Biomedical subjects

B A Rothermel

Publications and source records attributed to B A Rothermel.

5 recordsLinked to original sources

PubMed2001

Myocyte-enriched calcineurin-interacting protein, MCIP1, inhibits cardiac hypertrophy in vivo.

Signaling events controlled by calcineurin promote cardiac hypertrophy, but the degree to which such pathways are required to transduce the effects of various hypertrophic stimuli remains uncertain. In particular, the administration of immunosuppressive drugs that inhibit calcineurin has inconsistent effects in blocking cardiac hypertrophy in various animal models. As an alternative approach to inhibiting calcineurin in the hearts of intact animals, transgenic mice were engineered to overexpress a human cDNA encoding the calcineurin-binding protein, myocyte-enriched calcineurin-interacting protein-1 (hMCIP1) under control of the cardiac-specific, alpha-myosin heavy chain promoter (alpha-MHC). In unstressed mice, forced expression of hMCIP1 resulted in a 5-10% decline in cardiac mass relative to wild-type littermates, but otherwise produced no apparent structural or functional abnormalities. However, cardiac-specific expression of hMCIP1 inhibited cardiac hypertrophy, reinduction of fetal gene expression, and progression to dilated cardiomyopathy that otherwise result from expression of a constitutively active form of calcineurin. Expression of the hMCIP1 transgene also inhibited hypertrophic responses to beta-adrenergic receptor stimulation or exercise training. These results demonstrate that levels of hMCIP1 producing no apparent deleterious effects in cells of the normal heart are sufficient to inhibit several forms of cardiac hypertrophy, and suggest an important role for calcineurin signaling in diverse forms of cardiac hypertrophy. The future development of measures to increase expression or activity of MCIP proteins selectively within the heart may have clinical value for prevention of heart failure.

Animals↗

PubMed1997

Rtg3p, a basic helix-loop-helix/leucine zipper protein that functions in mitochondrial-induced changes in gene expression, contains independent activation domains.

Rtg3p and Rtg1p are basic helix-loop-helix/leucine zipper protein transcription factors in yeast that interact and bind to sites in an upstream activation sequence element in the 5'-flanking region of CIT2, a gene encoding a peroxisomal isoform of citrate synthase. These factors are required both for basal expression of CIT2 and its elevated expression in cells with dysfunctional mitochondria, such as in respiratory-deficient petite cells lacking mitochondrial DNA (rho degrees ). This elevated expression of CIT2 is called the retrograde response. Here we show that fusion constructs between the Gal4p DNA binding domain and Rtg3p transactivate the expression of a LacZ reporter gene under the control of a GAL1 promoter element. We have identified two activation domains in Rtg3p: a strong carboxyl-terminal domain from amino acids 375-486, and a weaker amino-terminal domain from amino acids 1-175; neither of these activation domains contain the bHLH/Zip motif. We have also identified a serine/threonine-rich domain of Rtg3p within amino acids 176-282 that is inhibitory to transactivation. In addition, the transcriptional activity of the Gal4-Rtg3p fusion proteins does not require either Rtg1p or Rtg2p; the latter is a protein containing an hsp70-like ATP binding domain that is also necessary for CIT2 expression. In contrast, transcriptional activation by Gal4-Rtg1p fusion proteins requires the Rtg1p basic helix-loop-helix/leucine zipper protein domain, as well as Rtg3p and Rtg2p. These data suggest that transcriptional activation by the Rtg1p-Rtg3p complex is largely the function of Rtg3p. Experiments are also presented suggesting that Rtg3p is limiting for gene expression in respiratory-competent (rho+) cells.

Antigens, Fungal↗

PubMed1995

Transactivation by Rtg1p, a basic helix-loop-helix protein that functions in communication between mitochondria and the nucleus in yeast.

Rtg1p is a basic helix-loop-helix transcription factor in the yeast Saccharomyces cerevisiae that is required for basal and regulated expression of CIT2, the gene encoding a peroxisomal isoform of citrate synthase. In respiratory incompetent rho degree petite cells, CIT2 transcription is elevated as much as 30-fold compared with respiratory competent rho + cells. Here we provide evidence that Rtg1p interacts directly with a CIT2 upstream activation site (UASr) and that the rho degree/rho + regulation is not due to a change in the levels of Rtg1p. A fusion protein consisting of the DNA binding domain of Gal4p fused to the NH2 terminus of the full-length wild-type Rtg1p was able to transactivate an integrated LacZ reporter under control of the Gal4p-responsive GAL1 UASG in a rho degree/rho(+)-dependent manner. Other Gal4p fusions to deletions or mutations of Rtg1p indicate that the helix-loop-helix domain is essential for transactivation. Regulated expression of CIT2 also requires the RTG2 gene product. The Gal4-Rtg1p fusion was unable to transactivate the LacZ reporter gene in a strain deleted for RTG2, suggesting that the RTG2 product does not act independently of Rtg1p in the rho degree/rho + transcriptional response.

Alleles↗

PubMed1989

Primary structure of the maize NADP-dependent malic enzyme.

Chloroplast-localized NADP-dependent malic enzyme (EC 1.1.1.40) (NADP-ME) provides a key activity for the carbon 4 fixation pathway. In maize, nuclear encoded NADP-ME is synthesized in the cytoplasm as a precursor with a transit peptide that is removed upon transport into the chloroplast stroma. We present here the complete nucleotide sequence for a 2184-base pair full-length maize NADP-ME cDNA. The predicted precursor protein is 636 amino acids long with a Mr of 69,800. There is a strong codon bias found in the amino-terminal portion of NADP-ME that is present in genes for the other enzymes of the C-4 photosynthetic pathway. The NADP-ME transit peptide has general features common to other known chloroplast stroma transit peptides. Comparison of mature maize NADP-ME to the amino acid sequences of known malic enzymes shows two conserved dinucleotide-binding sites. There is a third highly conserved region of unknown function. On the basis of amino acid sequence similarity, the maize chloroplastic enzyme is more closely related to eukaryotic cytosolic isoforms of malic enzyme than to prokaryotic isoforms. We discuss the functional and evolutionary relationship between the chloroplastic and cytosolic forms of NADP-ME.

Amino Acid Sequence↗

PubMed1988

Cellular pattern of photosynthetic gene expression in developing maize leaves.

Leaf development in C4 plants such as maize involves the differentiation of two photosynthetic cell types [bundle sheath (BS) and mesophyll (M)] to form Kranz-type leaf anatomy. This cellular dimorphism partitions photosynthetic activities so that each enzyme of the C4 pathway accumulates only in the appropriate cell type. We have exploited this property to study BS and M cell interactions in developing maize leaves. Our previous studies showed that C4 proteins appear concurrently with the appearance of Kranz anatomy. To look at earlier events in BS and M cell development we have used three of the corresponding C4 mRNAs as cell-specific markers. We have followed, in situ, the accumulation of malic enzyme (ME), phosphoenolpyruvate carboxylase (PEPCase), and ribulose bisphosphate carboxylase (RuBPCase) mRNAs in developing leaves of both normal and mutant argentia (ar) maize. We have isolated a partial cDNA clone for maize ME to examine ME mRNA expression. We show that throughout the development of light-grown seedlings, all three mRNAs accumulate in a cell-specific fashion in both normal and ar leaves. The pattern of C4 mRNA accumulation longitudinally along the veins, laterally across the leaf, and locally around individual veins reveals the spatial and temporal sequence of BS and M cell development. BS cell-specific mRNAs accumulate around developing veins before Kranz anatomy is evident morphologically. Our analysis of the ar mutant, in which C4 mRNA appearance is delayed relative to the appearance of Kranz anatomy, demonstrates first that BS and M cells develop in clusters across the leaf blade and second that BS cells surrounding any individual vein are activated asynchronously. We discuss our results in relation to models and mechanisms of BS and M cell development.

Cell Compartmentation↗