Functional domains of Pseudomonas exotoxin identified by deletion analysis of the gene expressed in E. coli

Pseudomonas exotoxin A is a single chain toxin with three structural domains that inhibits protein synthesis in eukaryotic cells by catalyzing ADP ribosylation of elongation factor 2. To study the function of these domains, we deleted different portions of the PE structural gene and expressed these constructs in E. coli using an inducible T7 promoter. These studies indicate that structural domain Ia is required for cell recognition, that structural domain II is required to translocate the toxin across a cellular membrane, and that structural domain III and a portion of domain Ib are required for ADP ribosylation activity. Toxin lacking domain Ia is about 100-fold less toxic to mice than intact PE and should be a useful molecule for the construction of immunotoxins.

The role of intracellular pH in ligand internalization

Internalization of EGF and transferrin measured as the rate of uptake of 125I-labeled ligands was compared in the cell line CCL39 and a mutant derivative, PS-120, lacking the Na+/H+ antiport system. No significant alteration was detected between the two cell lines. In contrast, pretreatment of the mutant cells PS-120 with 20 mM NH4Cl for 30 min to decrease persistently intracellular pH resulted in an increase in 125I-EGF and 125I-transferrin uptake by 60% and 25%, respectively. However, similar NH4Cl pretreatment of the parental cell line, CCL-39, which only affected intracellular pH very transiently did not cause an increase of ligand uptake. The binding of 125I-EGF to CCL-39 and PS-120 cells with or without NH4Cl pretreatment showed that NH4Cl pretreatment did not affect EGF binding in either CCL-39 or PS-120 cells. Since cells regulate intracellular pH by ion transport systems, we also examined the role of Na+, K+-ATPase. Ouabain, an inhibitor of Na+, K+-ATPases, showed no effect on 125I-EGF uptake in either of the cell types with or without NH4Cl pretreatment. Taken together, these results suggest that the plasma membrane-bound Na+/H+ antiport, a major pHi-regulating system in vertebrates, indirectly plays a role in ligand internalization through regulation of intracellular pH.

Multiple drug-resistant human KB carcinoma cells independently selected for high-level resistance to colchicine, adriamycin, or vinblastine show changes in expression of specific proteins

We have established four cell lines derived from the human KB carcinoma cell line which express high-level multiple drug resistance. One of these lines was selected for resistance to colchicine, one was selected for resistance to colchicine in the presence of the tumor promoter, mezerein, one for resistance to vinblastine, and one for resistance to adriamycin. All of these cell lines are cross-resistant to the other selective agents. The development of multidrug resistance in these cultured human carcinoma cells is associated with a limited number of specific protein alterations revealed by high resolution two-dimensional gel electrophoresis and Western blot analysis. These protein alterations in multidrug-resistant lines include the decreased prevalence of members of a family of proteins of molecular mass 70,000 to 80,000 daltons, pI 4.8-5.0, the increased synthesis of a protein of molecular mass 21,000 daltons, pI 5.0, in the colchicine-resistant cell lines only, and the increased expression of a 170,000-dalton protein in membrane preparations from all of the resistant cells. The loss of the 70,000- to 80,000-dalton proteins in the multidrug-resistant lines, which can also be demonstrated by immunoprecipitation of these proteins with specific antisera, is associated with a loss of translatable mRNA for these proteins. These studies suggest that only a limited number of protein changes occur in multidrug-resistant cell lines.

Binding of apolipoprotein A-I and A-II after recombination with phospholipid vesicles to the high density lipoprotein receptor of luteinized rat ovary

To determine the apolipoprotein specificity of high density lipoprotein (HDL) receptor, apolipoprotein A-I (apo-AI) and apolipoprotein A-II (apo-AII) purified from high density lipoprotein3 (HDL3) were reconstituted into dimyristoyl phosphatidylcholine vesicles (DMPC) and their ability to bind to luteinized rat ovarian membranes was examined. Both 125I-apo-A-I.DMPC and 125I-apo-A-II.DMPC were shown to bind to ovarian membranes with Kd = 2.87 and 5.70 micrograms of protein/ml, respectively. The binding of both 125I-apo-A-I.DMPC and 125I-apo-A-II.DMPC was inhibited by unlabeled HDL3, apo-A-I.DMPC, apo-A-II.DMPC, apo-C-I.DMPC, apo-C-II.DMPC, apo-C-III1.DMPC, and apo-C-III2.DMPC, but not by DMPC vesicles, bovine serum albumin.DMPC or low density lipoprotein. Since the binding labeled apo-A-I.DMPC and apo-A-II.DMPC was inhibited by the DMPC complexes of apo-C groups, the direct binding of 125I-apo-C-III1.DMPC was also demonstrated with Kd = 9.6 micrograms of protein/ml. In addition, unlabeled apo-A-I.DMPC, and apo-A-II.DMPC, as well as apo-C.DMPC, inhibited 125I-HDL3 binding. 125I-apo-A-I, 125I-apo-A-II, and 125I-apo-C-III1 in the absence of DMPC also bind to the membranes. These results suggest that HDL receptor recognizes apolipoprotein AI, AII, and the C group and that the binding specificity of the reconstituted lipoproteins is conferred by their apolipoprotein moiety rather than the lipid environment. In vivo pretreatment of rats with human chorionic gonadotropin resulted in an increase of 125I-apo-A-I.DMPC, 125I-apo-A-II.DMPC, and 125I-apo-C-III1.DMPC binding activities. However, no induction of binding activity was observed when the apolipoprotein was not included in DMPC vesicles. An examination of the equilibrium dissociation constant and binding capacity for 125I-apo-A-I.DMPC and 125I-apo-A-II.DMPC after human chorionic gonadotropin treatment revealed that the increase in binding activity was due to an increase in the number of binding sites rather than a change in the binding affinity. These results further support our contention that apo-A-I, apo-A-II, and the apo-C group bind to HDL receptor. In conclusion, the HDL receptor of luteinized rat ovary recognizes apolipoproteins A-I, A-II, and the C group but not low density lipoprotein, and the binding is induced by human chorionic gonadotropin in vivo.

The role of plasma lipoproteins in steroidogenic response of rat luteal cells during gonadotropin-induced refractory states

Administration of human chorionic gonadotropin (hCG) to pregnant mare's serum gonadotropin--hCG primed rats results in the loss of in vitro responsiveness of the ovaries to exogenous gonadotropins for progesterone production. This state is associated with a loss of membrane receptors for hCG and a concomitant increase in lipoprotein receptors. Although lipoproteins potentiated gonadotropin response in ovaries from saline-injected rats, no stimulation was observed in hCG-desensitized ovarian cells. Examination of the time course for the loss of lipoprotein response after hCG injection revealed that injection with 50 IU of hCG results in a loss of gonadotropin response as early as 1 h after injection, but exogenous cholesterol-carrying lipoprotein fractions, LDL and HDL, were capable of stimulating progesterone production up to 4 h after hormone injection. Measurement of endogenous cholesteryl ester content showed that there was a 72% decline during this period with a concomitant increase in the basal progesterone production. One hour after hCG injection there was no stimulation of steroidogenesis by hCG in the presence or absence of exogenous lipoproteins. The refractoriness to exogenous hCG appeared only 4 h later when the hCG dose was reduced to 10 IU, whereas with 25 IU of hCG, the effect was similar to that observed using 50 IU of hCG. Such diverse steroidogenic stimuli as hCG, LH, LDL, cAMP, and cholera enterotoxin failed to stimulate progesterone synthesis in vitro in luteal cells of rats injected with 50 IU of hCG 48 h prior to sacrifice.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial relationships of the human chorionic gonadotropin (hCG) subunits in the assembly of the hCG-receptor complex in the luteinized rat ovary

In an attempt to examine the spatial relationships of the human chorionic gonadotropin (hCG) subunits in the assembly of the hCG-receptor complex, the recombined 125I-labeled hCG, with label in either the alpha subunit or the beta subunit, was cross-linked to the luteinizing hormone (LH)/hCG receptor. The efficacy of the cross-linking of the 125I-alpha subunit or the 125I-beta subunit of hCG to the LH/hCG receptor was then examined. The autoradiographic profile of 125I-hCG-receptor complex containing the label in the alpha subunit of hCG showed that the alpha subunit can cross-link with all four subunits of the LH/hCG receptor. However, only one faint labeled band, corresponding to Mr = 68,000, was detected when the 125I-hCG-receptor complex with label in the beta subunit was subjected to sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing conditions. When the electrophoresis was performed under nonreducing conditions, the Mr 68,000 band disappeared concomitantly with the accumulation of radioactivity in the high molecular weight region. These results indicated that the beta subunit of hCG, unlike the alpha subunit, can cross-link only weakly with the smallest subunit of the LH/hCG receptor. A comparison of the differential effectiveness of the cross-linking of 125I-alpha subunit with 125I-beta subunit of hCG to the LH/hCG receptor suggests that both alpha and beta subunits of hCG are intimately associated with the receptor, but the bulk of the beta subunit of hCG is buried in between the receptor and the alpha subunit of hCG. On the basis of our data, a model for the spatial arrangement of hCG subunits in the hCG-receptor complex is proposed.

Characterization of the subunit structure of gonadotropin receptor in luteinized rat ovary

Gonadotropin receptors with specificity, high affinity and low capacity for luteinizing hormone and human chorionic gonadotropin (hCG) have been identified in rat luteal cells. To investigate the nature of the receptor, we have employed disuccinimidyl suberate, a cross-linker noncleavable by reducing agents, and dithiobis(succinimidyl propionate), a cleavable cross-linker, to covalently cross-link the 125I-hCG . receptor complex. The molecular weight of 125I-hCG-linked receptor complex and the receptor subunit structure were determined by electrophoresis in either 10 or 4.5% acrylamide in the presence of 0.1% sodium dodecyl sulfate with or without reducing agents. Autoradiographic analysis of the 125I-hCG-linked receptor separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing condition revealed a single labeled band corresponding to Mr = 305,000 +/- 15,000. However, electrophoresis performed in the presence of 50 mM dithiothreitol and 2% beta-mercaptoethanol resulted in the appearance of four labeled bands corresponding to Mr = 105,000 +/- 4,000, 96,000 +/- 5,000, 74,000 +/- 4,000, and 62,000 +/- 4,000 concomitant with the loss of the labeled band in the Mr = 305,000 region. Further experiments demonstrated that these four labeled bands were derived from the same molecular species. In addition, the 125I-hCG-linked receptor in the absence of reducing agent was not dissociated into subunits even by treatment with strong denaturing agent (8 M urea). The appearance of the cross-linked 125I-hCG . receptor was effectively inhibited by the unlabeled beta-subunit of hCG, intact hCG, and luteinizing hormone and partially inhibited by the alpha-subunit of hCG but not by choleratoxin, gonadotropin-releasing hormone, insulin or bovine serum albumin. These data suggest that 1) the hCG/luteinizing hormone receptor is an oligomeric complex linked by disulfide bonds and 2) that under reducing conditions, the oligomeric receptor dissociates into four nonidentical subunits.

Characterization of low density and high density lipoprotein receptors in the rat corpus luteum and regulation by gonadotropin

Freshly prepared plasma membranes from rat corpora lutea were examined for the presence of low density lipoprotein (LDL) and high density lipoprotein (HDL) receptors by determining the specific binding of 125I-LDL and 125I-HDL. These membranes have two types of binding site for 125I-LDL, one with high affinity (Kd = 7.7 micrograms of LDL protein/ml), the other with low affinity (Kd = 213 micrograms of LDL protein/ml) and one type of binding site for 125I-HDL with Kd = 17.8 micrograms of HDL protein/ml. LDL receptor is sensitive to pronase and trypsin; HDL receptor, however, is resistant. The binding reaction was further characterized with respect to effect of time and temperature of incubation, requirement of divalent metal ion, influence of ionic strength, and binding specificity. In vivo pretreatment of rats with human choriogonadotropin (hCG) resulted in induction of both LDL and HDL receptors in a dose- and time-dependent manner when compared with saline-injected controls. The induction of lipoprotein receptors by hCG treatment is target organ-specific since the increase was seen only in the ovarian tissue. Membranes prepared from liver, kidney, and heart did not show an increase in lipoprotein receptors after hCG injection. An examination of the equilibrium dissociation constants for 125I-LDL and 125I-HDL binding after hCG administration revealed that the increase in binding activity was due to an increase in the number of binding sites rather than to a change in the binding affinity. In conclusion, rat corpus luteum possesses specific receptors for both LDL and HDL and these receptors are regulated by gonadotropins.

Binding, degradation, and utilization of plasma high density and low density lipoproteins for progesterone production in cultured rat luteal cells

These studies were intended to examine the binding and degradation of plasma lipoprotein fractions and the utilization of lipoprotein-bound cholesterol for progesterone production in cultured rat luteal cells. These cells bound [125I]human low density lipoprotein ([125I]iodo-hLDL),[125I]human high density lipoprotein ([125I]iodo-hHDL), and [125I]iodorat HDL ([125I] iodo-rHDL) with high affinity. The equilibrium dissociation constants of the binding of labeled rHDL, hHDL, and hLDL were 90.5, 78.3, and 36.8 micrograms/ml, respectively. All three lipoproteins were also degraded in a concentration-dependent manner, with apparent Km values of 18.3, 17.5, and 22.4 micrograms/ml for rHDL, hHDL, and hLDL, respectively. The degradation of the lipoproteins was inhibited by lysosomotropic agents, transglutaminase inhibitors, and metabolic inhibitors, suggesting that these lipoproteins undergo internalization and lysosomal degradation. In addition, all three lipoproteins also augmented the hCG-stimulated steroidogenesis. When cells were incubated with reconstituted LDL (the cholesterol ester in the LDL was replaced with [3H]cholesteryl linoleate) and the steroids produced identified, incorporation of tritium label in the progesterone fraction was observed in a time- and concentration-dependent manner. The incorporation of tritium into progesterone was increased by hCG and inhibited by an excess of unlabeled LDL in the incubation medium. These results show that the ovarian cells use lipoproteins as a source of cholesterol for steroidogenesis through receptor-mediated uptake and internalization, and the evidence suggests that the lipoproteins are intracellularly degraded.

Multiple DNA fragment polymorphisms associated with immunoglobulin mu chain switch-like regions in man

DNA probes containing the switch region (S) associated with the human immunoglobulin heavy chain mu gene were used to investigate polymorphisms in the germ-line human DNA. Six polymorphisms, detected by a single restriction enzyme (Sst I) are described. Linkage studies in 29 families show that five of the six polymorphisms, although relatively unassociated in random individuals, segregate in complete linkage one to the other and to Gm allotypes (markers on the heavy chain of IgG), while the sixth segregates independently. Altogether, when one considers the DNA markers at the five closely linked loci and the IgG1 and IgG3 heavy chain allotypes, 33 different haplotypes have been described; of these, 28 are detected by the DNA polymorphism alone. Study of 158-187 random haplotypes showed strong linkage disequilibrium only between one DNA polymorphism (Sst A) and Gm. Of the polymorphic Sst I loci, one, Sst E [associated with 2.2- to 2.7-kilobase (kb) fragments], is included in the mu chain S region (S mu); another, Sst A (6.8-7.4 kb), must be very close to the gamma 1-gamma 3 chain gene cluster. Based on studies of an IgE human myeloma, a third polymorphism, Sst C (4.8-5.5 kb), should map 3' of the active epsilon chain gene. An Sst I restriction enzyme map of phage clones carrying the two alpha chain genes indicates that Sst A and Sst C loci probably overlap with the alpha 1 and alpha 2 S regions, respectively. Both deletion/duplications and point mutations were detected.

Specificity of the acid protease from Monascus kaoliang towards the B-chain of oxidized insulin

The proteolytic specificity of the acid protease from Monascus kaoliang has been investigated using the B-chain of performic acid-oxidized insulin as peptide substrate. Six splittings were detected after 1 h digestion and 12 splittings were found after 12 h incubation at 37 degrees C, pH 4.8. The bonds most susceptible to the acton of M. kaoliang acid protease were Phe(24)-Phe(25), Leu(15)-Tyr(16) and Tyr(16)-Leu(17). Among the acid proteases compared, the specificity of M. kaoliang acid protease on the B-chain of oxidized insulin is more closely related to that of penicillopepsin with which it has ten cleavage sites in common. N-Acetyl-L-phenylalanyl-L-3,5-diiodotyrosine, a synthetic substrate for pepsin, was resistant to the hydrolysis of M. kaoliang acid protease.

Thermostability of duck hepatitis virus

The comparative thermostability of 4 duck hepatitis (DH) viruses were tested at various temperatures for different times. Titer of duckling-passaged, pathogenic DH virus decreased from 10(4.50) to 10(2.33) and 10(2.20) median infective doses (ID50/0.1 ml, respectively, in 2 tests; titer of chicken embryo-passaged, nonpathogenic, but embryo-lethal, DH virus decreased from 10(6.00) to 10(0.46) and from 10(6.62) to 10(0.63) ID50/0.1 ml, respectively; duck embryo fibroblast culture-passaged and duck embryo liver cell culture-passaged, chicken ebryo-infective, but nonlethal, DH viruses were completely inactivated or nearly so after being kept at 56 C for 30 minutes. Duckling-passaged DH virus was not detected on day 21, whereas 10(0.62) ID50 of chicken embryo-passaged DH virus per 0.1 ml remained on day 32 when being kept at 37 C. Titer of chicken embryo-passaged DH virus decreased from 10(7.00) to 10(1.16) ID50/0.1 ml after being kept at room at room temperature for 150 days, to 10(5.17) ID50/0.1 ml after being kept at 4 C for 70 weeks, to 10(6.17) ID50/0.1 ml after being kept at -20 C for 70 weeks, and to 10(6.38) ID50/0.1 ml after being kept at -60 C for 1 year.

Occurrence of duck virus enteritis (duck plague) in Pennsylvania, 1968-74

During the 7-year period 1968-74 cases of duck virus enteritis (duck plague) were diagnosed in waterfowl in Pennsylvania. Muscovy ducks were affected in 8 cases, geese in 3 cases, and mallard ducks in 1 case. In 5 of these cases either domestic or wild ducks were closely associated with infected waterfowl but were unaffected.