Effects of Ambient Temperature on Growth Performance, Blood Metabolites, and Immune Cell Populations in Korean Cattle Steers

Exposure to cold may affect growth performance in accordance with the metabolic and immunological activities of animals. We evaluated whether ambient temperature affects growth performance, blood metabolites, and immune cell populations in Korean cattle. Eighteen Korean cattle steers with a mean age of 10 months and a mean weight of 277 kg were used. All steers were fed a growing stage-concentrate diet at a rate of 1.5% of body weight and Timothy hay ad libitum for 8 weeks. Experimental period 1 (P1) was for four weeks from March 7 to April 3 and period 2 (P2) was four weeks from April 4 to May 1. Mean (8.7°C) and minimum (1.0°C) indoor ambient temperatures during P1 were lower (p<0.001) than those (13.0°C and 6.2°C, respectively) during P2. Daily dry matter feed intake in both the concentrate diet and forage groups was higher (p<0.001) during P2 than P1. Average daily weight gain was higher (p<0.001) during P2 (1.38 kg/d) than P1 (1.13 kg/d). Feed efficiency during P2 was higher (p = 0.015) than P1. Blood was collected three times; on March 7, April 4, and May 2. Nonesterified fatty acids (NEFA) were higher on March 7 than April 4 and May 2. Blood cortisol, glucose, and triglyceride concentrations did not differ among months. Blood CD4+, CD8+, and CD4+CD25+ T cell percentages were higher, while CD8+CD25+ T cell percentage was lower, during the colder month of March than during May, suggesting that ambient temperature affects blood T cell populations. In conclusion, colder ambient temperature decreased growth and feed efficiency in Korean cattle steers. The higher circulating NEFA concentrations observed in March compared to April suggest that lipolysis may occur at colder ambient temperatures to generate heat and maintain body temperature, resulting in lower feed efficiency in March.

NAMPT suppresses glucose deprivation-induced oxidative stress by increasing NADPH levels in breast cancer

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme involved in NAD+ biosynthesis. Although NAMPT has emerged as a critical regulator of metabolic stress, the underlying mechanisms by which it regulates metabolic stress in cancer cells have not been completely elucidated. In this study, we determined that breast cancer cells expressing a high level of NAMPT were resistant to cell death induced by glucose depletion. Furthermore, NAMPT inhibition suppressed tumor growth in vivo in a xenograft model. Under glucose deprivation conditions, NAMPT inhibition was found to increase the mitochondrial reactive oxygen species (ROS) level, leading to cell death. This cell death was rescued by treatment with antioxidants or NAD+. Finally, we showed that NAMPT increased the pool of NAD+ that could be converted to NADPH through the pentose phosphate pathway and inhibited the depletion of reduced glutathione under glucose deprivation. Collectively, our results suggest a novel mechanism by which tumor cells protect themselves against glucose deprivation-induced oxidative stress by utilizing NAMPT to maintain NADPH levels.

Pyrosequencing Analysis of Subgingival Microbiota in Distinct Periodontal Conditions

Subgingival microorganisms are potentially associated with periodontal diseases. However, changes in the subgingival microbiota during the progress of periodontal diseases are poorly understood. In this study, we analyzed bacterial communities in the subgingival paper point samples from 32 Korean individuals with no sign of disease, gingivitis, or periodontitis using 454 FLX Titanium pyrosequencing. A total of 256,113 reads representing 26 phyla, 433 genera, and 1,016 species were detected. Bacteroidetes, Fusobacteria, Synergistetes, and Spirochaetes were the abundant phyla in periodontitis subjects, whereas Firmicutes and Proteobacteria were identified as the dominant phyla in the gingivitis and healthy subjects, respectively. Although high levels of Porphyromonas, Fusobacterium, Fretibacterium, Rothia, Filifactor, and Treponema genera were observed in the periodontitis subjects, Streptococcus, Capnocytophaga, Leptotrichia, and Haemophilus genera were found at high frequency in the gingivitis subjects. Species including Porphyromonas gingivalis, Fusobacterium nucleatum, and Fretibacterium fastidiosum were significantly increased in periodontitis subjects. On the other hand, Streptococcus pseudopneumoniae, Haemophilus parainfluenzae, and Leptotrichia hongkongensis were preferentially observed in the gingivitis subjects. Intriguingly, the halophile Halomonas hamiltonii was revealed as a predominant species in the healthy subjects. Based on Fast UniFrac analysis, distinctive bacterial clusters were classified for the healthy, gingivitis, and periodontitis state. The current findings might be useful for understanding the pathogenesis, diagnosis, and treatment of periodontal diseases.

The effects of fermented soybean meal on immunophysiological and stress-related parameters in Holstein calves after weaning

The present experiment was conducted to investigate the effects of partial substitution of soybean meal (SBM) with fermented SBM (FSBM) on immunophysiological and stress-related parameters in Holstein calves after weaning. Eighteen Holstein calves were randomly assigned to receive either SBM or FSBM (5% of SBM was replaced with FSBM) calf starter and calves were weaned at 42 d of age. It was noted that FSBM contained a lower content of trypsin inhibitor but higher crude protein, amino acids, and small-sized peptides than those of SBM. The group fed FSBM calf starter significantly increased body weight gain and intakes of both feed and milk, when compared with those fed SBM calf starter at 4 wk of age. Calves fed the FSBM calf starter had significantly lower fecal scores than those fed the SBM calf starter during both pre- and postweaning periods. Calves also had better health scores when fed the FSBM calf starter than those fed SBM during the preweaning period. Weaning challenge significantly increased proinflammatory cytokines, tumor necrosis factor α, IL-1β, and IL-6 levels at 1d postweaning (DPW). The TNF-α and IL-6 levels of the SBM group were significantly higher compared with those of the FSBM group at 3 DPW. Acute phase proteins (serum amyloid A and haptoglobin) in the serum were increased after weaning. Concentrations of serum amyloid A and haptoglobin in calves fed FSBM calf starter were significantly lower than those fed the SBM calf starter at 3 and 5 DPW, respectively. The concentration of cortisol was significantly lower in the FSBM group than that of the SBM group at 3 DPW. Weaning stress did not cause drastic changes in the total serum immunoglobulin levels and composition of peripheral lymphocytes. Our results indicate that FSBM may not only improve growth performance, feed intake, and health conditions during the preweaning period, but also alleviate stress responses, which was indicated by reduced induction of stress hormone, proinflammatory cytokines, and acute phase proteins in Holstein calves after weaning.

Intracranial ictal onset zone in nonlesional lateral temporal lobe epilepsy on scalp ictal EEG

OBJECTIVE

To determine the ictal focus and the role of seizure characteristics, fluorodeoxyglucose (FDG) PET, and subtraction ictal SPECT in patients diagnosed as having nonlesional lateral temporal lobe epilepsy by long-term scalp video-EEG monitoring.

METHODS

The authors studied 33 consecutive patients with nonlesional neocortical epilepsy who had a scalp ictal onset zone localized in the temporal lobe and good surgical outcome after focal neocortical resection. All patients were evaluated using intracranial recordings prior to resection. Semiology, FDG-PET, and ictal-interictal subtraction SPECT were used to verify the diagnostic role of these methods in the localization of epileptic foci.

RESULTS

The ictal onset zones, confirmed by intracranial study, were the lateral temporal (22 patients), parietal (5), frontal (3), temporoparietal (2), and occipital (1) areas. FDG-PET analyzed by statistical parametric mapping correctly localized the epileptogenic lobe in 18 of 33 patients and subtraction ictal SPECT correctly localized it in 13 of 25 patients. However, in patients with extratemporal ictal onset zones, FDG-PET and ictal SPECT in combination correctly localized the epileptogenic lobe in only 3 of 11 cases.

CONCLUSIONS

An extratemporal ictal onset zone was encountered in patients with nonlesional lateral temporal lobe seizures based on scalp video-EEG monitoring. FDG-PET and subtraction SPECT had localizing value in no more than half of patients.

Intracranial ictal onset zone in nonlesional lateral temporal lobe epilepsy on scalp ictal EEG

OBJECTIVE

To determine the ictal focus and the role of seizure characteristics, fluorodeoxyglucose (FDG) PET, and subtraction ictal SPECT in patients diagnosed as having nonlesional lateral temporal lobe epilepsy by long-term scalp video-EEG monitoring.

METHODS

The authors studied 33 consecutive patients with nonlesional neocortical epilepsy who had a scalp ictal onset zone localized in the temporal lobe and good surgical outcome after focal neocortical resection. All patients were evaluated using intracranial recordings prior to resection. Semiology, FDG-PET, and ictal-interictal subtraction SPECT were used to verify the diagnostic role of these methods in the localization of epileptic foci.

RESULTS

The ictal onset zones, confirmed by intracranial study, were the lateral temporal (22 patients), parietal (5), frontal (3), temporoparietal (2), and occipital (1) areas. FDG-PET analyzed by statistical parametric mapping correctly localized the epileptogenic lobe in 18 of 33 patients and subtraction ictal SPECT correctly localized it in 13 of 25 patients. However, in patients with extratemporal ictal onset zones, FDG-PET and ictal SPECT in combination correctly localized the epileptogenic lobe in only 3 of 11 cases.

CONCLUSIONS

An extratemporal ictal onset zone was encountered in patients with nonlesional lateral temporal lobe seizures based on scalp video-EEG monitoring. FDG-PET and subtraction SPECT had localizing value in no more than half of patients.

The antithrombotic efficacy of AT-1459, a novel, direct thrombin inhibitor, in rat models of venous and arterial thrombosis

The antithrombotic efficacy of AT-1459, a novel, direct thrombin inhibitor (Ki = 4.9 nM) was evaluated in rat models of venous thrombosis combined with a bleeding time test and arterial thrombosis. After drugs were given by i. v. bolus injection plus a continuous infusion, the ID50, (a dose that exhibits 50% inhibition of thrombus formation over each vehicle group) values of AT-1459, argatroban, and dalteparin were 0.04 mg/kg plus 0.04 mg/kg/h, 0.1 mg/kg plus 0.4 mg/ kg/h, and 13.0 IU/kg plus 26.0 IU/kg/h, respectively, in the venous thrombosis study. The BT2 (a dose that causes 2-fold prolongation of bleeding time over each vehicle group) values of AT-1459, argatroban, and dalteparin were 0.9 mg/kg plus 0.9 mg/kg/h, 1.0 mg/kg plus 0.6 mg/kg/h, and 345.5 IU/kg plus 691.0 IU/kg/h in the rat tail transection model. The ratios of BT2/ID50 of AT-1459, argatroban, and dalteparin were 22.5, 10.0, and 26.6, respectively. In a rat model of arterial thrombosis induced by topical FeCl2 application, intravenous administration of AT-1459, argatroban, and dalteparin improved the vessel patency significantly (P < 0.01) at 0.6 mg/kg plus 0.6 mg/kg/h, 0.6 mg/kg plus 2.4 mg/kg/h, and 300 IU/kg plus 600 IU/kg/h, respectively. The oral antithrombotic effect of AT-1459 lasted for 6 after administering 30 mg/kg and improved the vessel patency significantly 1 h after administering the same dose in venous and arterial thrombosis models, respectively, with a rapid onset of action. Warfarin also inhibited thrombus weight and improved the vessel patency significantly after oral administration of 0.3 mg/kg for three consecutive days in the same study. The antithrombotic and hemorrhagic effects of all drugs studied were correlated with plasma concentration or clotting times. These results suggest that AT-1459 may be clinically useful as an orally available antithrombotic agent for the prevention of venous and arterial thrombosis.

Effects of lipids on the interaction of SecA with model membranes

The effects of nonlamellar-prone lipids, diacylglycerol and phosphatidylethanolamine (PE), on the kinetic association of SecA with model membranes were examined by measuring changes in the intrinsic emission fluorescence with a stopped-flow apparatus. Upon interaction with standard liposomes composed of 50 mol% dioleolyphosphatidylcholine (DOPC) and 50 mol% of dioleoylphosphatidylglycerol (DOPG), the intrinsic fluorescence intensity of SecA was decreased after a lapse of time with a rate constant of 0.0049 s(-1). When the DOPC of the standard vesicles was gradually replaced with either dioeloyl PE (DOPE) or Escherichia coli (E. coli) PE, the rate constant increased appreciably as a function of PE concentration, in the order DOPE > E. coli PE. In addition, when the PE of E. coli PE/DOPG (50/50) vesicles was replaced with more than 5 mol% dioleoylglycerol (DOG), the rate constant further increased by 40%. The incorporation of nonlamellar-prone lipids in the vesicles also enhanced the binding of SecA to model membranes in the order DOPE > or = E. coli PE/DOG > E. coli PE > DOPC. These results provide the first kinetic evidence for the importance of nonlamellar-prone phospholipids for the association rate of SecA with membranes.

Bilateral tonic (Adie's) pupils in Vogt-Koyanagi-Harada syndrome

We report a 38-year-old woman with bilateral tonic (Adie's) pupils who was diagnosed as having Vogt-Koyanagi-Harada syndrome. The tonic pupils persisted after other clinical features of this syndrome had disappeared.

Oxidations of p-alkoxyacylanilides catalyzed by human cytochrome P450 1A2: structure-activity relationships and simulation of rate constants of individual steps in catalysis

Human cytochrome P450 (P450) 1A2 is involved in the oxidation of many important drugs and carcinogens. The prototype substrate phenacetin is oxidized to an acetol as well as the O-dealkylation product [Yun, C.-H., Miller, G. P., and Guengerich, F. P. (2000) Biochemistry 39, 11319-11329]. In an effort to improve rates of catalysis of P450 1A2 enzymes, we considered a set of p-alkoxyacylanilide analogues of phenacetin and found that variations in the O-alkyl and N-acyl substituents altered the rates of the two oxidation reactions and the ratio of acetol/phenol products. Moving one methylene group of phenacetin from the O-alkyl group to the N-acyl moiety increased rates of both oxidations approximately 5-fold and improved the coupling efficiency (oxidation products formed/NADPH consumed) from 6% to 38%. Noncompetitive kinetic deuterium isotope effects of 2-3 were measured for all O-dealkylation reactions examined with wild-type P450 1A2 and the E225I mutant, which has 6-fold higher activity. A trend of decreasing kinetic deuterium isotope effect for E225I > wild-type > mutant D320A was observed for O-demethylation of p-methoxyacetanilide, which follows the trend for k(cat). The set of O-dealkylation and acetol formation results for wild-type P450 1A2 and the E225I mutant with several of the protiated and deuterated substrates were fit to a model developed for the basic catalytic cycle and a set of microscopic rate constants in which the only variable was the rate of product formation (substrate oxygenation, including hydrogen abstraction). In this model, k(cat) is considerably less than any of the microscopic rate constants and is affected by several individual rate constants, including the rate of formation of the oxygenating species, the rate of substrate oxidation by the oxygenating species, and the rates of generation of reduced oxygen species (H(2)O(2), H(2)O). This analysis of the effects of the individual rate constants provides a framework for consideration of other P450 reactions and rate-limiting steps.

Inhibition mechanisms of bioflavonoids extracted from the bark of Pinus maritima on the expression of proinflammatory cytokines

The effect of bioflavonoids extracted from the bark of Pinus maritima, Pycnogenol (PYC), on gene expression of the proinflammatory cytokines interleukin-1beta (IL-1beta) and interleukin-2 (IL-2) were investigated in RAW 264.7 cells and Jurkat E6.1 cells, respectively. PYC exerted strong scavenging activities against reactive oxygen species (ROS) generated by H2O2 in RAW 264.7. In situ ELISA, immunoblot analysis, and competitive RT-PCR demonstrated that pretreatment of LPS-stimulated RAW 264.7 cells with PYC dose-dependently reduced both the production of IL-1beta and its mRNA levels. Furthermore, in the same cells, PYC blocked the activation of nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1), two major transcription factors centrally involved in IL-1beta gene expression. Concordantly, pretreatment of the cells with PYC abolished the LPS-induced IkappaB degradation. We also investigated the effect of PYC on IL-2 gene expression in phorbol 12-myristate 13acetate plus ionomycin (PMA/Io)-stimulated human T-cell line Jurkat E6.1. PYC inhibited the PMA/Io-induced IL-2 mRNA expression. However, as demonstrated in a reporter gene assay system, the mechanism of IL-2 gene transcriptional regulation by PYC was different from the regulation of IL-1beta. PYC inhibited both NF-AT and AP-1 chloramphenicol acetyltransferase (CAT) activities in transiently transfected Jurkat E6.1, but not NF-kappaB CAT activity. We also found that PYC can destabilize PMA/Io-induced IL-2 mRNA by posttranscriptional regulation. All these results suggest that bioflavonids can be useful therapeutic agents in treating many inflammatory, autoimmune, and cardiovascular diseases based on its diverse action mechanisms.

Short-term regulation of NHE3 by EGF and protein kinase C but not protein kinase A involves vesicle trafficking in epithelial cells and fibroblasts

NHE3 is an intestinal epithelial isoform Na+/H+ exchanger that is present in the brush border of small intestinal, colonic, and gallbladder Na(+)-absorbing epithelial cells. NHE3 is acutely up- and downregulated in response to some G protein-linked receptors, tyrosine kinase receptors, and protein kinases when studied in intact ileum, when stably expressed in PS120 fibroblasts, and in the few studies reported in the human colon cancer cell line Caco-2. In most cases this is due to changes in Vmax of NHE3, although in response to cAMP and squalamine there are also changes in the K'(H+)i of the exchanger. The mechanism of the Vmax regulation as shown by cell surface biotinylation and confocal microscopy in Caco-2 cells and biotinylation in PS120 cells involves changes in the amount of NHE3 on the plasma membrane. In addition, in some cases there are also changes in turnover number of the exchanger. In some cases, the change in amount of NHE3 in the plasma membrane is associated with a change in the amount of plasma membrane. A combination of biochemical studies and transport/inhibitor studies in intact ileum and Caco-2 cells demonstrated that the increase in brush border Na+/H+ exchange caused by acute exposure to EGF was mediated by PI 3-kinase. PI 3-kinase was also involved in FGF stimulation of NHE3 expressed in fibroblasts. Thus, NHE3 is another example of a transport protein that is acutely regulated in part by changing the amount of the transporter on the plasma membrane by a process that appears to involve vesicle trafficking and also to involve changes in turnover number.

Ezrin-radixin-moesin-binding phosphoprotein 50 is expressed at the apical membrane of rat liver epithelia

Ezrin-radixin-moesin (ERM)-binding phosphoprotein 50 (EBP50) and NHE3 Kinase A regulatory protein (E3KARP) are membrane-cytoskeleton linking proteins that utilize 2 PSD-95/DIg/ZO-1 (PDZ) domains and an ERM binding site to coordinate cyclic adenosine monophosphate (cAMP)-regulated ion transport in a number of distinct epithelia. ERM family members serve to anchor EBP50 and E3KARP to the actin cytoskeleton and sequester protein kinase A (PKA) to these protein complexes. In hepatocytes and cholangiocytes, the epithelial cells of the bile secretory unit, cAMP-activated PKA stimulates secretion and bile formation, but the molecular mechanisms, including the potential contribution of EBP50 and E3KARP, remain undetermined. The present studies evaluated the comparative expression and localization of EBP50 and E3KARP in rat hepatocytes and cholangiocytes. Complementary DNAs encoding rat EBP50 and E3KARP were identified by reverse transcription-polymerase chain reaction in both epithelial cell types and subsequently sequenced. Northern and Western analysis showed the presence of EBP50 messenger RNA and protein in both hepatocytes and cholangiocytes. Confocal immunofluorescence revealed EBP50 was concentrated at the apical domain of both cell types. E3KARP was also expressed in cholangiocytes but had a distinct cytoplasmic/nuclear distribution. In dominant-negative transfection studies, patch clamp analysis of Mz-ChA1 cholangiocarcinoma cells showed that expression of the PDZ1 domain of EBP50 selectively decreased the endogenous cAMP-mediated Cl secretory response. The apical expression of EBP50, presence of specific ERM proteins, and functional effects of PDZ1 expression on cholangiocyte secretion suggest EBP50 is positioned to contribute to the organization and regulation of bile secretory proteins in both hepatocytes and cholangiocytes.

Effects of flupyrazofos on liver microsomal cytochrome P450 in the male Fischer 344 rat

1. The effects of flupyrazofos on liver microsomal cytochrome P450 were investigated in the male Fischer 344 rat. When rats were treated intraperitoneally with flupyrazofos for 3 consecutive days, the activities of ethoxyresorufin O-deethylase and testosterone 2 beta-hydroxylase were significantly reduced, whereas the activities of pentoxyresorufin beta-depentylase and testosterone 6beta- and 7 alpha-hydroxylases were induced in liver microsomes. 2. Within 24 h after treatment with 50 m kg(-1) flupyrazofos, most enzyme activities were decreased, indicating the interaction of flupyrazofos with cytochrome P450. 3. In Western immunoblotting, cytochrome P4502B1/2 proteins were clearly induced by treatment with flupyrazofos, whereas P4501A1/2 and 2C6 proteins were reduced in liver microsomes. 4. The present results indicate that flupyrazofos modulates the expression of cytochrome P450 in rat.

Effect of bioflavonoids extracted from the bark of Pinus maritima on proinflammatory cytokine interleukin-1 production in lipopolysaccharide-stimulated RAW 264.7

Currently, bioflavonoids have been known to have strong antioxidant capacities, and a variety of efforts have been made to identify the utilities of bioflavonoids in treating various diseases based on their antioxidant capacities. The effects of bioflavonoids extracted from the bark of Pinus maritima Pycnogenol (PYC) on free radical formation, activation of redox sensitive transcription factors, as well as interleukin-1 beta (IL-1 beta) production were investigated in murine macrophage cell lines. PYC exerted strong scavenging activities against reactive oxygen species generated either by H(2)O(2) or PMA in RAW 264.7 and IC-21 cells, respectively. In situ ELISA, immunoblot analysis, and competitive RT-PCR demonstrated that PYC pretreatment of LPS-stimulated RAW 264.7 cells dose-dependently reduced both the production of IL-1 beta and its mRNA levels. Furthermore, in the same cells, PYC blocked the activation of nuclear factor kappa B (NF-kappa B) and activator protein-1 (AP-1), two major transcription factors centrally involved in IL-1 beta gene expression. When RAW 264.7 cells were stimulated with LPS, the inhibitor protein I kappa B largely disappeared from cytosolic fractions. However, pretreatment of the cells with PYC abolished the LPS-induced I kappa B degradation. These results suggest that PYC can inhibit the expression of the proinflammatory cytokine IL-1 by regulating redox-sensitive transcription factors. This study may support the possibility that bioflavonoids including PYC can be used as antiinflammatory and immunosuppressive drugs based on their radical scavenging activities.

E3KARP mediates the association of ezrin and protein kinase A with the cystic fibrosis transmembrane conductance regulator in airway cells

Although it is generally recognized that cystic fibrosis transmembrane conductance regulator (CFTR) contains a PSD-95/Disc-large/ZO-1 (PDZ)-binding motif at its COOH terminus, the identity of the PDZ domain protein(s) that interact with CFTR is uncertain, and the functional impact of this interaction is not fully understood. By using human airway epithelial cells, we show that CFTR associates with Na(+)/H(+) exchanger (NHE) type 3 kinase A regulatory protein (E3KARP), an EBP50/NHE regulatory factor (NHERF)-related PDZ domain protein. The PDZ binding motif located at the COOH terminus of CFTR interacts preferentially with the second PDZ domain of E3KARP, with nanomolar affinity. In contrast to EBP50/NHERF, E3KARP is predominantly localized (>95%) in the membrane fractions of Calu-3 and T84 cells, where CFTR is located. Moreover, confocal immunofluorescence microscopy of polarized Calu-3 monolayers shows that E3KARP and CFTR are co-localized at the apical membrane domain. We also found that ezrin associates with E3KARP in vivo. Co-expression of CFTR with E3KARP and ezrin in Xenopus oocytes potentiated cAMP-stimulated CFTR Cl(-) currents. These results support the concept that E3KARP functions as a scaffold protein that links CFTR to ezrin. Since ezrin has been shown previously to function as a protein kinase A anchoring protein, we suggest that one function served by the interaction of E3KARP with both ezrin and CFTR is to localize protein kinase A in the vicinity of the R-domain of CFTR. Since ezrin is also an actin-binding protein, the formation of a CFTR.E3KARP.ezrin complex may be important also in stabilizing CFTR at the apical membrane domain of airway cells.

Rate-determining steps in phenacetin oxidations by human cytochrome P450 1A2 and selected mutants

Mutants with altered activities were obtained from random libraries of human cytochrome P450 (P450) 1A2 with the putative substrate recognition sequences (SRS) mutated [Parikh, A., Josephy, P. D., and Guengerich, F. P. (1999) Biochemistry 38, 5283-5289]. Six mutants from SRS 2 (E225I, E225N, F226I, and F226Y) and 4 (D320A and V322A) regions were expressed as oligohistidine-tagged proteins, purified to homogeneity, and used to analyze kinetics of individual steps in the catalytic cycle, to determine which reaction steps have been altered. When the wild-type, E225I, E225N, F226I, F226Y, D320A, and V322A proteins were reconstituted with NADPH-P450 reductase, rates of 7-ethoxyresorufin O-deethylation and phenacetin O-deethylation were in accord with those expected from membrane preparations. Within each assay, the values of k(cat)/K(m) varied by 2-3 orders of magnitude, and in the case of E225I and E225N, these parameters were 7-8-fold higher than for the wild-type enzyme. The coupling efficiency obtained from the rates of product formation and NADPH oxidation was low (<20%) in all enzymes. No correlation was found between activities and several individual steps in the catalytic cycle examined, including substrate binding, reduction kinetics, NADPH oxidation, and H(2)O(2) formation. Quench reactions did not show a burst for either phenacetin O-deethylation or formation of the acetol, a minor product, indicating that rate-determining steps occur prior to product formation. Inter- and intramolecular kinetic deuterium isotope effects for phenacetin O-deethylation were 2-3. In the case of phenacetin acetyl hydroxylation (acetol formation), large isotope effects [(D)k(cat) or (D)(k(cat)/K(m)) > 10] were observed, providing evidence for rate-limiting C-H bond cleavage. We suggest that the very high isotope effect for acetol formation reflects rate-limiting hydrogen atom abstraction; the lower isotope effect for O-deethylation may be a consequence of a 1-electron transfer pathway resulting from the low oxidation potential of the substrate phenacetin. These pre-steady-state, steady-state, and kinetic hydrogen isotope effect studies indicate that the rate-limiting steps are relatively unchanged over an 800-fold range of catalytic activity. We hypothesize that these SRS mutations alter steps leading to the formation of the activated Michaelis complex following the introduction of the first electron.

A DNA vaccine encoding a conserved Eimeria protein induces protective immunity against live Eimeria acervulina challenge

Coccidiosis is caused by several distinct intestinal protozoa of Eimeria sp., and is responsible for intestinal lesions and severe body weight loss in chickens. To develop a DNA vaccination strategy for coccidiosis, an expression vector pMP13 encoding a conserved antigen of Eimeria was constructed by subcloning 3-1E cDNA into pBK-CMV and used to elicit protective immunity against E. acervulina. One-day-old chickens were immunized intramuscularly (IM) or subcutaneously (SC) with various doses of pMP13 expression vector ranging from 5 to 100 ug two weeks apart and were challenged with 5x10(3) E. acervulina. Chickens immunized with 5, 10, 50 or 100 ug of pMP13 plasmid, but not control plasmid, pBK-CMV, showed significantly reduced oocysts following challenge infection with E. acervulina. Two injections were in general more effective than one injection with higher dose of DNA eliciting better protection. At 10 days post challenge infection, maximum levels of circulating antibodies were detected regardless of the routes of injection, although IM injection provided higher levels of serum antibodies compared to SC injection. Serum antibody levels demonstrated a dose-dependent response showing higher antibody production at higher DNA dose. DNA immunization with pMP13 also induced significant changes in T-cell subpopulations in the spleen and duodenum intraepithelial lymphocytes. At 4 days post DNA immunization, pMP13-immunized chickens showed lower CD8, and higher CD4(+) and gammadelta T(+) cells in the duodenum compared to the pBK-CMV-immunized chickens. Following challenge infection with E. acervulina, pMP13-immunized chickens showed lower CD8(+) and alphabeta T(+) cells, and higher CD4(+) cells than pBK-CMV-immunized chickens in the duodenum. These findings demonstrate that DNA immunization with pMP13 induce local and systemic host immune responses against Eimeria.

Importance of phosphatidylethanolamine for the interaction of apocytochrome c with model membranes containing phosphatidylserine

The effect of phosphatidylethanolamine (PE) on the binding of apocytochrome c to model membranes was examined. When 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) of the standard vesicles composed of 80% of this lipid and 20% of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS) was gradually replaced with upward of 50% of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), the binding increased appreciably. Ca(2+), causing the phase separation of PS, also brought about increased binding of apocytochrome c in the PC/PS system, underlining the importance of PS properties in membranes for the protein binding. The resonance energy transfer between Trp-59 in apocytochrome c and pyrene-PS incorporated into bilayers showed that the replacement of PC with PE increased the extent of apocytochrome c penetration into membranes by a PE concentration-dependent manner. However, in the absence of PS, PE had no apparent effect on these functions of apocytochrome c, suggesting that PE-induced change(s) of acidic membrane properties is important to the association of apocytochrome c with vesicles. From the observations that the excimer to monomer fluorescence ratio of pyrene-PS increased and the fluorescence of NBD-PS was quenched with increasing concentration of PE, it was deduced that PE caused PS-enriched domains in PC/PE/PS membranes. The colocalization of pyrene-PS with BODIPY-PS by PE further supported the possibility. We suggest that PE-induced formation of PS-enriched domains acts as binding sites for apocytochrome c in membranes.

What makes P450s work? Searches for answers with known and new P450s

Random mutagenesis has been developed as an approach for the study of human cytochrome P450 (P450) enzymes and their structure and function. Sensitive screening methods are critical for the success of this approach. We have developed one system that takes advantage of the ability of human P450 1A2 to activate heterocyclic amines to mutagenic products [A. Parikh, P. D. Josephy, and F. P. Guengerich, Biochemistry, 38, 5283-5289 (1999)]. Mutants with both attenuated and enhanced activity have been recovered and subjected to further kinetic analysis. For phenacetin O-deethylation, the E225I mutant had kcat 6x > wild type; D320A had kcat 1/10x < wild type (and Km 15 x > wild type). With all three P450s, the rate of first electron reduction was similar, and all had similar binding constants for phenacetin (approximately 15 microM). All three forms yielded intermolecular, noncompetitive kinetic deuterium isotope effects of 1.5-2 [DV and D(V/K)] for O-deethylation of [OCD2CH3]-phenacetin. All three forms of P450 1A2 also formed a minor product, the acetol (C-hydroxylation of the acetyl group). This reaction had a deuterium isotope effect of approximately 14 with all three forms of the enzyme, and C-H bond breaking is the rate-determining step. Another approach to P450 2A6 involves the recent observation that this P450 can accumulate indigo [E. M. J. Gillam, A. M. A. Aguinaldo, L. M. Notley, D. Kim, R. G. Mundkowski, A. A. Volkov, F. H. Arnold, P. Soucek, J. T. DeVoss, and F. P. Guengerich, Biochem. Biophys. Res. Commun 265, 469-472 (1999)]. Current results indicate that this process involves the conversion of endogenous indole to indoxyl by the P450. The reaction may be used in assays of random mutants and has some potential applications in industry.

Interaction of human thiol-specific antioxidant protein 1 with erythrocyte plasma membrane

During the purification from human erythrocytes, human thiol-specific antioxidant protein 1 (hTSA1), one human member of the TSA/alkyl hydroperoxide reductase subunit C (AhpC) family, was fragmented to a molecular mass of 20 323.9300. The fragmented form, in contrast to the intact form, did not bind to the C-terminal peptide (Gln-185-Gln-197) antibody. On the basis of the molecular mass of the fragmented form, the cleavage site was calculated to be between Val-186 and Asp-187. The C-terminal region of hTSA1 appeared to be unnecessary for the antioxidant reaction. In addition to hTSA1, two isoenzymes (hORF06 and hTSA2) were detected in the soluble fraction, whereas only hTSA1 was detected in the membrane fraction. A membrane binding study shows that the intact form binds to erythrocyte plasma membrane but the fragment does not, which suggests that the deleted C-terminal legion (Asp-187-Gln-197) is required for the membrane binding. A model membrane study using phospholipid vesicle showed a strong association of hTSA1 with the phospholipid. Human TSA1 exhibited high catalytic activity for the reduction of the fatty acid hydroperoxide as indicated by K(m) and V(max) (89.9 microM for linoleic acid hydroperoxide, 28.64 micromol(-1) min(-1) mg(-1), respectively). In this paper, we are making the first report of the involvement of the C-terminal region of hTSA1 in membrane binding as evidence supporting the existence of the membrane-associated forms in the erythrocyte. On the basis of our observations, we suggest that hTSA1 can act as a very effective antioxidant to remove oxidative stresses not only in matrix as a free form but also in the membrane surface of red blood cells (RBC) as a membrane-associated form.

Vaccines against the avian enteropathogens Eimeria, Cryptosporidium and Salmonella

The worldwide poultry industry provides a substantial proportion of the nutritional requirement of the human population. To keep pace with the increasing demand for the high-quality, low-cost protein source that poultry provides, intensive rearing practices have been developed within the past few decades. For example, chickens are housed routinely in crowded environments under adverse conditions, and genetic strains have been selected for rapid growth, high protein-to-fat content and superior egg-laying characteristics. A major negative consequence of these practices has been an increase in the incidence of diseases. Enteric diseases in particular have emerged as a major problem threatening the future viability of the poultry industry. A variety of methods have been used to combat avian diseases in the commercial setting, including improved farm management practices, the use of antibiotic drugs, the selection of disease-resistant strains of chickens, and the manipulation of the chicken's immune system. In the latter category, the development of vaccines against the major avian diseases has become a priority in the poultry industry. This review will highlight recent progress in vaccine development against three major avian enteric pathogens: Eimeria, Cryptosporidium and Salmonella.

Analysis of disease resistance-associated parameters in broiler chickens challenged with Eimeria maxima

To determine an optimal dose for coccidial inoculation and to evaluate genetic resistance or susceptibility in individual chickens, broilers were inoculated with four different doses of Eimeria maxima oocysts. Body weight gain, fecal oocyst shedding, concentrations of plasma NO2- + NO3-, carotenoid, and interferon-gamma were measured at two different time periods postinfection. The results showed significant dose and sex effects on most parameters and interaction between dose and sex in some parameters. The dose effects were generally linear; however, some significant quadratic effects were also observed. The measurements from chickens inoculated with 10(4) oocysts displayed the highest correlation coefficients among oocyst shedding, body weight gain, and concentrations of carotenoid and NO2- + NO3-. An infection index, calculated from the correlated parameters, displayed high correlation coefficients with the parameters. The infection index may be a better parameter for evaluating individual genetic resistance against coccidial infection.

Kinetic differences in intestinal and systemic interferon-gamma and antigen-specific antibodies in chickens experimentally infected with Eimeria maxima

Kinetic differences between systemic vs. intestinal and humoral vs. cellular immune responses were elucidated in chickens experimentally infected with Eimeria maxima by comparing interferon-gamma (IFN-gamma) and parasite-specific antibody levels in the intestine and serum during the course of infection. The level of serum IFN-gamma correlated significantly with fecal oocyst shedding (r2 = 0.97), thereby establishing the importance of cell-mediated immunity in coccidia infection. Moreover, intestinal IFN-gamma levels increased sooner than those in sera (4 vs. 6 days postinfection) and both were observed prior to the appearance of parasite-specific antibodies (8-10 days postinfection), again indicating the importance of intestinal cellular immunity in coccidiosis. Although immunoglobulin (Ig)G, IgA, and IgM isotypes of the antigen-specific antibody response increased significantly in both the intestine and serum after E. maxima infection, intestinal IgA-specific antibodies showed the most dramatic increase. However, the relevance of this observation in the context of primary Eimeria infection is unclear because the coccidia parasites have reached the final stages of their life cycle by this time. These results thus demonstrate the importance of T-cell immune responses against coccidia, characterized by local IFN-gamma secretion in the intestine, in mediating host protective immune response to coccidia.

Chicken IFN-gamma monoclonal antibodies and their application in enzyme-linked immunosorbent assay

Twelve mabs against native or recombinant chicken IFN-gamma were produced and characterized by virus neutralization, ELISA, and Western blot assays. No data were obtained to suggest that the form of the immunogen (native versus recombinant) influenced the antigenic specificity of the mabs produced. While only two antibodies inhibited the in vitro virus neutralizing activity of IFN-gamma, other evidence indicated that the specificity of these mabs was indeed directed against IFN-gamma. By Western blot analysis, all antibodies identified a 17-kDa IFN-gamma polypeptide. Using a direct binding ELISA incorporating these mabs, a high correlation with IFN-gamma detected by in vitro virus neutralization was observed. The IFN-gamma ELISA was also capable of measuring cytokine levels in the sera of chickens orally infected with Eimeria maxima. At 8 and 10 days post-primary infection, significantly higher (p<0. 001) levels of serum IFN-gamma were detected in E. maxima infected chickens compared to uninfected controls. These results indicate that a mab-based direct binding ELISA is suitable to measure chicken IFN-gamma in a variety of formats.

Eimeria tenella infection induces local gamma interferon production and intestinal lymphocyte subpopulation changes

The role of intestinal lymphocytes and gamma interferon (IFN-gamma) production in protective immunity to Eimeria tenella infection was evaluated in two inbred strains of chickens (SC and TK) that display different patterns of susceptibility to coccidiosis. Oral inoculation of either strain with E. tenella led to parasite invasion of the intestinal cecum and cecal tonsils. Greater fecal oocyst shedding was seen in TK chickens. Flow cytometric analyses of cecal tonsil lymphocytes demonstrated greater numbers of CD4(+) and T-cell receptor gammadelta-positive (TCR1(+)) cells in SC chickens and elevated numbers of CD8(+) and TCR2(+) cells in TK chickens following primary infection. IFN-gamma mRNA expression was significantly increased in cecal tonsil and intraepithelial lymphocytes at days 6 and 8, respectively, after primary infection in SC compared to TK chickens. While no differences were noted between cecal tonsil lymphocytes of the two strains following secondary infection, TK chickens showed elevated IFN-gamma transcript levels in intestinal intraepithelial lymphocytes at this time. Selective depletion of CD4(+), but not CD8(+), cecal tonsil lymphocytes in SC chickens resulted in a reduced IFN-gamma mRNA expression, indicating that CD4(+) cells are the primary source of this cytokine. Collectively, these results indicate that local lymphocyte responses and production of IFN-gamma are influenced by host genetic factors.

Intestinal immune responses to coccidiosis

Intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and production efficiency of livestock and poultry. Coccidiosis is an intestinal infection caused by intracellular protozoan parasites belonging to several different species of Eimeria. Infection with coccidia parasites seriously impairs the growth and feed utilization of chickens and costs the US poultry industry more than $1.5 billion in annual losses. Although acquired immunity to Eimeria develops following natural infection, due to the complex life cycle and intricate host immune response to Eimeria, vaccine development has been difficult and a better understanding of the basic immunobiology of pertinent host-parasite interactions is necessary for developing effective immunological control strategies against coccidiosis. Chickens infected with Eimeria produce parasite specific antibodies in both the circulation and mucosal secretions but humoral immunity plays only a minor role in protection against this disease. Rather, recent evidence implicates cell-mediated immunity as the major factor conferring resistance to coccidiosis. This review will summarize current understanding of the avian intestinal immune system and its response to Eimeria as well as provide a conceptual overview of the complex molecular and cellular events involved in intestinal immunity to coccidiosis. It is anticipated that increased knowledge of the interaction between parasites and host immunity will stimulate the birth of novel immunological and molecular biological concepts in the control of intestinal parasitism.

Cloning and characterization of the chloroplast elongation factor EF-Tu cDNA of Oryza sativa L

From the rice leaf cDNA library, we have cloned a cDNA encoding rice chloroplast translational elongation factor EF-Tu (tufA). The rice tufA cDNA clone contains 1678 nucleotides and codes for a 467 amino acid protein including a putative chloroplast transit peptide of 59 amino acid residues. The predicted molecular mass of the mature protein is approximately 45 kDa. This cDNA clone contains the 61 nucleotides of the 5' untranslated region (UTR) and the 213 nucleotides of 3' UTR. Amino acid sequence identity of the rice tufA with the mature chloroplast EF-Tu proteins of tobacco, pea, arabidopsis, and soybean ranges from 83% to 86%. The deduced polypeptide of the rice tufA cDNA contains GTP binding domains in its N-terminal region and chloroplast EF-Tu signature regions in the C-terminal region. The rice tufA appears to exist as a single copy gene, although its homologues of maize and oat exist as multiple copy genes. The rice tufA gene is located in chromosome 1 and is more highly expressed in the leaf than in root tissue.

Phase properties of liquid-crystalline Phosphatidylcholine/Phosphatidylethanolamine bilayers revealed by fluorescent probes

The mixing properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were examined in liquid-crystalline phase using fluorescent probes incorporated into lipid bilayers. The excimer to monomer (E/M) fluorescence ratio of 1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (PPC) versus PPC concentration was higher for binary mixtures containing phosphatidylcholine (PC)/phosphatidylethanolamine (PE) (1:1) compared to PC matrix. When POPC was gradually replaced with POPE, the E/M ratio also increased suggesting the enhanced lateral mobility or the lateral enrichment of PPC into domains or both. Evidences for the PE-induced domain formation were further provided by resonance energy transfer between 2-(4, 4-difluoro-5-methyl-4-boro-3a, 4a-diaza-s-indacene-3-dodecanoyl)-1-hexadecanoyl-sn-glycero- 3-phospho choline and PPC, which was enhanced as a function of PE concentration, and by the polarization of 1,6-diphenyl-1,3, 5-hexatriene. In addition, PE reduced free volume and polarity of lipid bilayers as measured by the emission fluorescence of 1,2-bis PPC and 6-lauroyl-2-dimethylaminonaphthalene. When POPE analogs with a methylated head group instead of normal POPE were used, the diminished effect on the domain formation was shown in the order N-methyl PE > N,N-dimethyl PE. The results suggest that the mixing properties of POPE and POPC are not random but that lipid domains of phospholipids are formed.

cAMP-induced phosphorylation and inhibition of Na(+)/H(+) exchanger 3 (NHE3) are dependent on the presence but not the phosphorylation of NHE regulatory factor

The members of the regulatory factor (RF) gene family, Na(+)/H(+) exchanger (NHE)-RF and NHE3 kinase A regulatory factor (E3KARP) are necessary for cAMP to inhibit the epithelial brush border NHE isoform 3 (NHE3). The mechanism of their action was studied using PS120 fibroblasts stably transfected with rabbit NHE3 and wild type rabbit NHE-RF or wild type human E3KARP. 8-Bromo-cAMP (8-Br-cAMP) had no effect on Na(+)/H(+) exchange activity in cells expressing NHE3 alone. In contrast, in cells co-expressing NHE-RF, 8-Br-cAMP inhibited NHE3 by 39%. In vivo phosphorylation of NHE3 demonstrated that cAMP increased phosphorylation in two chymotrypsin-generated phosphopeptides of NHE3 in cells containing NHE-RF or E3KARP but not in cells lacking these proteins. The requirement for phosphorylation of NHE-RF in this cAMP-induced inhibition of NHE3 was examined by studying a mutant NHE-RF in which serines 287, 289, and 290 were mutated to alanines. Wild type NHE-RF was a phosphorylated protein under basal conditions, but treatment with 8-Br-cAMP did not alter its phosphorylation. Mutant NHE-RF was not phosphorylated either under basal conditions or after 8-Br-cAMP. 8-Br-cAMP inhibited NHE3 similarly in PS120/NHE3 cells containing wild type or mutant NHE-RF. NHE-RF and NHE3 co-precipitated and did so similarly with and without cAMP. Mutant NHE-RF also similarly immunoprecipitated NHE3 in the presence and absence of 8-Br-cAMP. This study shows that members of the regulatory factor gene family, NHE-RF and E3KARP, are necessary for cAMP inhibition of NHE3 by allowing NHE3 to be phosphorylated. This inhibition is not dependent on the phosphorylation of NHE-RF.

Phospholipase D activity of cytochrome P450 in human liver endoplasmic reticulum

Phospholipase D (PLD) activity in mammalian liver endoplasmic reticulum (ER) has not been characterized. Purified human liver microsomal cytochromes P450 (P450)-P450 1A2 and P450 2E1-were shown to have appreciable PLD activity, hydrolyzing phosphatidylcholine but not other phospholipids, generating PA and choline. The activity was confirmed using recombinant and mutated human P450s expressed in bacteria. In human liver microsomes, immunoinhibition of PLD activity was observed with anti-P450 1A2 > anti-P450 2C > anti-P450 2E1. Thus, P450 may act as a significant PLD in human liver ER and exert its biological effects by several mechanisms, including signaling functions and change of membrane properties.

Regulation of the Na/H exchanger regulatory factor in OK cells

The Na/H exchanger regulatory factor (NHE-RE), a recently cloned renal protein, is a necessary cofactor in protein kinase A-mediated inhibition of the renal brush border membrane Na/H exchanger. No studies to date, however, have examined the regulation of NHE-RF itself. The rabbit NHE-RF cDNA and an antibody to rabbit NHE-RF were used to study the effects of serum and cyclic adenosine monophosphate (cAMP) on the steady-state levels of NHE-RF mRNA and on the abundance and intracellular distribution of the protein in OK cells. Incubation of quiescent cells with serum was associated with a significant decrease in steady-state NHE-RF mRNA and protein abundance in the cytosolic and membrane fractions. Incubation of cells with cAMP for 6 h was associated with no change in NHE-mRNA at 24 h. There was, however, a 46% increase in protein abundance in the cytosolic fraction of the cell and a 43% decrease in the membrane fraction. Despite the decrease in membrane-associated NHE-RF in quiescent cells treated with serum of cAMP, there were no differences in either the basal rate of Na/H exchange transport or the inhibitory effect of the acute addition of cAMP on the transporter between experimental and control cells. These studies provide the first description of the regulation of NHE-RF. The results indicate that serum is associated with a decrease in NHE-RF mRNA and protein, while chronic exposure to cAMP is associated with an altered distribution of NHE-RF between the cytosolic and membrane fractions of OK cells.

NHE2 contains subdomains in the COOH terminus for growth factor and protein kinase regulation

The cloned epithelial cell-specific Na+/H+ exchanger (NHE) isoform NHE2 is stimulated by fibroblast growth factor (FGF), phorbol 12-myristate 13-acetate (PMA), okadaic acid (OA), and fetal bovine serum (FBS) through a change in maximal velocity of the transporter. In the present study, we used COOH-terminal truncation mutants to delineate specific domains in the COOH terminus of NHE2 that are responsible for growth factor and/or protein kinase regulation. Five truncation mutants (designated by the amino acid number at the truncation site) were stably expressed in NHE-deficient PS120 fibroblasts. The effects of PMA, FGF, OA, FBS, and W-13 [a Ca2+/calmodulin (CaM) inhibitor] were studied. Truncation mutant E2/660, but not E2/573, was stimulated by PMA. OA stimulated E2/573 but not E2/540. FGF stimulated E2/540 but not E2/499. The most truncated mutant, E2/499, was stimulated by FBS. W-13 stimulated the basal activity of the wild-type NHE2. However, W-13 had no effect on E2/755. By monitoring the emission spectra of dansylated CaM fluorescence, we showed that dansylated CaM bound directly to a purified fusion protein of glutathione S-transferase and the last 87 amino acids of NHE2 in a Ca2+-dependent manner, with a stoichiometry of 1:1 and a dissociation constant of 300 nM. Our results showed that the COOH terminus of NHE2 is organized into separate stimulatory and inhibitory growth factor/protein kinase regulatory subdomains. This organization of growth factor/protein kinase regulatory subdomains is very similar to that of NHE3, suggesting that the tertiary structures of the putative COOH termini of NHE2 and NHE3 are very similar despite the minimal amino acid identity in this part of the two proteins.

The role of NHERF and E3KARP in the cAMP-mediated inhibition of NHE3

NHE3 is the apically located Na+/H+ exchanger in the gut and in the renal proximal tubule. Acute inhibition of this transporter by cAMP requires the presence of either of two NHE3-associated proteins, NHERF or E3KARP. It has been suggested that these proteins either directly regulate NHE3 activity after being phosphorylated by protein kinase A (PKA) or that they may serve as adapters that localize PKA near NHE3. We studied the role of NHERF and E3KARP in opossum kidney cells, which endogenously express NHE3, NHERF, and ezrin and display cAMP-dependent inhibition of NHE3. In vivo phosphorylation studies showed that NHERF is a phosphoprotein under basal conditions, but does not change its phosphorylation state after 8-bromo-cAMP treatment, and that E3KARP is not phosphorylated at all. Co-immunoprecipitation showed that NHERF and E3KARP bind both NHE3 and ezrin. Using cAMP analogs it was demonstrated that NHE3 activity, measured as sodium-dependent recovery of the intracellular pH after intracellular acidification, is inhibited by PKA type II. Because others have shown that ezrin binds PKA type II and that NHE3 is phosphorylated by PKA we suggest that NHERF and E3KARP are adapters that link NHE3 to ezrin, thereby localizing PKA near NHE3 to allow NHE3 phosphorylation.

NHE3 kinase A regulatory protein E3KARP binds the epithelial brush border Na+/H+ exchanger NHE3 and the cytoskeletal protein ezrin

Cyclic AMP is a major second messenger that inhibits the brush border Na+/H+ exchanger NHE3. We have previously shown that either of two related regulatory proteins, E3KARP or NHERF, is necessary for the cAMP-dependent inhibition of NHE3. In the present study, we characterized the interaction between NHE3 and E3KARP using in vitro binding assays. We found that NHE3 directly binds to E3KARP and that the entirety of the second PSD-95/Dlg/ZO-1 (PDZ) domain plus the carboxyl-terminal domain of E3KARP are required to bind NHE3. E3KARP binds an internal region within the NHE3 C-terminal cytoplasmic tail, defining a new mode of PDZ domain interaction. Analyses of cellular distribution of NHE3 and E3KARP expressed in PS120 fibroblasts show that NHE3 and E3KARP are co-localized on the plasma membrane, but not in a distinct juxtanuclear compartment in which NHE3 is predominantly expressed. The distributions of NHE3 and E3KARP were not affected by treatment with 8-bromo-cAMP. As shown earlier for the human homolog of NHERF, we also found that the cytoskeletal protein ezrin binds to the carboxyl-terminal domain of E3KARP. These results are consistent with the possibility that E3KARP and NHERF may function as scaffold proteins that bind to both NHE3 and ezrin. Since ezrin is a protein kinase A anchoring protein, we suggest that the scaffolding function of E3KARP binding to both ezrin and NHE3 localizes cAMP-dependent protein kinase in the vicinity of the cytoplasmic domain of NHE3, which is phosphorylated by elevated cAMP.

Membrane insertion of cytochrome P450 1A2 promoted by anionic phospholipids

The role of phospholipids in the membrane binding and subsequent insertion of the microsomal protein rabbit cytochrome P450 (P450) 1A2 into phospholipid bilayers was investigated. The insertion of P450 1A2 into phospholipid bilayers was measured by the quenching of Trp fluorescence of P450 1A2 by pyrene and brominated and doxyl-labeled phospholipids. When the phosphatidylcholine (PC) matrix was replaced with acidic phospholipids [phosphatidic acid (PA), phosphatidylserine, and phosphatidylinositol] and phosphatidylethanolamine (PE), the extent of insertion into lipid bilayers was strictly dependent on the type of acidic phospholipids. All anionic phospholipids caused the penetration of P450 1A2 into lipid bilayers, but PA was the most efficient in facilitating deep penetration of P450 1A2 into bilayers. On the other hand, binding of P450 1A2 to liposomes was increased by acidic phospholipids to the same degree regardless of the type of acidic phospholipids. PE was found to act as an inert matrix phospholipid, similar to PC, as it exerted very little effect on the insertion of P450 1A2 into lipid bilayers and the binding of P450 1A2 to membranes. It was also found that the phospholipid-dependent membrane insertion of P450 1A2 was associated with altered enzyme activity, increased alpha-helix content, and increased Trp fluorescence of P450 1A2. These results indicate that negative charges on the acidic phospholipids are important for the initial binding of P450 1A2 to membranes, but the penetration of P450 1A2 into lipid bilayers is regulated by the type of acidic phospholipids, and that phospholipid-dependent insertion of P450 1A2 is accompanied by a structural change of P450 1A2.