Hogervorst F, Kuikman I, van Kessel A G, Sonnenberg A
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam.
Eur J Biochem. 1991 Jul 15;199(2):425-33. doi: 10.1111/j.1432-1033.1991.tb16140.x.
We have isolated cDNAs encoding the alpha 6 subunit from a lambda gt11 expression library from human keratinocytes by combined screening with a rabbit polyclonal anti-alpha 6 antibody and the polymerase chain reaction. The alpha 6 subunit encoded by this cDNA consists of 1050 amino acids with a 991-amino-acid extracellular, a 23-amino-acid transmembrane and a 36-amino-acid cytoplasmic domain. The extracellular domain contains three putative divalent cation-binding sites and nine potential N-linked glycosylation sites. From a cDNA library from normal human mammary gland cells two different cDNAs for alpha 6 were isolated, one of which is identical to the above cDNA. The two alpha 6 subunits, called alpha 6A and alpha 6B, encoded by the two cDNAs each have a unique cytoplasmic domain, that of alpha 6B being 18 amino acids longer than that of alpha 6A. Different carcinoma cell lines contain transcripts for both alpha 6 subunits. K562 leukemic cells have little alpha 6A or alpha 6B mRNAs. The overall level of expression varies in the carcinoma cell lines, but reflects alpha 6 cell surface expression. In A375 melanoma cells, however, cell surface expression of alpha 6 was low in spite of a high level of mRNA. This suggest that other mechanisms may be involved in regulating the expression of alpha 6 on the surface of these cells. The mRNA for both alpha 6 subunits is around 6 kb. The alpha 6 subunits are similar to other alpha subunits (26-31% identity with cleaved alpha subunits) of the integrin family but they are more similar to the alpha 3 subunit (40% identity). This high degree of similarity may be the basis for their functional resemblance since both alpha 3 and alpha 6 subunits, when associated with beta 1, function as laminin receptors and bind to the long arm of laminin. The genes for alpha 6 and beta 4, the alternative beta subunit with which alpha 6 combines on certain epithelial cells, were mapped to chromosome 2 and 17q11-qter, respectively.
我们通过用兔多克隆抗α6抗体和聚合酶链反应联合筛选，从人角质形成细胞的λgt11表达文库中分离出了编码α6亚基的cDNA。该cDNA编码的α6亚基由1050个氨基酸组成，具有一个991个氨基酸的细胞外结构域、一个23个氨基酸的跨膜结构域和一个36个氨基酸的胞质结构域。细胞外结构域包含三个假定的二价阳离子结合位点和九个潜在的N-糖基化位点。从正常人乳腺细胞的cDNA文库中分离出了两种不同的α6 cDNA，其中一种与上述cDNA相同。这两种cDNA编码的两种α6亚基，分别称为α6A和α6B，各自具有独特的胞质结构域，α6B的胞质结构域比α6A长18个氨基酸。不同的癌细胞系含有这两种α6亚基的转录本。K562白血病细胞几乎没有α6A或α6B mRNA。癌细胞系中的总体表达水平各不相同，但反映了α6在细胞表面的表达。然而，在A375黑色素瘤细胞中，尽管mRNA水平很高，但α6在细胞表面的表达却很低。这表明可能有其他机制参与调节这些细胞表面α6的表达。两种α6亚基的mRNA约为6 kb。α6亚基与整合素家族的其他α亚基相似（与裂解后的α亚基有26%-31%的同一性），但它们与α3亚基更相似（有40%的同一性）。这种高度的相似性可能是它们功能相似的基础，因为α3和α6亚基与β1结合时，都作为层粘连蛋白受体发挥作用，并与层粘连蛋白的长臂结合。α6和β4（α6在某些上皮细胞上与之结合的另一种β亚基）的基因分别定位于2号染色体和17q11-qter。
