Laminin γ2 chain as a stromal cell marker of the human bone marrow microenvironment

Laminins are large heterotrimeric molecules consisting of alpha, beta and gamma chains. At present, five alpha chains, three beta chains and three gamma chains have been characterized. Laminin-5 (alpha3beta3gamma2) is the only isoform known to date which contains a gamma2 chain. In human bone marrow, non-haematopoietic stromal cells expressed the laminin gamma2 chain, whereas bone marrow mononuclear cells did not. Co-localization of the gamma2 chain was detected with the laminin alpha4 and alpha5 chains, and co-immunoprecipitation studies revealed a new isoform consisting of alpha5, beta2 and gamma2 chains. The laminin gamma2 chain was also co-localized with alpha-sm-actin in bone marrow, but it was not expressed in endothelial cells or megakaryocytes, indicating that the gamma2 chain is exclusively expressed in vivo in bone marrow stromal cells. The laminin gamma2 chain containing isoform LN-5 was shown to be an adhesive substrate for a small subpopulation of bone marrow mononuclear cells and also for peripheral blood platelets. Taken together, these results indicate that (I) laminin isoforms containing the gamma2 chain can act as adhesive substrates for human haematopoietic cells, and (II) the laminin gamma2 chain can be used as a specific marker molecule for human bone-marrow-derived stromal cells.