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 alpha 5. Little is known, however, about the expression and function of laminins containing the alpha 5 chain in human
hepatocellular carcinoma (HCC). Here, using a specific antibody, we examined the expression of
laminin alpha 5 in normal liver and in HCCs. In normal liver, although
laminin alpha 5 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 alpha 5 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 alpha 5 heterotrimerized with beta and gamma chains and was secreted into the
culture media. To attempt to understand the function of laminins containing alpha 5, the expression of its receptors in HCCs was also determined. In this regard, alpha 3 beta 1/alpha 6 beta 1
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 alpha 5 chain, more so than did primary hepatocytes. In addition to alpha 3 beta 1/alpha 6 beta 1
integrins and Lu/B-CAM,
laminin alpha 5 was recognized by
integrin alpha 1 beta 1, which also was expressed in HCC cells. These results suggest that laminins containing alpha 5 serve as functional substrates regulating progression of HCC.