Human astrocytes express 14-3-3 sigma in response to oxidative and DNA-damaging stresses.
The 14-3-3 protein family consists of seven isoforms, most of which are expressed abundantly in neurons and glial cells, although the sigma isoform, a p53 target gene originally identified as an epithelium-specific marker, has not been identified in the human central nervous system. Here, we show that human astrocytes in culture expressed 14-3-3sigma under stress conditions. By Western blot, the expression of 14-3-3sigma, p53 and p21 was coordinately upregulated in astrocytes following exposure to hydrogen peroxide, 4-hydroxy-2-nonenal (4-HNE) or etoposide, a topoisomerase II inhibitor. 14-3-3sigma was induced by treatment with 5-aza-2'-deoxycytidine, suggesting a hypermethylated status of the gene promoter in astrocytes. In vivo, a small subset of hypertrophic reactive astrocytes, often showing a multinucleated morphology, expressed 14-3-3sigma in active demyelinating lesions of multiple sclerosis (MS) and ischemic lesions of cerebral infarction, where the expression of 4-HNE and 8-hydroxy-2'-deoxyguanosine was enhanced in reactive astrocytes. Microarray analysis of etoposide-treated astrocytes verified upregulation of p53-responsive genes and concurrent downregulation of mitotic checkpoint-regulatory genes. These observations suggest that 14-3-3sigma might serve as a marker of oxidative and DNA-damaging stresses inducing the mitotic checkpoint dysfunction in reactive astrocytes under pathological conditions.