Department of Pathology and Laboratory Medicine, University of Wisconsin, Madison, Wisconsin 53705, USA.
J Biol Chem. 2010 Apr 30;285(18):13569-79. doi: 10.1074/jbc.M110.102137. Epub 2010 Feb 24.
The alpha6beta4 integrin is a laminin 332 (LN332) receptor central to the formation of hemidesmosomes in epithelial layers. However, the integrin becomes phosphorylated by keratinocytes responding to epidermal growth factor in skin wounds or by squamous cell carcinomas that overexpress/hyperactivate the tyrosine kinase ErbB2, epidermal growth factor receptor, or c-Met. We show here that the beta4-dependent signaling in A431 human squamous carcinoma cells is dependent on the syndecan family of matrix receptors. Yeast two-hybrid analysis identifies an interaction within the distal third (amino acids 1473-1752) of the beta4 cytoplasmic domain and the conserved C2 region of the syndecan cytoplasmic domain. Via its C2 region, Sdc1 forms a complex with the alpha6beta4 integrin along with the receptor tyrosine kinase ErbB2 and the cytoplasmic kinase Fyn in A431 cells. Engagement of LN332 or clustering of the alpha6beta4 integrin with integrin-specific antibodies causes phosphorylation of ErbB2, Fyn, and the beta4 subunit as well as activation of phosphatidylinositol 3-kinase and Akt and their assimilation into this complex. This leads to phosphatidylinositol 3-kinase-dependent cell spreading and Akt-dependent protection from apoptosis. This is disrupted by RNA interference silencing of Sdc1 but can be rescued by mouse Sdc1 or Sdc4 but not by syndecan mutants lacking their C-terminal C2 region. This disruption does not prevent the phosphorylation of ErbB2 or Fyn but blocks the Fyn-mediated phosphorylation of the beta4 tail. We propose that syndecans engage the distal region of the beta4 cytoplasmic domain and bring it to the plasma membrane, where it can be acted upon by Src family kinases.
α6β4 整合素是层粘连蛋白 332（LN332）的受体，在上皮细胞中半桥粒的形成中起核心作用。然而，整合素在皮肤伤口中角质形成细胞响应表皮生长因子或鳞状细胞癌过度表达/过度激活酪氨酸激酶 ErbB2、表皮生长因子受体或 c-Met 时会被磷酸化。我们在这里表明，A431 人鳞状癌细胞中β4 依赖性信号转导依赖于基质受体的 syndecan 家族。酵母双杂交分析鉴定出β4 细胞质结构域的远端三分之一（氨基酸 1473-1752）与 syndecan 细胞质结构域的保守 C2 区域内的相互作用。通过其 C2 区域，Sdc1 在 A431 细胞中与受体酪氨酸激酶 ErbB2 和细胞质激酶 Fyn 一起与α6β4 整合素形成复合物。LN332 的结合或α6β4 整合素的聚集与整合素特异性抗体一起导致 ErbB2、Fyn 和β4 亚基的磷酸化以及磷脂酰肌醇 3-激酶和 Akt 的激活及其被纳入该复合物。这导致磷脂酰肌醇 3-激酶依赖性细胞扩展和 Akt 依赖性抗细胞凋亡。这被 Sdc1 的 RNA 干扰沉默所破坏，但可以通过小鼠 Sdc1 或 Sdc4 来挽救，但不能通过缺乏其 C 端 C2 区域的 syndecan 突变体来挽救。这种破坏不会阻止 ErbB2 或 Fyn 的磷酸化，但会阻止 Fyn 介导的β4 尾部磷酸化。我们提出 syndecans 结合β4 细胞质结构域的远端区域并将其带到质膜，在质膜中它可以被Src 家族激酶作用。
