T cell interactions with laminin, the major glycoprotein of basement membranes, are important to the inflammatory response. However, the interactions of lymphocyte surface receptors with laminin are only beginning to be understood. A search for genes expressed in activated T cells revealed that the non-integrin, 67 kD laminin binding protein (p67 LBP) is expressed on the surface of a subset (10-15 percent) of activated peripheral blood T cells. Surface p67 LBP expression is detectable by FACS using the anti-p67 LBP mAb, MLuC5, within 6 h of T cell activation with PDB and ionomycin, peaks 24 h post-activation, and persists for 7-10 days. The subset of T cells expressing p67 LBP are mature, single-positive cells (85 percent CD4+/8-, 15 percent CD4-/8+) of memory cell phenotype (100 percent CD45 RO+/CD45 RA-). The p67 LBP+ T cells also express the integrin alpha6 chain (CD49f), which is known to associate with p67 LBP on tumor cells. In addition, the p67 LBP+ T cells express the integrin beta1, which associates with alpha6 in the laminin-specific integrin receptor VLA-6 (alpha6beta1). Expression of an exogenous cDNA encoding the 37 kD LBP precursor (p37 LBPP) confers p67 LBP surface expression on a p67 LBP-negative Jurkat T cell line (B2.7). Expression of p67 LBP induces B2.7 transfectants to adhere to laminin, but avid laminin binding depends on co-expression of high level VLA-6. Taken together, these data indicate that p67 LBP is an activation-induced surface structure on memory T cells that, together with VLA-6, mediates cellular adherence to laminin. We propose to study p67 LBP on normal human T cells and on the Jurkat T cell line in order to address the following specific aims: (1) What stimuli induce the expression of p67 LBP on normal T cells? (2) What is the structure of p67 LBP? (3) What are the contributions of p67 LBP and the integrin alpha6 to lymphocyte laminin-specific adherence? and (4) What are the contributions of p67 LBP and alpha6 to laminin-mediated lamellipod formation, locomotion, and transendothelial migration?
