DR5 Knockout Mice Are Compromised in Radiation-Induced Apoptosis

Abstract

DR5 (also called TRAIL receptor 2 and KILLER) is an apoptosis-inducing membrane receptor for tumor necrosis factor-related apoptosis-inducing ligand (also called TRAIL and Apo2 ligand). DR5 is a transcriptional target of p53, and its overexpression induces cell death in vitro. However, the in vivo biology of DR5 has remained largely unexplored. To better understand the role of DR5 in development and in adult tissues, we have created a knockout mouse lacking DR5. This mouse is viable and develops normally with the exception of having an enlarged thymus. We show that DR5 is not expressed in developing embryos but is present in the decidua and chorion early in development. DR5-null mouse embryo fibroblasts expressing E1A are resistant to treatment with TRAIL, suggesting that DR5 may be the primary proapoptotic receptor for TRAIL in the mouse. When exposed to ionizing radiation, DR5-null tissues exhibit reduced amounts of apoptosis compared to wild-type thymus, spleen, Peyer's patches, and the white matter of the brain. In the ileum, colon, and stomach, DR5 deficiency was associated with a subtle phenotype of radiation-induced cell death. These results indicate that DR5 has a limited role during embryogenesis and early stages of development but plays an organ-specific role in the response to DNA-damaging stimuli.

The relative contribution of pro-apoptotic p53-target genes in the triggering of apoptosis following DNA damage in vitro and in vivo

“…Mice lacking Dr5 and Puma are protected from apoptosis in the brain, bone marrow, spleen and thymus following ionizing irradiation. 19 In vitro findings support a role for DR5 in the DNA damage response, as expression of dominant-negative DR5 or knockdown of DR5 protects different tumor cell lines, independently of exogenous TRAIL, from cell death induced by DNA damage. 21,34 Puma-deficient mice are protected from a number of pro-apoptotic cellular stresses that may cause cell death in a p53-dependent or p53-independent manner.…”

“…Mice harboring targeted mutations of the Dr5 alleles 19 were crossed with mice with targeted Puma alleles.…”

“…Previous studies demonstrated that p53 -/-, Dr5 -/-and Puma -/-mice are protected from apoptosis following ionizing radiation. 16,19,25 Neither Dr5 -/-nor Puma -/-mice display …”

“…19 These studies have established the importance of the p53-dependent pro-apoptotic target genes in the execution of apoptosis. However, it is largely unclear to what extent PPGs show redundancy and interdependency, perhaps due to the tedious nature of generating mice deficient in multiple genes.…”

“…This was somewhat surprising but consistent with what has been reported earlier with respect to death receptor signaling following DNA damage. [19][20][21][22][23] We further analyzed the results of concomitant gene silencing in order to address the relative impact and potential synergy between genes that trigger p53-dependent apoptosis. We found that only Bax, Puma and Bnip3L displayed additive inhibition effects on caspase 3/7 cleavage to that of DR5 knockdown (Fig.…”