CNS sirtuins in radiation-induced vascular permeability and neurodegeneration

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

We have determined that Sirtuin 2 (Sirt2), the most common isoform of sirtuin in the central nervous system (CNS), interacts with beta-catenin. Sirt2 levels are increased during mouse glial stem cell gOlig2 differentiation, and beta-catenin and its targets are believed to be essential in the nervous system for differentiation and de-differentiation of both adult and stem cell populations, as a component of adherens junctions in cellular adhesion and signaling, as well as oncogenesis. The interaction of beta-catenin and Sirt2 increases in a directly proportional manner with radiation exposure, suggesting a possible role for ionizing radiation in differentiation, function, and repair of CNS cellular components. Transport of beta-catenin into the nucleus is dependent on the presence of Sirt2 as demonstrated by subcellular fractionation of Sirt2 wild-type and knockout mouse embryonic fibroblasts (MEFs). Likewise, the active form of beta-catenin that is phosphorylated on Tyrosine-142 is increased in Sirt2 knockout MEFs, indicating that Sirt2 is necessary for the activation and downregulation of beta-catenin targets vital to differentiation, cellular interaction, and intercellular communication. Sirt2 regulates expression of the Wnt target genes c-Myc, survivin, c-Jun, and Cyclin D1, and a PI3Kinase inhibitor decreases the expression of c-Jun, c-Myc, survivin, and phosphorylated AKT in the absence of Sirt2. Additionally, antisense RNA knockdown of Sirt2 in wild-type cells increases expression of Cyclin D1, c-Myc, and survivin. Taken together, along with the observation that Sirt2 regulated the transcriptional activity of beta-catenin, the data suggest that Sirt2 directly affects Wnt target genes and PI3kinase pathways. Beta-catenin directly binds to c-Myc, survivin, Cyclin D1 promoter. Sirt2 regulates the direct interaction of beta-catenin to these target promoters and suggests that Sirt2 may directly deactylate and alter DNA binding. In support of this, Sirt2 regulates the binding of acetylated histone H3 to the Wnt target promoters Cyclin D1, c-Myc and survivin. The data also suggest the possibility that Sirt2 is part of a complex of proteins and that Sirt2 may deacetylate an intermediary that then alters beta-catenin mediated transcription and signaling. On PCR array, we have determined that Nkd1, Pitx1, Sfrp4 and Tle1 are negative regulators of the Wnt pathway that are Sirt2 dependent. The presence of Sirt2 reduces cellular migration via Sirt2 regulation of matrix metalloproteinase 9 and a possible novel modification of E-cadherin. These intracellular alterations by SIRT2 likely influence how Sirt2 regulates radiation-induced injury. Tumor and normal tissue cells develop a radioresistant phenotype in response to Sirt2 deletion and/or inhibition. DNA damage repair is improved and prolonged following loss of SIRT2 function and results in protection against radiation-induced injury.