Membrane-anchored prolyl hydroxylase with an export signal from the endoplasmic reticulum

We cloned a novel prolyl 4-hydroxylase (PH; EC 1.14.11.2) homolog cDNA from tobacco (Nicotiana tabacum) BY-2 cells based on expression sequence tag information. Like other PHs, this tobacco PH polypeptide has two conserved histidine residues, and it comprises 286 amino acids with a calculated molecular mass of 32 kDa. Interestingly, this protein and homologs in Arabidopsis and rice have predicted transmembrane sequences in their N-terminal regions. This PH homolog was expressed in BY-2 cells as a His-tagged protein, and the expressed protein showed PH activity. Incubation of membranes with high salt, urea, and protease with or without detergents indicated that this protein is an integral membrane protein with a type II configuration. Its membrane-anchored nature is specific for plants because no integral membrane PH has been found in animals. A membrane fractionation study and immunocytochemical studies indicate that this protein localizes in both the endoplasmic reticulum (ER) and Golgi apparatus. Analysis of this protein fused to green fluorescent protein indicated that basic amino acids in the cytoplasmic, N-terminal region of the PH play a role in its export from the ER.     

Activation of prolyl hydroxylase‐2 for stabilization of mitochondrial stress along with simultaneous downregulation of HIF‐1α/FASN in ER + breast cancer subtype

The present study was undertaken to inquest the chemical activation of prolyl hydroxylase‐2 for the curtailment of hypoxia‐inducible factor‐1α and fatty acid synthase. It was well documented that hypoxia‐inducible factor‐1α and fatty acid synthase were overexpressed in mammary gland carcinomas. After screening a battery of compounds, BBAP‐2 was retrieved as a potential prolyl hydroxylase‐2 activator and validates its activity using ER + MCF‐7 cell line and n‐methyl‐n‐nitrosourea‐induced rat in vivo model, respectively. BBAP‐2 was palpable for the morphological characteristics of apoptosis along with changes in the mitochondrial intergrity as visualized by acridine orange/ethidium bromide and JC‐1 staining against ER + MCF‐7 cells. BBAP‐2 also arrest the cell cycle of ER + MCF‐7 cells at G2/M phase. Afterward, BBAP‐2 has scrutinized against n‐methyl‐n‐nitrosourea‐induced mammary gland carcinoma in albino Wistar rats. BBAP‐2 restored the morphological architecture when screened through carmine staining, haematoxylin and eosin staining, and scanning electron microscopy. BBAP‐2 also delineated the markers of oxidative stress favourably. The immunoblotting and mRNA expression analysis validated that BBAP‐2 has a potentialty activate the prolyl hydroxylase‐2 with sequential downregulating effect on hypoxia‐inducible factor‐1α and its downstream checkpoint. BBAP‐2 also fostered apoptosis through mitochondrial‐mediated death pathway. The present study elaborates the chemical activation of prolyl hydroxylase‐2 by which the increased expression of HIF‐1α and FASN can be reduced in mammary gland carcinoma.     

E6AP ubiquitin ligase mediates ubiquitin‐dependent degradation of peroxiredoxin 1

E6‐associated protein (E6AP) is a cellular ubiquitin protein ligase that mediates ubiquitylation and degradation of tumor suppressor p53 in conjunction with the high‐risk human papillomavirus E6 protein. We previously reported that E6AP targets annexin A1 protein for ubiquitin‐dependent proteasomal degradation. To gain a better understanding of the physiological function of E6AP, we have been seeking to identify novel substrates of E6AP. Here, we identified peroxiredoxin 1 (Prx1) as a novel E6AP‐binding protein using a tandem affinity purification procedure coupled with mass spectrometry. Prx1 is a 25‐kDa member of the Prx family, a ubiquitous family of antioxidant peroxidases that regulate many cellular processes through intracellular oxidative signal transduction pathways. Immunoprecipitation analysis showed that E6AP binds Prx1 in vivo. Pull‐down experiments showed that E6AP binds Prx1 in vitro. Ectopic expression of E6AP enhanced the degradation of Prx1 in vivo. In vivo and in vitro ubiquitylation assays revealed that E6AP promoted polyubiquitylation of Prx1. RNAi‐mediated downregulation of endogenous E6AP increased the level of endogenous Prx1 protein. Taken together, our data suggest that E6AP mediates the ubiquitin‐dependent proteasomal degradation of Prx1. Our findings raise a possibility that E6AP may play a role in regulating Prx1‐dependent intracellular oxidative signal transduction pathways. J. Cell. Biochem. 111: 676–685, 2010. © 2010 Wiley‐Liss, Inc.     

Trametinib potentiates TRAIL‐induced apoptosis via FBW7‐dependent Mcl‐1 degradation in colorectal cancer cells

Trametinib is a MEK1/2 inhibitor and exerts anticancer activity against a variety of cancers. However, the effect of Trametinib on colorectal cancer (CRC) is not well understood. In the current study, our results demonstrate the ability of sub‐toxic doses of Trametinib to enhance TRAIL‐mediated apoptosis in CRC cells. Our findings also indicate that Trametinib and TRAIL activate caspase‐dependent apoptosis in CRC cells. Moreover, Mcl‐1 overexpression can reduce apoptosis in CRC cells treated with Trametinib with or without TRAIL. We further demonstrate that Trametinib degrades Mcl‐1 through the proteasome pathway. In addition, GSK‐3β phosphorylates Mcl‐1 at S159 and promotes Mcl‐1 degradation. The E3 ligase FBW7, known to polyubiquitinate Mcl‐1, is involved in Trametinib‐induced Mcl‐1 degradation. Taken together, these results provide the first evidence that Trametinib enhances TRAIL‐mediated apoptosis through FBW7‐dependent Mcl‐1 ubiquitination and degradation.     

Force‐ and kinesin‐8‐dependent effects in the spatial regulation of fission yeast microtubule dynamics

Microtubules (MTs) are central to the organisation of the eukaryotic intracellular space and are involved in the control of cell morphology. For these purposes, MT polymerisation dynamics are tightly regulated. Using automated image analysis software, we investigate the spatial dependence of MT dynamics in interphase fission yeast cells with unprecedented statistical accuracy. We find that MT catastrophe frequencies (switches from polymerisation to depolymerisation) strongly depend on intracellular position. We provide evidence that compressive forces generated by MTs growing against the cell pole locally reduce MT growth velocities and enhance catastrophe frequencies. Furthermore, we find evidence for an MT length‐dependent increase in the catastrophe frequency that is mediated by kinesin‐8 proteins (Klp5/6). Given the intrinsic susceptibility of MT dynamics to compressive forces and the widespread importance of kinesin‐8 proteins, we propose that similar spatial regulation of MT dynamics plays a role in other cell types as well. In addition, our systematic and quantitative data should provide valuable input for (mathematical) models of MT organisation in living cells.     

Differential and Reciprocal Regulation between Hypoxia-inducible Factor-α Subunits and Their Prolyl Hydroxylases in Pulmonary Arteries of Rat with Hypoxia-induced Hypertension

Hypoxia-inducible factor (HIF)-α subunits (HIF-1α,HIF-2α and HIF-3α),which play a pivotalrole during the development of hypoxia-induced pulmonary hypertension (HPH),are regulated through post-U'anslational hydroxylation by their three prolyl hydroxylase domain-containing proteins (PHD 1,PHD2 and PHD3).PHDs could also be regulated by HIF.But differential and reciprocal regulation between HIF-α and PHDs duringthe development of HPH remains unclear.To investigate this problem,a rat HPH model was established.Meanpulmonary arterial pressure increased significantly after 7 d of hypoxia.Pulmonary artery remodeling indexand right ventricular hypertrophy became evident after 14 d of hypoxia.HIF-1α and HIF-2α mRNA increasedslightly after 7 d of hypoxia,but HIF-3α increased significantly after 3 d of hypoxia.The protein expressionlevels of all three HIF-α were markedly upregulated after exposure to hypoxia.PHD2 mRNA and proteinexpression levels were upregulated after 3 d of hypoxia;PHD 1 protein declined after 14 d of hypoxia withoutsignificant mRNA changes.PHD3 mRNA and protein were markedly upregulated after 3 d of hypoxia,then themRNA remained at a high level,but the protein declined after 14 d of hypoxia.In hypoxic animals,HIF-lotproteins negatively correlated with PHD2 proteins,whereas HIF-2α and HIF-3α proteins showed negativecorrelations with PHD3 and PHD 1 proteins,respectively.All three HIF-α proteins were positively correlatedwith PHD2 and PHD3 mRNA.In the present study,HIF-α subunits and PHDs showed differential andreciprocal regulation,and this might play a key pathogenesis role in hypoxia-induced pulmonary hypertension.     

Evolution and diversity of the 2–oxoglutarate‐dependent dioxygenase superfamily in plants

The 2–oxoglutarate‐dependent dioxygenase (2OGD) superfamily is the second largest enzyme family in the plant genome, and its members are involved in various oxygenation/hydroxylation reactions. Despite their biochemical significance in metabolism, a systematic analysis of plant 2OGDs remains to be accomplished. We present a phylogenetic classification of 479 2OGDs in six plant models, ranging from green algae to angiosperms. These were classified into three classes – DOXA, DOXB and DOXC – based on amino acid sequence similarity. The DOXA class includes plant homologs of Escherichia coli AlkB, which is a prototype of 2OGD involved in the oxidative demethylation of alkylated nucleic acids and histones. The DOXB class is conserved across all plant taxa and is involved in proline 4–hydroxylation in cell wall protein synthesis. The DOXC class is involved in specialized metabolism of various phytochemicals, including phytohormones and flavonoids. The vast majority of 2OGDs from land plants were classified into the DOXC class, but only seven from Chlamydomonas, suggesting that this class has diversified during land plant evolution. Phylogenetic analysis assigned DOXC‐class 2OGDs to 57 phylogenetic clades. 2OGD genes involved in gibberellin biosynthesis were conserved among vascular plants, and those involved in flavonoid and ethylene biosynthesis were shared among seed plants. Several angiosperm‐specific clades were found to be involved in various lineage‐specific specialized metabolisms, but 31 of the 57 DOXC‐class clades were only found in a single species. Therefore, the evolution and diversification of DOXC‐class 2OGDs is partly responsible for the diversity and complexity of specialized metabolites in land plants.     

Deficiency of sterol regulatory element‐binding protein‐1c induces schizophrenia‐like behavior in mice

Schizophrenia is a hereditary disease that approximately 1% of the worldwide population develops. Many studies have investigated possible underlying genes related to schizophrenia. Recently, clinical studies suggested sterol regulatory element‐binding protein (SREBP) as a susceptibility gene in patients with schizophrenia. SREBP controls cellular lipid homeostasis by three isoforms: SREBP‐1a, SREBP‐1c and SREBP‐2. This study used SREBP‐1c knockout (KO) mice to examine whether a deficiency in SREBP‐1c would affect their emotional and psychiatric behaviors. Altered mRNA expression in genes downstream from SREBP‐1c was confirmed in the brains of SREBP‐1c KO mice. Schizophrenia‐like behavior, including hyperactivity during the dark phase, depressive‐like behavior, aggressive behavior and deficits in social interaction and prepulse inhibition, was observed in SREBP‐1c KO mice. Furthermore, increased volume of the lateral ventricle was detected in SREBP‐1c KO mice. The mRNA levels of several γ‐aminobutyric acid (GABA)‐receptor subtypes and/or glutamic acid decarboxylase 65/67 decreased in the hippocampus and medial prefrontal cortex of SREBP‐1c KO mice. Thus, SREBP‐1c deficiency may contribute to enlargement of the lateral ventricle and development of schizophrenia‐like behaviors and be associated with altered GABAergic transmission.     

Penicillin‐binding protein folding is dependent on the PrsA peptidyl‐prolyl cis‐trans isomerase in Bacillus subtilis

The PrsA protein is a membrane‐anchored peptidyl‐prolyl cis‐trans isomerase in Bacillus subtilis and most other Gram‐positive bacteria. It catalyses the post‐translocational folding of exported proteins and is essential for normal growth of B. subtilis. We studied the mechanism behind this indispensability. We could construct a viable prsA null mutant in the presence of a high concentration of magnesium. Various changes in cell morphology in the absence of PrsA suggested that PrsA is involved in the biosynthesis of the cylindrical lateral wall. Consistently, four penicillin‐binding proteins (PBP2a, PBP2b, PBP3 and PBP4) were unstable in the absence of PrsA, while muropeptide analysis revealed a 2% decrease in the peptidoglycan cross‐linkage index. Misfolded PBP2a was detected in PrsA‐depleted cells, indicating that PrsA is required for the folding of this PBP either directly or indirectly. Furthermore, strongly increased uniform staining of cell wall with a fluorescent vancomycin was observed in the absence of PrsA. We also demonstrated that PrsA is a dimeric or oligomeric protein which is localized at distinct spots organized in a helical pattern along the cell membrane. These results suggest that PrsA is essential for normal growth most probably as PBP folding is dependent on this PPIase.     

Bulk RNA degradation by nitrogen starvation‐induced autophagy in yeast

Autophagy is a catabolic process conserved among eukaryotes. Under nutrient starvation, a portion of the cytoplasm is non‐selectively sequestered into autophagosomes. Consequently, ribosomes are delivered to the vacuole/lysosome for destruction, but the precise mechanism of autophagic RNA degradation and its physiological implications for cellular metabolism remain unknown. We characterized autophagy‐dependent RNA catabolism using a combination of metabolome and molecular biological analyses in yeast. RNA delivered to the vacuole was processed by Rny1, a T2‐type ribonuclease, generating 3′‐NMPs that were immediately converted to nucleosides by the vacuolar non‐specific phosphatase Pho8. In the cytoplasm, these nucleosides were broken down by the nucleosidases Pnp1 and Urh1. Most of the resultant bases were not re‐assimilated, but excreted from the cell. Bulk non‐selective autophagy causes drastic perturbation of metabolism, which must be minimized to maintain intracellular homeostasis.     

N-(2-mercaptopropionyl)-glycine,a diffusible antioxidant,activates HIF-1 by inhibiting HIF prolyl hydroxylase-2: Implication in amelioration of rat colitis by the antioxidant

We investigated anti-colitic effects of N-(2-mercaptopropionyl)-glycine (NMPG), a diffusible antioxidant, in TNBS-induced rat colitis model and a potential molecular mechanism underlying the pharmacologic effect of the antioxidant. NMPG alleviated colonic injury and effectively lowered myeloperoxidase activity. Moreover, NMPG substantially attenuated expression of pro-inflammatory mediators in the inflamed colon. NMPG induced hypoxia-inducible factor-1α (HIF-1α) in human colon carcinoma cells, leading to elevated secretion of vascular endothelial growth factor (VEGF), a target gene product of HIF-1 involved in ulcer healing of gastrointestinal mucosa. NMPG induction of HIF-1α occurred by inhibiting HIF prolyl hydroxylase-2 (HPH-2), an enzyme that plays a major role in negatively regulating HIF-1α protein stability. In in vitro Von Hippel-Lindau protein binding assay, the inhibitory effect of NMPG on HPH-2 was attenuated by escalating dose of ascorbate but not 2-ketoglutarate, cofactors of the enzyme. Consistent with this, cell-permeable ascorbate significantly attenuated NMPG induction of HIF-1α in cells. Our data suggest that NMPG is an anti-colitic antioxidant that exerts its pharmacologic effects at least partly through activation of an ulcer healing pathway, HIF-1-VEGF.