Department of Tissue Development and Regeneration, Research Institute for Frontier Medicine, Sapporo Medical University School of Medicine, S-1, W-17, Chuo-ku, Sapporo, 060-8556, Japan.
J Biol Chem. 2012 Aug 17;287(34):28586-97. doi: 10.1074/jbc.M112.350488. Epub 2012 Jul 3.
Signals derived from basal lamina components are important for developing three-dimensional architecture of epithelial tissues. Laminins consisting of α, β, and γ subunits in basal lamina play pivotal roles in the formation and maintenance of epithelial tissue structures. However, it remains unclear which laminin isoforms transmit signals and how epithelial cells receive them to regulate multiple developmental processes. In three-dimensional culture of a liver progenitor cell line, Hepatic Progenitor Cells Proliferating on Laminin (HPPL), the cells establish apicobasal polarity and form cysts with a central lumen. Neutralizing antibody against β1 integrin blocked the formation and maintenance of the cyst structure, indicating that β1 integrin signaling was necessary throughout the morphogenesis. Although the addition of α1-containing laminin, a ligand of β1 integrin, induced cyst formation, it was dispensable for the maintenance of the cyst, suggesting that HPPL produces another ligand for β1 integrin to maintain the structure. Indeed, we found that HPPL produced α5-containing laminin, and siRNA against laminin α5 partially inhibited the lumen formation. In fetal liver, p75NTR(+) periportal fibroblasts and bile duct epithelial cells, known as cholangiocytes, expressed α1- and α5-containing laminins, respectively. In laminin α5 KO liver, cholangiocytes normally emerged, but the number of bile ducts was decreased. These results suggest that α1-containing laminin is sufficient as a component of the basal lamina for the commitment of bipotential liver progenitors to cholangiocytes and the apicobasal polarization, whereas α5-containing laminin is necessary for the formation of mature duct structures. Thus, α1- and α5-containing laminins differentially regulate the sequential events to form epithelial tissues via β1 integrin signals.
基底膜成分所产生的信号对于上皮组织的三维结构的形成非常重要。基底膜中的层粘连蛋白由α、β和γ亚基组成，在形成和维持上皮组织结构方面发挥着关键作用。然而，目前尚不清楚哪种层粘连蛋白异构体传递信号，以及上皮细胞如何接收这些信号来调节多种发育过程。在肝祖细胞系 Hepatic Progenitor Cells Proliferating on Laminin (HPPL) 的三维培养中，细胞建立了顶底极性，并形成具有中央腔的小囊。针对β1 整合素的中和抗体阻断了小囊结构的形成和维持，表明β1 整合素信号在整个形态发生过程中都是必需的。尽管添加α1 含有层粘连蛋白（β1 整合素的配体）诱导小囊形成，但对于小囊的维持却是可有可无的，这表明 HPPL 产生了另一种β1 整合素的配体来维持结构。事实上，我们发现 HPPL 产生了α5 含有层粘连蛋白，针对层粘连蛋白α5 的 siRNA 部分抑制了腔的形成。在胎肝中，p75NTR(+)门脉周围成纤维细胞和胆管上皮细胞，即胆管细胞，分别表达α1-和α5 含有层粘连蛋白。在层粘连蛋白α5 KO 肝中，胆管细胞正常出现，但胆管数量减少。这些结果表明，α1 含有层粘连蛋白足以作为基底膜的一部分，使双潜能肝祖细胞向胆管细胞分化，并进行顶底极性极化，而α5 含有层粘连蛋白对于成熟胆管结构的形成是必要的。因此，α1-和α5 含有层粘连蛋白通过β1 整合素信号差异调节形成上皮组织的连续事件。
