Raymond Karine, Kreft Maaike, Janssen Hans, Calafat Jero, Sonnenberg Arnoud
Division of Cell Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
J Cell Sci. 2005 Mar 1;118(Pt 5):1045-60. doi: 10.1242/jcs.01689.
The alpha6beta4 integrin is located at the basal surface of keratinocytes, in hemidesmosomal structures that mediate stable adhesion of epidermal cells to the underlying basement membrane component laminin-5. The absence of alpha6beta4 integrin causes junctional epidermolysis bullosa, a severe blistering disease of the skin leading to perinatal death, confirming its essential role in mediating strong keratinocyte adhesion. Several studies have suggested that alpha6beta4 integrin can also regulate signaling cascades that control cell proliferation, survival and migration through a mechanism independent of its adhesive function. We have generated a conditional knockout mouse strain, in which the gene encoding the beta4 integrin subunit (Itgb4) was inactivated only in small stretches of the skin. These mice were viable and permitted an accurate analysis of the consequences of the loss of beta4 on various biological processes by comparing beta4-positive and -negative parts of the skin in the same animal. Despite the complete loss of hemidesmosomes in regions lacking alpha6beta4 integrin, the distribution of a range of adhesion receptors and basement membrane proteins was unaltered. Moreover, loss of alpha6beta4 did not affect squamous differentiation, proliferation or survival, except for areas in which keratinocytes had detached from the basement membrane. These in vivo observations were confirmed in vitro by using immortalized keratinocytes - derived from beta4-subunit conditional knockout mice - from which the gene encoding beta4 had been deleted by Cre-mediated recombination. Consistent with the established role of alpha6beta4 in adhesion strengthening, its loss from cells was found to increase their motility. Our findings clearly demonstrate that, after birth, epidermal differentiation, proliferation and survival all proceed normally in the absence of alpha6beta4, provided that cell adhesion is not compromised.
α6β4整合素位于角质形成细胞的基底表面，存在于半桥粒结构中，该结构介导表皮细胞与下方基底膜成分层粘连蛋白-5的稳定粘附。α6β4整合素的缺失会导致交界性大疱性表皮松解症，这是一种严重的皮肤水疱病，可导致围产期死亡，证实了其在介导角质形成细胞强粘附方面的重要作用。多项研究表明，α6β4整合素还可通过一种独立于其粘附功能的机制调节控制细胞增殖、存活和迁移的信号级联反应。我们构建了一种条件性敲除小鼠品系，其中编码β4整合素亚基（Itgb4）的基因仅在小块皮肤中失活。这些小鼠能够存活，并通过比较同一只动物皮肤中β4阳性和阴性部分，准确分析β4缺失对各种生物学过程的影响。尽管在缺乏α6β4整合素的区域半桥粒完全缺失，但一系列粘附受体和基底膜蛋白的分布未发生改变。此外，α6β4的缺失并不影响鳞状分化、增殖或存活，除了角质形成细胞已从基底膜脱离的区域。通过使用源自β4亚基条件性敲除小鼠的永生化角质形成细胞，并通过Cre介导的重组删除编码β4的基因，这些体内观察结果在体外得到了证实。与α6β4在增强粘附中的既定作用一致，发现其从细胞中缺失会增加细胞的运动性。我们的研究结果清楚地表明，出生后，只要细胞粘附不受损害，在没有α6β4的情况下，表皮分化、增殖和存活均可正常进行。
