Amino acids involved in polyphosphate synthesis and its mobilization are distinct in polyphosphate kinase-1 from Mycobacterium tuberculosis

Background

In bacteria polyphosphates (poly-P) are involved in cellular metabolism and development especially during stress. The enzyme, principally involved in polyphosphate biosynthesis and its mobilization leading to generation of NTPs, is known as polyphosphate kinase (PPK).

Principal Findings

Among two genes of polyphosphate kinases present in Mycobacterium tuberculosis, we cloned and expressed PPK1 in Escherichia coli as histidine-tagged protein. This ∼86 kDa protein is capable of autophosphorylation and synthesis of poly-P as well as NTP. Among 22 conserved histidine residues, we found only His-491 is autophosphorylated and crucial for any enzymatic activity. Substitution of His-510 caused mPPK1 protein deficient but not defective in autophosphorylation, thereby contrary to earlier reports negating any role of this residue in the process. However, mutation of His-510 with either Ala or Gln affected ATP or poly-P synthesis depending on the substitution; while such effects were severe with H510A but mild with H510Q. Furthermore, mPPK1 also renders auxiliary nucleotide diphosphate kinase function by synthesizing virtually all NTPs/dNTPs from their cognate NDPs/dNDPs by utilizing poly-P as the phosphate donor albeit with varied efficiency. To assess the influence of other catalytic domain residues of mPPK1 towards its functionality, we designed mutations based on E. coli PPK1 crystal structure since it owes 68% amino acid sequence similarity with mPPK1. Interestingly, our results revealed that mutations in mPPK1 affecting poly-P synthesis always affected its ATP synthesizing ability; however, the reverse may not be true.

Conclusions/Significance

We conclude that amino acid residues involved in poly-P and ATP synthesizing activities of mPPK1 are distinct. Considering conserved nature of PPK1, it seems our observations have broader implications and not solely restricted to M. tuberculosis only.     

Regulation of C3a receptor signaling in human mast cells by G protein coupled receptor kinases

Background

The complement component C3a activates human mast cells via its cell surface G protein coupled receptor (GPCR) C3aR. For most GPCRs, agonist-induced receptor phosphorylation leads to receptor desensitization, internalization as well as activation of downstream signaling pathways such as ERK1/2 phosphorylation. Previous studies in transfected COS cells overexpressing G protein coupled receptor kinases (GRKs) demonstrated that GRK2, GRK3, GRK5 and GRK6 participate in agonist-induced C3aR phosphorylation. However, the roles of these GRKs on the regulation of C3aR signaling and mediator release in human mast cells remain unknown.

Methodology/Principal Findings

We utilized lentivirus short hairpin (sh)RNA to stably knockdown the expression of GRK2, GRK3, GRK5 and GRK6 in human mast cell lines, HMC-1 and LAD2, that endogenously express C3aR. Silencing GRK2 or GRK3 expression caused a more sustained Ca²⁺ mobilization, attenuated C3aR desensitization, and enhanced degranulation as well as ERK1/2 phosphorylation when compared to shRNA control cells. By contrast, GRK5 or GRK6 knockdown had no effect on C3aR desensitization, but caused a significant decrease in C3a-induced mast cell degranulation. Interestingly, GRK5 or GRK6 knockdown rendered mast cells more responsive to C3a for ERK1/2 phosphorylation.

Conclusion/Significance

This study demonstrates that GRK2 and GRK3 are involved in C3aR desensitization. Furthermore, it reveals the novel finding that GRK5 and GRK6 promote C3a-induced mast cell degranulation but inhibit ERK1/2 phosphorylation via C3aR desensitization-independent mechanisms. These findings thus reveal a new level of complexity for C3aR regulation by GRKs in human mast cells.     

miRNA expression in colon polyps provides evidence for a multihit model of colon cancer

Changes in miRNA expression are a common feature in colon cancer. Those changes occurring in the transition from normal to adenoma and from adenoma to carcinoma, however, have not been well defined. Additionally, miRNA changes among tumor subgroups of colon cancer have also not been adequately evaluated. In this study, we examined the global miRNA expression in 315 samples that included 52 normal colonic mucosa, 41 tubulovillous adenomas, 158 adenocarcinomas with proficient DNA mismatch repair (pMMR) selected for stage and age of onset, and 64 adenocarcinomas with defective DNA mismatch repair (dMMR) selected for sporadic (n = 53) and inherited colon cancer (n = 11). Sporadic dMMR tumors all had MLH1 inactivation due to promoter hypermethylation. Unsupervised PCA and cluster analysis demonstrated that normal colon tissue, adenomas, pMMR carcinomas and dMMR carcinomas were all clearly discernable. The majority of miRNAs that were differentially expressed between normal and polyp were also differentially expressed with a similar magnitude in the comparison of normal to both the pMMR and dMMR tumor groups, suggesting a stepwise progression for transformation from normal colon to carcinoma. Among the miRNAs demonstrating the largest fold up- or down-regulated changes (≥4), four novel (miR-31, miR-1, miR-9 and miR-99a) and two previously reported (miR-137 and miR-135b) miRNAs were identified in the normal/adenoma comparison. All but one of these (miR-99a) demonstrated similar expression differences in the two normal/carcinoma comparisons, suggesting that these early tumor changes are important in both the pMMR- and dMMR-derived cancers. The comparison between pMMR and dMMR tumors identified four miRNAs (miR-31, miR-552, miR-592 and miR-224) with statistically significant expression differences (≥2-fold change).     

Heterochromatin-Mediated Association of Achiasmate Homologs Declines With Age When Cohesion Is Compromised

Normally, meiotic crossovers in conjunction with sister-chromatid cohesion establish a physical connection between homologs that is required for their accurate segregation during the first meiotic division. However, in some organisms an alternative mechanism ensures the proper segregation of bivalents that fail to recombine. In Drosophila oocytes, accurate segregation of achiasmate homologs depends on pairing that is mediated by their centromere-proximal heterochromatin. Our previous work uncovered an unexpected link between sister-chromatid cohesion and the fidelity of achiasmate segregation when Drosophila oocytes are experimentally aged. Here we show that a weak mutation in the meiotic cohesion protein ORD coupled with a reduction in centromere-proximal heterochromatin causes achiasmate chromosomes to missegregate with increased frequency when oocytes undergo aging. If ORD activity is more severely disrupted, achiasmate chromosomes with the normal amount of pericentric heterochromatin exhibit increased nondisjunction when oocytes age. Significantly, even in the absence of aging, a weak ord allele reduces heterochromatin-mediated pairing of achiasmate chromosomes. Our data suggest that sister-chromatid cohesion proteins not only maintain the association of chiasmate homologs but also play a role in promoting the physical association of achiasmate homologs in Drosophila oocytes. In addition, our data support the model that deterioration of meiotic cohesion during the aging process compromises the segregation of achiasmate as well as chiasmate bivalents.     

Chain length specificity for activation of cPLA2�� by C1P: use of the dodecane delivery system to determine lipid-specific effects

Previously, our laboratory demonstrated that ceramide-1-phosphate (C1P) specifically activated group IVA cytosolic phospholipase A₂ (cPLA₂α) in vitro. In this study, we investigated the chain length specificity of this interaction. C1P with an acyl-chain of ≥6 carbons efficiently activated cPLA₂α in vitro, whereas C₂-C1P, was unable to do so. Delivery of C1P to cells via the newly characterized ethanol/dodecane system demonstrated a lipid-specific activation of cPLA₂α, AA release, and PGE₂ synthesis (EC₅₀ = 400 nM) when compared to structurally similar lipids. C1P delivered as vesicles in water also induced a lipid-specific increase in AA release. Mass spectrometric analysis demonstrated that C1P delivered via ethanol/dodecane induced a 3-fold increase in endogenous C1P with little metabolism to ceramide. C1P was also more efficiently delivered (>3-fold) to internal membranes by ethanol/dodecane as compared to vesiculated C1P. Using this now established delivery method for lipids, C₂-C1P was shown to be ineffective in the induction of AA release as compared with C₆-C1P, C₁₆-C1P, and C_18:1 C1P. Here, we demonstrate that C1P requires ≥6 carbon acyl-chain to activate cPLA₂α. Thus, published reports on the biological activity of C₂-C1P are not via eicosanoid synthesis. Furthermore, this study demonstrates that the alcohol/dodecane system can be used to efficiently deliver exogenous phospholipids to cells for the examination of specific biological effects.—Wijesinghe, D. S., P. Subramanian, N. F. Lamour, L. B. Gentile, M. H. Granado, A. Bielawska, Z. Szulc, A. Gomez-Munoz, and C. E. Chalfant. Chain length specificity for activation of cPLA₂α by C1P: use of the dodecane delivery system to determine lipid-specific effects.     

Two Distinct Pathways for Metabolism of Theophylline and Caffeine Are Coexpressed in Pseudomonas putida CBB5

Pseudomonas putida CBB5 was isolated from soil by enrichment on caffeine. This strain used not only caffeine, theobromine, paraxanthine, and 7-methylxanthine as sole carbon and nitrogen sources but also theophylline and 3-methylxanthine. Analyses of metabolites in spent media and resting cell suspensions confirmed that CBB5 initially N demethylated theophylline via a hitherto unreported pathway to 1- and 3-methylxanthines. NAD(P)H-dependent conversion of theophylline to 1- and 3-methylxanthines was also detected in the crude cell extracts of theophylline-grown CBB5. 1-Methylxanthine and 3-methylxanthine were subsequently N demethylated to xanthine. CBB5 also oxidized theophylline and 1- and 3-methylxanthines to 1,3-dimethyluric acid and 1- and 3-methyluric acids, respectively. However, these methyluric acids were not metabolized further. A broad-substrate-range xanthine-oxidizing enzyme was responsible for the formation of these methyluric acids. In contrast, CBB5 metabolized caffeine to theobromine (major metabolite) and paraxanthine (minor metabolite). These dimethylxanthines were further N demethylated to xanthine via 7-methylxanthine. Theobromine-, paraxanthine-, and 7-methylxanthine-grown cells also metabolized all of the methylxanthines mentioned above via the same pathway. Thus, the theophylline and caffeine N-demethylation pathways converged at xanthine via different methylxanthine intermediates. Xanthine was eventually oxidized to uric acid. Enzymes involved in theophylline and caffeine degradation were coexpressed when CBB5 was grown on theophylline or on caffeine or its metabolites. However, 3-methylxanthine-grown CBB5 cells did not metabolize caffeine, whereas theophylline was metabolized at much reduced levels to only methyluric acids. To our knowledge, this is the first report of theophylline N demethylation and coexpression of distinct pathways for caffeine and theophylline degradation in bacteria.Caffeine (1,3,7-trimethylxanthine) and related methylxanthines are widely distributed in many plant species. Caffeine is also a major human dietary ingredient that can be found in common beverages and food products, such as coffee, tea, and chocolates. In pharmaceuticals, caffeine is used generally as a cardiac, neurological, and respiratory stimulant, as well as a diuretic (3). Hence, caffeine and related methylxanthines enter soil and water easily through decomposed plant materials and other means, such as effluents from coffee- and tea-processing facilities. Therefore, it is not surprising that microorganisms capable of degrading caffeine have been isolated from various natural environments, with or without enrichment procedures (3, 10). Bacteria use oxidative and N-demethylating pathways for catabolism of caffeine. Oxidation of caffeine by a Rhodococcus sp.-Klebsiella sp. mixed-culture consortium at the C-8 position to form 1,3,7-trimethyluric acid (TMU) has been reported (8). An 85-kDa, flavin-containing caffeine oxidase was purified from this consortium (9). Also, Mohapatra et al. (12) purified a 65-kDa caffeine oxidase from Alcaligenes sp. strain CF8. Cells of a caffeine-degrading Pseudomonas putida strain (ATCC 700097) isolated from domestic wastewater (13) showed a fourfold increase in a cytochrome P450 absorption spectrum signal compared to cells grown on glucose. Recently, we reported a novel non-NAD(P)⁺-dependent heterotrimeric caffeine dehydrogenase from Pseudomonas sp. strain CBB1 (20). This enzyme oxidized caffeine to TMU stoichiometrically and hydrolytically, without producing hydrogen peroxide. Further metabolism of TMU has not been elucidated.Several caffeine-degrading bacteria metabolize caffeine via the N-demethylating pathway and produce theobromine (3,7-dimethylxanthine) or paraxanthine (1,7-dimethylxanthine) as the initial product. Theophylline (1,3-dimethylxanthine) has not been reported to be a metabolite in bacterial degradation of caffeine. Subsequent N demethylation of theobromine or paraxanthine to xanthine is via 7-methyxanthine. Xanthine is further oxidized to uric acid by xanthine dehydrogenase/oxidase (3, 10). Although the identities of metabolites and the sequence of metabolite formation for caffeine N demethylation are well established, there is very little information on the number and nature of N-demethylases involved in this pathway.The lack of adequate information on the metabolism and enzymology of theophylline, caffeine, and related methylxanthines prompted us to investigate the degradation of these compounds in detail. We isolated a unique caffeine-degrading bacterium, P. putida CBB5, from soil via enrichment with caffeine as the sole source of carbon and nitrogen. Here we describe a detailed study of the metabolism of theophylline, caffeine, and related di- and monomethylxanthines by CBB5. Our results indicate that CBB5 initially N demethylated caffeine to produce theobromine (major product) and paraxanthine (minor product) before the pathways converged to 7-methylxanthine and xanthine. Surprisingly, CBB5 was also capable of utilizing theophylline as a sole carbon and nitrogen source. CBB5 N demethylated theophylline to 1-methylxanthine and 3-methylxanthine, which were further N demethylated to xanthine. Theophylline N-demethylase activity was detected in cell extracts prepared from theophylline-grown CBB5 cells. 1-Methylxanthine and 3-methylxanthine were detected as products of this NAD(P)H-dependent reaction. To our knowledge, this is the first report of a theophylline degradation pathway in bacteria and coexpression of distinct caffeine and theophylline degradation pathways.     

Inhibition of Prolyl Hydroxylase Protects against 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Neurotoxicity: MODEL FOR THE POTENTIAL INVOLVEMENT OF THE HYPOXIA-INDUCIBLE FACTOR PATHWAY IN PARKINSON DISEASE*

Hypoxia-inducible factor (HIF) plays an important role in cell survival by regulating iron, antioxidant defense, and mitochondrial function. Pharmacological inhibitors of the iron-dependent enzyme class prolyl hydroxylases (PHD), which target α subunits of HIF proteins for degradation, have recently been demonstrated to alleviate neurodegeneration associated with stroke and hypoxic-ischemic injuries. Here we report that inhibition of PHD by 3,4-dihydroxybenzoate (DHB) protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced nigral dopaminergic cell loss and up-regulates HIF-1α within these neurons. Elevations in mRNA and protein levels of HIF-dependent genes heme oxygenase-1 (Ho-1) and manganese superoxide dismutase (Mnsod) following DHB pretreatment alone are also maintained in the presence of MPTP. MPTP-induced reductions in ferroportin and elevations in nigral and striatal iron levels were reverted to levels comparable with that of untreated controls with DHB pretreatment. Reductions in pyruvate dehydrogenase mRNA and activity resulting from MPTP were also found to be attenuated by DHB. In vitro, the HIF pathway was activated in N27 cells grown at 3% oxygen treated with either PHD inhibitors or an iron chelator. Concordant with our in vivo data, the MPP⁺-elicited increase in total iron as well as decreases in cell viability were attenuated in the presence of DHB. Taken together, these data suggest that protection against MPTP neurotoxicity may be mediated by alterations in iron homeostasis and defense against oxidative stress and mitochondrial dysfunction brought about by cellular HIF-1α induction. This study provides novel data extending the possible therapeutic utility of HIF induction to a Parkinson disease model of neurodegeneration, which may prove beneficial not only in this disorder itself but also in other diseases associated with metal-induced oxidative stress.Parkinson disease (PD)² is a neurodegenerative disorder primarily associated with loss of dopaminergic (DAergic) neurons of the pars compacta region of the substantia nigra (SNpc). Dopaminergic neurons are particularly prone to oxidative damage due to high levels of inherent reactive oxygen species that are produced during dopamine synthesis or its breakdown by monoamine oxidases or autoxidation to quinones (1–3). Importantly, iron bound to neuromelanin within DAergic neurons can subsequently react with metabolically liberated hydrogen peroxide through the Fenton reaction to produce extremely toxic hydroxyl radicals. If not properly buffered, hydroxyl radicals can stimulate protein oxidation and lipid peroxidation, which is thought to contribute to macromolecular injury and neuronal death. Iron is the most abundant metal in the brain and some degree of accessible reactive iron is necessary for brain viability as it serves as a cofactor in DNA, RNA, and protein synthesis and for heme and non-heme enzymes involved in both mitochondrial respiration and neurotransmitter synthesis (4). Although iron deficiencies early in life are known to result in impairments in brain development (5), high concentrations of iron may result in cellular toxicity (6) in part due to its ability to catalyze the production of toxic oxygen radicals.An important family of enzymes that require iron as an essential cofactor are the prolyl 4-hydroxylases (PHDs), which serve to hydroxylate proline residues situated within hypoxia-inducible factor proteins (HIFs) (7). Under hypoxic or iron-lacking conditions, PHDs are prevented from hydroxylating proline residues within the alpha (α) subunits of the HIF protein, preventing the ubiquitination and proteasomal degradation of the protein. Stabilization of HIFα results in its accumulation within the cytosol and translocation to the nucleus where it binds HIFβ and then to hypoxia response elements found on a variety of genes including heme oxygenase-1 (Ho-1) and manganese superoxide dismutase (Mnsod).Previous studies have demonstrated that deferoxamine, an iron chelator, can activate HIF-1α and prevent neuronal death in both in vitro and in vivo models of ischemia likely via inhibition of PHDs (8, 9). PHD inhibitors have been demonstrated to prevent oxidative cell death and ischemic injury via HIF pathway activation (10). More recently, it has been shown that inactivation of HIF-1α in specific cortical and striatal neurons exacerbated tissue damage in a mouse model of ischemia (11). With increasing evidence of the protective effects of induction of HIF-dependent gene products involved in iron regulation, cell survival, and energy metabolism, PHD inhibitors have been implicated as targets for neuroprotection in the central nervous system. We demonstrate here that PHD inhibition increases induction of HIF and HIF-related genes, functionally impacts on parameters of iron homeostasis and metabolic function, and, most importantly, significantly reduces the extent of DAergic nigrostriatal injury observed in the well established murine MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) PD model.     

Role of P450 Monooxygenases in the Degradation of the Endocrine-Disrupting Chemical Nonylphenol by the White Rot Fungus Phanerochaete chrysosporium

The white rot fungus Phanerochaete chrysosporium extensively degraded the endocrine disruptor chemical nonylphenol (NP; 100% of 100 ppm) in both nutrient-limited cultures and nutrient-sufficient cultures. The P450 enzyme inhibitor piperonyl butoxide caused significant inhibition (∼75%) of the degradation activity in nutrient-rich malt extract (ME) cultures but no inhibition in defined low-nitrogen (LN) cultures, indicating an essential role of P450 monooxygenase(s) in NP degradation under nutrient-rich conditions. A genome-wide analysis using our custom-designed P450 microarray revealed significant induction of multiple P450 monooxygenase genes by NP: 18 genes were induced (2- to 195-fold) under nutrient-rich conditions, 17 genes were induced (2- to 6-fold) in LN cultures, and 3 were induced under both nutrient-rich and LN conditions. The P450 genes Pff 311b (corresponding to protein identification number [ID] 5852) and Pff 4a (protein ID 5001) showed extraordinarily high levels of induction (195- and 167-fold, respectively) in ME cultures. The P450 oxidoreductase (POR), glutathione S-transferase (gst), and cellulose metabolism genes were also induced in ME cultures. In contrast, certain metabolic genes, such as five of the peroxidase genes, showed partial downregulation by NP. This study provides the first evidence for the involvement of P450 enzymes in NP degradation by a white rot fungus and the first genome-wide identification of specific P450 genes responsive to an environmentally significant toxicant.Endocrine-disrupting chemicals (EDCs) are widely distributed environmental contaminants. Surfactants are among the most commonly found environmental EDCs because of their extensive applications, which range from use as industrial chemicals to inclusion in common consumer products. In the United States, Japan, and Western Europe, surfactants are employed most frequently as detergents and as agents in textile, fiber, cosmetics, and pharmaceutical manufacturing. Nearly as common are uses in mining and flotation and in petroleum, paint, lacquer, plastic manufacturing, food, pulp and paper, agrochemical, and leather and fur industries (21).Alkylphenol ethoxylates are an important class of surfactants. Biodegradation of alkylphenol ethoxylates results in shortening of the ethoxylate chains, ultimately leading to the generation of alkylphenols, particularly nonyl- and octylphenols. Nonylphenol (NP) is the commercially predominant alkylphenol, representing nearly 85% of the total alkylphenol market. NP is a hydrophobic compound used primarily in the chemical manufacturing industry and exists as multiple congeners (11). Several congeners are relatively resistant to biodegradation and are therefore frequently detected in wastewater treatment plant effluents and rivers (15, 20, 25, 31, 48). In previous studies, 4-n-NP has been used as a test compound in risk assessment and biodegradation analyses (16, 23, 39). However, industrially generated technical-grade NP, consisting of more than 30 different isomers, is less biodegradable (14). This characteristic is due to the fact that more than 85% of these isomers possess a quaternary carbon atom in the branched alkyl chain, making them chemical contaminants of high environmental significance (28, 38, 40). Investigation of the susceptibility of technical-grade NP to biodegradation and assessment of health risks from this agent in in vitro and in vivo biological model systems are therefore warranted.NP is known to bind to the estrogen receptor, thereby mimicking the effects of endogenous hormones, and has been shown to induce synthesis of vitellogenin and inhibit testicular growth in rainbow trout (18, 37, 41). This observation has led to increased interest in the biodegradation and elimination of this class of xenobiotic surfactants from the environment.Certain microorganisms belonging to the bacterial and yeast groups have the ability to degrade NP (4, 5, 38, 39). Recent studies have shown the abilities of selected fungi, including white rot fungi, to degrade this chemical, albeit to various extents (33). Extracellular oxidases (laccases) have been implicated in the fungal oxidation of NP (2, 19).The model white rot fungus Phanerochaete chrysosporium is known for its ability to oxidize a wide variety of environmental toxicants. This unique characteristic has been attributed largely to its extracellular peroxidase system. Past studies have provided ample evidence, however, that environmental toxicants can be oxidized or biodegraded even in the absence of peroxidases under nutrient-sufficient (nonligninolytic) conditions (26, 44, 46), suggesting a primary role for other oxidative enzyme systems such as P450 monooxygenases.P. chrysosporium has recently been shown to possess an extensive P450 enzyme system, with ∼150 P450 monooxygenase genes in its genome (8, 30). Although there have been isolated reports indicating the involvement of P450 monooxygenation in the oxidation of xenobiotic chemicals in this organism, limited information on the identification of specific P450 genes/enzymes and related phase I and II metabolic genes important in such oxidations is available.It is well known that in other biological systems, inducers of P450 monooxygenases can also be substrates for oxidation by these enzymes (1). These considerations led us to study P450 genes inducible by NP, with the aim of identifying the putative P450 catalyst(s) involved in NP degradation. The results led to the first direct evidence for the involvement of fungal P450 enzymes in the degradation of the EDC NP and functional genomic identification of specific P450 monooxygenases responsive to an environmentally significant contaminant.     

Protein kinase‐A affects sorting and conformation of the sodium‐dependent glucose co‐transporter SGLT1

In Chinese hamster ovary cells expressing rabbit sodium‐dependent glucose transporter (rbSGLT1) protein kinase A (PKA) activators (forskolin and 8‐Br‐cAMP) stimulated α‐methyl D ‐glucopyranoside uptake. Kinetic analysis revealed an increase in both V_max and affinity of the transport. Immunohistochemistry and biotinylation experiments showed that this stimulation was accompanied by an increased amount of SGLT1 localized into the plasma membrane, which explains the higher V_max of the transport. Cytochalasin D only partly attenuated the effect of forskolin as did deletion of the PKA phosphorylation site of SGLT1 in transient transfection studies. Experiments using an anti‐phosphopeptide antibody revealed that forskolin also increased the extent of phosphorylation of SGLT1 in the membrane fraction. These results suggested that regulation of SGLT1 mediated glucose transport involves an additional direct effect on SGLT1 by phosphorylation. To evaluate this assumption further, phosphorylation studies of recombinant human SGLT1 (hSGLT1) in vitro were performed. In the presence of the catalytic subunit PKA and [³²P] ATP 1.05 mol of phosphate were incorporated/mol of hSGLT1. Additionally, phosphorylated hSGLT1 demonstrated a reduction in tryptophan fluorescence intensity and a higher quenching by the hydrophilic Trp quencher acrylamide, particularly in the presence of D ‐glucose. These results indicate that PKA‐mediated phosphorylation of SGLT1 changes the conformation of the empty carrier and the glucose carrier complex, probably causing the increase in transport affinity. Thus, PKA‐mediated phosphorylation of the transporter represents a further mechanism in the regulation of SGLT1‐mediated glucose transport in epithelial cells, in addition to a change in surface membrane expression. J. Cell. Biochem. 106: 444–452, 2009. © 2008 Wiley‐Liss, Inc.     

Water-soluble prodrugs of an Aurora kinase inhibitor

Compound 1 (SNS-314) is a potent and selective Aurora kinase inhibitor that is currently in clinical trials in patients with advanced solid tumors. This communication describes the synthesis of prodrug derivatives of 1 with improved aqueous solubility profiles. In particular, phosphonooxymethyl-derived prodrug 2g has significantly enhanced solubility and is converted to the biologically active parent (1) following iv as well as po administration to rodents.