Hypoxic mitochondria: accomplices in resistance.

Mitochondria originated from a distant ancestor: the α-proteobacteria. They evolved over millions of years in a symbiotic relationship in eukaryotic cells by favoring consumption of oxygen by the electron transport chain with production of ATP. Contemporary mitochondria still play a crucial role in providing energy but also in apoptosis. Because of this symbiotic relationship and their pivotal function, mitochondria undoubtedly participate in tumorigenesis. Genetic defects in mitochondrial DNA, blockade of oxidative phosphorylation and mitophagy in tumor cells modify the production of damaging reactive oxygen species and restrain apoptosis. As the environment of tumor cells becomes more and more hypoxic, the hypoxia-inducible factor (HIF) is stabilized and participates in the reprogramming of cell metabolism. Recently, we became interested in asking whether HIF and hypoxia affect mitochondrial function. In this review, we show that hypoxia induces enlargement of mitochondria, due to abnormal fusion, which results in resistance to apoptosis and thus in survival. The role of hypoxia-induced BNIP3 and BNIP3L, proteins recently described as pro-survival proteins, in survival is also discussed.

Highlights of the European Association of Cancer Research (EACR 2008).

The European Association of Cancer Research held its 20th biannual meeting (EACR-20) in the French city of Lyon in July 2008. The EACR-20 gathered together researchers from basic, translational and clinical cancer research who exchanged and discussed recent advances in many areas of major interest. This meeting report aims to provide the readers of the Bulletin of cancer with a summary of the research highlights presented at the EACR-20.

Protein kinases and the hypoxia-inducible factor-1, two switches in angiogenesis.

In the last few decades it has become clear that detailed understanding of the mechanisms of angiogenesis, a process leading to growth of new blood vessels, should lead to improved treatment of diseases such as ischemic disorders and cancer where neovascularization is impaired or activated, respectively. In this review, we will outline some of our recent findings concerning the regulation of the vascular endothelial growth factor (VEGF), a key player in angiogenesis and one of its transcription factors, the hypoxia-inducible factor-1 (HIF-1) a master gene product driving adaptation to hypoxia. We will discuss the observation that growth factors and oncogenic transformation via the mitogen-activated protein kinases p42/p44 MAPKs not only activate the VEGF promoter through the Sp1/AP-2 transcriptional factor complex but also phosphorylate HIF-1alpha leading in turn to enhance HIF-1 dependent transcriptional activation of VEGF. The stress-activated protein kinases (SAPK) also contribute to angiogenesis by stabilizing VEGF mRNA. Finally, we will present recent advances into oxygen-sensing, in particular the HIF-hydroxylases that govern HIF-1alpha instability (PHD2) or inactivation (FIH-1). The revelation of these oxygen sensors has provided pharmacologists with new molecular targets for the development of novel therapies to control angiogenesis either positively or negatively.

Gene transfer by adenovirus-mimetic peptides in the presence of a cationic lipid and/or adenovirus. Analysis of the contribution of the viral and nonviral components.

Peptide and cationic lipid-based gene transfer vectors have shown promise for gene therapy but are still less efficient than viral gene transfer vectors. We have examined the mechanism of gene transfer of different adenovirus-mimetic peptides in the presence and absence of a cationic lipid, lipofectamine and/or adenovirus with the aim of improving the design of nonviral vectors for efficient gene transfer. Three polylysine-adenovirus-mimetic peptides were synthesised and examined for their efficacy for gene transfer. Transfection levels in four cell lines: adenovirus permissive human tracheal epithelial (56FHTE8o(-)), human lung carcinoma (A549), human colon carcinoma (Caco-2) cells, and adenovirus low-permissive Chinese hamster ovary (CHO) cells, were examined. The polylysine-adenovirus-mimetic peptides increased the level of transfection of a reporter transgene in all cell lines. Transfection was substantially increased when an adenovirus was added to cells after pre-incubation with the vector complexes. Formulation of the peptide vector complexes with lipofectamine increased their transfection efficacy and the subsequent addition of an adenovirus increased transfection levels even further but only in permissive cells. Pre-incubation of cells with lipofectamine-peptide vector complexes increased cell binding of the adenovirus but uptake was only increased in intermediate- or non-permissive cells. The addition of lipofectamine increased transgene expression of a recombinant adenovirus in non-permissive cells but not in permissive cells. Enhancement with an adenovirus of peptide vector gene transfer is probably due to more efficient endosome escape while enhancement of gene transfer by peptide vectors complexed to lipofectamine is due to an increase in cellular binding and/or internalisation of the adenovirus.

Characterisation of LMD virus-like nanoparticles self-assembled from cationic liposomes, adenovirus core peptide mu and plasmid DNA.

Liposome:mu:DNA (LMD) is a ternary nucleic acid delivery system built around the mu peptide associated with the condensed core complex of the adenovirus. LMD is prepared by precondensing plasmid DNA (D) with mu peptide (M) in a 1:0.6 (w/w) ratio and then combining these mu:DNA (MD) complexes with extruded cationic liposomes (L) resulting in a final lipid:mu:DNA ratio of 12:0.6:1 (w/w/w). Correct buffer conditions, reagent concentrations and rates of mixing are all crucial to success. However, once optimal conditions are established, homogeneous LMD particles (120 +/- 30 nm) will result that each appear to comprise an MD particle encapsulated within a cationic bilammellar liposome. LMD particles can be formulated reproducibly, they are amenable to long-term storage (>1 month) at -80 degrees C and are stable to aggregation at a plasmid DNA concentration up to 5 mg/ml (15 mM nucleotide concentration). Furthermore, LMD transfections are significantly more time and dose efficient in vitro than cationic liposome-plasmid DNA (LD) transfections. Transfection times as short as 10 min and plasmid DNA doses as low as 0.001 microg/well result in significant gene expression. LMD transfections will also take place in the presence of biological fluids (eg up to 100% serum) giving 15-25% the level of gene expression observed in the absence of serum. Results from confocal microscopy experiments using fluorescent-labelled LMD particles suggest that endocytosis is not a significant barrier to LMD transfection, although the nuclear membrane still is. We also confirm that topical lung transfection in vivo by LMD is at least equal in absolute terms with transfection mediated by GL-67:DOPE:DMPE-PEG(5000) (1:2:0.05 m/m/m), an accepted 'gold-standard' non-viral vector system for topical lung transfection, and is in fact at least six-fold more dose efficient. All these features make LMD an important new non-viral vector platform system from which to derive tailor-made non-viral delivery systems by a process of systematic modular upgrading.

Glycoconjugate metabolism in a cystic fibrosis knockout mouse model.

Cystic fibrosis knockout mice (cftr(-/-)) die prematurely of obstruction of the intestine which may result from accumulation of dehydrated glycoconjugate-containing mucus. We noted an increase in the specific activity of [(14)C]glucosamine-labeled high-molecular weight glycoconjugates, probably mucin, in the lumen of the intestine of cftr(-/-) (homozygous) mice compared to cftr(+/+) (wild-type) and cftr(+/-) (heterozygous) mice and a decrease in the turnover of glycoconjugates of several organs of the cftr(-/-) mice. No difference in the anionic composition of secreted intestinal glycoconjugates was detected and no difference in the amount of mucin 1 (Muc1) was found in the small intestine, colon, pancreas, and lungs of the different genotypes. In addition, the spleen of the cftr(-/-) mice was significantly smaller than that of control mice and the small intestine and colon were, respectively, longer and shorter compared to control mice. These results indicate modified glycoconjugate metabolism in cystic fibrosis knockout mice and morphologic changes to the spleen and intestine where the latter modifications are possibly related to the intestinal malabsorption associated with cystic fibrosis.

The nuclear pore complex is involved in nuclear transfer of plasmid DNA condensed with an oligolysine-RGD peptide containing nuclear localisation properties.

One of the major barriers to efficient gene transfer and expression of nonviral vectors for gene therapy is passage across the nuclear envelope. We have previously shown that an oligolysine-RGD peptide that condenses plasmid DNA and binds to cell surface integrins can mediate increased internalisation of plasmid DNA into cells and synergistic enhancement of gene expression when complexed to a cationic lipid. In this report, we show that this enhancement is due to increased nuclear transfer of the plasmid DNA. We have applied the digitonin-permeabilised cell system that has been well established for the study of the nuclear transport of proteins to examine the nuclear transfer of plasmid DNA. Nuclear transfer of plasmid DNA complexed to an oligolysine-RGD peptide and lipofectamine appears to be an energy-dependent process involving the nuclear pore complex, since it is inhibited at 4 degrees C and by treatment with wheat germ agglutinin or with an antibody to the nuclear pore complex which all block nuclear protein import. In accordance with active nuclear transport, we have shown that all these treatments inhibit expression of a luciferase reporter plasmid in permeabilised cells. Nuclear transfer of pDNA is enhanced in mitotic cells, but cell division is not a prerequisite for transfer. We propose that the oligolysine-RGD peptide acts as a nuclear localisation signal and that the cationic lipid is more important for cell entry and endosome destabilisation than nuclear transfer.

Haemoglobin interferes with the ex vivo luciferase luminescence assay: consequence for detection of luciferase reporter gene expression in vivo.

The luciferase reporter gene is a useful tool for determining the efficacy of transfection of plasmid DNA and adenovirus-mediated gene transfer in vivo. However, we report here that the haemoglobin present in tissue samples can mask the detection of the luciferase activity and lead to underestimation of the luciferase levels. We evaluated the degree of interference in different organ samples of mice and investigated the possibilities for removal of haemoglobin from tissue samples by: (1) perfusion of the whole animal; (2) different hypotonic treatments lysing preferentially red blood cells; and (3) chromatographic separation. Removal of haemoglobin resulted in significantly improved detection of luciferase activity from tissue samples. The results indicate that the luciferase activity determined in tissue samples may not reflect the actual level of reporter gene expression, if contaminating blood is not taken into consideration.

Cell delivery, intracellular trafficking and expression of an integrin-mediated gene transfer vector in tracheal epithelial cells.

The mechanism of cell entry and intracellular fate of a gene transfer vector composed of a receptor-targeting, DNA-condensing peptide, RGD-oligolysine, a luciferase encoding plasmid DNA (pDNA) and a cationic liposome was examined. We demonstrate by confocal microscopy, electron microscopy and subcellular fractionation that the major mechanism of entry of the vector is endocytic. The vector complex rapidly (5 min) internalizes into early endosomes, then late endosomes and lysosomes. Entry involves, at least in part, clathrin-coated pit-mediated endocytosis since different conditions or drugs known to influence this pathway modify both uptake of pDNA and its expression. The observed increase in expression with addition of a lip some correlated with an increase in the rate of transfer of the pDNA to lysosomes, a decrease in intracellular recycling and exocytosis of the pDNA and an increase in the amount of pDNA in the nuclear fraction. Trafficking within the cell involved endosome fusion and the acid environment of the endosomes-lysosomes was beneficial for expression. After 30 min both the peptide and pDNA localized to the nucleus and the amount of intact pDNA in the nuclear fraction was highest with liposome and peptide. A better understanding of the cellular mechanisms by which vectors transfer to and traffic in cells should help design improved vectors.

Interrelationship between the Na+/glucose cotransporter and CFTR in Caco-2 cells: relevance to cystic fibrosis.

Both the Na+-dependent glucose cotransporter (SGLT1) and the cystic fibrosis transmembrane conductance regulator (CFTR) modulate Na+ and fluid movement, although in opposite directions. Yet few studies have investigated a possible interrelationship between these two transporters. By using the Caco-2 human colon carcinoma cell line, we confirmed that the activities of these transporters increased with spontaneous differentiation to the enterocytic phenotype. We showed that SGLT1 was positively regulated by Cl- and that optimal activity of CFTR was dependent on the presence of glucose. We also demonstrated that inhibition of CFTR by glibenclamide or diphenylamine-2-carboxylate did not modify the activity of SGLT1 and inhibition of SGLT1 by phlorizin did not modify the activity of CFTR, although it resulted in inhibition of glycoconjugate synthesis. These results point to positive substrate-cross regulation of SGLT1 and CFTR and suggest that NaCl and glucose are important for not only Na+ absorption and fluid movement, but also for cAMP-dependent Cl- efflux, and glycoconjugate synthesis, functions that are known to be anomalous in cystic fibrosis.

Liposomes enhance delivery and expression of an RGD-oligolysine gene transfer vector in human tracheal cells.

Nonviral gene delivery systems consist predominantly of lipoplexes or receptor-targeting and nontargeting polyplexes. We examined integrin-mediated gene delivery using an Arg-Gly-Asp/oligo-L-lysine ([K]16RGD) cyclic peptide and investigated its gene transfer efficiency when associated with a cationic liposome. We demonstrated that human cystic fibrosis and noncystic fibrosis tracheal epithelial cells in culture express integrins that recognise the RGD integrin-binding motif. We found a 10-fold (P < 0.01) increased expression of a luciferase encoding plasmid in these cells when complexing the plasmid to the [K]16RGD peptide as compared with plasmid alone. This increase was specific to the [K]16RGD peptide since neither a [K]16RGE nor a [K]16 peptide gave a comparable increase. Expression was further enhanced 30-fold (P < 0.01) with lipofectamine and the ratio of DNA/peptide/lipofectamine was critical for specificity and expression. Fluorescence and radioactive labelling of the complex showed that the [K]16RGD peptide increased the endocytic uptake of DNA into cells. The cell association of both DNA and peptide increased even further with lipofectamine. Confocal microscopy showed that the [K]16RGD peptide and the DNA internalised together within 30 min and localised to vesicles in the perinuclear region. These results show that an integrin-binding ligand can deliver genetic material to airway cells and that a cationic liposome can enhance the efficacy of this nonviral vector system.

CFTR gene transfer corrects defective glycoconjugate secretion in human CF epithelial tracheal cells.

We demonstrate that in immortalized normal human tracheal epithelial cells (NT-1 and 56FHTE8o-) 14C-labeled glycoconjugate secretion may be regulated independently by agonists of the protein kinase A (PKA) and protein kinase C (PKC) signaling pathways. In contrast, in immortalized cystic fibrosis (CF) human tracheal epithelial cells (CFT-1 and CFT-2), regulation is defective for agonists specific for the PKA but not for the PKC pathway. To characterize the involvement of the cystic fibrosis transmembrane conductance regulator (CFTR) in regulated glycoconjugate secretion, we examined the effect of adenovirus-mediated gene transfer of CFTR to CF and control cells. Forty-eight hours after infection, at a multiplicity of infection of 50 plaque-forming units per cell, high levels of CFTR mRNA were detected by reverse transcription-polymerase chain reaction, and de novo synthesis of CFTR protein was demonstrated by immunoblotting. Gene transfer to CF cells restored defective adenosine 3',5'-cyclic monophosphate (cAMP)-dependent secretion not only of chloride but also of glycoconjugates. Taken together, these results argue for a role for CFTR in cAMP-mediated glycoconjugate secretion.

Identification of decorin proteoglycan in bovine tracheal serous cells in culture and localization of decorin mRNA in situ.

Bovine tracheal submucosal gland serous cells in culture synthesize and secrete proteoglycans and not mucin glycoconjugates. We are interested in the characterization and role of these proteoglycans in airway secretions. The major [35S]methionine-labeled proteoglycan present is identified as the small chondroitin/dermatan sulfate proteoglycan decorin (PG II. PG40). Consistent with its identity as decorin this proteoglycan showed average apparent molecular weights of 75,000 to 130,000 with a core protein of an average, M(r) of about 40,000 and with glycosaminoglycan chains sensitive to chondroitinase ABC lyase of an average M(r) of about 25,000. These data were obtained from gel chromatographic and SDS-PAGE analyses. Northern blot analysis and partial amino acid sequencing of the purified protein further confirmed its identity as decorin. In situ hybridization studies using a decorin riboprobe revealed no expression of decorin in the surface epithelium and only low levels of expression in submucosal gland epithelial cells of bovine tracheal tissue. However, high levels of expression were localized to cells which are peripheral to tracheal submucosal gland epithelial cells and which contact with the extracellular matrix.

Synthesis of hydrolytic enzymes during production of tylosin by Streptomyces fradiae.

The exposure of a wild-type tylosin producing strain of Streptomyces fradiae to mutagenic agents resulted in the isolation of several tylosin over-producing strains. Examination of three mutants, T4310, 612 and 3204 showed that improved tylosin production was associated with increased hydrolytic enzyme activity and cell growth. The wild-type strain showed lower levels of hydrolytic activity including, protease, amylase, lipase and esterase activities and attained a lower cell density than the mutants.

Nondenaturing protein electrotransfer of the esterase activity of lipolytic preparations.

Lipolytic enzymes subjected to nondenaturing polyacrylamide gel electrophoresis were electrophoretically transferred under nondenaturing conditions onto a solid-state matrix. Electrotransfer permitted the visualization of hydrolytic activity to the long-chain water insoluble substrate alpha-naphthyl palmitate. Four commercial preparations: a lipase from Candida cylindracea, an esterase from porcine liver, a lipase from Pseudomonas sp., and a cholesterol esterase from Pseudomonas fluorescens were examined.

The esterase profile of a lipase from Candida cylindracea.

A commercial preparation of a lipase produced by Candida cylindracea catalysed the hydrolysis of both long- and short-chain esters of p-nitrophenol. Six major bands of hydrolytic activity to alpha-naphthyl acetate were detected on polyacrylamide gel electrophoresis and two on isoelectric focusing. The esterase activity fractionated into two major peaks of activity on ion-exchange chromatography and into several peaks of activity on hydrophobic interaction chromatography. These esterase activities showed different substrate specificities to p-nitrophenyl esters, tributyrin and cetyl palmitate.

Lipolytic enzymes of the digestive organs of the crown-of-thorns starfish (Acanthaster planci): comparison of the stomach and pyloric caeca.

1. Stomach and pyloric caeca homogenates from the crown-of-thorns starfish hydrolysed p-nitrophenyl esters, alpha-naphthyl esters, cholesteryl oleate and tributyrin. The pyloric caeca contained the highest activities. 2. The p-nitrophenyl acetate hydrolytic activity eluted at 0.23 M NaCl on ion exchange chromatography while the p-nitrophenyl palmitate hydrolytic activity eluted between 0.2 and 1.0 M NaCl. 3. Polyacrylamide gel zymograms for alpha-naphthyl acetate hydrolytic activity revealed one major band and several minor bands of activity for both tissues. 4. Isoelectric focusing zymograms revealed one major band with a pI = 4.2 for both tissues, with an additional band at pI = 3.5 for pyloric caeca. 5. The pyloric caeca contained twice as much lipid as the stomach. Lipid extracts contained mixtures of steroids and steroid-esters; a cholesterol-like sterol was tentatively identified.

Effect of insulin on sulfated proteoglycan synthesis in cultured smooth muscle cells from pig aorta.

The effect of insulin upon proteoglycan synthesis was studied in cultured smooth muscle cells from pig aorta blocked in the G0 phase by serum deprivation. Insulin enhanced [35S]sulfate incorporation into cell layer and medium-secreted proteoglycans. The increase in incorporation of the precursor was not due to a mitogenic response by smooth muscle cells to the hormone and the specific radioactivity of proteoglycans showed that the stimulation reflected a real increase in sulfated proteoglycan synthesis. Maximal stimulation was observed, for the cell layer as well as for the medium, 40 h after the addition of 1.7 x 10(-7) M insulin and reached respectively 65 and 53%. This stimulation was about 80 and 60% of the level achieved with 10% fetal calf serum for cell layer and medium-secreted proteoglycans, respectively. The half-maximal effect was attained, for both the cell layer and the medium, in the presence of 2.1 x 10(-9) M insulin. Proteoglycans secreted into the medium, in the presence of 1.7 x 10(-8) M insulin for 40 h, showed a higher proportion of complexes (24%) than those synthesized in control medium (11%) and at least 95% of the monomers from culture treated with insulin were characterized by a smaller hydrodynamic size than those synthesized by cells maintained in control medium. This decrease in the size of proteoglycans was partly due to a decrease in the size of their glycanic chains.

Characterization and macromolecular association of proteoglycans produced by pig arterial smooth muscle cells in culture.

1. Medium and cell-layer proteoglycans from pig aorta smooth muscle cells in culture were compared. In both compartments, the main proteoglycans contained chondroitin sulfate-dermatan sulfate chains of 40 kDalton. 2. However, cell-layer proteoglycans differed from those of the medium by the presence of: (a) some small-size proteoglycans; (b) a greater amount of heparan sulfate; (c) chondroitin sulfate-dermatan sulfate enriched in iduronate and in 4 sulfate- (instead of 6 sulfate-) residues. 3. During dissociation-reassociation assays of arterial proteoglycans with exogenous hyaluronate or "aggregate" proteoglycans, the in vitro formation of complexes appeared to involve inter-associations between proteoglycans molecules, in addition to aggregation with hyaluronate.

Synthesis of sulfated proteoglycans throughout the cell cycle in smooth muscle cells from pig aorta.

Cultured smooth muscle cells from pig aorta arrested in G0 phase by serum deprivation were stimulated to proliferate by replacing the medium with one containing 10% serum. Studies in DNA replication and proliferation of cells showed a relatively good synchrony: 90% of the cells were in G1 phase for 16 h after addition of serum; they entered S phase between 18 and 24 h, completed S phase and traversed G2 phase between 24 and 30-32 h; 75% of these cells multiplied after 30-32 h and the remainder were blocked at the end of G2 phase. The synthesis and secretion of sulfated proteoglycans were examined throughout a full cell cycle using metabolic labelling with [35S]sulfate. Smooth muscle cells in G1 or G2 phase synthesized and secreted sulfated proteoglycans with a possible pause at the end of the G2 phase but at the beginning of the S phase and during mitosis the incorporation of [35S]sulfate into these macromolecules stopped entirely. Structural characteristics of sulfated proteoglycans secreted into the medium during G1 phase and an entire cell cycle were investigated. The proportion of proteoglycan complexes and the relative hydrodynamic size of monomers and of constituent subunits of complexes were determined after chromatography on Sepharose CL-2B and CL-6B columns run under both associative and dissociative conditions. No significant differences were observed for the periods of the cell cycle that were studied: [35S]Proteoglycan complexes represented at the end of G1 phase and of the cell cycle respectively 19 and 16% of the total [35S]proteoglycans secreted into the medium. More than 90% of the subunits, obtained after dissociation of complexes, were characterized by a similar kav after chromatography on Sepharose CL-2B columns eluted under dissociative conditions (kav 0.68 at the end of G1 phase and 0.65 at the end of full cell cycle). About 95% of monomers synthesized at the two stages of the cell cycle were eluted at kav 0.25 after chromatography on Sepharose CL-6B column run under associative conditions and were characterized by a similar glycosaminoglycan distribution. These results suggest that smooth muscle cells in culture liberate similar populations of proteoglycans into the medium during the G1 and G2 phases.