Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuhoku, Nagoya, Japan.
Cell Biol Int. 2010 Mar 29;34(5):485-92. doi: 10.1042/CBI20090466.
Mouse ES (embryonic stem) cells are maintained in an undifferentiated state in the presence of LIF (leukaemia-inhibitory factor). In general, LIF engages a heterodimeric receptor complex composed of a low-affinity LIF receptor (LIFRbeta) and gp130, and activates STAT3 (signal transducers and activators of transcription 3) and ERKs (extracellular signal-regulated kinases). However, in undifferentiated ES cells in the presence of LIF, STAT3 is phosphorylated but ERKs are not. The removal of LIF-induced dephosphorylation of phospho-STAT3 and phosphorylation of ERKs resulted in the differentiation of ES cells. Here, we show that the dephosphorylation of phospho-STAT3 corresponds to the activation of ERKs pathway from the time-courses of the phosphorylation levels in detail. We found that the treatment of membrane-permeable STAT3IP (STAT3 inhibitory peptide), which inhibits homodimeric formation of STAT3, induced the phosphorylation of ERKs in ES cells in the presence of LIF. In addition, the removal of LIF decreased the expression level of SOCS3 (suppressor of cytokine signalling 3), a negative regulator of LIF signalling, and the phosphorylation of ERKs was efficiently induced in the ES cells where SOCS3 was down-regulated. These results suggested that LIF-induced SOCS3 suppressed the ERKs activation pathway in undifferentiated ES cells, and the down-regulation of SOCS3 by the removal of LIF triggered the phosphorylation of ERKs.
小鼠胚胎干细胞（ES 细胞）在白血病抑制因子（LIF）的存在下维持未分化状态。通常，LIF 与由低亲和力 LIF 受体（LIFRβ）和 gp130 组成的异二聚体受体复合物结合，并激活 STAT3（信号转导和转录激活因子 3）和 ERKs（细胞外信号调节激酶）。然而，在存在 LIF 的未分化 ES 细胞中，STAT3 被磷酸化但 ERKs 没有。去除 LIF 诱导的磷酸化 STAT3 的去磷酸化和 ERKs 的磷酸化导致 ES 细胞分化。在这里，我们详细展示了从磷酸化水平的时间进程来看，磷酸化 STAT3 的去磷酸化对应于 ERKs 途径的激活。我们发现，处理膜可渗透的 STAT3IP（STAT3 抑制肽），它抑制 STAT3 的同源二聚体形成，在存在 LIF 的情况下诱导 ES 细胞中 ERKs 的磷酸化。此外，去除 LIF 降低了 LIF 信号的负调节剂 SOCS3（细胞因子信号转导抑制因子 3）的表达水平，并且在 SOCS3 下调的 ES 细胞中，ERKs 的磷酸化被有效地诱导。这些结果表明，LIF 诱导的 SOCS3 抑制了未分化 ES 细胞中 ERKs 激活途径，并且去除 LIF 下调 SOCS3 触发了 ERKs 的磷酸化。
