Cyclophilin C‐associated protein is an intracellular mediator between tissue transglutaminase to TNFa

Abstract

Introduction. Previous study reveals that cyclophilin C-associated protein (CyCAP) null cells do not release MMP-13 after treatment with 45 kd fibronectin fragment (FN45). Since FN45 has a tissue transglutaminase (tTG) binding site but not integrin binding motif, therefore, the effects of FN45 may through tTG binding. In the present study, the connection of CyCAP with tTG, TACE and TNFa release was tested. Methods. The expression of tTG in CyCAP null fibroblasts was tested with Western blot. The release of TNFa by FN45, FN70, IL-1b, tTG and heparin in CyCAP null and wild-type fibroblasts was examined with ELISA. The gene expression of TACE, tTG and TNFa in CyCAP null and wild-type dermal fibroblasts was tested by real-time quantitative PCR. Results. Western blots indicate that tTG expression in CyCAP null cell is lower than wild-type cells. FN45 induces TNFa gene expression more than 13 folds at eight-hour time point only in wild-type cells but not in CyCAP null cells. The released TNFa is 57 fold higher by FN45 and 43 folds higher by tTG in wild-type comparing to CyCAP null cells. The tTG inhibitory antibody showed slight inhibitory effects on MMP-13 expression in wild-type cells. Conclusion. Our data indicate that deletion of CyCAP reduces tTG activity, which in turn damages the function of TACE, i.e. decrease the cleavage of TNFa into extracellular matrix. The release of MMP-13 by FN45 is abolished in CyCAP null cells, suggesting FN45 induced MMP-13 is through the effect of TNFa. Our data give first evidence that CyCAP has intracellular connection with tTG. Deletion of CyCAP abolished TACE effects on cleaving TNFa, therefore, CyCAP may play important role in anti-inflammatory diseases.