CD53

Abstract: A novel cDNA clone termed R2 was isolated by subtractive hybridization of a cDNA library of phytohemagglutinin (PHA)/phorbol myristate acetate-stimulated Jurkat cells and by rescreening a cDNA library of PHA-stimulated peripheral blood lymphocytes. It hybridizes to a single mRNA species of about 2.2 kb, which is inducible in lymphoid cells and codes for a protein of 267 amino acids which contains four potential transmembrane domains. A computer-aided comparison showed strong homology to four other membrane proteins, the pan B cell marker CD37, the pan leukocyte marker CD53, the melanoma antigen ME491 and surprisingly, the Schistosoma mansoni antigen Sm23. The four human proteins share a number of additional similarities in their overall structure. These include identical spacing of the transmembrane domains, similar hydro-phobicity plots, possible N-linked glycosylation sites of similar number and position as well as similar distribution of the cysteine residues. The majority of these characteristics are still conserved in the evolutionary most distant member of this family, the Schistosoma mansoni antigen Sm23. Here we introduce this new protein superfamily and characterize the inducible, lymphoid-specific member R2.

Abstract: Spinal cord injury (SCI) induces secondary tissue damage that is associated with inflammation. We have previously demonstrated that inflammation-related gene expression after SCI occurs in two waves - an initial cluster that is acutely and transiently up-regulated within 24 hours, and a more delayed cluster that peaks between 72 hours and 7 days. Here we extend the microarray analysis of these gene clusters up to 6 months post-SCI. Adult male rats were subjected to mild, moderate or severe spinal cord contusion injury at T9 using a well-characterized weight-drop model. Tissue from the lesion epicenter was obtained 4 hours, 24 hours, 7 days, 28 days, 3 months or 6 months post-injury and processed for microarray analysis and protein expression. Anchor gene analysis using C1qB revealed a cluster of genes that showed elevated expression through 6 months post-injury, including galectin-3, p22PHOX, gp91PHOX, CD53 and progranulin. The expression of these genes occurred primarily in microglia/macrophage cells and was confirmed at the protein level using both immunohistochemistry and western blotting. As p22PHOX and gp91PHOX are components of the NADPH oxidase enzyme, enzymatic activity and its role in SCI were assessed and NADPH oxidase activity was found to be significantly up-regulated through 6 months post-injury. Further, treating rats with the nonspecific, irreversible NADPH oxidase inhibitor diphenylene iodinium (DPI) reduced both lesion volume and expression of chronic gene cluster proteins one month after trauma. These data demonstrate that inflammation-related genes are chronically up-regulated after SCI and may contribute to further tissue loss.

Abstract: CD53 is a member of a novel family of molecules with four presumably membrane-spanning domains. The structure and functional characteristics of these molecules indicate that they may play an important role in transmembrane communication. We therefore investigated whether CD53 is involved in activation of human leukocytes. Cross-linking of cell-bound F(ab')2 fragments of two different anti-CD53 mAb with F(ab')2 anti-mouse Ig led to cytoplasmic calcium fluxes in B cells, monocytes, and granulocytes and activation of the monocyte oxidative burst. These responses were specific for CD53, as cross-linking of CD11a, CD18, CD35, CD43, CD44, CD45, or CDw50 did not induce leukocyte activation. Low concentrations of staurosporine (10 to 20 nM) completely inhibited PMA-mediated activation, but had no effect on CD53-mediated calcium fluxes and inhibited only partially CD53-mediated oxidative burst. This suggests that CD53-mediated signaling is largely independent of protein kinase C. CD53-mediated calcium fluxes were inhibited by high concentrations of staurosporine (300 to 500 nM) but not by ADP-ribosylating toxins, suggesting dependence on tyrosine kinases rather than GTP-binding proteins. The results indicate that CD53, like several other leukocyte Ag with four membrane-spanning regions, has the ability to mediate cell activation, and support the view that these molecules are involved in transmembrane communication.