Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
J Cell Physiol. 2010 Jun;223(3):687-94. doi: 10.1002/jcp.22074.
Activin A is a member of the transforming growth factor (TGF)-beta superfamily that regulates cell proliferation and differentiation. Using the p38 inhibitor SB203580, our previous studies demonstrated that p38 was involved in activin A-mediated hemoglobin (Hb) synthesis in K562 cells. SB203580 is an inhibitor of p38alpha and p38beta isoforms. In this study, we show that p38alpha and p38beta mRNA were expressed in K562 cells and that activin A activated the kinase activities of these isoforms. To investigate the roles of p38alpha and p38beta isoforms in activin A-mediated erythroid differentiation, we generated stable clones that over-expressed the dominant negative p38 isoforms p38alpha(AF) and p38beta(AF) in K562 cells. The expressions of either p38alpha(AF) or p38beta(AF) reduced activin A-induced p38 activation, Hb synthesis, and zeta-globin promoter activity. Similarly, down-regulation of either p38alpha or p38beta by isoform-specific siRNAs also reduced activin A-induced zeta-globin promoter activity. Co-expressions of p38alpha(AF) and p38beta(AF), together, greatly inhibited the transcription activity of the zeta-globin promoter. Conversely, expression of mitogen-activated protein kinase kinase (MKK) 6b(E), a constitutive activator of p38, significantly activated zeta-globin promoter. Co-expressions of either p38alpha or p38beta with MKK6b had a similar activation of zeta-globin promoter. Activin A induction of erythroid differentiation was inhibited by follistatin. Activin A-induced phosphorylation of MKK6 and p38 was also inhibited by follistatin. Moreover, over-expression of MKK6b(E) reverted follistatin inhibition of activin A-induced zeta-globin promoter activity. These results demonstrate that activin A induces erythroid differentiation of K562 cells through activation of MKK6-p38alpha/p38beta pathway and follistatin inhibits those effects.
激活素 A 是转化生长因子 (TGF)-β 超家族的成员，可调节细胞增殖和分化。我们之前的研究使用 p38 抑制剂 SB203580 表明 p38 参与了 activin A 在 K562 细胞中诱导的血红蛋白 (Hb) 合成。SB203580 是 p38alpha 和 p38beta 同工型的抑制剂。在这项研究中，我们表明 p38alpha 和 p38beta mRNA 在 K562 细胞中表达，并且 activin A 激活了这些同工型的激酶活性。为了研究 p38alpha 和 p38beta 同工型在 activin A 介导的红细胞分化中的作用，我们在 K562 细胞中生成了稳定的克隆，这些克隆过表达了显性负性 p38 同工型 p38alpha(AF) 和 p38beta(AF)。表达 p38alpha(AF) 或 p38beta(AF) 均可降低 activin A 诱导的 p38 激活、Hb 合成和 ζ-珠蛋白启动子活性。同样，用同工型特异性 siRNA 下调任一 p38alpha 或 p38beta 也降低了 activin A 诱导的 ζ-珠蛋白启动子活性。共表达 p38alpha(AF) 和 p38beta(AF) 大大抑制了 ζ-珠蛋白启动子的转录活性。相反，组成型激活 p38 的丝裂原激活蛋白激酶激酶 (MKK) 6b(E) 的表达显著激活了 ζ-珠蛋白启动子。共表达 p38alpha 或 p38beta 与 MKK6b 对 ζ-珠蛋白启动子具有相似的激活作用。Follistatin 抑制 activin A 诱导的红细胞分化。Follistatin 还抑制 activin A 诱导的 MKK6 和 p38 的磷酸化。此外，MKK6b(E) 的过表达逆转了 follistatin 对 activin A 诱导的 ζ-珠蛋白启动子活性的抑制作用。这些结果表明，激活素 A 通过激活 MKK6-p38alpha/p38beta 途径诱导 K562 细胞的红细胞分化，而 follistatin 抑制这些作用。
