Transforming growth factor-beta-induced transcription of the Alzheimer beta-amyloid precursor protein gene involves interaction between the CTCF-complex and Smads.
Transforming growth factor-beta-1 (TGF-beta), a key regulator of the brain responses to injury and inflammation, has been implicated in upregulating the expression of the Alzheimer amyloid precursor protein (APP) and Alzheimer's disease (AD) pathogenesis. However, little is known about the mechanisms underlying the effects of TGF-beta on APP expression. Analysis of APP promoter activity upstream of the chloramphenicol acetyltransferase reporter gene in normal human astrocytes (NHAs), revealed that the APP promoter binding beta (APBbeta) site (-93/-82) is responsive to TGF-beta. This site interacts with the zinc finger nuclear factor CTCF, involved in APP transcriptional activity. As determined by gel shift assay, there was no significant difference in the CTCF-APBbeta complex binding activity in the presence or absence of TGF-beta treatment of NHAs. To further investigate the contributions of the CTCF-complex and Smad proteins to the TGF-beta induced APP promoter activity, we examined the distribution of these factors and their DNA binding activity. Interestingly, upon TGF-beta treatment both Smads 3 and 4 were translocated to the nuclei in contrast to Smad 2, which was cytoplasmic. However, CTCF was predominantly localized in the nuclei irrespective of TGF-beta treatment. Gel super shift assay coupled with Western blot analysis showed that Smads 3 and 4 specifically associated with the CTCF-APBbeta complex. In addition, AD brain sections showed increased expression and nuclear localization of Smad 4, which correlated with higher levels of APP and TGF-beta. However, over expression of Smad 4 on its own was not sufficient to affect APP expression. These results demonstrate that TGF-beta activation of Smad protein complexes promotes transcription of the APP gene. Increased synthesis of APP may in part determine Abeta production and deposition in affected AD brain.
Burton
Teralee
T
The Dr. John Foerster Centre for Health Research on Aging. St. Boniface General Hospital Research Centre, 351 Taché Avenue, Winnipeg, MB, Canada R3E 0W3.
Liang
Binhua
B
Dibrov
Alex
A
Amara
Francis
F
D001253:Astrocytes / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D000076246:CCCTC-Binding Factor; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007150:Immunohistochemistry; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D021381:Protein Transport; D012097:Repressor Proteins; D015398:Signal Transduction; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014466:Ultraviolet Rays
C450760:APP protein, Neisseria meningitidis; D001425:Bacterial Outer Membrane Proteins; D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta