NFAT directly regulates Nkx2-5 transcription during cardiac cell differentiation.
BACKGROUND
The transcription factor NFAT (nuclear factor of activated T-cell) family comprises important regulators in immuno-responses and mouse embryonic development, including early cardiovascular and heart valve development. The mechanism involved, however, is not fully understood. Nkx2-5 (NK2 transcription factor related, locus 5) is one of the earliest genes expressed in early cardiac progenitor cells and is essential for heart tube development by control of a subset of cardiac muscle-specific genes. Previously we found that downregulation of mitochondrial respiratory chain complex I caused severe cardiac deficiencies during heart tube development in Xenopus embryos associated with compromised Nkx2-5 expression. However, the heart defects and Nkx2-5 expression could be rescued by a constitutively activated NFAT, suggesting a possible link between NFAT and Nkx2-5 during early heart development.


RESULTS
In the present study, we demonstrate that NFAT regulates Nkx2-5 expression in both mouse ES (embryonic stem) cells and P19 cells, a mouse model for embryonic differentiation. We found that there are six core NFAT-binding elements in the 5' regulatory region of the Nkx2-5 gene. Although NFAT is able to bind directly to all but one of these elements, it activates Nkx2-5 transcription only via a specific binding site in the distal enhancer region. Interestingly, the transcriptional activity of NFAT is largely dependent on the co-factor GATA (GATA-binding transcription factor), which binds to an element adjacent to this key NFAT-binding site. Furthermore, binding of the endogenous NFAT to this particular site was observed during cardiac differentiation in mouse ES and P19 cells.


CONCLUSIONS
The results suggest that Nkx2-5 is a direct target of NFAT that co-ordinates with other transcription factors such as GATA4 to regulate Nkx2-5 during cardiogenesis.
Chen
Yong
Y
Institute of Molecular and Cell Biology, A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Singapore City 138673, Singapore.
Cao
Xinmin
X
D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D053595:Embryonic Stem Cells; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D009206:Myocardium / Q000166:cytology*; D050778:NFATC Transcription Factors / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; D050778:NFATC Transcription Factors; C484469:Nkx2-5 protein, mouse; D014157:Transcription Factors