| Abstract: |
T cell receptor activation induces inositol 1,4,5 trisphosphate (IP3)-mediated calcium signaling that is essential for cell metabolism and survival. Moreover, inhibitors of IP3 or pharmacological agents that disrupt calcium homeostasis readily induce autophagy. Using a glucocorticoid-sensitive CD4/CD8 positive T cell line, we found that dexamethasone prevented both IP3-mediated and spontaneous calcium signals within a timeframe that correlated with the induction of autophagy. We determined that this loss in IP3-mediated calcium signaling was dependent upon the downregulation of the Src kinase Fyn at the mRNA and protein level. Because it has previously been shown that Fyn positively regulates IP3-mediated calcium release by phosphorylating Type I IP3 receptors (IP3R1), we investigated the effect of glucocorticoids on IP3R1 phosphorylation at Tyr353. Accordingly, glucocorticoid-mediated downregulation of Fyn prevented IP3R1 phosphorylation at Tyr353. Moreover, selective knockdown of Fyn or treatment with a Src inhibitor also attenuated IP3-mediated calcium release and induced autophagy. Collectively, these data indicate that glucocorticoids promote autophagy by inhibiting IP3-dependent calcium signals. These findings carry important therapeutic implications given the widespread use of dexamethasone as both a chemotherapeutic and immunosuppressive agent. © 2010 Landes Bioscience. |
| Keywords: |
protein phosphorylation; unclassified drug; nonhuman; cd8+ t lymphocyte; t-lymphocytes; animal cell; mouse; animals; mice; cell death; apoptosis; cell line; down-regulation; rna, small interfering; calcium; dexamethasone; tyrosine; receptors, antigen, t-cell; cd4+ t lymphocyte; autophagy; glucocorticoids; inositol 1,4,5 trisphosphate receptor; calcium transport; calcium signaling; inositol 1,4,5-trisphosphate; inositol 1,4,5-trisphosphate receptors; fyn; ip3 receptor; inositol 1,4,5 trisphosphate; inositol 1,4,5 trisphosphate receptor1; protein kinase fyn; proto-oncogene proteins c-fyn
|
