Activation of protein phosphatase 1. Formation of a metalloenzyme

The recombinant catalytic subunit of protein phosphatase 1 is produced as an inactive enzyme which can be activated by Mn2+ (Zhang, Z., Bai, G., Deans-Zirattu, S., Browner, M. F., and Lee, E. Y. C. (1992) J. Biol. Chem. 267, 1484-1490). In this report, we have investigated the effects of divalent cations on the activity of recombinant catalytic subunit of protein phosphatase 1. Latent phosphatase 1 can be activated by Co2+ or Mn2+, whereas other metal ions tested including Fe2+, Zn2+, Mg2+, Ca2+, Cu2+, or Ni2+ were not effective or were only weakly effective in activating the enzyme. The Mn(2+)-stimulated activity was susceptible to inactivation by EDTA; however, the Co(2+)-activated phosphatase was stable after dilution and chelation of the Co2+ with excess EDTA. After stable activation of phosphatase 1 using 57Co2+, a stoichiometric amount of 57Co2+ was shown to be tightly bound to phosphatase 1. These findings demonstrate for the first time the generation of a stable metalloenzyme form of phosphatase 1. Fe2+ reversibly deactivated the Co(2+)-stimulated activity, but did not displace the bound Co2+. Interestingly, treatment of the enzyme with a combination of Fe2+ and Zn2+ (but not the individual metal ions) significantly activated phosphatase 1. These results suggest that at least two metal binding sites exist on the enzyme and that protein phosphatase 1 may be an iron/zinc metalloprotein in vivo.

Comparison of the solid-matrix luminescence properties of benzo(a)pyrene-DNA adducts on alpha-cyclodextrin/NaCl and trehalose/NaCl matrices

The solid-matrix luminescence properties of (+/-)-trans-7,8-dihydroxy-anti-9, 10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene-DNA ([+/-]-anti-BPDE-DNA) adducts were compared on alpha-cyclodextrin (CD)/NaCl and trehalose/NaCl solid matrices. Both the optimum composition for the solid matrices and the best solvent system were obtained experimentally for acquiring the maximum room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) signals for the (+/-)-anti-BPDE-DNA. Most of the solid-matrix RTF and RTP data were obtained at 296 K and 93 K for (+/-)-anti-BPDE-DNA adducts adsorbed on 1% alpha-CD/NaCl and 80% trehalose/NaCl. The RTF signals were strong for (+/-)-BPDE-DNA adducts on both solid matrices, but RTP was only obtained on the trehalose/NaCl solid matrices with the 80% trehalose yielding the strongest RTP signal for (+/-)-anti-BPDE-DNA. The fluorescence lifetime data for (+/-)-anti-BPDE-DNA gave two components on 1% alpha-CD/NaCl. For 80% trehalose/NaCl, three components were revealed, but two components were obtained with 80% trehalose/NaCl after ether extraction of the solid matrix. The third component was ascribed to the formation of the tetrols from (+/-)-anti-BPDE-DNA adducts during the drying step in the sample preparation of 80% trehalose/NaCl. The results give the first reported data on the solid-matrix luminescence of the (+/-)-anti-BPDE-DNA adducts. These results should be of considerable interest not only from an analytical viewpoint but as a new means of studying the luminescence characteristics of the adducts.

[Urinary proteins during pregnancy in women with and without pregnancy induced hypertension]

OBJECTIVE

To study the excretion of urinary proteins in women at different periods of pregnancy and women with pregnancy induced hypertension.

METHODS

Urinary proteins (albumin, IgA, IgG, IgM) were measured at random with enzyme-linked immunosorbent assay (ELISA) in 101 normal pregnant women, 25 women with pregnancy induced hypertension and 28 nonpregnant women.

RESULTS

Urinary albumin and IgM levels in women of early pregnancy were significantly higher than those in nonpregnant women (P < 0.05-0.01). Urinary IgG level was also increased during pregnancy. Urinary excretion of albumin, IgA, and IgG, but not IgM excretion was significantly elevated in women with pregnancy induced hypertension compared to normal pregnant women at different gestational ages (P < 0.05-0.01). Urinary IgM level in postpartum period was significantly lower than that in late pregnancy (P < 0.05). Urinary protein excretion increased with gestational age during normal pregnancy, but the changes were not statistically significant. However, the protein excretion was associated with severity of the diseases. Urinary albumin and IgG excretions in hypertensive pregnant women were correlated positively with mean arterial blood pressure.

CONCLUSIONS

The change in glomerular filtration in pregnant women with mild to moderate hypertension is reversible. It is important to control blood perssure to avoid impairment of kidney function in pregnancy induced hypertension.

A metal-dependent form of protein phosphatase 2A

Highly purified bovine heart protein phosphatase 2A catalytic subunit lost virtually all of its activity during storage at -70 degrees. When the enzyme was preincubated with Co2+, over 35% of the original activity was restored. Freshly prepared protein phosphatase 2A purified from bovine heart was stimulated at least 3 to 4-fold by pretreatment with Co2+ or Mn2+. Activation by Co2+ appeared to be irreversible whereas activation by Mn2+ was partially reversed after the cation was chelated with excess EDTA/EGTA. The sensitivity of Co2(+)-stimulated protein phosphatase 2A to okadaic acid or inhibitor-2 was similar to that of spontaneously active protein phosphatase 2A. The enzyme was converted to a latent form by treatment with phosphate or pyrophosphate. The latent form was completely reactivated by preincubation with Co2+. These results demonstrate that protein phosphatase 2A, like phosphatase 1, can exist in a metal ion-dependent form and may represent a new mechanism for the regulation of protein phosphatase 2A activity.

A latent form of protein phosphatase 1 alpha associated with bovine heart myofibrils

The catalytic subunit of the major protein phosphatase associated with bovine cardiac myofibrils was purified to homogeneity. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the enzyme revealed only one band with an apparent molecular weight of 37,000. On gel filtration chromatography, the phosphatase activity and the protein co-eluted as a single peak with an apparent molecular weight of 37,000. The purified enzyme was identified as the catalytic subunit of protein phosphatase 1, as determined by sensitivity to inhibitor 1, inhibitor 2, okadaic acid and by specific immunostaining. Evidence obtained with specific antipeptide antibodies demonstrated that this myofibril protein phosphatase was predominantly the alpha isoform of protein phosphatase 1. The purified catalytic subunit was completely inactive. It was activated by pretreatment with Co2+/trypsin in the presence of high ionic strength. Treatment with trypsin alone did not activate the latent enzyme. The enzyme was also activated by Co2+ or Mn2+ alone but not by Ca2+, Mg2+, Ni2+, Cu2+ or Zn2+. Activation of the enzyme was not reversed by removal of Co2+, but Mn(2+)-activated phosphatase activity was partially reversed when Mn2+ was removed. The catalytic subunit could form a 1:1 complex with inhibitor 2 in vitro. The resulting holoenzyme was also activated by pretreatment with Co2+. Since phosphatase 1 alpha is the major phosphatase associated with cardiac myofibril, it is suggested that it is responsible for the dephosphorylation of myosin and other myofibril phosphoproteins.

Comparison of the solid-matrix luminescence properties and photophysical parameters of two products from benzo(a)pyrene-DNA adducts

The solid-matrix luminescence properties and several calculated photophysical parameters of two important products from the benzo(a)pyrene-DNA adducts were compared. The products were benzo(a)pyrene-r-7,t-8,9,c-10-tetrahydrotetrol (I-1) and 7R,8S,9S-trihydroxy-10R-(N2-deoxyguanosyl-3'-phosphate)-7,8,9,10- tetrahydrobenzo(a)pyrene (BPDE-dG). The solid-matrix luminescence data were obtained for I-1 and BPDE-dG adsorbed on two different solid matrices, namely, 1% alpha-cyclodextrin (CD)/NaCl and 25% trehalose/NaCl and at two different temperatures (93 K and 296 K). The 25% trehalose/NaCl gave higher fluorescence and phosphorescence quantum yields from both I-1 and BPDE-dG in contrast to the 1% alpha-CD/NaCl matrix. The BPDE-dG showed lower fluorescence quantum yields on the solid matrices compared to I-1. The lower fluorescence quantum yields for BPDE-dG were attributed to a photoinduced electron transfer mechanism. In contrast to the room-temperature solution fluorescence of BPDE-dG, BPDE-dG gave rather high fluorescence quantum yields at room temperature when adsorbed on the two solid matrices. From solid-matrix luminescence quantum yields and solid-matrix luminescence lifetimes, many photophysical parameters were calculated and compared. Several differences among the rate constants were noted with the two solid matrices for BPDE-dG and I-1. For example, BPDE-dG showed internal conversion at 296 K with 25% trehalose/NaCl, but no internal conversion was observed at 93 K with this solid matrix. Also, for BPDE-dG the phosphorescence rate constants at 296 K and 93 K were very small with 25% trehalose/NaCl, but the intersystem crossing rate constants from the triplet state to the ground state were very large.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of trifluoroacetoprimaquine on erythrocytic schizonts of rodent malaria]

Effect of trifluoroacetoprimaquine oxalate (M8506) and primaquine (PQ) on blood schizonts of Plasmodium berghei were determined using the method of 4-day suppressive test within extended observation period of 60 d. When mice infected with Plasmodium berghei ANKA strain were treated ig with M8506 or PQ at a same daily dose of 20 mg/kg for 4 d, the cure rates were 100% and 90%, respectively. The two drugs also showed prominent suppressive effects on chloroquine-resistant P. berghei NS line and pyronarine-resistant P. berghei RP line, but the parasitemia still remained positive or all of the mice treated recrudesced, indicating the existence of cross resistance between trifluoroacetoprimaquine and other erythrocytic schizonticides, including chloroquine and pyronaridine.

A quantitative study of the lateral spread of Müller cell responses to retinal lesions in the rabbit

A wide variety of retinal pathology is associated with an increase in Müller glial cell expression of glial fibrillary acidic protein (GFAP). In this study the time course and spatial spread of the Müller cell GFAP response following argon laser photocoagulation lesions was examined in wholemounted rabbit retina. At 24 hours single focal lesions were surrounded by GFAP positive Müller cell end feet which declined in density with distance but extended as far as 2-3 mm from the lesion. The Müller cell reaction reached a maximal spread of 4-5 mm at 14 to 21 days and had started to contract by 30 days, leaving a core of GFAP positive processes immediately around the lesion site at 60 days. This zone of spread was much larger than the area of disrupted pigment epithelium. Isodensity plots did not reveal any correlation with the trajectory of retinal ganglion cell axons. The spread of reaction was more confined for lesions within the visual streak than in the dorsal or ventral retinal periphery. Multiple lesions within a focal region of retina resulted in a greater density of GFAP reactive end feet with a corresponding greater spread. However, when five to ten lesions were made in a horizontal row, the Müller cells over the entire retina became GFAP immunoreactive. This pan-retinal reaction took several days to spread, peaked at 7-14 days, and contracted back to the primary lesion sites by 2 months. This spread of Müller cell reactivity may be triggered by the diffusion of substances released by injury or it may be due to direct cellular communication. The extensive indirect effect on Müller cells of laser irradiation might be an important component of the clinical effect of laser photocoagulation and indicates a long distance communication mechanism between retinal glia which is poorly understood. This study also shows the importance of the time at which the Müller cell response is assessed.

Horizontal cells of the normal and dystrophic rat retina: a wholemount study using immunolabelling for the 28-kDa calcium-binding protein

Immunocytochemistry with a monoclonal antibody against the 28-kDa calcium-binding protein (28-kDa CaBP) was used to study horizontal cells in both congenic control (RCS-rdy+) and dystrophic (RCS) 3-month-old rat retina. We found that horizontal cells in the RCS-rdy+ rat retinas were distributed evenly from the centre to the peripheral retina with a mean density of 783 cells mm-2. Cell size ranged between 6.5-12.5 microns in diameter with a mean of 8.87 microns. Individual cell processes could not be followed readily, however they formed a narrow plexus within the outer plexiform layer with the primary dendrites extending radially from each cell soma in an organized manner. In the RCS rat, by contrast, the horizontal cell processes were more disorganized than in the congenic controls. The degree of disorganization varied across the retina. In the posterior pole, where all outer layers had been lost, many processes were grossly swollen along their length and at the tips. The cell somas were also distributed more widely in the depth of the retina. In the peripheral retina, where a debris layer was still present, the processes were less swollen but they extended abnormally widely in depth. Despite the disorganized structure the mean and range of cell size (9.23 microns, 5.5-15.5 microns), and cell density (796 cells mm-2) were similar to that of the control RCS-rdy+ animals. These findings indicate that in dystrophic retinas beyond a certain stage of degeneration the horizontal cells become abnormal in their structure but are present at a normal density and the somas are not grossly swollen or shrunken.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient preservation of photoreceptors on the flanks of argon laser lesions in the RCS rat

In the RCS rat there is a progressive degeneration of the photoreceptors which starts at two to three weeks after birth. We have demonstrated that there is prolonged survival of photoreceptors on the flanks of argon laser lesions made at post-natal day 23, just as degeneration begins. The cells in the outer nuclear layer retained a relatively normal appearance on the flanks of the lesions for the first two weeks and there was a very low percentage of pyknotic cells. By one month some cell loss occurred but much less than in non-irradiated regions where very few cells remained. At two months after lesion there were still elevated numbers on the flanks but only 2-3 rows of cells remained. The prolonged survival correlated with disruption to the pigment epithelial layer, increased migration of phagocytic cells into the outer segment/debris layer and a reduction in thickness of the debris layer at late stages. The mechanisms of this effect are unknown however laser lesions provide a well controlled and reproducible situation in which to study these mechanisms.

Expression of basic fibroblast growth factor and its receptor in the retina of Royal College of Surgeons rats. A comparative study

PURPOSE

The aim of this study was to identify whether abnormalities in the synthesis of basic fibroblast growth factor (bFGF) or its receptor (bFGF-R) were responsible for the photoreceptor dystrophy in Royal College of Surgeons (RCS) rats.

METHODS

The polymerase chain reaction was used to detect the expression of bFGF and bFGF-R messenger RNA in the retinal pigment epithelial (RPE) cells and the neural retina of RCS dystrophic rats and in PVG/C and RCS-rdy+ control animals.

RESULTS

In the RPE, it was found that there was no significant difference in the expression of bFGF and bFGF-R between RCS rats and the controls at the ages of 21 days and 3 mo. In the neural retina, the level of bFGF expression was lower in the 21-day-old RCS rats compared with the control group, but bFGF-R expression was as strong as in the PVG/C and RCS-rdy+ animals. However, in 3-mo-old RCS rat neural retina, the bFGF and bFGF-R expression was found to be significantly lower than in the control animals.

CONCLUSIONS

Although the mutant gene in RCS rats is expressed in the RPE cells, these results suggest that there is no significant defect in bFGF or bFGF-R expression in the RPE cells of RCS rats, which would be an initiating factor in the development of photoreceptor degeneration in these animals. The lowered bFGF levels in the neural retina at early stages (postnatal day 21) may explain the prolongation of photoreceptor survival when exogenous bFGF is injected.

Experimental study of the effect of IH764-3 on pulmonary fibrosis

IH764-3 is a potent component isolated from Salvia miltiorrhiza. We have studied the effect of IH764-3 on experimental pulmonary fibrosis in rats and mice treated with a single intratracheal instillation of bleomycin-A6. Three groups of animals were assigned as BLM+saline, BLM+IH764-3 and normal control. The results indicated that in the treated group, lung coefficient, surfactant, hydroxyproline content and FGF activity were significantly lower than those in the control group (P < 0.05, 0.05, 0.001 and 0.05, respectively). Electron microscopic examination showed that pulmonary ultrastructure was markedly better in the treated group: type II alveolar epithelial cells, infiltrating inflammatory cells, proliferating collagen-forming cells, collagen and elastic fibers were obviously fewer in the treated group. These results demonstrate that IH764-3 has prophylactic and therapeutic effects on pulmonary fibrosis.

The effect of IH764-3 on fibroblast proliferation and function

The effect of IH764-3, a potent component isolated from Salvia miltiorrhiza, on the proliferation and function of cultured fibroblasts was studied. It was found that the fibroblast growth curve had a dose-dependent relationship with IH764-3 concentration. The incorporation of 3H-TdR and 3H-proline into fibroblasts was significantly inhibited by IH764-3, and calmodulin, fibronectin and thrombospondin contents in the test group were obviously lower than those in the control group. Flow cytometry showed that in the IH764-3-treated group, the percentage of cells in G0/G1 phase was higher than that in the control. Electron microscopic observation (TEM and SEM) showed that in the treated group, collagen secretion was decreased. All of these results indicate that IH764-3 exerts a direct inhibitory effect on fibroblast proliferation and affects their ability to synthesize collagen.

Ellipticine increases the superhelical density of intracellular SV40 DNA by intercalation

We investigated the in vivo effect of ellipticine, a mammalian topoisomeraseII(topoII) inhibitor, on SV40 DNA topology. In contrast to epipodophyllotoxins, ellipticine did not cause significant double stranded cleavage of intracellular SV40 DNA. Furthermore, ellipticine reduced cleavage induced by epipodophyllotoxins, VP16 and VM26. Unexpectedly, ellipticine dramatically increased the superhelical density of a fraction of intracellular SV40 DNA. Several lines of evidence suggest that the formation of this highly supercoiled DNA species (Ih form DNA) is not due to the inhibition of topoII per se, but is the result of intercalation by ellipticine in a subfraction of the intracellular SV40 chromatin followed by the fixation of DNA linking number by a topoisomerase activity. Based on the linking number change and the known unwinding angle of ellipticine, the intercalation density was calculated as one ellipticine molecule per 10-20 bp in the Ih DNA. This result suggests the existence of different populations of intracellular SV40 chromatin with respect to the accessibility to ellipticine intercalation.

Developmental study of chondroitin-6-sulphate in normal and dystrophic rat retina

The RCS rat is a widely studied model of human retinal dystrophies including retinitis pigmentosa. Chondroitin-6-sulphate (C6S) in the interphotoreceptor matrix was localised immunocytochemically in both the normal congenic and dystrophic strains of the RCS rat up to 65 days postnatally. From postnatal days 5 to 15 the distribution of C6S in both strains was similar, being localised in the interstices of developing inner and outer segments and adjacent to the RPE surface. In the normal rats, the distribution of C6S did not change with age. In the RCS rats, however, at postnatal days 20 to 35 staining was observed as a dense band at the junction of inner and outer segments and no staining was observed adjacent to the surface of the RPE. At postnatal day 45 onwards there was a decrease and a complete absence of C6S staining in these rats. This change in the pattern of staining correlated with the morphological observation of the progressive degeneration of photoreceptor cells suggesting that C6S may be important in photoreceptor degeneration in the RCS rat.

Persistent infection of human adenovirus type 5 in human monocyte cell lines

Adenovirus infection of human monocyte hybridoma cell lines and the fusion partner U937 was investigated. Adenovirus adsorbed poorly to these cells as well as primary human alveolar macrophages. The virus-binding experiments showed a 100-fold reduction in apparent viral binding to these cells compared to the permissive HeLa cells. Adsorption of adenovirus to these cells could be enhanced by preincubation of adenovirus with its antiserum. Following entry into the cells amplification of adenovirus DNA was detected starting at 2 days postinfection but few mature virus particles were produced. The infected cultures survived the infection and continued to grow for more than a year. In these chronically infected cultures, linear adenovirus DNA persisted up to 200 copies per cell and a small amount of mature virus was produced. Infectious center assay and cell cloning experiments showed that the majority of the cells in the chronically infected cultures harbor adenovirus genome. These results indicate that restriction of replication of human adenovirus type 5 at the late phase results in persistent infection of U937 and the human monocyte hybridoma cell lines.

Specific binding and internalization of monoclonal antibody HI98-daunorubicin conjugate by human leukemic cells (HL60)

McAb-HI98 has been proved to bind specifically to HL60 cells. In this study, we further observed the specific binding of HI98-Daunorubicin (DNR) conjugate to HL60 cells, the transmembranal transport of HI98-DNR and the process of internalization by immunoelectron microscopy. After HL60 cells were incubated with HI98-DNR-Au, gold particles were first found on the surface membranes of HL60 cells, and then inside the cells. Internalization was found to occur through the formation of endocytic vesicles. Results indicate that the immunoconjugate selectively binds to target cells and enters the cells specifically and rapidly, thus enhancing intracellular drug concentration.

A rapid method for screening vaccinia virus recombinants

A rapid and small-scale method for screening vaccinia virus recombinants employing micrococcal nuclease is described. This protocol utilizes the differential sensitivity of cellular and viral DNA to the nuclease, which can be selectively activated by addition of Ca2+ and inactivated by elimination of Ca2+. Two to five micrograms of viral DNA can be obtained from one infected L cell plate (50 mm) after overnight incubation.

P1 nuclease defines a subpopulation of active SV40 chromatin--a new nuclease hypersensitivity assay

Under exhaustive digestion conditions P1 nuclease was found to cleave a subpopulation of intracellular SV40 chromatin only once. The major P1 cleavage site in SV40 DNA was mapped at the origin of DNA replication, and the two minor sites at the SV40 enhancers. The P1-sensitive SV40 chromatin subpopulation was found to have higher superhelical density than the bulk of the intracellular SV40 chromatin. Furthermore, pulse labeled SV40 DNA which had higher superhelical density than that of the steady state viral DNA (S.S. Chen and M.T.Hsu, J. Virol 51:14-19, 1984) was also found to be preferentially cleaved by P1 nuclease. These results are consistent with a supercoil-dependent alteration of chromatin conformation near the regulatory region of the viral genome that can be recognized by P1 nuclease. Since P1 nuclease cleaves the subpopulation of SV40 chromatin only once without further degradation, this nuclease can be used as a general tool to define viral or cellular chromatin fraction with altered chromatin conformation and to map nuclease hypersensitive sites. Preliminary studies indicate that P1 makes limited double stranded cleavages in cellular chromatin to generate large DNA fragments.

Monocyte function in chickens with hereditary muscular dystrophy

Monocyte functions of Storrs strain muscular dystrophic (MD) chickens and Storrs control strain were compared. After short-term in vitro culture of monocytes, cells taken from Storrs MD chickens had a significantly lower incidence of cells capable of phagocytizing sheep red blood cells than did cells cultured from the control strain. In contrast, no difference was found in the ability of MD vs. control strain blood mononuclear cells to undergo in vitro chemotaxis in response to a bacterial culture supernatant. The study also revealed a distinct peripheral blood leukocyte profile of young MD chickens: elevated percentages and absolute numbers of granulocytes. The total leukocyte count in MD chickens was not significantly different from that of normal chickens. These findings extend previous observations concerning altered reticuloendothelial system function in MD strain chickens.