The PAS-domain kinase PASKIN: a new sensor in energy homeostasis

The PAS domain kinase PASKIN, also termed PAS kinase or PASK, is an evolutionarily conserved potential sensor kinase related to the heme-based oxygen sensors of nitrogen-fixing bacteria. In yeast, the two PASKIN homologs link energy flux and protein synthesis following specific stress conditions. In mammals, PASKIN may regulate glycogen synthesis and protein translation. Paskin knock-out mice do not show any phenotype under standard animal husbandry conditions. Interestingly, these mice seem to be protected from the symptoms of the metabolic syndrome when fed a high-fat diet. Energy turnover might be increased in specific PASKIN-deficient cell types under distinct environmental conditions. According to the current model, binding of a putative ligand to the PAS domain disinhibits the kinase domain and activates PASKIN auto- and target phosphorylation. Future research needs to be conducted to elucidate the nature of the putative ligand and the molecular mechanisms of downstream signalling by PASKIN.

Surgical management of retraction pockets of the pars tensa with cartilage and perichondrial grafts

Stable, self-cleansing retraction pockets of the pars tensa are common incidental findings and require no treatment. In other cases, recurrent discharge occurs and there may also be associated conductive hearing loss. In a minority of cases, cholesteatoma may develop.

This paper presents the results of surgery using a graft composed of cartilage and perichondrium for retraction pockets involving the posterior half of the tympanic membrane, as well as early results using a larger graft designed to manage retraction of the entire tympanic membrane. Data on 51 patients with posterior retraction pockets are presented. Forty-two (82 per cent) patients had no aural discharge one year following surgery and the tympanic membrane was not retracted in 43 (84 per cent). The larger ‘Mercedes-Benz’ graft was used in four patients and the results obtained suggested that it may prove a successful technique for extensive retraction pockets.

Oxygen-regulated expression of TGF-beta 3, a growth factor involved in trophoblast differentiation

The transforming growth factor-beta 3 (TGF-beta 3) is involved in oxygen-dependent differentiation processes during placental development and pregnancy disorders. However, the importance of oxygen partial pressure for the regulation of TGF-beta 3 expression is presently unclear. We and others presented preliminary evidence that the hypoxia-inducible factor-1 (HIF-1) confers TGF-beta 3 transcription but it was unknown whether this occurred directly or indirectly. To analyze how HIF-1 regulates TGF-beta 3 gene transcription, we cloned and sequenced the mouse TGF-beta 3 promoter region. Multiple putative HIF-1 binding sites (HBSs) were identified, many of which co-localized with two G+C rich CpG islands 5' to the TGF-beta 3 transcription start site. A 6.8 kb fragment of the TGF-beta 3 promoter induced reporter gene expression under hypoxic conditions or when treated with an iron chelator known to stabilize and activate the HIF-1 alpha subunit. Deletion of a 2.4 kb fragment upstream of the distal CpG island abolished inducibility of reporter gene expression. Two HBSs (HBS1 and HBS6) that bound the HIF-1 protein could be identified within this 2.4 kb fragment. These results suggest that TGF-beta 3 gene expression is directly regulated by HIF-1.

Mammalian PASKIN, a PAS-serine/threonine kinase related to bacterial oxygen sensors

The PAS domain is a versatile protein fold found in many archaeal, bacterial, and plant proteins capable of sensing environmental changes in light intensity, oxygen concentration, and redox potentials. The oxygen sensor FixL from Rhizobium species contains a heme-bearing PAS domain and a histidine kinase domain that couples sensing to signaling. We identified a novel mammalian PAS protein (PASKIN) containing a domain architecture resembling FixL. PASKIN is encoded by an evolutionarily conserved single-copy gene which is ubiquitously expressed. The human PASKIN and mouse Paskin genes show a conserved intron-exon structure and share their promoter regions with another ubiquitously expressed gene that encodes a regulator of protein phosphatase-1. The 144-kDa PASKIN protein contains a PAS region homologous to the FixL PAS domain and a serine/threonine kinase domain which might be involved in signaling. Thus, PASKIN is likely to function as a mammalian PAS sensor protein.

Dominant suppressor mutation bypasses the sphingolipid requirement for growth of Saccharomyces cells at low pH: role of the CWP2 gene

Strains of Saccharomyces cerevisiae termed sphingolipid compensatory (SLC) do not grow at low pH when the cells lack sphingolipids. To begin to understand why sphingolipids are required for growth at low pH, we isolated derivatives of SLC strains, termed low pH resistant (LprR), carrying the LPR suppressor gene that allows growth at pH 4.1 when cells lack sphingolipids. Suppression is due to mutation of a single nuclear gene. The LPR suppressor gene functions, at least in part, by enhancing the ability of cells lacking sphingolipids to generate a net efflux of protons in suspension fluid with a pH range of 4.0-6.0. The LPR suppressor gene also enables cells lacking sphingolipids to maintain their intracellular pH near neutrality when the pH of the suspension fluid is low, unlike cells lacking the suppressor gene, which cannot maintain their intracellular pH in the face of a low external pH. These results demonstrate that some functions(s) of sphingolipids necessary for growth at low pH can be bypassed by a suppressor mutation. Attempts to clone the LPR suppressor gene were not successful, but they led to the isolation of the CWP2 gene, which encodes a major mannoprotein component of the outer cell wall. It was isolated because an increased copy number has the unusual property of increasing the frequency at which LprR strains arise. As we show here, part of the reason for this effect is that the CWP2 gene is essential for generating a net efflux of protons and for controlling intracellular pH in LprR strains that lack sphingolipids. These results suggest new cellular functions for the Cwp2 protein.

Epolones induce erythropoietin expression via hypoxia-inducible factor-1 alpha activation

Induction of erythropoietin (Epo) expression under hypoxic conditions is mediated by the heterodimeric hypoxia-inducible factor (HIF)-1. Following binding to the 3' hypoxia-response element (HRE) of the Epo gene, HIF-1 markedly enhances Epo transcription. To facilitate the search for HIF-1 (ant)agonists, a hypoxia-reporter cell line (termed HRCHO5) was constructed containing a stably integrated luciferase gene under the control of triplicated heterologous HREs. Among various agents tested, we identified a class of substances called epolones, which induced HRE-dependent reporter gene activity in HRCHO5 cells. Epolones are fungal products known to induce Epo expression in hepatoma cells. We found that epolones (optimal concentration 4-8 micromol/L) potently induce HIF-1 alpha protein accumulation and nuclear translocation as well as HIF-1 DNA binding and reporter gene transactivation. Interestingly, the activity of a compound related to the fungal epolones, ciclopirox olamine (CPX), was blocked after addition of ferrous iron. This suggests that CPX might interfere with the putative heme oxygen sensor, as has been proposed for the iron chelator deferoxamine mesylate (DFX). However, about 10-fold higher concentrations of DFX (50-100 micromol/L) than CPX were required to maximally induce reporter gene activity in HRCHO5 cells. Moreover, structural, functional, and spectrophotometric data imply a chelator:iron stoichiometry of 1:1 for DFX but 3:1 for CPX. Because the iron concentration in the cell culture medium was determined to be 16 micromol/L, DFX but not CPX function can be explained by complete chelation of medium iron. These results suggest that the lipophilic epolones might induce HIF-1 alpha by intracellular iron chelation. (Blood. 2000;96:1558-1565)

General applicability of chicken egg yolk antibodies: the performance of IgY immunoglobulins raised against the hypoxia-inducible factor 1alpha

Avian embryos and neonates acquire passive immunity by transferring maternal immunoglobulins from serum to egg yolk. Despite being a convenient source of antibodies, egg yolk immunoglobulins (IgY) from immunized hens have so far received scant attention in research. Here we report the generation and rapid isolation of IgY from the egg yolk of hens immunized against the alpha subunit of the human hypoxia-inducible factor 1 (HIF-1alpha). Anti-HIF-1alpha IgY antibodies were affinity purified and tested for their performance in various applications. Abundant HIF-1alpha protein was detected by Western blot analysis in nuclear extracts derived from hypoxic cells of human, mouse, monkey, swine, and dog origin whereas in hypoxic quail and frog cells, the HIF-1alpha signal was weak or absent, respectively. In electrophoretic mobility shift assays, affinity-purified IgY antibody was shown to recognize the native HIF-1 (but not the related HIF-2) complex that specifically binds an oligonucleotide containing the HIF-1 DNA binding site. Furthermore, IgY antibody immunoprecipitated HIF-1alpha from hypoxic cell extracts. Immunofluorescence experiments using IgY antibody allowed the detection of HIF-1alpha in the nucleus of hypoxic COS-7 cells. For comparison, the application of a mouse monoclonal antibody raised against the identical HIF-1alpha fragment was more restricted. Because chicken housing is inexpensive, egg collection is noninvasive, isolation and affinity purification of IgY antibodies are fast and simple, and the applicability of IgY is widespread, immunization of hens represents an excellent alternative for the generation of polyclonal antibodies.

Mouse hypoxia-inducible factor-1alpha is encoded by two different mRNA isoforms: expression from a tissue-specific and a housekeeping-type promoter

Hypoxic induction of erythropoietin (Epo) and other oxygen-dependent genes is mediated by the hypoxia-inducible factor-1 (HIF-1), a heterodimeric transactivator consisting of an alpha and a beta subunit. We previously found that the mouse gene encoding HIF-1alpha harbors two alternative first exons (I.1 and I.2), giving rise to two different HIF-1alpha mRNA isoforms. Here, we show by RNase protection analysis that the exon I.1-derived mRNA isoform is differentially expressed in mouse tissues, being highest in kidney, tongue, stomach, and testis, but undetectable in liver, whereas the exon I.2 mRNA isoform is ubiquitously expressed. Sequence and methylation analysis showed that, in contrast to exon I.1, exon I.2 resides within a region showing typical features of a CpG island, known to be associated with the 5' end of housekeeping genes. We identified a 232-bp minimal exon I.2 promoter that strongly induced reporter gene expression in mouse L929 fibroblasts and Hepa1 hepatoma cells. In contrast to L929 cells, the exon I.1 promoter was inactive in Hepa1 cells and hypoxic exposure (1% O2) markedly reduced exon I.2 promoter activity in Hepa1 cells. Prolonged exposure of mice to hypoxia (7.5% O2 for up to 72 hours) also caused a decrease in liver HIF-1alpha mRNA, whereas aldolase mRNA levels increased. These findings might be related to the relatively low Epo levels in the adult liver.

The mouse gene for hypoxia-inducible factor-1alpha--genomic organization, expression and characterization of an alternative first exon and 5' flanking sequence

The ubiquitously expressed hypoxia-inducible factor-1 (HIF-1) is involved in expression of a large number of oxygen-regulated genes. HIF-1 is a heterodimer consisting of an alpha and a beta subunit, both belonging to the basic-helix-loop-helix Per-aryl hydrocarbon receptor nuclear translocator-Sim (PAS) family of transcription factors. Whereas HIF-1alpha is a novel member of this family, HIF-1beta is identical to the aryl hydrocarbon receptor nuclear translocator, previously recognized to be involved in xenobiotic metabolism. cDNA cloning revealed that mouse HIF-1alpha can be expressed as two mRNA isoforms containing alternative 5' untranslated regions and two different predicted translational start sites. We cloned and characterized 20.5 kb of the mouse HIF-1alpha gene (Hif1a) containing exon II-XV. The two alternative first exons, I.1 and I.2, are separated from exon II by approximately 24 kb and 17 kb, respectively. We also sequenced Hif1a exon I.1 and flanking regions, and mapped a single exon I.1 transcription initiation site. Reverse transcription PCR analysis of total RNA derived from normoxic and hypoxic mouse hepatoma and fibroblast cell lines suggested that the two alternative mRNA isoforms are constitutively coexpressed in these cells, and that two different promoters drive transcription of HIF-1alpha. A minimal exon I.1 promoter was identified which moderately activated heterologous gene expression, indicating that additional cis-elements are required for efficient HIF-1alpha transcription in vivo.

Molecular genetics of aristaless, a prd-type homeo box gene involved in the morphogenesis of proximal and distal pattern elements in a subset of appendages in Drosophila

Viable aristaless (al) mutations of Drosophila affect pattern elements at both ends of the proximodistal axis in a subset of adult appendages. The al gene has been cloned and identified by P-element-mediated germ-line transformation with a genomic DNA fragment, which rescues a lethal mutation of al as well as aspects of the adult al phenotype. The al gene contains a prd-type homeo domain and a Pro/Gln-rich domain and, hence, probably encodes a transcription factor. Its transcript distribution in third-instar imaginal discs closely corresponds to the anlagen of the tissues that later become visibly affected in adult al mutants. The striking similarity of a bimodal al expression in different imaginal discs indicates that al is under the control of a "prepattern," which is shared at least among antennal, leg, and wing discs. The al gene is also transcribed during embryogenesis. Apart from a function in the ontogeny of specific larval head and tail organs, its embryonic transcript pattern suggests a possible role in early imaginal disc development.

The paired box gene pox neuro: A determiant of poly-innervated sense organs in Drosophila

This study describes the structure and function of pox neuro (poxn), a gene previously isolated by virtue of a conserved domain, the paired box, which it shares with the segmentation genes paired and gooseberry. Its expression pattern has been analyzed, particularly during development of the PNS. We propose that poxn is a "neuroblast identity" gene acting in both the PNS and the CNS on the basis of the following evidence. Its expression is restricted to four neuronal precursors in each hemisegment: two neuronal stem cells (neuroblasts) in the CNS, and two sensory mother cells (SMCs) in the PNS. The SMCs that express poxn produce the poly-innervated external sense organs of the larva. In poxn- embryos, poly-innervated sense organs are transformed into mono-innervated. Conversely, ectopic expression of poxn in embryos transformed with a heat-inducible poxn gene can switch mono-innervated to poly-innervated sense organs. Expression of poxn in the wing disc is restricted to the SMCs of the poly-innervated sense organs, suggesting that poxn also determines the lineage of poly-innervated adult sense organs.

Removal of psoralen monoadducts and crosslinks by human cell free extracts

Human cell free extracts are capable of carrying out damage-induced DNA synthesis in response to DNA damage by UV, psoralen, and cisplatin. We show that this damage-induced DNA synthesis is associated with removal of psoralen adducts and therefore is 'repair synthesis' and not an aberrant DNA synthesis reaction potentiated by DNA deformed by adducts. By comparing the denaturable fraction of psoralen adducted DNA which becomes labeled in the repair reaction to that of terminally labeled DNA (without repair) we have found that all DNA synthesis induced by psoralen monoadducts is the consequence of removal of these adducts. By the same approach we have obtained preliminary evidence that this in vitro system is capable of removing psoralen crosslinks as well.

[Preliminary results concerning the value of chemotherapy in the treatment of inoperable bronchial carcinoma (excluding small-cell anaplastic carcinoma)]

Inoperable non- microcellular primary bronchial carcinomas have been reputed up to now to be chemo-resistant. The introduction of Cis-platinum into a polychemotherapy protocol leads to revision of this concept. The authors report the preliminary results of a polychemotherapy protocol (including Cis-platinum, Vindesine, CCNU, Cyclophosphamide) associated, in cases of non- metastasized carcinomas, with radiotherapy to the tumour itself, the mediastinum and the supraclavicular fossae. These results confirmed the value of such chemotherapy in forms with metastases. In localised inoperable forms, conclusions could be reached only on the basis of a randomised comparative trial of chemotherapy + radiotherapy versus radiotherapy alone.