Impact of differential P450c17 phosphorylation by cAMP stimulation and by starvation conditions on enzyme activities and androgen production in NCI-H295R cells

CYP17A1 plays a pivotal role in the biosynthesis of androgens in the adrenals and the gonads. Although this enzyme catalyzes two different reactions on one single active site, its specific activities are regulated independently. Although the 17alpha-hydroxylase activity is rather constant and regulated by gene expression, the 17,20-lyase activity varies significantly with the amount of cofactors or by protein phosphorylation. cAMP increases CYP17A1 expression, P450c17 phosphorylation, and androgen production. However, the exact mechanism(s) and the specific regulators of CYP17A1 remain unknown. Therefore, we studied the regulation of adrenal androgen biosynthesis in human adrenal H295R cells focusing on CYP17A1. We analyzed androgen production and P450c17 activities in H295R cells grown under normal and serum-free conditions and/or after stimulation with 8-bromoadenosine-cAMP. H295R cells grown in starvation medium produced more androgens and had decreased HSD3B2 expression and activity but increased P450c17-17,20-lyase activity and serine phosphorylation. Although starvation increased serine phosphorylation of P450c17 specifically, cAMP stimulation enhanced threonine phosphorylation exclusively. Time-course experiments revealed that a short cAMP stimulation augmented threonine phosphorylation of P450c17 but did not increase 17,20-lyase activity. By contrast, long cAMP stimulation increased androgen production through increased P450c17 activities by enhancing CYP17A1 gene expression. We conclude that serum withdrawal shifts steroidogenesis of H295R cells towards androgen production, providing a suitable model for detailed studies of androgen regulation. In addition, our study shows that starvation and cAMP stimulation regulate P450c17 phosphorylation differentially and that an increase in P450c17 phosphorylation does not necessarily lead to enhanced enzyme activity and androgen production.

Epigenetic regulation of somatic angiotensin-converting enzyme by DNA methylation and histone acetylation

Somatic angiotensin-converting enzyme (sACE) is crucial in cardiovascular homeostasis and displays a tissue-specific profile. Epigenetic patterns modulate genes expression and their alterations were implied in pathologies including hypertension. However, the influence of DNA methylation and chromatin condensation state on the expression of sACE is unknown. We examined whether such epigenetic mechanisms could participate in the control of sACE expression in vitro and in vivo. We identified two CpG islands in the human ace-1 gene 3 kb proximal promoter region. Their methylation abolished the luciferase activity of ace-1 promoter/reporter constructs transfected into human liver (HepG2), colon (HT29), microvascular endothelial (HMEC-1) and lung (SUT) cell lines (p < 0.001). Bisulphite sequencing revealed a cell-type specific basal methylation pattern of the ace-1 gene -1,466/+25 region. As assessed by RT-qPCR, inhibition of DNA methylation by 5-aza-2'-deoxycytidine and/or of histone deacetylation by trichostatin A highly stimulated sACE mRNA expression cell-type specifically (p < 0.001 vs. vehicle treated cells). In the rat, in vivo 5-aza-cytidine injections demethylated the ace-1 promoter and increased sACE mRNA expression in the lungs and liver (p = 0.05), but not in the kidney. In conclusion, the expression level of somatic ACE is modulated by CpG-methylation and histone deacetylases inhibition. The basal methylation pattern of the promoter of the ace-1 gene is cell-type specific and correlates to sACE transcription. DNMT inhibition is associated with altered methylation of the ace-1 promoter and a cell-type and tissue-specific increase of sACE mRNA levels. This study indicates a strong influence of epigenetic mechanisms on sACE expression.

Deubiquitylating enzyme USP2 counteracts Nedd4-2-mediated downregulation of KCNQ1 potassium channels

KCNQ1 (Kv7.1), together with its KCNE β subunits, plays a pivotal role both in the repolarization of cardiac tissue and in water and salt transport across epithelial membranes. Nedd4/Nedd4-like (neuronal precursor cell-expressed developmentally downregulated 4) ubiquitin-protein ligases interact with the KCNQ1 potassium channel through a PY motif located in the C terminus of KCNQ1. This interaction induces ubiquitylation of KCNQ1, resulting in a reduced surface density of the channel. It was reported recently that the epithelial sodium channel is regulated by the reverse process-deubiquitylation-mediated by USP2 (ubiquitin-specific protease 2).

Bacterial expression of mutant argininosuccinate lyase reveals imperfect correlation of in-vitro enzyme activity with clinical phenotype in argininosuccinic aciduria

The urea cycle defect argininosuccinate lyase (ASL) deficiency has a large spectrum of presentations from highly severe to asymptomatic. Enzyme activity assays in red blood cells or fibroblasts, although diagnostic of the deficiency, fail to discriminate between severe, mild or asymptomatic cases. Mutation/phenotype correlation studies are needed to characterize the effects of individual mutations on the activity of the enzyme.

DNase 2 is the main DNA-degrading enzyme of the stratum corneum

The cornified layer, the stratum corneum, of the epidermis is an efficient barrier to the passage of genetic material, i.e. nucleic acids. It contains enzymes that degrade RNA and DNA which originate from either the living part of the epidermis or from infectious agents of the environment. However, the molecular identities of these nucleases are only incompletely known at present. Here we performed biochemical and genetic experiments to determine the main DNase activity of the stratum corneum. DNA degradation assays and zymographic analyses identified the acid endonucleases L-DNase II, which is derived from serpinB1, and DNase 2 as candidate DNases of the cornified layer of the epidermis. siRNA-mediated knockdown of serpinB1 in human in vitro skin models and the investigation of mice deficient in serpinB1a demonstrated that serpinB1-derived L-DNase II is dispensable for epidermal DNase activity. By contrast, knockdown of DNase 2, also known as DNase 2a, reduced DNase activity in human in vitro skin models. Moreover, the genetic ablation of DNase 2a in the mouse was associated with the lack of acid DNase activity in the stratum corneum in vivo. The degradation of endogenous DNA in the course of cornification of keratinocytes was not impaired by the absence of DNase 2. Taken together, these data identify DNase 2 as the predominant DNase on the mammalian skin surface and indicate that its activity is primarily targeted to exogenous DNA.

PU.1 is linking the glycolytic enzyme HK3 in neutrophil differentiation and survival of APL cells

The transcription factor PU.1 is a master regulator of myeloid differentiation and function. On the other hand, only scarce information is available on PU.1-regulated genes involved in cell survival. We now identified the glycolytic enzyme hexokinase 3 (HK3), a gene with cytoprotective functions, as transcriptional target of PU.1. Interestingly, HK3 expression is highly associated with the myeloid lineage and was significantly decreased in acute myeloid leukemia patients compared with normal granulocytes. Moreover, HK3 expression was significantly lower in acute promyelocytic leukemia (APL) compared with non-APL patient samples. In line with the observations in primary APL patient samples, we observed significantly higher HK3 expression during neutrophil differentiation of APL cell lines. Moreover, knocking down PU.1 impaired HK3 induction during neutrophil differentiation. In vivo binding of PU.1 and PML-RARA to the HK3 promoter was found, and PML-RARA attenuated PU.1 activation of the HK3 promoter. Next, inhibiting HK3 in APL cell lines resulted in significantly reduced neutrophil differentiation and viability compared with control cells. Our findings strongly suggest that HK3 is: (1) directly activated by PU.1, (2) repressed by PML-RARA, and (3) functionally involved in neutrophil differentiation and cell viability of APL cells.

Use of an indirect enzyme-linked immunosorbent assay for detection of antibodies in sheep naturally infected with Salmonella Abortusovis

An indirect enzyme-linked immunosorbent assay (ELISA) was modified and validated to detect antibodies against Salmonella Abortusovis in naturally infected sheep. The ELISA was validated with 44 positive and 45 negative control serum samples. Compared with the immunoblot, the sensitivity and specificity of the assay were 98% and 100%, respectively. To follow antibody levels over time, samples from 12 infected ewes were collected at 1, 3, and 10 months after abortion. All animals showed antibody levels above the cutoff value throughout the observation period. One and 3 months after abortion, high antibody levels could be detected in all but one animal, whereas after 10 months, 9 animals had markedly lower but still positive antibody levels. The test characteristics and evidence for the persistence of detectable antibody levels in all infected animals for up to 10 months indicates that the ELISA can be used for herd surveillance testing.

Echinococcus multilocularis phosphoglucose isomerase (EmPGI): a glycolytic enzyme involved in metacestode growth and parasite-host cell interactions

In Echinococcus multilocularis metacestodes, the surface-associated and highly glycosylated laminated layer, and molecules associated with this structure, is believed to be involved in modulating the host-parasite interface. We report on the molecular and functional characterisation of E. multilocularis phosphoglucose isomerase (EmPGI), which is a component of this laminated layer. The EmPGI amino acid sequence is virtually identical to that of its homologue in Echinococcus granulosus, and shares 64% identity and 86% similarity with human PGI. Mammalian PGI is a multi-functional protein which, besides its glycolytic function, can also act as a cytokine, growth factor and inducer of angiogenesis, and plays a role in tumour growth, development and metastasis formation. Recombinant EmPGI (recEmPGI) is also functionally active as a glycolytic enzyme and was found to be present, besides the laminated layer, in vesicle fluid and in germinal layer cell extracts. EmPGI is released from metacestodes and induces a humoral immune response in experimentally infected mice, and vaccination of mice with recEmPGI renders these mice more resistant towards secondary challenge infection, indicating that EmPGI plays an important role in parasite development and/or in modulating the host-parasite relationship. We show that recEmPGI stimulates the growth of isolated E. multilocularis germinal layer cells in vitro and selectively stimulates the proliferation of bovine adrenal cortex endothelial cells but not of human fibroblasts and rat hepatocytes. Thus, besides its role in glycolysis, EmPGI could also act as a factor that stimulates parasite growth and potentially induces the formation of novel blood vessels around the developing metacestode in vivo.

Structure-Function Relations in the PI-PLC/GDPD Enzyme Superfamily

Phosphatidylinositol-specific phospholipases C (PI-PLC) are known to participate in many eukaryotic signal transduction pathways and act as virulence factors in lower organisms. Glycerophosphoryl diester phosphodiesterase (GDPD) enzymes are involved in phosphate homeostasis and phospholipid catabolism for energy production. Streptomyces antibioticus phosphatidylinositol-specific phospholipase C (SaPLC1) is a 38 kDa enzyme that displays characteristics of both enzyme superfamilies, representing an evolutionary link between these divergent enzyme classes. SaPLC1 also boasts a unique catalytic mechanism that involves a trans 1,6-cyclic inositol phosphate intermediate instead of the typical cis 1,2-cyclic inositol phosphate. The mechanism by which this occurs is still unclear. To attack this problem, we established a wide mutagenesis scan of the active site and measured activities of alanine mutants. A chemical rescue assay was developed to verify that the activity loss was due to the removal of the functional role of the mutated residue. 31P-NMR was employed in characterizing and quantifying intermediates in mutants that slowed the reaction sufficiently. We found that the H37A and H76A mutations support the hypothesis that these structurally conserved residues are also conserved in terms of their catalytic roles. H37 was found to be the general base (GB), while H76 plays the role of general acid (GA). K131 was identified as a semi-conserved key positive charge donor found at the entrance of the active site. By elucidating the SaPLC1 mechanism in relation to its active site architecture, we have increased our understanding of the structure-function relations that support catalysis in the PI-PLC/GDPD superfamily. These findings provide groundwork for in vivo studies of SaPLC1 function and its possible role in novel signaling or metabolism in Streptomyces.