithelial cell transformation. Therefore, to understand how ErbB1/ErbB2 signaling contributes to this process, we used the ErbB kinase inhibitor AG1478in ErbB2-dependent BT-474 and SKBR-3 human breast cancer cells. These cells overexpress ErbB2 and also display moderate levels of ErbB1. Treatment with AG1478 resulted in rapid ErbB2 dephosphorylation, reversible G(1) arrest, and interruption of constitutive mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling. Consequently, both MAPK-dependent transcription of cyclin D1 and phosphorylation of the cyclin-dependent kinase (Cdk) inhibitor p27 were inhibited. The inhibition of PI3K/Akt resulted in increased activity of glycogen synthase kinase-3beta, which phosphorylated cyclin D1, potentially reducing its steady-state levels. The loss of cyclin D1 reduced the amount of cyclin D1/Cdk4 complexes that can sequester p27 in the cytosol. This plus the reduced phosphorylation of p27 by MAPK enhanced the stability of p27 that associated with nuclear Cdk2 at high stoichiometry and inhibited its kinase activity. Antisense p27 oligonucleotides decreased p27 levels and abrogated the G(1) arrest induced by AG1478. Similarly, infection with an adenovirus encoding inducible cyclin D1 also counteracted the antiproliferative effect of AG1478. These data imply that: (a) modulation of both p27 and cyclin D1 are required for the growth arrest that results from blockade of the ErbB2 kinase; and (b) ErbB2 overexpressing cells use both MAPK and PI3K/Akt to modulate p27 and cyclin D1 and, hence, subvert the G(1)-to-S transition.
已有充分证据表明，表皮生长因子受体1（ErbB1）和表皮生长因子受体2（ErbB2）在乳腺上皮细胞转化过程中存在协同作用。因此，为了了解ErbB1/ErbB2信号通路如何促成这一过程，我们在依赖ErbB2的BT - 474和SKBR - 3人乳腺癌细胞中使用了ErbB激酶抑制剂AG1478。这些细胞过度表达ErbB2，同时也呈现中等水平的ErbB1。用AG1478处理导致ErbB2迅速去磷酸化、可逆性G1期阻滞以及组成型丝裂原活化蛋白激酶（MAPK）和磷脂酰肌醇3激酶（PI3K）/蛋白激酶B（Akt）信号通路的中断。结果，细胞周期蛋白D1的MAPK依赖性转录以及细胞周期蛋白依赖性激酶（Cdk）抑制剂p27的磷酸化均受到抑制。PI3K/Akt信号通路的抑制导致糖原合酶激酶 - 3β活性增加，该酶使细胞周期蛋白D1磷酸化，可能降低其稳态水平。细胞周期蛋白D1的缺失减少了能够将p27隔离在细胞质中的细胞周期蛋白D1/Cdk4复合物的数量。这与MAPK介导的p27磷酸化减少共同增强了以高化学计量与核Cdk2相关联的p27的稳定性，并抑制了其激酶活性。反义p27寡核苷酸降低了p27水平，并消除了AG1478诱导的G1期阻滞。同样，用编码可诱导性细胞周期蛋白D1的腺病毒感染也抵消了AG1478的抗增殖作用。这些数据表明：（a）阻断ErbB2激酶导致生长停滞需要同时调节p27和细胞周期蛋白D1；（b）过度表达ErbB2的细胞利用MAPK和PI3K/Akt两者来调节p27和细胞周期蛋白D1，从而破坏G1期到S期的转换。
