Nuclear Factor-1-X Regulates Astrocyte-specific Expression of the α1-Antichymotrypsin and Glial Fibrillary Acidic Protein Genes

Abstract

Discrete tissue-specific changes in chromatin structure of the distal serpin subcluster on human chromosome 14q32.1 allow a single gene encoding ␣ 1 -antichymotrypsin (ACT) to be expressed in astrocytes and glioma cells. This astrocyte-specific regulation involves activatory protein-1 (AP-1) because overexpression of dominantnegative c-jun(TAM67) abolishes ACT expression in glioma cells. Here we identify a new regulatory element, located within the ؊13-kb enhancer of the ACT gene, that binds nuclear factor-1 (NFI) and is indispensable for the full basal transcriptional activity of the ACT gene. Furthermore, down-regulation of NFI expression by siRNA abolishes basal ACT expression in glioma cells. However, NFI does not mediate astrocyte-specific expression by itself, but likely cooperates with AP-1. A detailed analysis of the 14-kb long 5-flanking region of the ACT gene indicated the presence of adjacent NFI and AP-1 elements that colocalized with DNase I-hypersensitive sites found in astrocytes and glioma cells. Interestingly, knock-down of NFI expression also specifically abrogates the expression of glial acidic fibrillary protein (GFAP), which is an astrocyte-specific marker protein. Mutations introduced into putative NFI and AP-1 elements within the 5-flanking region of the GFAP gene also diminished basal expression of the reporter. In addition, we found, using isoform-specific siRNAs, that NFI-X regulates the astrocytespecific expression of ACT and GFAP. We propose that NFI-X cooperates with AP-1 by an unknown mechanism in astrocytes, which results in the expression of a subset of astrocyte-specific genes.2 is expressed at low levels by astrocytes in the brain under normal physiological conditions. However, elevated ACT levels have been observed in several neuropathological disorders of the central nervous system, including Alzheimer disease (1, 2). This drastic change in ACT expression is caused by proinflammatory cytokines, including IL-1, IL-6, oncostatin M (OSM), and tumor necrosis factor (TNF)␣, which are released at the site of tissue damage (3, 4). ACT secreted by reactive astrocytes subsequently associates with the ␤-amyloid peptide, which is the major component of pathological deposits found in the brains of Alzheimer disease patients (1).ACT belongs to the serine protease inhibitor (serpin) family of proteins and is also expressed in the liver and secreted into the plasma (5). The gene encoding ACT is clustered with 10 additional serpin genes on human chromosome 14q32.1 and resides within the distal serpin subcluster that also contains genes encoding kallistatin, protein C inhibitor, and the kallistatin-like protein (6, 7). The expression profile of the distal serpin subcluster is dramatically different between astrocytes and hepatocytes. All four genes are expressed in hepatocytes, whereas only the ACT gene is expressed in astrocytes (8). Investigations of the regulatory mechanisms controlling the selective expression of ACT in astrocytes and glioma cells demonstrated that the ACT gene is localize...

NFIA Controls Telencephalic Progenitor Cell Differentiation through Repression of the Notch Effector Hes1

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The role of Nfix in the development of the embryonic and postnatal cerebral cortex

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“…Nfix −/− mice also display severe neurological phenotypes , and NFIX has previously been implicated in driving the expression of astrocytic genes during neural development (Gopalan et al 2006;. However, the mechanism by which NFIX regulates morphogenesis of the nervous system in vivo remains undefined.…”

“…Mice lacking either Nfia or Nfib display neurological phenotypes including dysgenesis of the corpus callosum Shu, Puche, et al 2003;), hippocampal malformation , and delays in cerebellar development (SteelePerkins et al 2005;. Mechanistically, Nfi genes have been implicated in regulating glial development via promoting the expression of astrocyte-specific genes (Gopalan et al 2006;, and Nfia and Nfib were recently shown to promote progenitor cell differentiation in a complementary fashion within the developing telencephalon through the repression of the Notch signaling pathway .…”

Nuclear Factor 1 and T-Cell Factor/LEF Recognition Elements Regulate Pitx2 Transcription in Pituitary Development

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