Purpose: CD26 is a 110-kDa cell surface antigen with a role in tumor development. In this report, we show that CD26 is highly expressed on the cell surface of malignant mesothelioma and that a newly developed humanized anti-CD26 monoclonal antibody (mAb) has an inhibitory effect on malignant mesothelioma cells in both in vitro and in vivo experiments. Experimental Design: Using immunohistochemistry, 12 patients' surgical specimens consisting of seven malignant mesothelioma, three reactive mesothelial cells, and two adenomatoid tumors were evaluated for expression of CD26. The effects of CD26 on malignant mesothelioma cells were assessed in the presence of transfection of CD26-expressing plasmid, humanized anti-CD26 mAb, or small interfering RNA against CD26. The in vivo growth inhibitory effect of humanized anti-CD26 mAb was assessed in human malignant mesothelioma cell mouse xenograft models. Results: In surgical specimens, CD26 is highly expressed in malignant mesothelioma but not in benign mesothelial tissues. Depletion of CD26 by small interfering RNA results in the loss of adhesive property, suggesting that CD26 is a binding protein to the extracellular matrix. Moreover, our in vitro data indicate that humanized anti-CD26 mAb induces cell lysis of malignant mesothelioma cells via antibody-dependent cell-mediated cytotoxicity in addition to its direct anti-tumor effect via p27 kip1 accumulation. In vivo experiments with mouse xenograft models involving human malignant mesothelioma cells show that humanized anti-CD26 mAb treatment drastically inhibits tumor growth in tumor-bearing mice, resulting in enhanced survival. Conclusions: Our data strongly suggest that humanized anti-CD26 mAb treatment may have potential clinical use as a novel cancer therapeutic agent in CD26-positive malignant mesothelioma.

CD26 is a widely distributed 110-kDa cell surface glycoprotein with an important role in T-cell costimulation. We demonstrated previously that CD26 binds to caveolin-1 in antigen-presenting cells, and following exogenous CD26 stimulation, Tollip and IRAK-1 disengage from caveolin-1 in antigen-presenting cells. IRAK-1 is then subsequently phosphorylated to up-regulate CD86 expression, resulting in subsequent T-cell proliferation. However, it is unclear whether caveolin-1 is a costimulatory ligand for CD26 in T-cells. Using soluble caveolin-1-Fc fusion protein, we now show that caveolin-1 is the costimulatory ligand for CD26, and that ligation of CD26 by caveolin-1 induces T-cell proliferation and NF-B activation in a T-cell receptor/ CD3-dependent manner. We also demonstrated that the cytoplasmic tail of CD26 interacts with CARMA1 in T-cells, resulting in signaling events that lead to NF-B activation. Ligation of CD26 by caveolin-1 recruits a complex consisting of CD26, CARMA1, Bcl10, and IB kinase to lipid rafts. Taken together, our findings provide novel insights into the regulation of T-cell costimulation via the CD26 molecule.

Purpose: CD26 is a 110-kDa cell surface glycoprotein with a role in tumor development through its association with key intracellular proteins. In this report, we show that binding of soluble anti-CD26 monoclonal antibody (mAb) inhibits the growth of the human renal carcinoma cells in both in vitro and in vivo experiments. Experimental Design: Growth inhibition by anti-CD26 mAb was assessed using proliferation assay and cell cycle analysis. Anti-CD26 mAb, chemical inhibitors, dominant-negative, or constitutively active forms of specific signaling molecules were used to evaluate CD26-associated pathways. The in vivo growth-inhibitory effect of anti-CD26 mAb was also assessed in a human renal carcinoma mouse xenograft model. Results:In vitro experiments show that anti-CD26 mAb induces G 1 -S cell cycle arrest associated with enhanced p27 kip1 expression, down-regulation of cyclin-dependent kinase 2, and dephosphorylation of retinoblastoma substrate. Moreover, our data show that enhanced p27 kip1 expression is dependent on the attenuation of Akt activity. Anti-CD26 mAb also internalizes cell surface CD26, leading to decreased binding to collagen and fibronectin. Experiments with a mouse xenograft model involving human renal carcinoma cells show that anti-CD26 mAb treatment drastically inhibits tumor growth in tumor-bearing mice, resulting in enhanced survival. Conclusions:Taken together, our data strongly suggest that anti-CD26 mAb treatment may have potential clinical use for CD26-positive renal cell carcinomas.

The cooperative action of multiple Cu(II) nuclear centers is shown to be effective and selective in the hydrolysis of 2'-5' and 3'-5' ribonucleotides. Reported herein is the specific catalysis by two trinuclear Cu(II) complexes of L3A and L3B. Pseudo first-order kinetic studies reveal that the L3A trinuclear Cu(II) complex effects hydrolysis of Up(2'-5')U with a rate constant of 28 x 10(-)(4) min(-)(1) and Up(3'-5')U with a rate constant of 0.5 x 10(-)(4) min(-)(1). The hydrolyses of Ap(3'-5')A and Ap(2'-5')A proceed with rate constants of 24 x 10(-)(4) min(-)(1) and 0.5 x 10(-)(4) min(-)(1) respectively. The L3A trinuclear Cu(II) complex demonstrates high specificity for Up(2'-5')U and Ap(3'-5')A. Similar studies with the more rigid L3B trinuclear Cu(II) complex shows no selectivity and yields lower rate constants for hydrolysis. The selectivity observed with the L3A ligand is attributed to the geometry of the ligand-bound diribonucleotide which ultimately dictates the proximity of the attacking hydroxyl and the phosphoester to a Cu(II) center for activation and subsequent hydrolysis.

Although protein-tyrosine phosphorylation is important for hippocampus-dependent learning, its role in cerebellum-dependent learning remains unclear. We previously found that PTPMEG, a cytoplasmic protein-tyrosine phosphatase expressed in Purkinje cells (PCs), bound to the carboxyl-terminus of the glutamate receptor delta2 via the postsynaptic density-95/discs-large/ZO-1 domain of PTPMEG. In the present study, we generated PTPMEG-knockout (KO) mice, and addressed whether PTPMEG is involved in cerebellar plasticity and cerebellum-dependent learning. The structure of the cerebellum in PTPMEG-KO mice appeared grossly normal. However, we found that PTPMEG-KO mice showed severe impairment in the accelerated rotarod test. These mice also exhibited impairment in rapid acquisition of the cerebellum-dependent delay eyeblink conditioning, in which conditioned stimulus (450-ms tone) and unconditioned stimulus (100-ms periorbital electrical shock) were co-terminated. Moreover, long-term depression at parallel fiber-PC synapses was significantly attenuated in these mice. Developmental elimination of surplus climbing fibers and the physiological properties of excitatory synaptic inputs to PCs appeared normal in PTPMEG-KO mice. These results suggest that tyrosine dephosphorylation events regulated by PTPMEG are important for both motor learning and cerebellar synaptic plasticity.