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Thomas A Gorr

Publications and source records attributed to Thomas A Gorr.

9 recordsLinked to original sources
PubMed2006

Regulating cellular oxygen sensing by hydroxylation.

Oxygen homeostasis under conditions of limited O2 supply requires hypoxia-dependent gene regulation. The transcription factor complex hypoxia-inducible factor 1 (HIF-1) has been recognized as the master regulator that mediates the adaptational genetic response to ensure restoration of energy supply. This review will focus on the recent advances in understanding the hypoxia-induced cellular response with particular respect to cellular O2 sensing for adequate control of HIF-1 activation.

Animals↗
PubMed2006

Linker chains of the gigantic hemoglobin of the earthworm Lumbricus terrestris: primary structures of linkers L2, L3, and L4 and analysis of the connectivity of the disulfide bonds in linker L1.

The extracellular hemoglobin (Hb) of the earthworm, Lumbricus terrestris, has four major kinds of globin chains: a, b, c, and d, present in equimolar proportions, and additional non-heme, non-globin scaffolding chains called linkers that are required for the calcium-dependent assembly of the full-sized molecule. The amino acid sequences of all four of the globin chains and one of the linkers (L1) have previously been determined. The amino acid sequences via cDNA of each of the three remaining linkers, L2, L3, and L4, have been determined so that the sequences of all constituent polypeptides of the hemoglobin are now known. Each linker has a highly conserved cysteine-rich segment of approximately 40 residues that is homologous with the seven ligand-binding repeats of the human low-density lipoprotein receptor (LDLR). Analysis of linker L1 shows that the connectivity of the three disulfide bonds is exactly the same as in the LDLR ligand-binding repeats. The presence of a calcium-binding site comprising one glutamyl and three aspartyl residues in both the LDLR repeats and in the linkers supports the suggestion that calcium is required for the folding and disulfide connectivity of the linkers as in the LDLR repeats. Linker L2 is markedly heterogeneous and contains unusual glycine-rich sequences near the NH2-terminus and a polar zipper-like sequence with imperfect repeats of Asp-Asp-His at the carboxyl terminus. Similar Asp-Asp-His repeats have been found in a protein homologous to superoxide dismutase in the hemolymph of certain mussels. These repeats may function as metal-binding sites.

Amino Acid Sequence↗
PubMed2006

Sensing and responding to hypoxia via HIF in model invertebrates.

This past decade has brought considerable progress towards elucidating the molecular mechanisms of oxygen sensing pathways by which mammalian cells are able to detect and adjust, or succumb, to hypoxia. In contrast, far less is known about the protein and DNA constituents that endow many invertebrate species to withstand and recover from even more severe and prolonged O2 limitations. In spite of these differences in hypoxia tolerance, inadequacy in oxygen supply is, from mammals to insects to nematodes, signaled onto the DNA level predominantly by hypoxia-inducible factors (HIFs). Across the animal kingdom, HIF accumulates in hypoxic, but not normoxic, cells and functions in a remarkably conserved pathway. Using crustacean (Daphnia magna) and insect (Drosophila melanogaster) models, work by us and others has implicated HIF in restoring O2 delivery via stimulated hemoglobin synthesis (Daphnia) or tracheal remodeling (Drosophila). HIF is essential for these arthropods to adapt and survive during moderate O2 limitations. A similar life-preserving role for HIF-signaling in hypoxic, but not anoxic, environments had previously been established for another stress-tolerant invertebrate model, the nematode Caenorhabditis elegans. Exploring regulations of oxygen-dependent Daphnia and Drosophila genes in cell culture and in vivo have furthermore aided in uncovering novel HIF-targeting mechanisms that might operate to fine-tune the activity of this transcription factor under steadily hypoxic, rather than changing, oxygen tensions. We conclude our review with yet another addition to the growing list of HIF's many functions: the control of cellular growth during fly development.

Animals↗
PubMed2006

A candidate juvenoid hormone receptor cis-element in the Daphnia magna hb2 hemoglobin gene promoter.

Hemoglobin levels are significantly elevated in the crustacean Daphnia magna by juvenoid hormones. The present study was undertaken to identify the specific globin (hb) genes that are induced by juvenoids and to identify putative juvenoid response elements (JREs) that may mediate this induction. Gene product of globin 2 (hb2), but not globin 1 and globin 3, was robustly elevated following juvenoid treatment of daphnids. A candidate JRE, located in the promoter of hb2, bound activated factor(s) in response to juvenoid treatment of daphnids. This hormone-induced protein:JRE interaction was robust when daphnids were reared at high oxygen tension but was inhibited when daphnids were reared under low pO2, implying that hypoxia might act to disrupt juvenoid-mediated endocrine signaling. The candidate JRE consists of a steroid/retinoid-response element-like core adjacent to a 5' AT-rich extension and thus bears resemblance to response elements that bind monomeric nuclear receptors. The induction of hb2 mRNA levels by juvenoid treatment occurred rapidly (within 4 h of exposure) and was not attenuated by treatment of daphnids with cycloheximide. In contrast, cycloheximide treatment did block hormone-mediated elevations in hemoglobin protein levels. Thus, induction of hb2 by juvenoids was not dependent upon the synthesis of secondary transcription factors that bound the JRE but was likely due to activation of the gene directly by the juvenoid-receptor complex. Affinity pull-down experiments with nuclear proteins extracted from juvenoid-treated daphnids using the JRE as bait yielded a 52kDa candidate for a monomeric nuclear receptor in D. magna that may mediate the regulatory activity of juvenoids.

Animals↗
PubMed2005

Stress signaling: coregulation of hemoglobin and male sex determination through a terpenoid signaling pathway in a crustacean.

Environmental signals can activate neuro-endocrine cascades that regulate various physiological processes. In the present study, we demonstrate that two responses to environmental stress signaling in the crustacean Daphnia magna--hemoglobin accumulation and male offspring production--are co-elevated by the crustacean terpenoid hormone methyl farnesoate and several synthetic analogs. Potency of the hormones with respect to the induction of both hemoglobin and male offspring was highly correlated, suggesting that both processes are regulated by the same terpenoid signaling pathway. Six clones of the D. pulex/pulicaria species complex that were previously characterized as unable to produce male offspring and five clones that were capable of producing males were evaluated for both hemoglobin induction and male offspring production in response to methyl farnesoate. Four of the five male-producing clones produced both hemoglobin and male offspring in response to the hormone. Five of the six non-male-producing clones produced neither hemoglobin nor males in response to the hormone. These results provide additional evidence that both physiological processes are regulated by the same signaling pathway. Furthermore, the results indicate that the non-male-producing clones are largely defective in some methyl farnesoate signaling component, downstream from methyl farnesoate synthesis but upstream from the genes regulated by the hormone. A likely candidate for the site of the defect is the methyl farnesoate receptor. As a consequence of this defect, non-male-producing clones have lost their responsiveness to environmental signals that are transduced by this endocrine pathway. This defect in signaling would be likely to enhance population growth in stable environments due to the elimination of males from the population, assuming that other processes critical to population growth are not also compromised by this defect.

Analysis of Variance↗
PubMed2004

Hypoxia-induced synthesis of hemoglobin in the crustacean Daphnia magna is hypoxia-inducible factor-dependent.

Of the four known globin genes that exist in the fresh-water crustacean Daphnia magna, several are individually induced by hypoxia, lending pale normoxic animals a visible red color when challenged by oxygen deprivation. The promoter regions of the Daphnia globin genes each contain numerous hypoxia response elements (HREs) as potential binding sites for hypoxia-inducible factors (HIFs). Daphnia HIF, bound to human HRE sequences, was detected in extracts from hypoxic (red), but not normoxic (pale), animals. Taking advantage of the phylogenetically conserved HIF/HRE recognition, we employed heterologous transfections of HIF-expressing human and Drosophila cells to model HIF signaling in Daphnia. These experiments revealed that three functional HREs within the promoter of the D. magna globin-2 gene cooperate for maximal hypoxic induction of a downstream luciferase reporter gene. Two of these three cis-elements, at promoter positions -258 and -107, are able to specifically bind human, Drosophila, or Daphnia HIF complexes in vitro. The same two sites are also necessary for maximal induction of reporter transcription under low oxygen tension in the presence of either endogenous human or overexpressed Drosophila HIF proteins. The third motif of the globin-2 gene promoter, a CACGTG palindrome at position -146, functions as a docking site for an unknown constitutive transcription factor. In human cells, this -146 complex interferes with HIF occupancy at the adjacent -107 HRE and thus controls the extent of HIF-mediated hypoxic activation of the downstream target.

Animals↗
PubMed2004

Regulation of Drosophila hypoxia-inducible factor (HIF) activity in SL2 cells: identification of a hypoxia-induced variant isoform of the HIFalpha homolog gene similar.

Although hypoxia-inducible factor-alpha (HIFalpha) subunit-specific hydroxylation and proteolytic breakdown explain the binary switch between the presence (hypoxia) and absence (normoxia) of HIFs, little is known of the mechanisms that fine-tune HIF activity under constant, rather than changing, oxygen tensions. Here, we report that the Drosophila HIFalpha homolog, the basic helix-loop-helix/PAS protein Sima (Similar), in hypoxic cultures of SL2 cells is expressed in full-length (fl) and splice variant (sv) isoforms. The following evidence supports the role of flSima as functional HIFalpha and the role of SL2 HIF as a transcriptional activator or suppressor. The pO(2) dependence of Sima abundance matched that of HIF activity. HIF-dependent changes in candidate target gene expression were detected through variously effective stimuli: hypoxia (strong) > iron chelation, e.g. desferrioxamine (moderate) >> transition metals, e.g. cobalt approximately normoxia (ineffective). Sima overexpression augmented hypoxic induction or suppression of different targets. In addition to the full-length exon 1-12 transcript yielding the 1510-amino acid HIFalpha homolog, the sima gene also expressed, specifically under hypoxia, an exon 1-7/12 splice variant, which translated into a 426-amino acid Sima truncation termed svSima. svSima contains basic helix-loop-helix and PAS sequences identical to those of flSima, but, because of deletion of exons 8-11, lacks the oxygen-dependent degradation domain and nuclear localization signals. Overexpressed svSima failed to transactivate reporter genes. However, it attenuated HIF (Sima.Tango)-stimulated reporter expression in a dose-dependent manner. Thus, svSima has the potential to regulate Drosophila HIF function under steady and hypoxic pO(2) by creating a cytosolic sink for the Sima partner protein Tango.

Amino Acid Sequence↗