Specific inhibition of apoptosis after cerebral hypoxia-ischaemia by moderate post-insult hypothermia

In piglets studied on the first day of life transient hypoxia-ischaemia caused an increase in the fractions of necrotic and apoptotic cells in the cingulate sulcus compared to sham-operated controls. In animals subjected to the same hypoxic-ischaemic insult but cooled to 34.9 degrees C (mean tympanic membrane temperature) for 12 hours commencing after resuscitation the fraction of cells undergoing necrosis was unchanged and comparable to that in animals which were not cooled. However, the fraction of apoptotic cells was reduced and was similar to that in sham-operated controls. Thus hypothermia specifically inhibited apoptosis. This result has implications for understanding the mechanisms of delayed cerebral injury and for the use of hypothermia as a neural rescue strategy in the developing brain.

Increased apoptosis in the cingulate sulcus of newborn piglets following transient hypoxia-ischaemia is related to the degree of high energy phosphate depletion during the insult

An increase in the number of cells undergoing apoptosis was observed in the cingulate sulcus of newborn piglets 48 h after a global hypoxic-ischaemic insult. Apoptotic death was identified morphologically (by light and electron microscopy) and by DNA fragmentation, detected by in situ end labelling. The number of apoptotic cells was directly related to the degree of high-energy phosphate depletion during hypoxia-ischaemia, measured using continuous 31P magnetic resonance spectroscopy. These results may have implications for the understanding and treatment of perinatal hypoxic-ischaemic brain injury.

Insecticide resistance and cross-resistance in the house fly (Diptera: Muscidae)

A house fly strain, ALHF, was collected from a poultry farm in Alabama after a control failure with permethrin, and further selected in the laboratory with permethrin for five generations. The level of resistance to permethrin in ALHF was increased rapidly from an initial 260-fold to 1,800-fold after selection. Incomplete suppression of permethrin resistance by piperonyl butoxide (PBO) and S,S,S,-tributylphosphorotrithioate (DEF) reveals that P450 monooxygenase- and hydrolase-mediated detoxication, and one or more additional mechanisms are involved in resistance to permethrin. The ALHF strain showed a great ability to develop resistance or cross-resistance to different insecticides within and outside the pyrethroid group including some relatively new insecticides. Resistance to beta-cypermethrin, cypermethrin, deltamethrin, and propoxur (2,400-4,200-, 10,000-, and > 290-fold, respectively, compared with a susceptible strain, aabys) in ALHF house flies was partially or mostly suppressed by PBO and DEF, indicating that P450 monooxygenases and hydrolases are involved in resistance to these insecticides. Partial reduction in resistance with PBO and DEF implies that multiresistance mechanisms are responsible for resistance. Fifteen- and more than fourfold resistance and cross-resistance to chlorpyrifos and imidacloprid, respectively, were not effected by PBO or DEF, indicating that P450 monooxygenases and hydrolases are not involved in resistance to these two insecticides. Forty-nine-fold cross-resistance to fipronil was mostly suppressed by PBO and DEF, revealing that monooxygenases are a major mechanism of cross-resistance to fipronil. Multiresistance mechanisms in the ALHF house fly strain, however, do not confer cross-resistance to spinosad, a novel insecticide derived from the bacterium Saccharopolyspora spinosa. Thus, we propose that spinosad be used as a potential insecticide against house fly pests, especially resistant flies.

Apoptosis in the brains of infants suffering intrauterine cerebral injury

This study addressed the hypothesis that in human infants severe in utero insults induce a significant proportion of brain cells to undergo apoptosis. Morphologic criteria were used to quantify apoptosis and necrosis in the cingulate gyrus of two groups of infants: six infants who died after severe birth asphyxia with hypoxic-ischemic encephalopathy, and six others who suffered unexpected and apparently sudden intrauterine death at or close to term. The fraction of apoptotic cells was much higher than basal levels determined in animal experiments, and within both groups increased in proportion to the severity of injury as determined by total cell death (p < 0.05). The mean fraction of apoptotic cells was similar in asphyxiated infants, 8.3% (95% confidence interval for the population, 3.7-12%), and in stillbirths, 6.7% (0.2-13.6%). In the asphyxiated group, 20.8% (11-30.6%) of cells were necrotic, but significantly less necrosis, 3% (0.4-5.6%), was seen in stillborn infants (p < 0.05). Cell death was apoptotic after birth asphyxia in 26% (1-51%) and 78% (41-100%) in stillborn infants. In situ end labeling studies confirmed the presence of DNA fragmentation in apoptotic cells. These results demonstrate that infants who die after intrauterine insults, both those with evidence of delayed cerebral injury after hypoxia-ischemia and those without, have a significant number of cells in the brain with the morphologic characteristics of apoptosis. They confirm that apoptosis contributes significantly to cerebral damage in the perinatal period.

Opposing actions of c-ets/PU.1 and c-myb protooncogene products in regulating the macrophage-specific promoters of the human and mouse colony-stimulating factor-1 receptor (c-fms) genes

The receptor for macrophage colony stimulating factor (CSF-1), the c-fms gene product, is a key determinant in the differentiation of monocytic phagocytes. Dissection of the human and mouse c-fms proximal promoters revealed opposing roles for nuclear protooncogenes in the transcriptional regulation of this gene. On the one hand, c-ets-1, c-ets-2, and the macrophage-specific factor PU.1, but not the ets-factor PEA3, trans-activated the c-fms proximal promoter. On the other hand c-myb repressed proximal promoter activity in macrophages and blocked the action of c-ets-1 and c-ets-2. Basal c-fms promoter activity was almost undetectable in the M1 leukaemia line, which expressed high levels of c-myb, but was activated as cells differentiated in response to leukemia inhibitory factor and expressed c-fms mRNA. The repressor function of c-myb depended on the COOH-terminal domain of the protein. We propose that ets-factors are necessary for the tissue-restricted expression of c-fms and that c-myb acts to ensure correct temporal expression of c-fms during myeloid differentiation.

Vascular endothelial growth factor expression coincides with coronary vasculogenesis and angiogenesis

Vascular endothelial growth factor (VEGF) plays an important role in early embryonic vasculogenesis. To establish its temporal expression and localization in the heart during development, we studied rat hearts from the first embryonic day (E) of myocardial vascular tube formation through the early postnatal period. Ventricular VEGF immunoreactivity was noted in the epicardium and the thin underlying myocardium in E10 ventricles. During the earliest stages of vascularization (E13-E16) immunoreactivity was highest in the compact myocardium nearest the epicardium, and subsequently (E18 and thereafter) became more evenly distributed transmurally. By birth (E22) immunoreactivity was most intense around microvessels. Similarly, VEGF mRNA localization, demonstrated by in situ hybridization, was initially highest near the epicardium and then became more evenly distributed transmurally by late gestation. Within the interventricular septum, the highest expression occurred in the middle of the wall where it correlated with the greatest vascularization. Northern blot analysis showed that from E12 through the first 10 days of postnatal life, VEGF was two to three times higher than in the adult. Western blot analysis showed that VEGF tended to be higher in the atria than the ventricles, and negligible in the outflow tract. Our data indicate that VEGF localization and expression 1) correspond to the pattern of vascularization in the embryonic/fetal heart, and 2) remain high during the early postnatal period when capillary proliferation is high. Because VEGF is stimulated by hypoxia, its preferential mRNA expression near the epicardium, that is, farthest from the ventricular lumen and the O2 source, fits with the hypothesis that a hypoxic gradient is a driving force in the transmural vascularization process.

Interaction between PU.1 and another Ets family transcription factor promotes macrophage-specific Basal transcription initiation

Numerous macrophage-restricted promoters lack TATA boxes or other conventional initiation motifs but contain high affinity binding sites (PU boxes) for the macrophage-restricted Ets family transcription factor PU.1. In RAW264 murine macrophages, multimerized PU boxes were not active as enhancers when placed upstream of a minimal promoter. To model their role in basal promoters, we inserted PU boxes into a promoterless luciferase reporter plasmid. Two sites, regardless of orientation, were necessary and sufficient to direct reporter gene expression in transient transfections of the RAW264 macrophage-like cell line. This activity was absent in transfected 3T3 fibroblasts but could be induced by PU.1 coexpression. Both the model promoter and the macrophage-specific mouse and human c-fms promoters were activated in RAW264 cells by other Ets family transcription factors, Ets-2 and Elf-1. In fibroblasts, the effects of PU.1 and Ets-2 were multiplicative, whereas overexpression of PU.1 in RAW264 cells reduced activation of c-fms or model promoters by the other Ets factors. The PU.1 and Ets-2 binding sites of the mouse c-fms promoter have been located by DNase footprinting. A conserved Ets-like motif at the transcription site, CAGGAAC, that bound only weakly to PU.1, was identified as an additional critical basal c-fms promoter element. Comparison of studies on the model promoter, c-fms and other myeloid promoters provides evidence for a conserved mechanism that involves three separate and functionally distinct Ets-like motifs.

Mechanism of phosphatidylinositol-specific phospholipase C: a unified view of the mechanism of catalysis

The mechanism of phosphatidylinositol-specific phospholipase C (PI-PLC) has been suggested to resemble that of ribonuclease A. The goal of this work is to rigorously evaluate the mechanism of PI-PLC from Bacillus thuringiensis by examining the functional and structural roles of His-32 and His-82, along with the two nearby residues Asp-274 and Asp-33 (which form a hydrogen bond with His-32 and His-82, respectively), using site-directed mutagenesis. In all, twelve mutants were constructed, which, except D274E, showed little structural perturbation on the basis of 1D NMR and 2D NOESY analyses. The H32A, H32N, H32Q, H82A, H82N, H82Q, H82D, and D274A mutants showed a 10(4)-10(5)-fold decrease in specific activity toward phosphatidylinositol; the D274N, D33A, and D33N mutants retained 0. 1-1% activity, whereas the D274E mutant retained 13% activity. Steady-state kinetic analysis of mutants using (2R)-1, 2-dipalmitoyloxypropane-3-(thiophospho-1d-myo-inositol) (DPsPI) as a substrate generally agreed well with the specific activity toward phosphatidylinositol. The results suggest a mechanism in which His-32 functions as a general base to abstract the proton from 2-OH and facilitates the attack of the deprotonated 2-oxygen on the phosphorus atom. This general base function is augmented by the carboxylate group of Asp-274 which forms a diad with His-32. The H82A and D33A mutants showed an unusually high activity with substrates featuring low pKa leaving groups, such as DPsPI and p-nitrophenyl inositol phosphate (NPIPs). These results suggest that His-82 functions as the general acid with assistance from Asp-33, facilitating the departure of the leaving group by protonation of the glycerol O3 oxygen. The Bronsted coefficients obtained for the WT and the D33N mutant indicate a high degree of proton transfer to the leaving group and further underscore the "helper" function of Asp-33. The complete mechanism also includes activation of the phosphate group toward nucleophilic attack by a hydrogen bond between Arg-69 and a nonbridging oxygen atom. The overall mechanism can be described as "complex" general acid-general base since three elements are required for efficient catalysis.

Stimulation of coronary vasculogenesis/angiogenesis by hypoxia in cultured embryonic hearts

Hypoxia is known to stimulate vascular growth by up-regulating vascular endothelial growth factor (VEGF), but little is known about the function of hypoxia in the development of the coronary vasculature, and the relationship between hypoxia and VEGF in this event. To test the effects of hypoxia and VEGF on coronary vasculogenesis/angiogenesis in the developing heart, ventricles from 6-day-old quail embryos were cultured on three-dimensional collagen gels. After 2 days of growth in normal medium and 1 day of starvation in low serum medium (0.5% fetal bovine serum), the heart explants were further cultured under various oxygen levels for another 24, 48, and 72 hr. Angioblasts and endothelial cells, which migrated out from the heart explants, were identified by QH1 antibody using immunofluorescence and confocal microscopy. In the normoxic culture environment, the endothelial cells began to proliferate and migrate out from the heart explants after 3 days of growth; they formed tubes mainly after another 72 hr. In contrast, this vascular growth was accelerated under hypoxic conditions, as evidenced by increased tube formation with significant differences observed at 48 hr. On the other hand, hyperoxia delayed this process. Reverse transcription-polymerase chain reaction results indicated that VEGF (including VEGF(122), VEGF(166), and VEGF(190)) was up-regulated in the heart explants under hypoxia and down-regulated under hyperoxia. VEGF neutralizing antibody added to the culture medium partially blocked this vascular growth. We conclude from this study that hypoxia can stimulate or up-regulate coronary vasculogenesis/angiogenesis and that VEGF signaling plays a major role in this event. Dev Dyn 1999;216:28-36.

Endomorphins fully activate a cloned human mu opioid receptor

Endomorphins were recently identified as endogenous ligands with high selectivity for mu opioid receptors. We have characterized the ability of endomorphins to bind to and functionally activate the cloned human mu opioid receptor. Both endomorphin-1 and endomorphin-2 exhibited binding selectivity for the mu opioid receptor over the delta and kappa opioid receptors. Both agonists inhibited forskolin-stimulated increase of cAMP in a dose-dependent fashion. When the mu opioid receptor was coexpressed in Xenopus oocytes with G protein-activated K+ channels, application of either endomorphin activated an inward K+ current. This activation was dose-dependent and blocked by naloxone. Both endomorphins acted as full agonists with efficacy similar to that of [D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAMGO). These data indicate that endomorphins act as full agonists at the human mu opioid receptor, capable of stimulating the receptor to inhibit the cAMP/adenylyl cyclase pathway and activate G-protein-activated inwardly rectifying potassium (GIRK) channels.

Effects of VEGF(165) and VEGF(121) on vasculogenesis and angiogenesis in cultured embryonic quail hearts

It has been documented that hypoxia enhances coronary vasculogenesis and angiogenesis in cultured embryonic quail hearts via the upregulation of vascular endothelial growth factor (VEGF). In this study, we compared the functions of two VEGF splice variants. Ventricles from 6-day-old embryonic quail hearts were cultured on three-dimensional collagen gels. Recombinant human VEGF(121) or VEGF(165) were added to the culture medium for 48 h, and vascular growth was visualized by immunostaining with a quail-specific endothelial cell (EC) marker, QH1. VEGF(165) enhanced vascular growth in a dose-dependent manner: 5 ng/ml of VEGF(165) slightly increased the number of ECs, 10 ng/ml of VEGF(165) increased the incorporation of ECs into tubular structures, and at 20 ng/ml of VEGF(165) wider tubes were formed. This pattern plateaued at the 50 ng/ml dose. In contrast, VEGF(121) did not enhance either the number of ECs or tube formation at these or higher dosages. Combined effects of hypoxia and exogenous VEGF(165) were then compared. Tube formation from the heart explants treated with both hypoxia and 50 ng/ml of VEGF(165) had a morphology intermediate to those treated with hypoxia or VEGF(165) alone. Immunocytochemistry study revealed EC lumenization under all culture conditions. However, the addition of VEGF(165) stimulated the coalescence of ECs to form larger vessels. We conclude the following: 1) VEGF(121) and VEGF(165) induced by hypoxia have different functions on coronary vascular growth, 2) unknown factors induced by hypoxia can modify the effect of VEGF(165), and 3) EC lumenization observed in the heart explant culture closely mimics in vivo coronary vasculogenesis.

Comparative study of the neurotrophic effects elicited by VEGF-B and GDNF in preclinical in vivo models of Parkinson's disease

Vascular endothelial growth factor B (VEGF-B) has recently been shown to be a promising novel neuroprotective agent for several neurodegenerative conditions. In the current study we extended previous work on neuroprotective potential for Parkinson's disease (PD) by testing an expanded dose range of VEGF-B (1 and 10 μg) and directly comparing both neuroprotective and neurorestorative effects of VEGF-B in progressive unilateral 6-hydroxydopamine (6-OHDA) PD models to a single dose of glial cell line-derived neurotrophic factor (GDNF, 10 μg), that has been established by several groups as a standard in both preclinical PD models. In the amphetamine-induced rotational tests the treatment with 1 and 10 μg VEGF-B resulted in significantly improved motor function of 6-OHDA-lesioned rats compared to vehicle-treated 6-OHDA-lesioned rats in the neuroprotection paradigm. Both doses of VEGF-B caused an increase in tyrosine hydroxylase (TH)-positive cell and fiber count in the substantia nigra (SN) and striatum in the neuroprotective experiment. The effect size was comparable to the effects seen with GDNF. In the neurorestoration paradigm, VEGF-B injection had no significant effect in either the behavioral or the immunohistochemical analyses, whereas GDNF injection significantly improved the amphetamine-induced rotational behavior and reduced TH-positive neuronal cell loss in the SN. We also present a strong positive correlation (p=1.9e-50) of the expression of VEGF-B with nuclear-encoded mitochondrial genes involved in fatty acid metabolism in rat midbrain, pointing to the mitochondria as a site of action of VEGF-B. GDNF showed a positive correlation with nuclear-encoded mitochondrial genes that was not nearly as strong (p=0.018). VEGF-B counteracted rotenone-induced reduction of (a) fatty acid transport protein 1 and 4 levels and (b) both Akt protein and phosphorylation levels in SH-SY5Y cells. We further verified VEGF-B expression in the human SN pars compacta of healthy controls and PD patients, in neuronal cells that show co-expression with neuromelanin. These results have demonstrated that VEGF-B has potential as a neuroprotective agent for PD therapy and should be further investigated.

Pontin, a new mutant p53-binding protein, promotes gain-of-function of mutant p53

Tumor-suppressor p53 is frequently mutated in human cancers. Many tumor-associated mutant p53 (mutp53) proteins gain new functions in promoting tumorigenesis, defined as gain-of-function (GOF). The mechanisms for mutp53 GOF are not well understood. Here, we report Pontin, a highly conserved AAA+ ATPase important for various cellular functions, as a new mutp53-binding protein. This Pontin-mutp53 interaction promotes mutp53 GOF in invasion, migration and anchorage-independent growth of tumor cells. The ATPase domain of Pontin is crucial for its promoting effect on mutp53 GOF; blocking the ATPase activity of Pontin by a Pontin-specific ATPase inhibitor or an ATPase-deficient dominant-negative Pontin expression vector greatly diminished mutp53 GOF. Pontin promotes mutp53 GOF through regulation of mutp53 transcriptional activity; knockdown of Pontin abolished the transcriptional regulation of mutp53 toward a group of genes. Furthermore, overexpression of Pontin in tumors is associated with the poor survival in cancer patients, especially those containing mutp53. Our results highlight an important role and mechanism for Pontin, a new mutp53 partner, in promoting mutp53 GOF in tumorigenesis.

Reference values for the Chinese population of skin autofluorescence as a marker of advanced glycation end products accumulated in tissue

AIM

Advanced glycation end products play an important role in the pathophysiology of several chronic and age-related diseases, especially diabetes mellitus. Skin autofluorescence is a non-invasive method for assessing levels of tissue advanced glycation end products. This study aims to establish the normal reference value of advanced glycation end products accumulated in tissue measured by the advanced glycation end product reader--skin autofluorescence--and discusses some factors influencing it.

METHODS

The values of autofluorescence in healthy individuals in China were determined by the advanced glycation end product reader; age, gender, skin reflectance, smoking habits and alcohol consumption of the subjects were also recorded.

RESULTS

The mean reference values of autofluorescence in healthy Chinese subjects are (95% confidence interval) 20-29 years: 1.54-1.62 arbitrary units; 30-39 years: 1.66-1.75; 40-49 years: 1.78-1.89; 50-59 years: 1.87-2.03; 60-69 years: 1.86-2.09; 70-79 years: 1.97-2.31. The value of autofluorescence is strongly related to age, but no significant difference between males and females were found (all P > 0.05). Autofluorescence was higher in smokers than in non-smokers (P < 0.05). In persons with low skin reflectance (< 10%), skin autofluorescence was dependent on skin colour, but was still related to age.

CONCLUSIONS

The mean reference values of autofluorescence we established could be used for a Chinese population in a clinical setting and are agreement with those in a Caucasian population. Future developments are needed to make the advanced glycation end product reader reliable for lower skin reflections as well, independently of the skin colour.

Altered growth factor expression during toxic proximal tubular necrosis and regeneration

Growth factor expression was investigated during the regenerative response after toxic proximal tubular necrosis. Therefore, gentamicin was administered to rats to achieve an experimental model, characterized by the appearance of segment-specific proximal tubular necrosis, that is followed by a regenerative response leading to functional and morphological recovery in a limited time. Four days after the administration of the highest dose, serum creatinine rose to a mean value of 5.8 mg/dl and returned to normal values ten days after the treatment. The S1-S2 segment of the proximal tubules in the cortex became clearly affected by severe toxic necrosis one day after the treatment, while maximal necrosis was observed at days 2 to 4. Only minor injuries were noticed in the other renal compartments. The proliferative response started in the interstitial cells first. The major proliferative wave was localized in the convoluted part of the proximal tubules at days 6 to 8, although proliferation was also prominent among non-proximal tubular cells. A profound interstitial infiltration of leukocytes, including macrophages and T lymphocytes, was observed. Ten days after the treatment the functional and morphological recovery were completed. Slot blot hybridization revealed a decreased EGF and IGF-I mRNA expression from the start of the observation period. While IGF-I mRNA had regained its normal expression at day 10, EGF mRNA was still below control levels. The PDGF-B transcript became more abundant towards the end of our observation. No major changes in the expression of TGF-alpha, TGF-beta 1 and c-fos were detected. Renal EGF-immunoreactivity disappeared from the luminal plasma membrane of the distal tubular cells analogous to the results obtained at the messenger level. However, EGF-staining was lost in the cortex first, hence a topographical association between the loss of EGF-immunoreactivity in the distal tubules and the observed necrotic lesions in the proximal tubules was found. Immunoreactive EGF was never observed in proximal tubular cells from normal, injured or regenerating rat kidneys. We conclude that in this experimental rat model, EGF and IGF-I mRNA expression is decreased during the regenerative response upon severe toxic tubular necrosis. No evidence for a participation of EGF or IGF-I of renal origin in the recovery of the kidney is found.

Efficacy and safety of telbivudine treatment: an open-label, prospective study in pregnant women for the prevention of perinatal transmission of hepatitis B virus infection

We evaluated the efficacy and safety of telbivudine (LdT, 600 mg/day) vs control patients (no treatment) in decreasing vertical transmission of HBV, in HBeAg-positive mothers (HBVDNA >6log(10) copies/mL). HBeAg-positive pregnant women either in the second or third trimester were recruited in a prospective, case-control, open-label study, at the Second Affiliated Hospital of the Southeast University, China (February 2008-December 2010). Efficacy (month 7: HBVDNA (+), HBsAg (+) infants) in either the overall group or the treated group and control group was analysed using student's t-test. Infants were followed for at least 1 year. 362 women received LdT (second trimester n = 257; third trimester n = 105) and 92 were untreated. Before delivery, the mean maternal HBVDNA was 2.73, 2.47, 3.34 and 7.94 log10 copies/mL in the overall, second and third trimester treated and control groups, respectively (P < 0.001). At birth, 11.8% of babies overall (43/365), 13.5% (35/259) of those treated in the second trimester, 7.5% of those treated in the third trimester (8/106) and 20.7% (19/92) of untreated infants were HBsAg positive. At month 7, none of the LdT-treated infant had detectable HBVDNA, while eight infants from control mothers were HBsAg positive. Vertical transmission was 0% in LdT treated and 9.3% (8/86) in the control groups (P < 0.001). No difference in the vertical transmission rate was found in mothers treated in the second or third trimester. LdT treatment was safe for mothers and infants, and no congenital deformities were reported.

Relation of impaired energy metabolism to apoptosis and necrosis following transient cerebral hypoxia-ischaemia

This study investigated whether both mild and severe hypoxia-ischaemia (HI) caused significant numbers of cells to die by apoptosis in the developing brain in vivo. Newborn piglets were subjected to transient global HI and the fraction of all cells in the cingulate gyrus that were apoptotic or necrotic counted 48 h after resuscitation. The mean (S.D.) proportion of apoptotic cells was 11.9% (6.7%) (sham operated controls 4.1% (2.7%)), while 11.4% (8.4%) were necrotic (controls 0.7% (1.3%)) (P<0.05). Apoptotic and necrotic cell counts were both linearly related to the severity of impaired cerebral energy metabolism measured by magnetic resonance spectroscopy (P<0.05), as shown by: (1) the decline in the ratio of nucleotide triphosphates to the exchangeable phosphate pool during HI; (2) the fall in the ratio of phosphocreatine to inorganic phosphate 8 - 48 h after HI; and (3) an increased ratio of lactate to total creatine at both these times. Thus both apoptosis and necrosis occurred in the cingulate gyrus after both severe and mild HI in vivo in proportion to the severity of the insult.

Regulation of CSF-1 receptor expression

Cells of the mononuclear phagocyte lineage possess receptors for macrophage colony-stimulating factor (CSF-1) encoded by the c-fms protooncogene and respond to CSF-1 with increased survival, growth, differentiation, and reversible changes in function. The c-fms gene is itself a macrophage differentiation marker. In whole mount analyses of mRNA expression in embryos, c-fms is expressed at very high levels on placental trophoblasts. It is detectable on individual cells in the yolk sac around 8.5 to 9 days postcoitus, appears on isolated cells in the head of the embryo around 9.5 dpc, and appears on numerous cells throughout the embryo by day 10.5. The extent of c-fms expression is much greater than for other macrophage-specific genes including lysozyme and a macrophage-specific protein tyrosine phosphatase. Our studies of the cis-acting elements of the c-fms promoter have indicated a key role for collaboration between the macrophage-specific transcription factor, Pu.1, which functions in determining the site of transcription initiation, and other members of the Ets transcription factor family. This is emerging as a common pattern in macrophage-specific promoters. We have shown that two PU box elements alone can function as a macrophage-specific promoter. The activity of both the artificial promoter and the c-fms promoter is activated synergistically by coexpression of Pu.1 and another Ets factor, c-Ets-2. A 3.5kb c-fms exon 2 promoter (but not the 300bp proximal promoter) is also active in a wide diversity of tumor cell lines. The interesting exception is the melanoma cell line K1735, in which the promoter is completely shut down and expression of c-fms causes growth arrest and cell death. The activity of the exon 2 promoter in these nonmacrophages is at least as serum responsive as the classic serum-responsive promoter of the c-fos gene. It is further inducible in nonmacrophages by coexpression of the c-fms product. Unlike other CSF-1/c-fms-responsive promoters, the c-fms promoter is not responsive to activated Ras even when c-Ets-2 is coexpressed. In most lines, production of full length c-fms is prevented by a downstream intronic terminator, but in Lewis lung carcinoma, read-through does occur, and expression of both c-fms and other macrophage-specific genes such as lysozyme and urokinase becomes detectable in conditions of serum deprivation.

Involvement of the Arg-Asp-His catalytic triad in enzymatic cleavage of the phosphodiester bond

Phosphatidylinositol-specific phospholipase C (PI-PLC) catalyzes the cleavage of the P-O bond in phosphatidylinositol via intramolecular nucleophilic attack of the 2-hydroxyl group of inositol on the phosphorus atom. Our earlier stereochemical and site-directed mutagenesis studies indicated that this reaction proceeds by a mechanism similar to that of RNase A, and that the catalytic site of PI-PLC consists of three major components analogous to those observed in RNase A, the His32 general base, the His82 general acid, and Arg69 acting as a phosphate-activating residue. In addition, His32 is associated with Asp274 in forming a catalytic triad with inositol 2-hydroxyl, and His82 is associated with Asp33 in forming a catalytic diad. The focus of this work is to provide a global view of the mechanism, assess cooperation between various catalytic residues, and determine the origin of enzyme activation by the hydrophobic leaving group. To this end, we have investigated kinetic properties of Arg69, Asp33, and His82 mutants with phosphorothioate substrate analogues which feature leaving groups of varying hydrophobicity and pK(a). Our results indicate that interaction of the nonbridging pro-S oxygen atom of the phosphate group with Arg69 is strongly affected by Asp33, and to a smaller extent by His82. This result in conjunction with those obtained earlier can be rationalized in terms of a novel, dual-function triad comprised of Arg69, Asp33, and His82 residues. The function of this triad is to both activate the phosphate group toward the nucleophilic attack and to protonate the leaving group. In addition, Asp33 and His82 mutants displayed much smaller degrees of activation by the fatty acid-containing leaving group as compared to the wild-type (WT) enzyme, and the level of activation was significantly reduced for substrates featuring the leaving group with low pK(a) values. These results strongly suggest that the assembly of the above three residues into the fully catalytically competent triad is controlled by the hydrophobic interactions of the enzyme with the substrate leaving group.