TGF-beta1 induction of the adenine nucleotide translocator 1 in astrocytes occurs through Smads and Sp1 transcription factors.

Law AK, Gupta D, Levy S, Wallace DC, McKeon RJ, Buck CR
BMC Neurosci. 2004 5: 1

PMID: 14720305 · PMCID: PMC324399 · DOI:10.1186/1471-2202-5-1

BACKGROUND - The adenine nucleotide translocator 1 (Ant1) is an inner mitochondrial membrane protein involved with energy mobilization during oxidative phosphorylation. We recently showed that rodent Ant1 is upregulated by transforming growth factor-beta (TGF-beta) in reactive astrocytes following CNS injury. In the present study, we describe the molecular mechanisms by which TGF-beta1 regulates Ant1 gene expression in cultured primary rodent astrocytes.

RESULTS - Transcription reporter analysis verified that TGF-beta1 regulates transcription of the mouse Ant1 gene, but not the gene encoding the closely related Ant2 isoform. A 69 basepair TGF-beta1 responsive element of the Ant1 promoter was also identified. Electrophoretic mobility shift assays demonstrated that astrocyte nuclear proteins bind to this response element and TGF-beta1 treatment recruits additional nuclear protein binding to this element. Antibody supershift and promoter deletion analyses demonstrated that Sp1 consensus binding sites in the RE are important for TGF-beta1 regulation of Ant1 in astrocytes. Additionally, we demonstrate that Smad 2, 3 and 4 transcription factors are expressed in injured cerebral cortex and in primary astrocyte cultures. TGF-beta1 activated Smad transcription factors also contribute to Ant1 regulation since transcription reporter assays in the presence of dominant negative (DN)-Smads 3 and 4 significantly reduced induction of Ant1 by TGF-beta1.

CONCLUSION - The specific regulation of Ant1 by TGF-beta1 in astrocytes involves a cooperative interaction of both Smad and Sp1 binding elements located immediately upstream of the transcriptional start site. The first report of expression of Smads 2, 3 and 4 in astrocytes provided here is consistent with a regulation of Ant1 gene expression by these transcription factors in reactive astrocytes. Given the similarity in TGF-beta1 regulation of Ant1 with other genes that are thought to promote neuronal survival, this interaction may represent a general mechanism that underlies the neuroprotective effects of TGF-beta1.

MeSH Terms (24)

Adenine Nucleotide Translocator 1 Animals Astrocytes Binding Sites Cells, Cultured Cerebral Cortex Collodion DNA-Binding Proteins Electrophoretic Mobility Shift Assay Gene Expression Regulation Implants, Experimental Mice Mutagenesis, Site-Directed Promoter Regions, Genetic Response Elements Sequence Deletion Signal Transduction Smad2 Protein Smad3 Protein Smad4 Protein Sp1 Transcription Factor Trans-Activators Transforming Growth Factor beta Transforming Growth Factor beta1

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