Role of laminin alpha5 and its receptors in fibrotic liver and hepatocellular carcinoma

层粘连蛋白是由5个α、3个β和3个伽马链组成的一组不同的α/β/伽马杂三聚体；它们是所有基底膜(BLS)的主要成分。层粘连蛋白的一条链由于其广泛的表达模式和在发育过程中的重要性而引起了特别的兴趣，那就是层粘连蛋白α5。然而，人们对含有Alpha5链的层粘连蛋白在人肝细胞癌中的表达和功能知之甚少。在这里，我们使用一种特定的抗体，检测了层粘连蛋白α5在正常肝脏和肝癌中的表达。在正常肝脏中，层粘连蛋白α5虽然存在于肝内血管和胆管下的BLS中，但在肝实质中缺失，这可能是肝细胞癌的起源。另一方面，无论肿瘤分级如何，层粘连蛋白α5在所有被测试的肝癌中均可观察到沉积。在分化良好的肝细胞癌中，它沿着肿瘤的小梁定位。在低分化的肝癌中，它存在于周围的肿瘤结节中。在肝癌细胞系中，层粘连蛋白α5与β链和伽马链发生异源三聚，并分泌到培养上清液中。为了了解含有Alpha5的层粘连蛋白的功能，我们还检测了其受体在肝癌细胞中的表达。在这方面，肝癌细胞表达α3β/α6β整合素和路德/基底细胞黏附分子(Lu/B-CAM)。体外研究表明，肝癌细胞比原代肝细胞更容易附着于含有Alpha5链的层粘连蛋白。除了α3β/α6β整合素和Lu/B-CAM外，层粘连蛋白α5还被整合素αβ1识别，在肝癌细胞中也有表达。这些结果表明，含有Alpha5的层粘连蛋白是调节肝细胞癌进展的功能底物。

Laminins are a diverse group of alpha/beta/gamma heterotrimers formed from five alpha, three beta and three gamma chains ; they are major components of all basal laminae (BLs). One laminin chain that has garnered particular interest due to its widespread expression pattern and importance during development is laminin alpha5. Little is known, however, about the expression and function of laminins containing the alpha5 chain in human hepatocellular carcinoma (HCC). Here, using a specific antibody, we examined the expression of laminin alpha5 in normal liver and in HCCs. In normal liver, although laminin alpha5 was observed in hepatic BLs underlying blood vessels and bile ducts, it was absent from the parenchyma, which may be the origin of HCC. On the other hand, laminin alpha5 deposition was observed throughout all HCCs tested, regardless of tumor grade. In well differentiated HCCs, it localized along the trabecules of the tumor. In poorly-differentiated HCCs, it was present in surrounding tumor nodules. In HCC cell lines, laminin alpha5 heterotrimerized with beta and gamma chains and was secreted into the culture media. To attempt to understand the function of laminins containing alpha5, the expression of its receptors in HCCs was also determined. In this regard, alpha3betal/alpha6betal integrins and Lutheran/basal cell adhesion molecule (Lu/B-CAM) were expressed in HCC cells. In vitro studies showed that HCC cells readily attached to laminin containing the alpha5 chain, more so than did primary hepatocytes. In addition to alpha3betal/alpha6betal integrins and Lu/B-CAM, laminin alpha5 was recognized by integrin alphalbetal, which also was expressed in HCC cells. These results suggest that laminins containing alpha5 serve as functional substrates regulating progression of HCC.