GATA and FOG2 transcription factors differentially regulate the promoter for Kv4.2 K+ channel gene in cardiac myocytes and PC12 cells

Objective: Kv4.2 subunits are major components of transient outward K+ channels in cardiac myocytes and somatodendritic A-type channels in neurons. To identify molecular mechanisms underlying transcriptional regulation of Kv4.2 gene, we have isolated and characterized the promoter for the rat Kv4.2 gene. Methods: PCR-based amplification of cDNA end (5'RACE) and RNase protection assays were used to determine transcription start sites. Transient transfection of Kv4.2 promoter-luciferase reporter constructs into neonatal cardiac myocytes and PC 12 cells was employed to measure activity of the Kv4.2 promoter. Cotransfection of expression vectors for the transcription factors, GATA and/or FOG2, was performed to determine the effects of these transcription factors on the Kv4.2 promoter. Results: Transcription of the gene initiates at 552 bp upstream from the translation initiation site in the brain and heart. Deletion analysis revealed that the similar to200-bp fragment encompassing this start site drives significant transcription in neonatal cardiac myocytes and PC 12 cells. The transcription factors GATA4 and 6 differentially enhance activity of the minimum promoter in the two cell types: GATA4 produces a larger increase than GATA6 in cardiac myocytes, whereas the latter results in a more substantial enhancement in PC12 cells. Furthermore, the coregulator of GATA, FOG2, markedly suppresses the GATA-induced increase in myocytes, but enhances it in PC12 cells. The use of GATA mutants that are incapable of forming complexes with FOG2 indicates that the formation of GATA-FOG complexes is required for the FOG2-induced suppression in myocytes, but not for the FOG2-mediated enhancement in PC12 cells. Conclusion: These results indicate that GATA and FOG2 transcription factors use distinct mechanisms to control the expression of Kv4.2 gene in cardiac myocytes and PC12 cells. The lack of a GATA-binding consensus sequence in the Kv4.2 minimum promoter suggests that these transcription factors indirectly influence the channel gene transcription. (C) 2003 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.