Involvement of thyrotroph embryonic factor in calcium-mediated regulation of gene expression.
In the present study, we used an expression cloning strategy to identify transcription factors that bind specifically to a limited region of the inducible cAMP early repressor (ICER) promoter and regulate transcription. Murine thyrotroph embryonic factor (mTEF) was isolated and was shown to bind to a site located at nucleotides -117 to -108 from the transcriptional start site. Transient expression of reporter constructs containing either a consensus TEFRE or the icerTEF binding site demonstrated that TEF-dependent transcription correlated with relative binding affinities, i.e. the consensus TEFRE bound TEF more tightly and was more responsive to TEF than the icerTEFRE. Because the icerTEFRE overlapped a cAMP response element, the responsiveness of these sequences to either cAMP or Ca(2+) was tested. Although TEF expression had no effect on the cAMP-regulated transcriptional response of the ICER promoter, TEF did confer calcium responsiveness to these sequences. Calcium also modestly increased the TEF-mediated transcription from a consensus TEFRE. Additional studies using Ca(2+)-activated kinases indicate that Ca(2+)/TEF/TEFRE-regulated transcription may be mediated through Ca(2+)/calmodulin-dependent kinase (CaMK) IV. Moreover, studies with the icerTEFRE in a CaMK IV-deficient cell line demonstrated that these cells were transcriptionally unresponsive to thapsigargin; however, responsiveness was restored by co-expression of the active CaMK IV. These studies are the first to demonstrate that TEF is a calcium-responsive transcription factor, and they suggest that there are two classes of TEF-regulated genes. One class, represented by a consensus TEFRE, is regulated by TEF in the resting cell; the second class, represented by icerTEFRE, is regulated by TEF in the calcium-activated cell.
Krueger
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E. A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University Health Sciences Center, St. Louis, Missouri 63104, USA.
Warner
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Dowd
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D002118:Calcium / Q000502:physiology*; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D003001:Cloning, Molecular; D051786:Cyclic AMP Response Element Modulator; D004247:DNA; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins; D012689:Sequence Homology, Nucleic Acid; D013950:Thymus Gland / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D014157:Transcription Factors / Q000502:physiology*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D050976:Basic-Leucine Zipper Transcription Factors; D017931:DNA Primers; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; C489491:Tef protein, mouse; D014157:Transcription Factors; D051786:Cyclic AMP Response Element Modulator; D004247:DNA; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517685:Camk4 protein, mouse; D002118:Calcium