AMADA: analysis of microarray data

SUMMARY

AMADA is a Windows program for identifying co-expressed genes from microarray data. It performs data transformation, principal component analysis, a variety of cluster analyses and extensive graphic functions for visualizing expression profiles.

Calcium- and vitamin D-regulated keratinocyte differentiation

Calcium and 1,25 dihydroxyvitamin D (1,25(OH)(2)D) regulate the differentiation of keratinocytes. We have examined the mechanisms by which such regulation takes place, focusing primarily on the events leading to cornified envelope (CE) formation, in particular the mechanisms by which calcium and 1,25(OH)(2)D regulate the induction of involucrin, a component of the CE, and transglutaminase, the enzyme cross-linking involucrin and other substrates to form the CE. Both extracellular calcium (Ca(o)) and 1,25(OH)(2)D raise intracellular free calcium (Ca(i)) as a necessary step toward stimulating differentiation. Cells lacking the calcium sensing receptor (CaR) or phospholipase C-gamma 1 (PLC-gamma 1) fail to respond to Ca(o) or 1,25(OH)(2)D with respect to differentiation. Residing in the promoter of involucrin is a region responsive to calcium and 1,25(OH)(2)D, the calcium response element (CaRE). The CaRE contains an AP-1 site, mutations of which result in loss of responsiveness to Ca(o) and 1,25(OH)(2)D, indicating a role for protein kinases C (PKC). PKC alpha is the major PKC isozyme involved at least for calcium-induced differentiation. Thus, the regulation of keratinocyte differentiation by calcium and 1,25(OH)(2)D involves a number of signaling pathways including PLC and PKC activation, leading to the induction of proteins required for the differentiation process.

An important role of an inducible RNA-dependent RNA polymerase in plant antiviral defense

Plants contain RNA-dependent RNA polymerase (RdRP) activities that synthesize short cRNAs by using cellular or viral RNAs as templates. During studies of salicylic acid (SA)-induced resistance to viral pathogens, we recently found that the activity of a tobacco RdRP was increased in virus-infected or SA-treated plants. Biologically active SA analogs capable of activating plant defense response also induced the RdRP activity, whereas biologically inactive analogs did not. A tobacco RdRP gene, NtRDRP1, was isolated and found to be induced both by virus infection and by treatment with SA or its biologically active analogs. Tobacco lines deficient in the inducible RDRP activity were obtained by expressing antisense RNA for the NtRDRP1 gene in transgenic plants. When infected by tobacco mosaic virus, these transgenic plants accumulated significantly higher levels of viral RNA and developed more severe disease symptoms than wild-type plants. After infection by a strain of potato virus X that does not spread in wild-type tobacco plants, the transgenic NtRDRP1 antisense plants accumulated virus and developed symptoms not only locally in inoculated leaves but also systemically in upper uninoculated leaves. These results strongly suggest that inducible RdRP activity plays an important role in plant antiviral defense.

Absence of protease-resistant prion protein in the cerebrospinal fluid of Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD), believed to be caused by a protease-resistant isoform of prion protein (PrP(Sc)), usually manifests itself as a clinically distinctive age-related dementia because of its rapid progression, occasionally accompanied by cerebellar ataxia. Recently, a variant CJD (vCJD) has been described, which has prominent early psychiatric symptoms and an earlier age of death. Although cerebrospinal fluid (CSF) is part of the extracellular fluid of the central nervous system (CNS), the bulk of its proteins are derived from the plasma and there is increasing concern about possible transmission of prion disease by blood. As investigation of CSF has played a significant role in the diagnosis and management of several neurological diseases, it was decided to characterize PrP present in the CSF of CJD individuals. Significant variation was observed in the level of PrP in the CSF from both non-CJD and CJD (including vCJD) patients, and the detected PrP forms are protease-sensitive. Using a conformation-dependent immunoassay, it was further demonstrated that the PrP detected in the CSF from CJD patients was broadly similar in conformation to that found in non-CJD patients. Taken together, the results of this study fail to demonstrate any correlation between the presence of protease-resistant PrP isoform (PrP(Sc)) in the CSF and disease manifestation.

Autocorrelation function analysis of ECG signals in 20 rabbits

In this experiment, we measured ECG signals of lead I, respectively, during normal and arrhythmia after 20 rabbits were anaesthetized. These signals were recorded, then the information was put into a computer and it analyzed Autocorrelation (AC) Function, and Power Spectrum. The results make us know: (1) periodicity corresponding relationship of ECG in normal rabbits can derive reflects from changes of ECG AC function changes of ECG signals in arrhythmia rabbits can derive relatively sensitive reflection from changes of ECG function (attenuating area S and the value of k) in normal rabbits. (2) The Autocorrelation Function of Electrocardio change but ECG in the normal. All these provide another useful method for the diagnosis of arrhythmia.

Evidence for an intrinsic toxicity of phosphatidylcholine to Sec14p-dependent protein transport from the yeast Golgi complex

Yeast phosphatidylinositol-transfer protein (Sec14p) is essential for Golgi secretory function and cell viability. This requirement of Sec14p is relieved by genetic inactivation of the cytidine diphosphate-choline pathway for phosphatidycholine (PtdCho) biosynthesis. Standard phenotypic analyses indicate that inactivation of the phosphatidylethanolamine (PtdEtn) pathway for PtdCho biosynthesis, however, does not rescue the growth and secretory defects associated with Sec14p deficiency. We now report inhibition of choline uptake from the media reveals an efficient "bypass Sec14p" phenotype associated with PtdEtn-methylation pathway defects. We further show that the bypass Sec14p phenotype associated with PtdEtn-methylation pathway defects resembles other bypass Sec14p mutations in its dependence on phospholipase D activity. Finally, we find that increased dosage of enzymes that catalyze phospholipase D-independent turnover of PtdCho, via mechanisms that do not result in a direct production of phosphatidic acid or diacylglycerol, effect a partial rescue of sec14-1(ts)-associated growth defects. Taken together, these data support the idea that PtdCho is intrinsically toxic to yeast Golgi secretory function.

A novel enhancer of the Apaf1 apoptosome involved in cytochrome c-dependent caspase activation and apoptosis

Apaf1/CED4 family members play central roles in apoptosis regulation as activators of caspase family cell death proteases. These proteins contain a nucleotide-binding (NB) self-oligomerization domain and a caspase recruitment domain (CARD). A novel human protein was identified, NAC, that contains an NB domain and CARD. The CARD of NAC interacts selectively with the CARD domain of Apaf1, a caspase-activating protein that couples mitochondria-released cytochrome c (cyt-c) to activation of cytosolic caspases. Cyt-c-mediated activation of caspases in cytosolic extracts and in cells is enhanced by overexpressing NAC and inhibited by reducing NAC using antisense/DNAzymes. Furthermore, association of NAC with Apaf1 is cyt c-inducible, resulting in a mega-complex (>1 MDa) containing both NAC and Apaf1 and correlating with enhanced recruitment and proteolytic processing of pro-caspase-9. NAC also collaborates with Apaf1 in inducing caspase activation and apoptosis in intact cells, whereas fragments of NAC representing only the CARD or NB domain suppress Apaf1-dependent apoptosis induction. NAC expression in vivo is associated with terminal differentiation of short lived cells in epithelia and some other tissues. The ability of NAC to enhance Apaf1-apoptosome function reveals a novel paradigm for apoptosis regulation.

Requirements and effects of palmitoylation of rat PLD1

Rat brain phospholipase D1 (rPLD1) has two highly conserved motifs (HXKX(4)D), denoted HKD, located in the N- and C-terminal halves, which are required for phospholipase D activity. The two halves of rPLD1 can associate in vivo, and the association is essential for catalytic activity and Ser/Thr phosphorylation of the enzyme. In this study, we found that this association is also required for palmitoylation of rPLD1, which occurs on cysteines 240 and 241. In addition, palmitoylation of rPLD1 requires the N-terminal sequence but not the conserved C-terminal sequence, since rPLD1 that lacks the first 168 amino acids is not palmitoylated in vivo, while the inactive C-terminal deletion mutant is. Palmitoylation of rPLD1 is not necessary for catalytic activity, since N-terminal truncation mutants lacking the first 168 or 319 amino acids exhibit high basal activity although they cannot be stimulated by protein kinase C (PKC). The lack of response to PKC is not due to the lack of palmitoylation, since mutation of both Cys(240) and Cys(241) to alanine in full-length rPLD1 abolishes palmitoylation, but the mutant still retains basal activity and responds to PKC. Palmitoylation-deficient rPLD1 can associate with crude membranes; however, the association is weakened. Wild type rPLD1 remains membrane-associated when extracted with 1 m NaCl or Na(2)CO(3) (pH 11), while rPLD1 mutants that lack palmitoylation are partially released. In addition, we found that palmitoylation-deficient mutants are much less modified by Ser/Thr phosphorylation compared with wild type rPLD1. Characterization of the other cysteine mutations of rPLD1 showed that mutation of cysteine 310 or 612 to alanine increased basal phospholipase D activity 2- and 4-fold, respectively. In summary, palmitoylation of rPLD1 requires interdomain association and the presence of the N-terminal 168 amino acids. Mutations of cysteines 240 and 241 to alanine abolish the extensive Ser/Thr phosphorylation of the enzyme and weaken its association with membranes.

Effects of hypokalemia on cardiac growth

In neonatal myocytes grown in culture, reductions in extracellular potassium concentration produced a hypertrophic response as assessed by induction of early response genes, atrial natriuretic peptide and skeletal actin, and repression of the alpha3 isoform of the sodium pump in a dose dependent manner. The degree of alpha3 repression appeared to be dose dependent with decreases in media (K). Similarly, decreases in media potassium concentrations caused increases in cytosolic calcium concentration in a dose dependent manner; moreover these increases in cytosolic calcium concentration correlated quite well with repression of alpha3 expression. In contrast, although moderate reductions of potassium concentration induced upregulation of skACT and ANP, severely reduced potassium concentrations caused repression of skACT and ANP expression. In parallel studies performed in vivo, 3-5 weeks dietary K restriction induced molecular phenotypical changes similar to that seen in the neonatal myocyte model without demonstrable growth as assessed by the heart weight/body weight ratio. However, when rates subjected to dietary K restriction were subsequently subjected to acute aortic constriction, cardiac growth was greater than in rats fed a control diet. These data suggest that hypokalemia may produce molecular phenotypic alterations consistent with cardiac hypertrophy as well as contribute to hypertrophy in an in vivo model.

The role of phospholipase C-gamma1 in 1alpha,25-dihydroxyvitamin D(3) regulated keratinocyte differentiation

Phospholipase C-gamma1 (PLC-gamma1) is the most abundant member of the phospholipase C family expressed in human keratinocytes. PLC-gamma1 is induced by 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) in normal keratinocytes via a DR6-type vitamin D responsive element. This regulation is not observed in transformed keratinocytes. The role of PLC-gamma1 in mediating 1alpha,25(OH)(2)D(3) and calcium-regulated differentiation was then tested. Both specific PLC inhibitors and antisense constructs which selectively block PLC-gamma1 production prevented 1alpha,25(OH)(2)D(3) and calcium from inducing markers of differentiation such as involucrin and transglutaminase. These studies demonstrate that PLC-gamma1 induction by 1alpha,25(OH)(2)D(3) is critical to the ability of this hormone to regulate keratinocyte differentiation.

Ouabain interaction with cardiac Na/K-ATPase reveals that the enzyme can act as a pump and as a signal transducer

Na/K-ATPase hydrolyzes ATP to maintain the transmembrane gradients of Na+ and K+ found in most mammalian cells and is inhibited specifically by cardiac glycosides such as ouabain. Recently, we have shown that partial inhibition of Na/K-ATPase by non-toxic concentrations of ouabain causes hypertrophic growth and transcriptional regulation of several growth-related marker genes in neonatal rat cardiac myocytes. These ouabain effects involve the activation of multiple signal transduction pathways, including the activation of Src kinase and tyrosine phosphorylation of the epidermal growth factor receptors and other proteins, followed by the activation of Ras, the Ras/Raf/MEK/MAPK cascade, and increased production of reactive oxygen species. The gene regulatory actions of ouabain, like its classical effect on cardiac contractility, are dependent on the net influx of Ca2+ and rise in [Ca2+]i, indicating that the latter is a shared second messenger for the ouabain effects on cardiac contractility and growth. Significantly, the effects of ouabain on several early signaling events including stimulation of tyrosine phosphorylation and production of reactive oxygen species are independent of changes in intracellular Na and Ca2+ concentrations. Taken together, these new findings have led us to propose that when ouabain binds to Na/K-ATPase, it converts the enzyme to a signal transducer and initiates multiple gene regulatory pathways through either direct or indirect interactions with tyrosine kinases in cardiac myocytes.

[Fluoride emission from different soil minerals at high temperatures]

The emission characteristics of fluoride pollutants from montmorillonite, kaolinite, vermiculite, geothite and allophane were studied to elucidate the mechanism of fluoride-releasing from soils during brick and tile making at high temperatures from 300 degrees C to 1000 degrees C. The rate of fluoride emission varied with temperature, mineral type, heating time, specific surface area and cations added to minerals. The escape of crystalline water resulting from crystal lattice collapse at a certain high temperature was found to affect the rate of fluoride emission. Calcium compounds could decrease fluoride emission rate from montmorillonite. At 800 degrees C, the rate of fluoride emission from Ca-treated montmorillonite decreased by 59.6% compared to untreated montmorillonite. The order for fluoride-fixing capacity of the 5 calcium compounds at 800 degrees C was as follows: CaCO3 > CaO > Ca3(PO4)2 > Ca(OH)2 > CaSO4.

Downregulation of cardiac myocyte Na(+)-K(+)-ATPase by adenovirus-mediated expression of an alpha-subunit fragment

Cultured rat cardiac myocytes and A7r5 cells were transfected with an adenoviral vector used earlier for in vivo expression of functional alpha(2)-isoform of the catalytic subunit of rat Na(+)-K(+)-ATPase. Expressions of truncated forms of alpha(2), but little or no intact alpha(2), were detected, suggesting the rapid degradation of alpha(2) in these cultured cells. In neonatal myocytes normally containing the alpha(1)- and the alpha(3)-isoforms, expression of the alpha(2)-fragment led to 1) a significant decrease in the level of endogenous alpha(1)-protein and a modest decrease in alpha(3)-protein, 2) decreases in mRNAs of alpha(1) and alpha(3), 3) decrease in Na(+)-K(+)-ATPase function measured as ouabain-sensitive Rb(+) uptake, 4) increase in intracellular Ca(2+) concentration similar to that induced by ouabain, and 5) eventual loss of cell viability. These findings indicate that the alpha(2)-fragment downregulates endogenous Na(+)-K(+)- ATPase most likely by dominant negative interference either with folding and/or assembly of the predominant housekeeping alpha(1)-isoform or with signal transducing function of the enzyme. Demonstration of rise in intracellular Ca(2+) resulting from alpha(1)-downregulation 1) does not support the previously suggested special roles of less abundant alpha(2)- and alpha(3)-isoforms in the regulation of cardiac Ca(2+), 2) lends indirect support to proposals that observed decrease in total Na(+)-K(+)-ATPase of the failing heart may be a mechanism to compensate for impaired cardiac contractility, and 3) suggests the potential therapeutic utility of dominant negative inhibition of Na(+)-K(+)-ATPase.

[A multi-centered clinical study an domestic intravenous Turbutalin sulfate in the treatment of asthma and chronic asthmatic bronchitis]

OBJECTIVE

This multi-centered clinical trial was designed to assess the efficacy and safety of domestic intravenous Turbutalin Sulfate in the treatment of asthma and chronic asthmatic bronchitis.

METHODS

Bricanyl was used as control. A total of 120 patients were included in this randomized controlled study. The two medications, both at a dose of 0.25 mg intravenous drip, were given three times a day for 3-5 days.

RESULTS

The two drugs' clinical excellent rates were 66.7% and 73.3%; overall efficacy rates were 98.3% and 100.0%, respectively. Their pulmonary functional excellent rates were 78.4% and 76.6%; overall effect rates were 88.3% and 90.0%, respectively. Composite curative evaluation showed that the two drug's composite excellent rates were 61.6% both; their overall efficacy rates were 88.3% and 90.0%, respectively. All of these showed no significant difference (P > 0.05). The incidence rates of adverse side effects of the two groups were 13.5% and 15.0%, respectively; most of them were mild and tolerable.

CONCLUSION

Domestic intravenous Terbutalin Sulfate is effective and safe in treating asthma and chronic asthmatic bronchitis.

Apoptosis induction by the photosensitizer verteporfin: identification of mitochondrial adenine nucleotide translocator as a critical target

We report that the photosensitizer verteporfin kills lymphoma cells by an apoptotic process involving a dissipation of the mitochondrial inner transmembrane potential (deltapsim). Light-activated verteporfin-induced apoptosis was abolished by transfection with Bcl-2, a procedure reported to inhibit the mitochondrial permeability transition pore complex (PTPC). Verteporfin triggered the deltapsim loss in isolated mitochondria in vitro, and this effect was suppressed by bongrekic acid and cyclosporin A. Verteporfin plus light also permeabilized proteoliposomes containing the semipurified PTPC or the purified PTPC component adenine nucleotide translocator (ANT), yet had no effect on protein-free control liposomes. Verteporfin phototoxicity on ANT proteoliposomes was mediated by reactive oxygen species and was prevented by recombinant Bcl-2 or the adenine nucleotides ATP and ADP. In conclusion, verteporfin belongs to a class of clinically used chemotherapeutic agents acting on PTPC and ANT.

Relics: penguin population programs

What has been responsible for the increase in Chinstrap penguin populations during the past 40 years in maritime Antarctica? One view ascribes it to an increase in availability of their prey brought on by the decrease in baleen whale stocks. The contrary opinion, attributes it to environmental warming. This causes a gradual decrease in the frequency of cold years with extensive winter sea ice cover. A number of penguin monitoring programs are in progress and are expected to provide some answers to these questions. Unfortunately, it is not easy to distinguish natural variability from anthropogenic change since penguins are easily accessible predators of krill and the feeding range of the penguins has almost overlapped with the krill fishery in time and space in the last four decades. Therefore it is important to reconstruct the change of ancient penguin abundance and distribution in the absence of human activity. Many efforts have focused on surveying the abandoned penguin rookeries, but this method has not been able to give a continuous historical record of penguin populations. In several recent studies, ancient penguin excreta was scooped from the penguin relics in the sediments of the lake on penguin rookery, Ardley Island, maritime Antarctica. In these studies, penguin droppings or guano soil deposited in the lake and changes in sediment geochemistry have been used to calculate penguin population changes based upon the geochemical composition of the sediment core. The results suggest that climate change has a significant impact on penguin populations.

Endocytic routes of exogenous antigen in murine dendritic cells and macrophages

OBJECTIVE

To compare the endocytic routes of exogenous antigen between murine dendritic cells (DCs) and macrophages (M phi s).

METHODS

Murine bone marrow-derived DCs and peritoneal M phi s were pulsed with horseradish peroxidase (HRP)-5 nm colloidal gold for 10 minutes, then grouped and chased for 0-120 minutes in culture medium. Intracellular distribution of 5 nm colloidal gold was explored by means of the cellular enzymatic-chemistry of acid phosphatase and MHC II immuno-cytochemistry under electron microscope.

RESULTS

After 10 minutes of pulse with HRP-5 nm colloidal gold and 30 minutes of chase, most HRP-5 nm gold particles internalized by DCs entered into MHC class II compartments (M II Cs), and a small portion entered into acid phosphatase-positive lysosomes. In contrast to DCs, most M phi s lysosomes were accessed by HRP-5 nm gold particles, and a small portion of HRP-5 nm gold particles entered into M II Cs. After 60 minutes of chase, 5 nm gold particles could hardly be seen within M phi s, whereas most 5 nm gold particles were still retained in DCs.

CONCLUSIONS

The endocytic route of exogenous antigen in DCs seems to be different from that in M phi s. Antigens taken by M phi s mainly enter into lysosomes within 30 minutes. In the case of DCs, most internalized antigens enter into M II Cs, which may be related to their unique antigen-presenting function. In addition, M phi s seem to have more powerful capacity to scavenge exogenous antigen than DCs.

Genetic manipulation of the odor-evoked distributed neural activity in the Drosophila mushroom body

Odor-induced neural activity was recorded by Ca2+ imaging in the cell body region of the Drosophila mushroom body (MB), which is the second relay of the olfactory central nervous system. The signals recorded are mainly from the cell layers on the brain surface because of the limited penetration of Ca2+-sensitive dyes. The densely packed cell bodies and their accessibility allow visualization of odor-induced population neural activity. It is revealed that odors evoke diffused neural activities in the MB. Although the signals cannot be attributed to individual neurons, patterns of the population neural activity can be analyzed. The activity pattern, but not the amplitude, of an odor-induced population response is specific for the chemical identity of an odor and its concentration. The distribution pattern of neural activity can be altered specifically by genetic manipulation of an odor binding protein and this alteration is closely associated with a behavioral defect of odor preference. These results suggest that the spatial pattern of the distributed neural activity may contribute to coding of odor information at the second relay of the olfactory system.

Neurotoxicity of 2-bromopropane and 1-bromopropane, alternative solvents for chlorofluorocarbons

To clarify the neurotoxicity of 2-bromopropane (2-BP) in comparison with 1-bromopropane (1-BP), 36 Wistar strain male rats were divided into 4 groups of 9 and exposed daily to 100-ppm 2-BP, 1000-ppm 2-BP, 1000-ppm 1-BP, or fresh air for 8 h a day. Exposure to 1000 ppm of 1-BP was discontinued after 5 or 7 weeks' exposure because of the unexpected appearance of incomplete hindlimb paralysis followed by serious emaciation. The other groups were sacrificed at the end of 12 weeks' exposure. Exposure to 1000 ppm of 2-BP resulted in significant decreases in body weight and motor nerve conduction velocity (MCV) and elongation in distal latency (DL). A ball-like enlargement of myelin sheaths was observed. Significant reductions in the number of erythrocytes, platelets, and leukocytes, testicular germ cell loss, and seminiferous atrophy were also observed in this group, but not in 100-ppm 2-BP group. Exposure to 1000 ppm of 1-BP for 5 or 7 weeks caused a significant decrease in body weight and MCV and elongation in DL. Linearly arranged ovoid- or bubble-like debris of the axons and myelin sheaths in the teased tibial nerves and axonal swelling in gracilis nucleus were found in this group. No significant changes in hematological indices or histopathological findings of the testis were found in this group. In conclusion, 2-BP is neurotoxic to the peripheral nerves in addition to its toxic effects on the reproductive and hematopoietic systems at 1000 ppm. No noticeable changes were found in the rats exposed to 100 ppm of 2-BP. 1-BP is a potent neurotoxicant at 1000 ppm for 5 or 7 weeks, while testicular and hematopoietic toxicity was not found.

Weakly coordinating nature of a carborane cage bearing different halogen atoms. Synthesis and structural characterization of icosahedral mixed halocarborane anions, 1-H-CB11Y5X6- (X, Y = Cl, Br, I)

Mixed halocarborane anions, 1-H-CB11Y5X6- (X, Y = Cl, Br, I), have been prepared by treatment of [Me3NH][1-H-CB11H5X6] (X = Cl, Br, I) with proper halogenating reagents at 180-220 degrees C in a sealed tube in high yield. These new anions are fully characterized by 1H, 13C, and 11B NMR, IR, and negative-ion MALDI MS spectroscopy. Some are further confirmed by single-crystal X-ray analyses. The weakly coordinating nature of these anions is probed by 29Si chemical shifts of the resulting Pri3Si(1-H-CB11Y5X6) compounds. The results suggest that the coordinating ability of these anions is mainly dependent on the substituents at 7-12 positions (namely, X atoms), and the contribution from the upper belt substituents Y is relatively small. These suggestions are consistent with the results obtained from the structural study of silver salts of mixed halo- and perhalocarborane anions.

[Element concentrations in Rheum palmatum and R. likiangense plants and soil in Tibet plateau]

The characteristics of element concentrations in Rheum palmatum and R. likiangense plants and soil were studied using ICP method. The results showed that the P concentrations in soil was significantly lower than that in leaves and rhizomes; Fe concentration was 50-100 times higher in soil than in rhizomes, and leaves, and without significant difference between rhizomes and leaves; Na, Mn and Cu concentrations appeared soil > leaves > rhizomes; and Ca concentration showed soil < leaves < rhizomes for R. palmatum, and soil > leaves > rhizomes for R. likiangense. Although K, Mg, Ca, Mn and Zn concentrations were obviously different between soils of the 2 species, K and Mg concentrations were consistent in their leaves or rhizomes, and the difference of Ca, Mn and Zn concentrations between their rhizomes was insignificant.

Conserved amino acids at the C-terminus of rat phospholipase D1 are essential for enzymatic activity

Rat brain phospholipase D1 (rPLD1) has two highly conserved motifs [H(X)K(X)4D, denoted HKD] located at the N-terminal and C-terminal halves, which are required for activity. Association of the two halves is essential for rPLD1 activity, which probably brings the two HKD domains together to form a catalytic center. In the present study, we find that an intact C-terminus is also essential for the catalytic activity of rPLD1. Serial deletion of the last four amino acids, EVWT, which are conserved in all mammalian PLD isoforms, abolished the catalytic activity of rPLD1. This loss of catalytic activity was not due to a lack of association of the N-terminal and C-terminal halves. Mutations of the last three amino acids showed that substitutions with charged or less hydrophobic amino acids all reduced PLD activity. For example, mutations of Thr1036 and Val1034 to Asp or Lys caused marked inactivation, whereas mutation to other amino acids had less effect. Mutation of Trp1035 to Leu, Ala, His or Tyr caused complete inactivation, whereas mutation of Glu1033 to Ala enhanced activity. The size of the amino acids at the C-terminus also affected the catalytic activity of PLD, reduced activity being observed with conservative mutations within the EVWT sequence (such as T/S, V/L or W/F). The enzyme was also inactivated by the addition of Ala or Val to the C-terminus of this sequence. Interestingly, the inactive C-terminal mutants could be complemented by cotransfection with a wild-type C-terminal half to restore PLD activity in vivo. These data demonstrate that the integrity of the C-terminus of rPLD1 is essential for its catalytic activity. Important features are the hydrophobicity, charge and size of the four conserved C-terminal amino acids. It is proposed that these play important roles in maintaining a functional catalytic structure by interacting with a specific domain within rPLD1.