Alt A, Ohba M, Li L, Gartsbein M, Belanger A, Denning M F, Kuroki T, Yuspa S H, Tennenbaum T
Faculty of Life Sciences, Bar Ilan University, Ramat-Gan 52900, Israel.
Cancer Res. 2001 Jun 1;61(11):4591-8.
In mammalian epidermis, expression of the alpha6beta4 integrin is restricted to the hemidesmosome complexes, which connect the proliferative basal cell layer with the underlying basement membrane. Keratinocyte differentiation is associated with down-regulation of alpha6beta4 expression and detachment of keratinocytes from the basement membrane. Neoplastic keratinocytes delay maturation, proliferate suprabasally, and retain the expression of the alpha6beta4 integrin in suprabasal cells disassociated from the hemidesmosomes. We now show that the alpha6beta4 integrin is a substrate for serine phosphorylation by protein kinase C in keratinocytes. Furthermore, protein kinase C-mediated phosphorylation of alpha6beta4 is associated with redistribution of this integrin from the hemidesmosome to the cytosol. Specifically, in vitro kinase assays identified the protein kinase Cdelta as the primary isoform phosphorylating alpha6 and beta4 integrin subunits. Using recombinant protein kinase C adenoviruses, overexpression of protein kinase Cdelta but not protein kinase Calpha in primary keratinocytes increased beta4 serine phosphorylation, decreased alpha6beta4 localization to the hemidesmosome complexes, and reduced keratinocyte attachment. Taken together, these results establish a link between protein kinase Cdelta-mediated serine phosphorylation of alpha6beta4 integrin and its effects on alpha6beta4 subcellular localization and keratinocyte attachment to the laminin underlying matrix.
在哺乳动物表皮中，α6β4整合素的表达局限于半桥粒复合体，该复合体将增殖的基底细胞层与下方的基底膜相连。角质形成细胞的分化与α6β4表达的下调以及角质形成细胞从基底膜的脱离有关。肿瘤性角质形成细胞延迟成熟，在基底上层增殖，并在与半桥粒分离的基底上层细胞中保留α6β4整合素的表达。我们现在表明，α6β4整合素是角质形成细胞中蛋白激酶C进行丝氨酸磷酸化的底物。此外，蛋白激酶C介导的α6β4磷酸化与该整合素从半桥粒向细胞质的重新分布有关。具体而言，体外激酶分析确定蛋白激酶Cδ是磷酸化α6和β4整合素亚基的主要亚型。使用重组蛋白激酶C腺病毒，在原代角质形成细胞中过表达蛋白激酶Cδ而非蛋白激酶Cα会增加β4丝氨酸磷酸化，减少α6β4在半桥粒复合体中的定位，并降低角质形成细胞的附着。综上所述，这些结果建立了蛋白激酶Cδ介导的α6β4整合素丝氨酸磷酸化与其对α6β4亚细胞定位以及角质形成细胞与层粘连蛋白下层基质附着的影响之间的联系。
