Chikao Morimoto

Tyrosine Phosphorylation of Crk-associated Substrates by Focal Adhesion Kinase A PUTATIVE MECHANISM FOR THE INTEGRIN-MEDIATED TYROSINE PHOSPHORYLATION OF Crk-ASSOCIATED SUBSTRATES

Integrin-ligand binding induces the tyrosine phosphorylation of various proteins including focal adhesion kinase (pp125FAK) and Crk-associated substrate (Cas). FAK is activated and autophosphorylated by the ligation of integrins, although the substrate of FAK has not been revealed. We show here that p130Cas and Cas-L are FAK substrates. FAK directly phosphorylates Cas proteins primarily at the YDYVHL sequence that is conserved among all Cas proteins. Furthermore, the phosphorylated YDYVHL sequence is a binding site for Src family protein-tyrosine kinases, and the recruited Src family kinase phosphorylates the other tyrosine residues within Cas. The Cas-L YDYVHL sequence is phosphorylated upon integrin-ligand binding, and this integrin-mediated tyrosine phosphorylation is inhibited by the cotransfection of the FAK COOH-terminal domain that does not contain a kinase domain. These findings strongly suggest that FAK initiates integrin-mediated tyrosine phosphorylation of Cas proteins; then, Src family tyrosine kinases, which are recruited to phosphorylated Cas and FAK, further phosphorylate Cas proteins.

Abnormalities in CD4+ T-lymphocyte subsets in inflammatory rheumatic diseases

The monoclonal antibodies anti-2H4 and anti-4B4 identify the suppressor-inducer (CD4+2H4+) and helper-inducer (CD4+4B4+) subpopulations of CD4 (T4+) lymphocytes, respectively. The cell surface phenotype of peripheral blood lymphocytes and synovial fluid lymphocytes in patients with rheumatoid arthritis and other inflammatory joint diseases was analyzed by use of these and other well-characterized anti-T-cell monoclonal antibodies. In the synovial fluid of patients with rheumatoid arthritis, there was a markedly decreased percentage of T4+2H4+ suppressor-inducer cells (3.1 +/- 1 percent) and an increased percentage of T4+4B4+ helper-inducer cells (29.1 +/- 9 percent) as compared with the proportions found in the peripheral blood of normal individuals (T4+2H4+: 19.0 +/- 6 percent, T4+4B4+: 23.0 +/- 7 percent). Moreover, patients with other chronic and acute inflammatory joint diseases exhibited highly similar synovial T-cell findings to those of the patients with rheumatoid arthritis (T4+2H4+: 4.2 +/- 3 percent, T4+4B4+: 33.1 +/- 9 percent). In contrast, there were no significant differences between the normal control subjects and patients with rheumatoid arthritis in the percentage of T4+2H4+ cells in peripheral blood lymphocytes, nor were there significant differences between normal control subjects, patients with rheumatoid arthritis, and patients with other joint diseases (osteoarthritis, gout, B27+ spondyloarthropathy, and psoriatic arthritis) in the number of T4+4B4+ cells or in the T4/T8 ratio of peripheral blood lymphocytes. However, very low numbers of T4+2H4+ (suppressor-inducer) peripheral blood lymphocytes were seen in a subgroup of patients, including five of seven with Reiters syndrome and several patients with systemic rheumatic disease syndromes. In addition, although the percentage of T4+2H4+ cells in peripheral blood lymphocytes of patients with osteoarthritis (13.7 +/- 7 percent) and gout (14.3 +/- 7 percent) was decreased compared with that of normal controls (19.0 +/- 6 percent) (osteoarthritis versus normal controls p less than 0.025), this difference appeared to reflect alterations due to age rather than disease. Consistent with the phenotypic changes observed, synovial T cells were also functionally defective, since autologous mixed lymphocyte reaction-activated T4 cells from the synovial fluid of patients with rheumatoid arthritis failed to exhibit suppressor-inducer activity.(ABSTRACT TRUNCATED AT 400 WORDS)

The Development of Monoclonal Antibodies against Human Immunoregulatory T Cell Subsets: The Isolation of Human Suppressor Inducer T Cell Subset

It is now well established that T cells are involved in a complex series of interactions which regulate the immune response (1,2). Considerable impetus to the dissection of T cell heterogeneity came with development of monoclonal antibodies capable of dividing T cells into functionally distinct T4 and T8 populations which also show preferential recognition of class II and I antigens, respectively (3–8).