The β3 chain short arm of laminin-332 (laminin-5) induces matrix assembly and cell adhesion activity of laminin-511 (laminin-10)

The basement membrane (BM) protein laminin-332 (Lm332) (laminin-5) has unique activity and structure as compared with other laminins: it strongly promotes cellular adhesion and migration, and its α3, β3, and γ2 chains are all truncated in their N-terminal regions (short arms). In the present study, we investigated the biological function of the laminin β3 chain. When the β3 chain short arm (β3SA) was overexpressed in HEK293 cells (β3SA-HEK), they deposited a large amount of β3SA and a small amount of laminin-511 (Lm511) (laminin-10) on culture plates. Control HEK293 cells secreted Lm511 but failed to deposit it. The extracellular matrix (ECM) deposited by β3SA-HEK cells strongly promoted cell attachment and spreading. The β3SA-HEK ECM did not directly bind Lm511, but it stimulated control HEK293 cells to deposit Lm511 on the culture plates. Although purified β3SA did not support cell adhesion by itself, it enhanced the cell adhesion activity of Lm511. Experiments with anti-integrin antibodies also suggested that the strong cell adhesion activity of the β3SA-HEK ECM was derived from the synergistic action of β3SA and Lm511. It has previously been found that β3SA binds an unknown cell surface receptor. Taken together, the present study suggests that the short arm of the laminin β3 chain enhances the matrix assembly of Lm511 and its cell adhesion activity by interacting with its receptor. J. Cell. Biochem. 100: 545–556, 2007. © 2006 Wiley-Liss, Inc.