PubMed · 1168836
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R P Mortlock. 1975. D-ribulose.. https://doi.org/10.1016/s0076-6879(75)41026-6
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The most commonly used expression platform for production of recombinant proteins in the methylotrophic yeast Hansenula polymorpha relies on the strong and strictly regulated promoter from the gene encoding peroxisomal enzyme alcohol (or methanol) oxidase (P(MOX)). Expression from P(MOX) is induced by methanol and is partially derepressed in glycerol or xylose medium, whereas in the presence of hexoses, disaccharides or ethanol, it is repressed. The need for methanol for maximal induction of gene expression in large-scale fermentation is a significant drawback, as this compound is toxic, flammable, supports a slow growth rate and requires extensive aeration. We isolated H. polymorpha mutants deficient in glucose repression of P(MOX) due to an impaired HpGCR1 gene, and other yet unidentified secondary mutations. The mutants exhibited pronounced defects in P(MOX) regulation only by hexoses and xylose, but not by disaccharides or ethanol. With one of these mutant strains as hosts, we developed a modified two-carbon source mode expression platform that utilizes convenient sugar substrates for growth (sucrose) and induction of recombinant protein expression (glucose or xylose). We demonstrate efficient regulatable by sugar carbon sources expression of three recombinant proteins: a secreted glucose oxidase from the fungus Aspergillus niger, a secreted mini pro-insulin, and an intracellular hepatitis B virus surface antigen in these mutant hosts. The modified expression platform preserves the favorable regulatable nature of P(MOX) without methanol, making a convenient alternative to the traditional system.
NADP(H)-dependent retinol dehydrogenase/reductase (NRDR) plays an important role in maintaining the homeostasis of retinoid. Aberrations in retinoid metabolism are considered as early events in carcinogenesis. We identified a novel alternatively spliced variant, NRDRB1, in HeLa cell and human cervical squamous carcinoma tissues, which is characterized by a complete deletion of exon 3. The latter resulted in changes in subcellular localization of NRDRB1 when compared with the peroxisomal localization of NRDR. To clarify the clinical significance of NRDRB1, we investigated its mRNA and protein expressions in normal cervical and cervical squamous carcinoma tissues, using RT-PCR, quantitative real-time PCR, Gateway expressing system, immunoprecipitation, immunoblotting, MALDI-TOF mass spectrometry and immunohistochemistry. We detected NRDRB1 mRNA in 14 of 26 (53.9%) cervical cancer tissues, but in none of the 12 normal cervical tissues. NRDRB1 protein was expressed in NRDRB1 mRNA-positive cases. While the full-length NRDR mRNA was observed in both normal and neoplastic cervical tissues, its protein was only expressed in normal cervical epithelium. The results presented here provide evidence that metabolic disturbances of retinal and retinoic acid, due to abnormal splicing and functional disorder of NRDR, may be involved in cervical tumorigenesis.
The 5-lipoxygenase product 5-oxo-ETE (5-oxo-eicosatetraenoic acid) is a highly potent granulocyte chemoattractant that is synthesized from 5-HETE (5-hydroxyeicosatetraenoic acid) by 5-HEDH (5-hydroxyeicosanoid dehydrogenase). In the present study, we found that 5-HEDH activity is induced in U937 monocytic cells by differentiation towards macrophages with PMA and in HL-60 myeloblastic cells by 1,25-dihydroxy-vitamin D3. We used PMA-differentiated U937 cells to investigate further the regulation of 5-HEDH. This enzyme exhibits approx. 10000-fold selectivity for NADP+ over NAD+ as a cofactor for the oxidation of 5-HETE, which is maximal at pH 10.2. In contrast, the reverse reaction (5-oxo-ETE-->5-HETE) is NADPH-dependent and is maximal at pH 6. Although the K(m) for the forward reaction (670 nM) is about twice that for the reverse reaction at neutral pH, the V(max) is approx 8-fold higher. The oxidation of 5-HETE to 5-oxo-ETE is supported by very low concentrations of NADP(+) (K(m) 139 nM), inhibited by NADPH (K(i) 224 nM) and is consistent with a ping-pong mechanism. The amount of 5-oxo-ETE synthesized by 5-HEDH depends on the ratio of NADP+ to NADPH. Exposure of U937 cells to oxidative stress (t-butyl hydroperoxide) increased the ratio of NADP+ to NADPH from approx. 0.08 in resting cells to approx. 3, and this was accompanied by a dramatic increase in 5-HETE oxidation to 5-oxo-ETE. We conclude that differentiation of monocytic cells towards macrophages results in enhanced 5-oxo-ETE synthesis and that the ability of cells to synthesize 5-oxo-ETE is tightly regulated by the ratio of intracellular NADP+ to NADPH.