Deletion ofPDE2, the gene encoding the high-affinity cAMP phosphodiesterase, results in changes of the cell wall and membrane inCandida albicans

A role for the cAMP-dependent pathway in regulation of the cell wall in the model yeast Saccharomyces cerevisiae has recently been demonstrated. In this study we report the results of a phenotypic analysis of a Candida albicans mutant, characterized by a constitutive activation of the cAMP pathway due to deletion of PDE2, the gene encoding the high cAMP-affinity phosphodiesterase. Unlike wild-type strains, this mutant has an increased sensitivity to cell wall and membrane perturbing agents such as SDS and CFW, and antifungals such as amphotericin B and flucytosine. Moreover, the mutant is characterized by an altered sensitivity and a significantly reduced tolerance to fluconazole. The mutant's membrane has around 30% higher ergosterol content and the cell wall glucan was 22% lower than in the wild-type. These cell wall and membrane changes are manifested by a considerable reduction in the thickness of the cell wall, which in the mutant is on average 60-65 nm, compared to 80-85 nm in the wild-type strains as revealed by electron microscopy. These results suggest that constitutive activation of the cAMP pathway affects cell wall and membrane structure, and biosynthesis, not only in the model yeast S. cerevisiae but also in the human fungal pathogen C. albicans.

Characterization of an Escherichia coli elaC deletion mutant

The elaC gene of Escherichia coli encodes a binuclear zinc phosphodiesterase (ZiPD). ZiPD homologs from various species act as3' tRNA processing endoribonucleases, and although the homologous gene in Bacillus subtilis is essential for viability [EMBO J. 22(2003) 4534], the physiological function of E. coli ZiPD has remained enigmatic. In order to investigate the function of E. coli ZiPDwe generated and characterized an E. coli elaC deletion mutant. Surprisingly, the E. coli elaC deletion mutant was viable and had wild-type like growth properties. Microarray-based transcriptional analysis indicated expression of the E. coli elaC gene at basal levels during aerobic growth. The elaC gene deletion had no effect on the expression of genes coding for RNases or amino-acyl tRNA synthetases or any other gene among a total of > 1300 genes probed. 2D-PAGE analysis showed that the elaC mutation, like-wise, had no effect on the proteome. These results strengthen doubts about the involvement of E. coli ZiPD in tRNA maturation and suggest functional diversity within the ZiPD/ElaC1 protein family. In addition to these unexpected features of the E. coli elaC deletion mutant, a sequence comparison of ZiPD (ElaC1) proteins revealed specific regions for either enterobacterial or mammalian ZiPD (ElaC1) proteins.

Concerted regulation of inorganic pyrophosphate and osteopontin by akp2, enpp1, and ank: an integrated model of the pathogenesis of mineralization disorders

Tissue-nonspecific alkaline phosphatase (TNAP) hydrolyzes the mineralization inhibitor inorganic pyrophosphate (PP(i)). Deletion of the TNAP gene (Akp2) in mice results in hypophosphatasia characterized by elevated levels of PP(i) and poorly mineralized bones, which are rescued by deletion of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) that generates PP(i). Mice deficient in NPP1 (Enpp1(-/-)), or defective in the PP(i) channeling function of ANK (ank/ank), have decreased levels of extracellular PP(i) and are hypermineralized. Given the similarity in function between ANK and NPP1 we crossbred Akp2(-/-) mice to ank/ank mice and found a partial normalization of the mineralization phenotypes and PP(i) levels. Examination of Enpp1(-/-) and ank/ank mice revealed that Enpp1(-/-) mice have a more severe hypermineralized phenotype than ank/ank mice and that NPP1 but not ANK localizes to matrix vesicles, suggesting that failure of ANK deficiency to correct hypomineralization in Akp2(-/-) mice reflects the lack of ANK activity in the matrix vesicle compartment. We also found that the mineralization inhibitor osteopontin (OPN) was increased in Akp2(-/-), and decreased in ank/ank mice. PP(i) and OPN levels were normalized in [Akp2(-/-); Enpp1(-/-)] and [Akp2(-/-); ank/ank] mice, at both the mRNA level and in serum. Wild-type osteoblasts treated with PP(i) showed an increase in OPN, and a decrease in Enpp1 and Ank expression. Thus TNAP, NPP1, and ANK coordinately regulate PP(i) and OPN levels. The hypomineralization observed in Akp2(-/-) mice arises from the combined inhibitory effects of PP(i) and OPN. In contrast, NPP1 or ANK deficiencies cause a decrease in the PP(i) and OPN pools that leads to hypermineralization.

Linked deficiencies in extracellular PP(i) and osteopontin mediate pathologic calcification associated with defective PC-1 and ANK expression

Osteopontin and PP(i) both suppress hydroxyapatite deposition. Extracellular PP(i) deficiency causes spontaneous hypercalcification, yet unchallenged osteopontin knockout mice have only subtle mineralization abnormalities. We report that extracellular PP(i) deficiency promotes osteopontin deficiency and correction of osteopontin deficiency prevents hypercalcification, suggesting synergistic inhibition of hydroxyapatite deposition. Nucleotide pyrophosphatase phosphodiesterase (NPP) isozymes including PC-1 (NPP1) function partly to generate PP(i), a physiologic calcification inhibitor. PP(i) transport is modulated by the membrane channel protein ANK. Spontaneous articular cartilage calcification, increased vertebral cortical bone formation, and peripheral joint and intervertebral ossific ankylosis are associated with both PC-1 deficiency and expression of truncated ANK in ank/ank mice. To assess how PC-1, ANK, and PP(i) regulate both calcification and cell differentiation, we studied cultured PC-1 -/- and ank/ank mouse calvarial osteoblasts. PC-1 -/- osteoblasts demonstrated approximately 50% depressed NPP activity and markedly lowered extracellular PP(i) associated with hypercalcification. These abnormalities were rescued by transfection of PC-1 but not of the NPP isozyme B10/NPP3. PC-1 -/- and ank/ank cultured osteoblasts demonstrated not only comparable extracellular PP(i) depression and hypercalcification but also marked reduction in expression of osteopontin (OPN), another direct calcification inhibitor. Soluble PC-1 (which corrected extracellular PP(i) and OPN), and OPN itself (> or = 15 pg/ml), corrected hypercalcification by PC-1 -/- and ank/ank osteoblasts. Thus, linked regulatory effects on extracellular PP(i) and OPN expression mediate the ability of PC-1 and ANK to regulate calcification.

Tissue-nonspecific alkaline phosphatase and plasma cell membrane glycoprotein-1 are central antagonistic regulators of bone mineralization

Osteoblasts mineralize bone matrix by promoting hydroxyapatite crystal formation and growth in the interior of membrane-limited matrix vesicles (MVs) and by propagating the crystals onto the collagenous extracellular matrix. Two osteoblast proteins, tissue-nonspecific alkaline phosphatase (TNAP) and plasma cell membrane glycoprotein-1 (PC-1) are involved in this process. Mutations in the TNAP gene result in the inborn error of metabolism known as hypophosphatasia, characterized by poorly mineralized bones, spontaneous fractures, and elevated extracellular concentrations of inorganic pyrophosphate (PP(i)). PP(i) suppresses the formation and growth of hydroxyapatite crystals. PP(i) is produced by the nucleoside triphosphate pyrophosphohydrolase activity of a family of isozymes, with PC-1 being the only member present in MVs. Mice with spontaneous mutations in the PC-1 gene have hypermineralization abnormalities that include osteoarthritis and ossification of the posterior longitudinal ligament of the spine. Here, we show the respective correction of bone mineralization abnormalities in knockout mice null for both the TNAP (Akp2) and PC-1 (Enpp1) genes. Each allele of Akp2 and Enpp1 has a measurable influence on mineralization status in vivo. Ex vivo experiments using cultured double-knockout osteoblasts and their MVs demonstrate normalization of PP(i) content and mineral deposition. Our data provide evidence that TNAP and PC-1 are key regulators of the extracellular PP(i) concentrations required for controlled bone mineralization. Our results suggest that inhibiting PC-1 function may be a viable therapeutic strategy for hypophosphatasia. Conversely, interfering with TNAP activity may correct pathological hyperossification because of PP(i) insufficiency.

DNA synthesis and dRPase activities of polymerase beta are both essential for single-nucleotide patch base excision repair in mammalian cell extracts

In mammalian cells the majority of altered bases in DNA are processed through a single-nucleotide patch base excision repair mechanism. Base excision repair is initiated by a DNA glycosylase that removes a damaged base and generates an abasic site (AP site). This AP site is further processed by an AP endonuclease activity that incises the phosphodiester bond adjacent to the AP site and generates a strand break containing 3'-OH and 5'-sugar phosphate ends. In mammalian cells, the 5'-sugar phosphate is removed by the AP lyase activity of DNA polymerase beta (Pol beta). The same enzyme also fills the gap, and the DNA ends are finally rejoined by DNA ligase. We measured repair of oligonucleotide substrates containing a single AP site in cell extracts prepared from normal and Pol beta-null mouse cells and show that the reduced repair in Pol beta-null extracts can be complemented by addition of purified Pol beta. Using this complementation assay, we demonstrate that mutated Pol beta without dRPase activity is able to stimulate long patch BER. Mutant Pol beta deficient in DNA synthesis, but with normal dRPase activity, does not stimulate repair in Pol beta-null cells. However, under conditions where we measure base excision repair accomplished exclusively through a single-nucleotide patch BER, neither dRPase nor DNA synthesis mutants of Pol beta alone, or the two together, were able to complement the repair defect. These data suggest that the dRPase and DNA synthesis activities of Pol beta are coupled and that both of these Pol beta functions are essential during short patch BER and cannot be efficiently substituted by other cellular enzymes.

Control of 5',5'-dinucleoside triphosphate catabolism by APH1, a Saccharomyces cerevisiae analog of human FHIT

The putative human tumor suppressor gene FHIT (fragile histidine triad) (M. Ohta et al., Cell 84:587-597, 1996) encodes a protein behaving in vitro as a dinucleoside 5',5"'-P1,P3-triphosphate (Ap3A) hydrolase. In this report, we show that the Saccharomyces cerevisiae APH1 gene product, which resembles human Fhit protein, also hydrolyzes dinucleoside 5',5'-polyphosphates, with Ap3A being the preferred substrate. Accordingly, disruption of the APH1 gene produced viable S. cerevisiae cells containing reduced Ap3A-hydrolyzing activity and a 30-fold-elevated Ap3N concentration.

Glycerophosphorylcholine phosphocholine phosphodiesterase activity in cultured oligodendrocytes, astrocytes, and central nervous tissue of dysmyelinating rodent mutants

The levels of GPC phosphocholine phosphodiesterase, pNP phosphocholine phosphodiesterase, CNPase, and UDP galactose: ceramide galactosyltransferase activities were estimated with pure cultures of oligodendrocytes and astrocytes; mixed primary glial cells cultures; C-6 cells; and CNS tissue of the dysmyelinating md rat, the jimpy mouse, and the quaking mouse. The highest activity of GPC and pNP phosphocholine phosphodiesterases as with CNPase and C gal T was found in the pure cultured oligodendrocytes. C-6 cells had very low or undetectable activities for these two phosphodiesterases but possessed very high CNPase activity. The activity of GPC phosphocholine phosphodiesterase was significantly decreased in the CNS tissue of the md rat and the jimpy and the quaking mouse. Similar reductions were observed for the pNP phosphocholine phosphodiesterase, CNPase, and C gal T activities. The selective cellular enrichment in oligodendrocytes of the GPC phosphocholine phosphodiesterase activity and decreases of its activity in three dysmyelinating mutants in the same ratio as for CNPase and C gal T suggest that GPC phosphocholine phosphodiesterase is a myelin marker enzyme and it may reflect the quantity of myelin and oligodendrocyte present.

Expression of human recombinant cAMP phosphodiesterase isozyme IV reverses growth arrest phenotypes in phosphodiesterase-deficient yeast

The low-Km cAMP-specific phosphodiesterases (PDEases) are of great pharmacological significance because of their involvement in regulating cAMP concentrations, which, in turn, are responsible for mediating the cellular response to extracellular signals such as hormones and neurotransmitters. We recently reported the isolation of a cDNA clone that encodes a human monocyte low-Km, rolipram-sensitive, cAMP PDEase (isozyme IV). We have engineered the inducible expression of this human PDEase in yeast. Cells of Saccharomyces cerevisiae contain two genes that encode cAMP PDEases. PDEase-deficient mutants are viable but exhibit specific growth arrest phenotypes associated with elevated intracellular cAMP content; these phenotypes include heat shock sensitivity and the inability to grow on acetate as a carbon source. We show that functional expression of our human cAMP PDEase in a genetically engineered PDEase-deficient strain of S. cerevisiae reverses these aberrant phenotypes. Furthermore, under conditions for growth arrest, rolipram is cytotoxic to PDEase-deficient mutants expressing the human cAMP PDEase, indicating that it is capable of inhibiting the human recombinant enzyme in vivo. This system can be used in the development of a yeast cell-based assay for isozyme-selective inhibitors of the human recombinant cAMP PDEase.

Adult sphingomyelinase deficiency: report of 2 patients who initially presented with psychiatric disorders

We studied 2 unrelated adult patients under neuroleptic treatment who met all phenotypic and biochemical criteria for Niemann-Pick disease type B. In addition, they had chronic psychiatric disorders and low blood levels of HDL cholesterol. The marked and persistent deficiency of acid sphingomyelinase and the disturbance of sphingomyelin metabolism in skin fibroblast subcultures ruled out a pure drug-induced lipidosis. The association of Niemann-Pick disease type B with psychiatric disorders and with low levels of HDL cholesterol could be a chance association of 2 diseases, a new phenotype of Niemann-Pick type B, or the revelation by the neuroleptic treatment of a subclinical inborn sphingomyelinase deficiency.

Partial sphingomyelinase deficiency with sea-blue histiocytosis and neurovisceral dysfunction

A case of partial sphingomylinase deficiency with supranuclear vertical ophthalmoplegia, perceptive hearing loss and renal failure is reported. Extensive studies revealed sea-blue histiocytosis in bone marrow, delayed peripheral nerve conduction velocity, selective IgG and IgM deficiency, mild hepatosplenomegaly and testicular hypotrophy and retention. Although renal failure, perceptive deafness, immunoglobulin deficiency and testicular malformation are rare conditions in sphingomyelinase deficiency, this case mimicked to lipidosis reported by Neville. The association of congenital malformation and uremia might accentuate the symptoms.

Transitory type of sphingomyelinase deficient Niemann-Pick disease: clinical and morphological studies and follow-up of two sisters

The transitory type is a rare and ill-defined variant of sphingomyelinase deficient NPD. Here reported are full clinical and morphological studies on two sisters with the transitory type. Our cases have the following features in common: 1) prominent visceral involvement from early infancy, such as marked hepatosplenomegaly, pulmonary infiltration, and numerous characteristic foam cells in the bone marrow aspirates; 2) very low sphingomyelinase activities in cultured skin fibroblasts; 3) atypical cherry-red spots in the retina; despite 4) absence of any neurological symptoms even at the age of 5 years and 6 months, and 3 years and 9 months, respectively. Furthermore, a few lines of evidence indicating nervous system involvement are also disclosed, that is, 5) vacuolated macrophages in the cerebrospinal fluid and ultrastructurally typical inclusion bodies in axons and Schwann cells in the rectal biopsy specimens, which were firstly revealed in this type of NPD. It is stressed that every case with apparent type B NPD should be searched for the presence or absence of neuronal involvement by not merely fundoscopy but other available means as we employed, which would greatly contribute to elucidate the clinico-pathogenetical knowledge not to mention the current classification of NPD.

Successful therapy of Niemann-Pick disease by implantation of human amniotic membrane

In a patient with a lysosomal storage disorder, not involving the CNS, repeated implantations of human amniotic sheets have proved to provide a successful approach to enzyme replacement therapy. Implantation of pure epithelial cells, separated from the other cell types of the amnion, might markedly improve the procedure, avoiding some risks of host-versus-graft rejection.

Heterozygosity for phosphodiester glycosidase deficiency: a novel human mutation of lysosomal enzyme processing

We have carried out studies on the fibroblasts of III-3, a clinically normal Lebanese individual previously reported to have abnormally high plasma lysosomal enzyme levels. Mannose-6-phosphate (man-6-P) receptors in III-3 fibroblasts were found to be functioning normally, but the cells had only half normal levels of phosphodiester glycosidase activity. Pinocytosis of III-3 fibroblast secreted beta-hexosaminidase B (hex B) into Sandhoff disease fibroblasts was 18% of control, and the apparent KD for binding of III-3 hex B to man-6-P receptors was 3.7 X 10(-9) M compared to 1.25 X 10(-9) M for control enzyme. Hex B secreted by III-3 fibroblasts included an enzyme pool less electro-negative than control enzyme which had a very low affinity for man-6-P receptors and which did not bind to DEAE-Sephadex. Treatment of this abnormal hex B with exogenous placental phosphodiester glycosidase increased its binding to man-6-P receptors three-fold. Secretion rates of seven lysosomal enzymes from III-3 fibroblasts were, on average, twice as great as rates measured for two I-cell disease heterozygote fibroblast lines. The results suggest that III-3 fibroblasts are heterozygous for phosphodiester glycosidase deficiency. The possibility that an individual homozygous for this enzyme deficiency would develop I-cell disease is discussed.

Clinical and biochemical diagnostics of Niemann-Pick disease

Niemann-Pick disease (NPD) is an inherited lysosomal storage disorder characterised biochemically by a deficiency of sphingomyelinase activity and massive accumulation of undegraded sphingomyelin. There are three main clinical types of the disorder (NPD type A, B and C). NPD type A and B is diagnosed biochemically on the basis of measuring sphingomyelinase activity in leukocytes or cultured fibroblasts. The diagnosis may be established with the chromatographic method by the high level of sphingomyelin concentration in liver samples. Because in NPD type C the decrease of sphingomyelinase activity is moderate and only occurs in fibroblasts the thin-layer chromatography of the total liver lipid extracts is necessary for establishing the diagnosis. The thin-layer chromatography of the total liver lipids is sufficient for the diagnosis of all types of NPD.

Splenic histiocytosis in idiopathic thrombocytopenic purpura: a relative sphingomyelinase deficiency?

The case of a patient in whom idiopathic thrombocytopenic purpura (ITP) was associated with diffuse splenic histiocytosis is described; the patient's subsequent sphingomyelinase level was at the lower limits of the normal range. The patient's splenic lecithin:sphingomyelin ratio was not significantly different from that of 11 age-matched control subjects. It is postulated that the sporadic cases of splenic histiocytosis in patients with ITP are due to a relative, acquired sphingomyelinase deficiency.

Phosphodiesterase-probes show distinct defects in rd mice and Irish setter dog disorders

The phosphodiesterase from the visual cells of rd mice and affected Irish setter dogs has been analyzed, using biochemical, biophysical, and immunological techniques. The authors' findings demonstrate that the mechanisms that cause a deficiency in phosphodiesterase activity in rd mice and Irish setter dogs are distinctly different. Apparently, the phosphodiesterase complex is normal in affected Irish setter dogs but is abnormal in rd mice. The criteria used for determining the normalcy of the phosphodiesterase complex were sedimentation characteristics, immuno-cross-reactivity, and histone-activation, which is shown to be a unique characteristic of the visual cell enzyme. According to these criteria, the phosphodiesterase complex in the visual cells of rd mice is either absent or abnormal from the onset of visual cell differentiation until degeneration, because it exhibits no cross-reactivity with antibody to phosphodiesterase; it is not activated by histone; and if present, it exhibits abnormal sedimentation characteristics and perhaps subunit structure. On the other hand, phosphodiesterase from the visual cells of affected Irish setter dogs is normal by the same criteria, because it cross-reacts with antibody against phosphodiesterase; it is activated by histone; and it exhibits normal sedimentation and electrophoretic patterns. It is proposed that depressed levels of phosphodiesterase activity in affected setter photoreceptors are due, perhaps, to a defect in the light-initiated cascade which activates the enzyme normally, in situ.

Adrenal changes in Niemann-Pick disease: differences between sphingomyelinase deficiency and type C

Structural, chemical, and histochemical analyses of adrenal tissue performed in 8 cases of Niemann-Pick disease (NPD) revealed stark differences of storage between spingomyelinase (SMase) deficiency (6 cases) and type C (2 cases). In all the full-blown cases of the SMase deficiency group, pronounced sphingomyelin (SM) storage was found in all the zones of the cortical epithelium with slightly increasing centripetal gradient. The storage resulted in the reduction or even disappearance of lipofuscinogenesis in the reticular zone, in the reduction of the physiological fat content, in the generalized foamy transformation of the epithelium, and in moderate organomegaly. The storage was expressed in both A and B types and was roughly proportional to the storage in other viscera. The stromal storage was confined to the vascular endothelium, and in particular, to the macrophages. One of the cases showed the presence of typical spirolactone bodies unmodified in fine structure by the lysosomal storage. Their most conspicuous enzymatic activity was that of non-specific esterase and NADH tetrazolium reductase. The adrenals in type C were macroscopically and histologically normal except for a variable population of stromal foam cells. Chemically, there was slight increase in all phospholipids with borderline or moderate percentual increase of SM. There was also slight increase in some of the lower neutral glycosphingolipids. Electron microscopy dislosed rudimentar storage in lower cortical layer epithelium which by its fine structure and according to results of lipid histochemistry was qualitatively different from that in SMase deficiency. The stromal storage was expressed mainly in macrophages in which there was histochemically detectable amount of SM. There was no storage detectable in medullary cells in neither group of NPD complex. The results point not only to striking quantitative differences in storage intensity between the 2 basic groups of NPD showing the cortical epithelium in type C as being remarkably resistant to the metabolic disorder, but also to difference in quality of the storage very much like that found in other tissues, too.

Immunological studies on lysosomal sphingomyelinase: identification of a 28 000-Da component deficient in urine from patients with Niemann-Pick disease types A and B

The immunoblotting technique was used to identify sphingomyelinase protein in samples of tissue and urine after subjection to polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. In a sphingomyelinase preparation purified from control urine a prominent band was seen with an Mr of 28 000 Da. Glycoprotein fractions from urine and placenta, a membrane extract from spleen, and a partially purified sphingomyelinase preparation from placenta contained the 28 000-Da band plus additional, higher-Mr bands. The 28 000-Da band was detectable in urine from a patient with Niemann-Pick disease type C, but not in urine from patients with Niemann-Pick disease types A and B. It is concluded that sphingomyelinase is composed of at least one polypeptide with an Mr of 28 000 Da and that this polypeptide is deficient in the urine of patients with Niemann-Pick disease types A and B.

Time course of hepatic lipids accumulation in a strain of mice with an inherited deficiency of sphingomyelinase

Sphingomyelinosis (gene symbol, spm) is a recessive autosomal mutation in mice that causes a condition analogous to the human disease known as Niemann-Pick disease. The time course of hepatic lipids accumulation in this murine model was investigated. Hepatosplenomegaly in spm/ spm mice was noticeable as early as 4 weeks of age, and reached its maximum level at 6 weeks of age. Thereafter the weights of liver and spleen decreased in parallel with a decrease in body weight and an increase in severity of neurological symptoms. Hepatic concentrations of unesterified cholesterol and sphingomyelin were considerably elevated by 4 weeks of age, and further increased linearly to the terminal stages of the disorder. Sphingomyelinase activities in the livers of spm/ + and +/+ mice showed normal adult levels from as early as 4 weeks of age, whereas the activity in spm/ spm mice was consistently 30-40 percent of the normal level from 4 to 12 weeks of age.