Integrin-mediated activation of MAP kinase is independent of FAK: evidence for dual integrin signaling pathways in fibroblasts.
Integrin-mediated activation of MAP kinase is independent of FAK: evidence for dual integrin signaling pathways in fibroblasts.
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DOI：
10.1083/jcb.136.6.1385
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发表时间：
1997-03-24
期刊：
影响因子：
--
通讯作者：
Juliano RL
中科院分区：
文献类型：
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作者：
Lin TH;Aplin AE;Shen Y;Chen Q;Schaller M;Romer L;Aukhil I;Juliano RL
整合素介导的细胞粘附导致 MAP 激酶激活并增加粘附斑激酶 (FAK) 的酪氨酸磷酸化。 FAK 的自磷酸化导致 SH2 结构域蛋白（包括 Src 家族激酶和 Grb2-Sos 复合物）的结合。由于 Grb2-Sos 是 Ras 信号转导途径的关键调节因子，因此一种可能的假设是，整合素介导的 FAK 酪氨酸磷酸化会导致 Ras 级联的激活，并最终导致丝裂原激活蛋白 (MAP) 激酶的激活。因此，在这种情况下，FAK 将充当 MAP 激酶活性的上游调节器。然而，在本报告中，我们提出了几条证据，表明成纤维细胞中整合素介导的 MAP 激酶活性独立于 FAK。首先，影响假定的 FAK 结合位点的 β1 整合素亚基缺失突变体支持粘附成纤维细胞中 MAP 激酶的激活，但不支持 FAK 的酪氨酸磷酸化。其次，成纤维细胞粘附细菌表达的纤连蛋白片段表明，MAP 激酶的强烈激活可以先于 FAK 的酪氨酸磷酸化。最后，我们使用 FRNK（FAK 的非催化 COOH 末端结构域）作为 FAK 自磷酸化和焦点接触点酪氨酸磷酸化的显性负性抑制剂。使用逆转录病毒感染，我们证明足以完全阻断 FAK 酪氨酸磷酸化的 FRNK 表达水平对整合素介导的 MAP 激酶激活没有影响。这些结果强烈表明整合素介导的 MAP 激酶激活独立于 FAK，并表明成纤维细胞中可能存在至少两种不同的整合素信号传导途径。
Integrin-mediated cell adhesion causes activation of MAP kinases and increased tyrosine phosphorylation of focal adhesion kinase (FAK). Autophosphorylation of FAK leads to the binding of SH2-domain proteins including Src-family kinases and the Grb2–Sos complex. Since Grb2–Sos is a key regulator of the Ras signal transduction pathway, one plausible hypothesis has been that integrin-mediated tyrosine phosphorylation of FAK leads to activation of the Ras cascade and ultimately to mitogen activated protein (MAP) kinase activation. Thus, in this scenario FAK would serve as an upstream regulator of MAP kinase activity. However, in this report we present several lines of evidence showing that integrin-mediated MAP kinase activity in fibroblasts is independent of FAK. First, a β1 integrin subunit deletion mutant affecting the putative FAK binding site supports activation of MAP kinase in adhering fibroblasts but not tyrosine phosphorylation of FAK. Second, fibroblast adhesion to bacterially expressed fragments of fibronectin demonstrates that robust activation of MAP kinase can precede tyrosine phosphorylation of FAK. Finally, we have used FRNK, the noncatalytic COOH-terminal domain of FAK, as a dominant negative inhibitor of FAK autophosphorylation and of tyrosine phosphorylation of focal contacts. Using retroviral infection, we demonstrate that levels of FRNK expression sufficient to completely block FAK tyrosine phosphorylation were without effect on integrin-mediated activation of MAP kinase. These results strongly suggest that integrin-mediated activation of MAP kinase is independent of FAK and indicate the probable existence of at least two distinct integrin signaling pathways in fibroblasts.