The lymphocyte adhesion molecule CD44 recognizes a non-hyaluronate proteoglycan, gp600, secreted by mouse T cell line CTLL2. We now demonstrate that gp600 is identical to serglycin, a member of the small proteoglycan family stored in intracellular secretory granules of lymphoid, myeloid, and some tumor cells. Purified gp600 has the ability to bind specifically to CD44, and the binding is dependent on activation of CD44. The CD44-binding elements on gp600 or serglycin are glycosaminoglycans consisting of chondroitin 4-sulfate. Serglycin is readily exocytosed, and its interaction with active form CD44 augments the CD3-dependent degranulation of CD44 positive CTL clones. We conclude that the serglycin secreted from secretory granules of hematopoietic cells is a novel ligand for CD44, and could regulate lymphoid cell adherence and activation.

SummaryThe interleukin 2 receptor ~ chain (IL-21~) is preferentially expressed in natural killer (NK) cells, but is not detected in a majority of resting T and B cells. We recently established a novel monoclonal antibody (mAb) to murine IL-2RB and examined in vivo the effect of the mAb in mice. We found that intraperitoneal injection of the anti-IL-2RB mAb into adult mice resulted in a selective in vivo elimination of splenic NK function in various mouse strains. The reduction of NK cell function is associated with complete disappearance of NKI.1 + cells in C57BL/6 mice. Other lymphocyte subsets in the thymus and spleen were uncompromised. T cell function was not affected by the mAb treatment as judged by allogeneic cytotoxic T cell induction. The single injection of anti-IL-2RB mAb caused a long-term elimination of splenic NK cells, lasting for at least 5 wk. We also found that NK and/or NK precursor cells become susceptible to the mAb treatment only after birth, suggesting that functional maturation of NK cells in terms of IL-2RB expression is a later event in the course of NK cell development. The use of the anti-IL-2RB mAb will be useful in defining the physiological role of NK cells in host defense as well as dissecting their developmental pathway in vivo.

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p94/calpain 3 is a skeletal muscle-specific Ca(2+)-regulated cysteine protease (calpain), and genetic loss of p94 protease activity causes muscular dystrophy (calpainopathy). In addition, a small in-frame deletion in the N2A region of connectin/titin that impairs p94-connectin interaction causes a severe muscular dystrophy (mdm) in mice. Since p94 via its interaction with the N2A and M-line regions of connectin becomes part of the connectin filament system that serves as a molecular scaffold for the myofibril, it has been proposed that structural and functional integrity of the p94-connectin complex is essential for health and maintenance of myocytes. In this study, we have surveyed the interactions made by p94 and connectin N2A inside COS7 cells. This revealed that p94 binds to connectin at multiple sites, including newly identified loci in the N2A and PEVK regions of connectin. Functionally, p94-N2A interactions suppress p94 autolysis and protected connectin from proteolysis. The connectin N2A region also contains a binding site for the muscle ankyrin repeat proteins (MARPs), a protein family involved in the cellular stress responses. MARP2/Ankrd2 competed with p94 for binding to connectin and was also proteolyzed by p94. Intriguingly, a connectin N2A fragment with the mdm deletion possessed enhanced resistance to proteases, including p94, and its interaction with MARPs was weakened. Our data support a model in which MARP2-p94 signaling converges within the N2A connectin segment and the mdm deletion disrupts their coordination. These results also implicate the dynamic nature of connectin molecule as a regulatory scaffold of p94 functions.