GATA-4 and Serum Response Factor Regulate Transcription of the Muscle-specific Carnitine Palmitoyltransferase I β in Rat Heart

Abstract

Transcriptional regulation of nuclear encoded mitochondrial proteins is dependent on nuclear transcription factors that act on genes encoding key components of mitochondrial transcription, replication, and heme biosynthetic machinery. Cellular factors that target expression of proteins to the heart have been well characterized with respect to excitation-contraction coupling. No information currently exists that examines whether parallel transcriptional mechanisms regulate nuclear encoded expression of heart-specific mitochondrial isoforms. The muscle CPT-I␤ isoform in heart is a TATAless gene that uses Sp-1 proteins to support basal expression. The rat cardiac fatty acid response element (؊301/؊289), previously characterized in the human gene, is responsive to oleic acid following serum deprivation. Deletion and mutational analysis of the 5-flanking sequence of the carnitine palmitoyltransferase I␤ (CPT-I␤) gene defines regulatory regions in the ؊391/ ؉80 promoter luciferase construct. When deleted or mutated constructs were individually transfected into cardiac myocytes, CPT-I/luciferase reporter gene expression was significantly depressed at sites involving a putative MEF2 sequence downstream from the fatty acid response element and a cluster of heart-specific regulatory regions flanked by two Sp1 elements. Each site demonstrated binding to cardiac nuclear proteins and competition specificity (or supershifts) with oligonucleotides and antibodies. Individual expression vectors for Nkx2.5, serum response factor (SRF), and GATA4 enhanced CPT-I reporter gene expression 4 -36-fold in CV-1 cells. Although cotransfection of Nkx and SRF produced additive luciferase expression, the combination of SRF and GATA-4 cotransfection resulted in synergistic activation of CPT-I␤. The results demonstrate that SRF and the tissue-restricted isoform, GATA-4, drive robust gene transcription of a mitochondrial protein highly expressed in heart. Expression of nuclear and mitochondrial encoded expression of respiratory chain subunits occurs despite physical separation of transcriptional events within separate genomes. Stimulation and coordination of mitochondrial gene expression from these two sites is accomplished by the nuclear respiratory factors, NRF-1 and NRF-2 (1, 2). Using electrical stimulation to produce hypertrophic growth of neonatal cardiac myocytes, the transcriptional activation of cytochrome c is preceded by induction of NRF-1 mRNA (3). This observation is consistent with NRF-1 induction as a prerequisite for synthesis of respiratory chain components. These basic insights into cellular factors that link nuclear events to mitochondrial gene activation are critical for adaptation to environmental stresses and the necessity for enhanced energy production.In contrast to subcellular coordination of mitochondrial biogenesis and respiratory chain synthesis, less is known concerning tissue-specific transcriptional regulation of nuclear encoded genes involved in energy metabolism. These genes are particularly important in cardiac...

Dictyostelium discoideum Developmentally Regulated Genes Whose Expression Is Dependent on MADS Box Transcription Factor SrfA

“…The existence of genes whose expression is dependent on both SrfA and StkA suggests the interaction of both transcription regulatory pathways in spore differentiation. Cooperation of the vertebrate SRF with GATA 4 and GATA 6 has been described previously (4,21,22). In D. discoideum, the two pathways are not completely overlapping, however, since there are genes whose expression is dependent on StkA but not on SrfA.…”

Physical Interaction between GATA-5 and Hepatocyte Nuclear Factor-1α Results in Synergistic Activation of the Human Lactase-Phlorizin Hydrolase Promoter

“…a critical biological mechanism for gene regulation. For example, similar to the model presented here is the well characterized model for the synergistic activation of cardiac promoters by GATA-4 and Nkx2.5 (47,48,(57)(58)(59)(60), a homeodomain-containing transcription factor like HNF-1␣. In this model, the C-terminal zinc finger and basic regions of GATA-4 and the homeodomain of Nkx2.5 are required for physical association, which, in turn, is necessary for synergistic activation of several genes (47,48,57).…”

Calcineurin and Calcium/Calmodulin-dependent Protein Kinase Activate Distinct Metabolic Gene Regulatory Programs in Cardiac Muscle

“…M-CPT I catalyzes the rate-limiting step in mitochondrial fatty acid oxidation and is a nodal point of regulation at both the transcriptional and post-transcriptional levels. Multiple transcription factors have been shown to regulate M-CPT I gene expression, including GATA4, MEF2, SRF (30), and PPAR␣ (22). Based on the presence of consensus binding sites in the human M-CPT I promoter, MEF2 and NFAT proteins are likely candidates for mediating the PPAR␣-independent activation of this gene by Cn.…”