Glucocorticoid-induced activation of caspase-8 protects the glucocorticoid-induced protein Gilz from proteasomal degradation and induces its binding to SUMO-1 in murine thymocytes |
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Authors: | D V Delfino S Spinicelli N Pozzesi S Pierangeli E Velardi S Bruscoli M P Martelli V Pettirossi L Falchi T-b Kang C Riccardi |
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Institution: | 1.Section of Pharmacology Toxicology and Chemotherapy, Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy;2.Section of Hematology, Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy;3.Section of Onco-hematology, Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy;4.Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel |
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Abstract: | In this study, we evaluated the possible cross-talk between glucocorticoid (GC)-induced leucine zipper (Gilz) and caspase-8 in dexamethasone (Dex)-treated thymocytes. We determined that expression of Dex-induced Gilz protein was reduced when caspase-8 activity was inhibited, and this effect was not partially due to altered Gilz mRNA expression. Inhibition of the proteasome abrogated this reduction in Gilz expression, suggesting that Dex-induced caspase-8 activation protects Gilz from degradation. We hypothesized that the caspase-8-dependent protection of Gilz could be due to caspase-8-driven sumoylation. As a putative small ubiquitin-like modifier (SUMO)-binding site was identified in the Gilz sequence, we assessed whether SUMO-1 interacted with Gilz. We identified a 30-kDa protein that was compatible with the size of a Gilz–SUMO-1 complex and was recognized by the anti-SUMO-1 and anti-Gilz antibodies. In addition, Gilz bound to SUMO ubiquitin-conjugating (E2)-conjugating enzyme Ube21 (Ubc9), the specific SUMO-1 E2-conjugating enzyme, in vitro and coimmunoprecipitated with Ubc9 in vivo. Furthermore, Gilz coimmunoprecipitated with SUMO-1 both in vitro and in vivo, and this interaction depended on caspase-8 activation. This requirement for caspase-8 was further evaluated in caspase-8-deficient thymocytes and lymphocytes in which Gilz expression was reduced. In summary, our results suggest that caspase-8 activation protects Gilz from proteasomal degradation and induces its binding to SUMO-1 in GC-treated thymocytes. |
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Keywords: | GC caspase-8 SUMO-1 Gilz thymocyte apoptosis |
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