Busk M, Pytela R, Sheppard D
Lung Biology Center, University of California, San Francisco 94143.
J Biol Chem. 1992 Mar 25;267(9):5790-6.
Integrins are a complex family of divalent cation-dependent cell adhesion receptors composed of one alpha and one beta subunit noncovalently bound to one another. A subset of integrins contains the alpha v subunit in association with one of several beta subunits (e.g. beta 3, beta 5, beta 1). We have recently identified a novel integrin beta subunit, beta 6, that is present in a number of epithelial cell lines. Using a polyclonal antibody raised against the carboxyl-terminal peptide of beta 6, we have now identified the integrin heterodimer, alpha v beta 6, on the surface of two human carcinoma cell lines. Using affinity chromatography of lysates from the pancreatic carcinoma cell line, FG-2, we demonstrate that alpha v beta 6 binds to fibronectin, but not to vitronectin or collagen I. In contrast, the alpha v beta 5 integrin, which is also expressed on FG-2 cells, binds exclusively to vitronectin. Immobilized collagen I does not interact with alpha v integrins, but binds beta 1-containing integrins. Both alpha v beta 6 and alpha v beta 5 are eluted from their respective immobilized ligands by a hexa-peptide containing the sequence Arg-Gly-Asp (RGD). RGD is highly effective in the presence of Ca2+, somewhat less effective in Mg2+, and virtually inactive in Mn2+. These results suggest that alpha v beta 6 functions as an RGD-dependent fibronectin receptor in FG-2 carcinoma cells. In agreement with this notion, cell adhesion assays show that FG-2 cell attachment to fibronectin is only partially inhibited by anti-beta 1 integrin antibodies, implying that other fibronectin receptors may be involved. Taken together with recent reports on the vitronectin receptor function of alpha v beta 5, our results suggest that the previously described carcinoma cell integrin, alpha v beta x (Cheresh, D. A., Smith, J. W., Cooper, H. M., and Quaranta, V. (1989) Cell 57, 59-69), is a mixture of at least two different receptors: alpha v beta 5, mediating adhesion to vitronectin, and alpha v beta 6, mediating adhesion to fibronectin.
整合素是一个复杂的二价阳离子依赖性细胞粘附受体家族，由一个α亚基和一个β亚基非共价结合而成。一部分整合素包含αv亚基与几种β亚基之一结合（例如β3、β5、β1）。我们最近鉴定出一种新型整合素β亚基β6，它存在于多种上皮细胞系中。使用针对β6羧基末端肽产生的多克隆抗体，我们现已在两个人类癌细胞系表面鉴定出整合素异二聚体αvβ6。通过对胰腺癌细胞系FG-2的裂解物进行亲和层析，我们证明αvβ6与纤连蛋白结合，但不与玻连蛋白或I型胶原结合。相比之下，FG-2细胞上也表达的αvβ5整合素仅与玻连蛋白结合。固定化的I型胶原不与αv整合素相互作用，但能结合含β1的整合素。αvβ6和αvβ5都通过含有序列Arg-Gly-Asp（RGD）的六肽从各自固定化的配体上洗脱下来。RGD在Ca2+存在时非常有效，在Mg2+存在时效果稍差，而在Mn2+存在时几乎无活性。这些结果表明，αvβ6在FG-2癌细胞中作为一种RGD依赖性纤连蛋白受体发挥作用。与此观点一致，细胞粘附试验表明，FG-2细胞与纤连蛋白的附着仅部分受到抗β1整合素抗体的抑制，这意味着可能涉及其他纤连蛋白受体。结合最近关于αvβ5玻连蛋白受体功能的报道，我们的结果表明，先前描述的癌细胞整合素αvβx（Cheresh, D. A., Smith, J. W., Cooper, H. M., and Quaranta, V. (1989) Cell 57, 59 - 69）是至少两种不同受体的混合物：αvβ5介导与玻连蛋白的粘附，αvβ6介导与纤连蛋白的粘附。
