Hara M, Yaar M, Tang A, Eller M S, Reenstra W, Gilchrest B A
Boston University School of Medicine, Department of Dermatology, MA 02118-2394.
J Cell Sci. 1994 Oct;107 ( Pt 10):2739-48. doi: 10.1242/jcs.107.10.2739.
Integrins are a family of proteins known to mediate attachment of cells to extracellular matrix materials. The substratum specificity and cation dependence of specific integrin heterodimers have been extensively characterized, and to a lesser degree specialized roles in cell attachment versus dendricity have been defined in some cell types. In the past decade, melanocyte attachment rate and morphology have been found to have strong substratum dependence, suggesting a major role for integrins in these processes. In order to investigate this aspect of pigment cell biology, human newborn melanocytes were subjected to flow cytometry analysis and plated on a variety of substrata under conditions known to promote or block the binding of specific integrin pairs. Melanocyte attachment to laminin and type IV collagen was promoted by Mg2+ and Mn2+ but not by Ca2+, in the range of concentrations examined. However, dendrite outgrowth from melanocytes already attached on laminin or type IV collagen was promoted by Ca2+ to a far greater degree than by Mg2+, and Mn2+ had no effect on dendrite outgrowth. Flow cytometry analysis revealed that melanocytes expressed beta 1, alpha 2, alpha 3, alpha 5, alpha 6 and alpha v integrin subunits as well as the alpha v beta 3 heterodimer. The influence of substratum on the profile of integrin expression was minimal, but alpha 6 and beta 1 integrins were observed by confocal microscopy to be expressed over the entire cell surface, while alpha 2, alpha 5 and alpha v beta 3 integrins localized along dendritic processes or at their tips. In accordance with the implications of these distribution patterns, anti-beta 1 and anti-alpha 6 integrin monoclonal antibodies blocked melanocyte attachment to laminin, while anti-alpha 2, anti-alpha 5 and anti-alpha v beta 3 inhibited dendrite outgrowth but did not block substratum attachment on either laminin or type IV collagen. On the basis of these data and the known characteristics of integrin molecules, we conclude that melanocyte attachment to laminin is mediated primarily by alpha 6 beta 1 integrin in a Ca(2+)-independent, Mg(2+)- and/or Mn(2+)-dependent manner, while dendrite outgrowth on laminin and type IV collagen requires extracellular Ca2+ and is mediated by alpha v beta 3 as well as alpha 2 and alpha 5 integrins.
整合素是一类已知可介导细胞与细胞外基质物质附着的蛋白质家族。特定整合素异二聚体的底物特异性和阳离子依赖性已得到广泛表征，并且在某些细胞类型中，在细胞附着与树突状形态方面的特殊作用也有一定程度的明确。在过去十年中，已发现黑素细胞的附着率和形态对底物有很强的依赖性，这表明整合素在这些过程中起主要作用。为了研究色素细胞生物学的这一方面，对人类新生儿黑素细胞进行了流式细胞术分析，并将其接种在各种底物上，这些条件已知可促进或阻断特定整合素对的结合。在所检测的浓度范围内，Mg2+和Mn2+促进黑素细胞与层粘连蛋白和IV型胶原的附着，但Ca2+无此作用。然而，Ca2+比Mg2+更能促进已附着在层粘连蛋白或IV型胶原上的黑素细胞长出树突，而Mn2+对树突生长没有影响。流式细胞术分析显示，黑素细胞表达β1、α2、α3、α5、α6和αv整合素亚基以及αvβ3异二聚体。底物对整合素表达谱的影响很小，但通过共聚焦显微镜观察到α6和β1整合素在整个细胞表面表达，而α2、α5和αvβ3整合素则沿树突状突起或其顶端定位。根据这些分布模式的含义，抗β1和抗α6整合素单克隆抗体可阻断黑素细胞与层粘连蛋白的附着，而抗α2、抗α5和抗αvβ3则抑制树突生长，但不阻断在层粘连蛋白或IV型胶原上的底物附着。基于这些数据和整合素分子的已知特性，我们得出结论，黑素细胞与层粘连蛋白的附着主要由α6β1整合素以不依赖Ca2+、依赖Mg2+和/或Mn2+的方式介导，而在层粘连蛋白和IV型胶原上的树突生长需要细胞外Ca2+，并由αvβ3以及α2和α5整合素介导。
