Abstract 19581: Embryonic Lethality of Mice Deficient for IRF2BP2: An Essential Ischemia-Inducible Transcriptional Coactivator of VEGFA
Background - VEGF (vascular endothelial growth factor) is a master regulator of angiogenesis is a major player in ischemic heart disease. In 2010, we found that IRF2BP2 (interferon regulatory factor-2 binding protein-2) coactivates VEGFA expression in muscle. IRF2BP2 protein levels show a 7-fold increase is ischemic muscle whereas its mRNA expression is not increased, indicating that IRF2BP2 is translational repressed in normoxic tissues and becomes translationally derepressed during ischemia.
Methods - To characterize the mechanisms repressing translation of IRF2BP2 mRNA in normoxic conditions and enabling derepression during ischemia, luciferase reporter plasmids were transiently transfected in cultured cells. In addition, we generated transgenic mice with targeted deletion of the IRF2BP2 gene and others with a floxed IRF2BP2 allele enabling tissue specific ablation by Cre-transgene expression.
Results - In the 3’UTR of IRF2BP2 mRNA, microRNAs miR-17 and -20a were found to differentially regulate translation. A common 9 nucleotide deletion polymorphism (rs3045215) disrupted the miRNA target sequence in IRF2BP2 mRNA and associated with coronary artery disease risk in the Ottawa Heart Genomics study (p<0.0045). The RNA binding protein Staufen-1 (Stau1) binds to the 3’UTR of IRF2BP2 mRNA and inhibits its translation. Stau1 levels increased during C2C12 skeletal muscle differentiation, coincident with the downregulation of IRF2BP2 protein levels. Of interest, IRF2BP2 knockout mice died during embryonic development. Out of 11 litters from hemizygous matings, 42 offspring were born: 15 wild type (35.7%), 25 hemizygous (59.5%), and 2 homozygous null (4.8%) mice, deviating from the expected Mendelian ratio of 25% wild type:50% hemizygous: 25% null. The 2 surviving IRF2BP2 null mice displayed severe growth retardation. We are currently characterizing the phenotype of embryonic lethality in these mice.
Conclusion - Translational derepression enables expression of IRF2BP2 protein in ischemic tissues, an emerging mechanism of gene regulation. Our data show the IRF2BP2 gene is critical for mouse development. These transgenic models will enable the elucidation of IRF2BP2 function in angiogenesis and the response to ischemia.
- © 2012 by American Heart Association, Inc.