Regulation of inhibitor of apoptosis expression by nitric oxide and cytokines: Relation to apoptosis induction in rat mesangial cells and RAW 264.7 macrophages

Mesangial cells and RAW 264.7 macrophages respond to different nitric oxide (NO) donors within 16 to 24 h or 6 to 8 h, respectively, with apoptotic ce ll death. RAW 264.7 macrophages also die in response to endogenous NO produ ction. In contrast, endogenous NO production fails to significantly induce cell death in mesangial cells. It was hypothesized that differences in the expression of antiapoptotic proteins, in particular the inhibitor of apopto sis (IAP) protein family, might be responsible for this cell type-specific behavior. Therefore, IAP expression was investigated in relation to apoptos is induction in response to NO and cytokines in both cell types. In mesangi al cells, interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha in duced cellular inhibitor of apoptosis 1 (cIAP1) mRNA expression within 3 h. In contrast, X chromosome-linked inhibitor of apoptosis (XIAP) mRNA levels remained unaffected by cytokines. Although coincubation of cells with IL-1 beta and tumor necrosis factor-alpha or IL-1 beta and basic fibroblast gro wth factor resulted in synergistic induction of inducible NO synthase, comp arable potentiating effects on cIAP1 induction were absent. Exogenously rel eased NO from NO donors promoted cIAP1 mRNA upregulation in mesangial cells , whereas XIAP mRNA was downregulated. However, the changes observed on the mRNA level were not adequately translated to the protein level, and corres ponding values for cIAP1 and XIAP were only slightly affected. In contrast, in lipopolysaccharide/interferon-gamma -stimulated RAW 264.7 macrophages, massive NO-dependent downregulation of cIAP1 and XIAP protein levels, which correlated temporally with the induction of apoptosis, was observed. This effect was at least partially reversed by N-G-monomethyl-L-arginine, an inh ibitor of NO synthase activity. In summary, a direct correlation between th e downregulation of IAP protein levels and the induction of apoptosis by en dogenous NO was observed in macrophages. In contrast, a stable level of IAP protein in mesangial cells might represent a mechanism for the resistance of the cells to endogenously produced NO.