A Biologically Active Sequence of the Laminin alpha 2 Large Globular 1 Domain Promotes Cell Adhesion through Syndecan-1 by Inducing Phosphorylation and Membrane Localization of Protein Kinase C delta

Abstract

Laminin-2 promotes basement membrane assembly and peripheral myelinogenesis; however, a receptor-binding motif within laminin-2 and the downstream signaling pathways for motif-mediated cell adhesion have not been fully established. The human laminin-2 alpha 2 chain cDNAs cloned from human keratinocytes and fibroblasts correspond to the laminin alpha 2 chain variant sequence from the human brain. Individually expressed recombinant large globular (LG) 1 protein promotes cell adhesion and has heparin binding activities. Studies with synthetic peptides delineate the DLTIDDSYWYRI motif (Ln2-P3) within the LG1 as a major site for both heparin and cell binding. Cell adhesion to LG1 and Ln2-P3 is inhibited by treatment of heparitinase I and chondroitinase ABC. Syndecan-1 from PC12 cells binds to LG1 and Ln2-P3 and colocalizes with both molecules. Suppression of syndecan-1 with RNA interference inhibits cell adhesion to LG1 and Ln2-P3. The binding of syndecan-1 with LG1 and Ln2-P3 induces the recruitment of protein kinase C delta (PKC delta) into the membrane and stimulates its tyrosine phosphorylation. A decrease in PKC delta activity significantly reduces cell adhesion to LG1 and Ln2-P3. Taken together, these results indicate that the Ln2-P3 motif and LG1 domain, containing the motif, within the human laminin-2 alpha 2 chain are major ligands for syndecan-1, which mediates cell adhesion through the PKC delta signaling pathway.