158 PRODUCTION OF RECOMBINANT LH FOR USE IN TIGER (TIGRIS ALTAICA) ASSISTED REPRODUCTION:A PRELIMINARY REPORT

Genetically, porcine LH is the closest commercially available gonadotropin analog to tiger LH (93% homologous); however, its use may lead to possible autoimmune reactions, lessening ovarian responses in stimulated tigresses over time (Crichton et al. 2005 Biol. Reprod. 68, 105–113). To overcome this problem for use in assisted reproduction, we produced recombinant tiger LH (tLH), and tested the bioactivity of several tLH constructs using heterologous (rat) and homologous (cat) Leydig cell assays. To clone tLH, mRNA was isolated from an Amur tiger pituitary by TRIzol extraction (Invitrogen, Carlsbad, CA). DNA was synthesized from the mRNA using reverse transcriptase (Stratagene, La Jolla, CA) and PCR was performed using tiger-specific primers for glycoprotein hormone α subunit or LH β subunit. The α subunit was cloned into the double-expression vector pIRES (Invitrogen). The tLH β subunit was cloned into the second site of pIRES and also into the plasmid pGS. Chinese hamster ovary (CHO) K1 and human granulosa cell tumor (COV 434) cells were transfected with plasmid DNA by calcium-phosphate precipitation: (1) pIRES containing α and pGS containing LH β, or (2) pIRES containing α and LH β. Cells were grown in selection media (250 µg mL–1 geneticine for pIRES, or 25 µm methionine sulfoximine for pGS). Media was collected and clarified at 1500g for 30 min. An immature rat Leydig cell assay protocol (Bousfield et al. 2001 Biol. Reprod. 64, 136–147) detected biological activity (testosterone production) by RIA. Of 14 tLH constructs created, 1 wild-type construct (LH WTCHO8) had LH activity 3 times greater than any other. A domestic kitten Leydig cell assay was performed in order to assess comparative sensitivities and specificities. Domestic kitten testicles, obtained from a local spay clinic, were disassociated with collagenase (225 U mg–1, Worthington Biochemical, Lakewood, NJ); however, the cells were more difficult to disperse than rat testicles, leading to low Leydig cell yields as determined histologically. Modification of the Leydig cell collagenase protocol for the cat was achieved by increasing the temperature and surface area, and agitating the minced tissue in medium on a stir plate. Samples of the 14 tLH constructs were run in parallel using rat and cat Leydig cell assays. Although rat Leydig cell testosterone concentrations (3.4 ng mL–1) were nearly 10-fold greater, the same trend for the different constructs was found in the cat Leydig cells with the same wild-type construct (LH WTCHO8, 0.37 ng mL–1) having greater LH activity than any other. The lower testosterone concentrations in the cat bioassay may be explained by insufficient Leydig cell numbers, age (sensitivity), damaging effect(s) of collagenase, or felid specificity. Still, these results lend validity to the use of the heterologous rat Leydig cell bioassay for recombinant tiger LH.

Functional contributions of noncysteine residues within the cystine knots of human chorionic gonadotropin subunits

Human chorionic gonadotropin (hCG) is a heterodimeric member of a family of cystine knot-containing proteins that contain the consensus sequences Cys-X(1)-Gly-X(2)-Cys and Cys-X(3)-Cys. Previously, we characterized the contributions that cystine residues of the hCG subunit cystine knots make in folding, assembly, and bioactivity. Here, we determined the contributions that noncysteine residues make in hCG folding, secretion, and assembly. When the X(1), X(2), and X(3) residues of hCG-alpha and -beta were substituted by swapping their respective cystine knot motifs, the resulting chimeras appeared to fold correctly and were efficiently secreted. However, assembly of the chimeras with their wild type partner was almost completely abrogated. No single amino acid substitution completely accounted for the assembly inhibition, although the X(2) residue made the greatest individual contribution. Analysis by tryptic mapping, high performance liquid chromatography, and SDS-polyacrylamide gel electrophoresis revealed that substitution of the central Gly in the Cys-X(1)-Gly-X(2)-Cys sequence of either the alpha- or beta-subunit cystine knot resulted in non-native disulfide bond formation and subunit misfolding. This occurred even when the most conservative change possible (Gly --> Ala) was made. From these studies we conclude that all three "X" residues within the hCG cystine knots are collectively, but not individually, required for the formation of assembly-competent hCG subunits and that the invariant Gly residue is required for efficient cystine knot formation and subunit folding.

Intracellular folding pathway of the cystine knot-containing glycoprotein hormone alpha-subunit

Three of the five disulfide bonds in the glycoprotein hormone alpha-subunit (GPH-alpha) form a cystine knot motif that stabilizes a three-loop antiparallel structure. Previously, we described a mutant (alpha(k)) that contained only the three knot disulfide bonds and demonstrated that the cystine knot was necessary and sufficient for efficient GPH-alpha folding and secretion. In this study, we used alpha(k) as a model to study the intracellular GPH-alpha folding pathway. Cystine knot formation proceeded through a 1-disulfide intermediate that contained the 28-82 disulfide bond. Formation of disulfide bond 10-60, then disulfide bond 32-84, followed the formation of 28-82. Whether the two non-cystine knot bonds 7-31 and 59-87 could form independent of the knot was also tested. Disulfide bond 7-31 formed rapidly, whereas 59-87 did not form when all cysteine residues of the cystine knot were converted to alanine, suggesting that 7-31 forms early in the folding pathway and that 59-87 forms during or after cystine knot formation. Finally, loop 2 of GPH-alpha has been shown to be very flexible, suggesting that loop 2 does not actively drive GPH-alpha folding. To test this, we replaced residues 36-55 in the flexible loop 2 with an artificially flexible glycine chain. Consistent with our hypothesis, folding and secretion were unaffected when loop 2 was replaced with the glycine chain. Based on these findings, we describe a model for the intracellular folding pathway of GPH-alpha and discuss how these findings may provide insight into the folding mechanisms of other cystine knot-containing proteins.

Cystine knot mutations affect the folding of the glycoprotein hormone alpha-subunit. Differential secretion and assembly of partially folded intermediates

The common glycoprotein hormone alpha-subunit (GPH-alpha) contains five intramolecular disulfide bonds, three of which form a cystine knot motif (10-60, 28-82, and 32-84). By converting each pair of cysteine residues of a given disulfide bond to alanine, we have studied the role of individual disulfide bonds in GPH-alpha folding and have related folding ability to secretion and assembly with the human chorionic gonadotropin beta-subunit (hCG-beta). Mutation of non-cystine knot disulfide bond 7-31, bond 59-87, or both (leaving only the cystine knot) resulted in an efficiently secreted folding form that was indistinguishable from wild type. Conversely, the cystine knot mutants were inefficiently secreted (<25%). Furthermore, mutation of the cystine knot disulfide bonds resulted in multiple folding intermediates containing 1, 2, or 4 disulfide bonds. High performance liquid chromatographic separation of intracellular and secreted forms of the folding intermediates demonstrated that the most folded forms were preferentially secreted and combined with hCG-beta. From these studies we conclude that: (i) the cystine knot of GPH-alpha is necessary and sufficient for folding and (ii) there is a direct correlation between the extent of GPH-alpha folding, its ability to be secreted, and its ability to heterodimerize with hCG-beta.

A naturally occurring genetic variant in the human chorionic gonadotropin-beta gene 5 is assembly inefficient

The hCGbeta gene family is composed of six homologous genes linked in tandem repeat on chromosome 19; the order of the genes is 7, 8, 5, 1, 2, and 3. Previous studies have shown that hCGbeta gene 5 is highly expressed during the first trimester of pregnancy. The purpose of our study was to identify naturally occurring polymorphisms in hCGbeta gene 5 and determine whether these alterations affected hCG function. The data presented here show that hCGbeta gene 5 was highly conserved in the 334 asymptomatic individuals and 41 infertile patients examined for polymorphisms using PCR followed by single stranded conformational polymorphism analysis. Most of the polymorphisms detected were either silent or located in intron regions. However, one genetic variant identified in beta gene 5 exon 3 was a G to A transition that changed the naturally occurring valine residue to methionine in codon 79 (V79M) in 4.2% of the random population studied. The V79M polymorphism was always linked to a silent C to T transition in codon 82 (tyrosine). To determine whether betaV79M hCG had biological properties that differed from those of wild-type hCG, a beta-subunit containing the V79M substitution was created by site-directed mutagenesis and was coexpressed with the glycoprotein hormone alpha-subunit in Chinese hamster ovary cells and 293T cells. When we examined betaV79M hCG biosynthesis, we detected atypical betaV79M hCG folding intermediates, including a betaV79M conformational variant that resulted in a beta-subunit with impaired ability to assemble with the alpha-subunit. The inefficient assembly of betaV79M hCG appeared to be independent of beta-subunit glycosylation or of the cell type studied, but, rather, was due to the inability of the betaV79M subunit to fold correctly. The majority of the V79M beta-subunit synthesized was secreted as unassembled free beta. Although the amount of alphabeta hCG heterodimer formed and secreted by betaV79M-producing cells was less than that by wild-type beta-producing cells, the hCG that was secreted as alphabeta V79M heterodimer exhibited biological activity indistinguishable from that of wild-type hCG.

Dissociation of early folding events from assembly of the human lutropin beta-subunit

The human LH of the anterior pituitary is a member of the glycoprotein hormone family that includes FSH, TSH, and placental CG. All are noncovalently bound heterodimers that share a common alpha-subunit and beta-subunits that confer biological specificity. LHbeta and CGbeta share more than 80% amino acid sequence identity; however, in transfected Chinese hamster ovary (CHO) cells, LHbeta assembles with the alpha-subunit more slowly than does hCGbeta, and only a fraction of the LHbeta synthesized is secreted, whereas CGbeta is secreted efficiently. To understand why the assembly and secretion of these related beta-subunits differ, we studied the folding of LHbeta in CHO cells transfected with either the LHbeta gene alone, or in cells cotransfected with the gene expressing the common alpha-subunit, and compared our findings to those previously seen for CG. We found that the rate of conversion of the earliest detectable folding intermediate of LH, pbeta1, to the second major folding form, pbeta2, did not differ significantly from the pbeta1-to-pbeta2 conversion of CGbeta, suggesting that variations between the intracellular fates of the two beta-subunits cannot be explained by differences in the rates of their early folding steps. Rather, we discovered that unlike CGbeta, where the folding to pbeta2 results in an assembly-competent product, apparently greater than 90% of the LH pbeta2 recovered from LHbeta-transfected CHO cells was assembly incompetent, accounting for inefficient LHbeta assembly with the alpha-subunit. Using the formation of disulfide (S-S) bonds as an index, we observed that, in contrast to CGbeta, all 12 LHbeta cysteine residues formed S-S linkages as soon as pbeta2 was detected. Attempts to facilitate LH assembly with protein disulfide isomerase in vitro using LH pbeta2 and excess urinary alpha-subunit as substrate were unsuccessful, although protein disulfide isomerase did facilitate CG assembly in this assay. Moreover, unlike CGbeta, LHbeta homodimers were recovered from transfected CHO cells. Taken together, these data suggest that differences seen in the rate and extent of LH assembly and secretion, as compared to those of CG, reflect conformational differences between the folding intermediates of the respective beta-subunits.

Human chorionic gonadotropin-beta gene expression in first trimester placenta

The hCGbeta gene family contains six genes linked in tandem on chromosome 19 and labeled beta genes 7, 8, 5, 1, 2, and 3. Previous studies on a small number of placentas have indicated that beta gene 5 was the most highly expressed gene during the first trimester of pregnancy, followed by genes 3 and 8. Beta genes 7, 1, and 2 were expressed at very low levels. The purpose of this study was to determine 1) whether this pattern of expression was typical during normal pregnancy by sampling a large number of first trimester placentas, and 2) whether there was a correlation between gestational age and the pattern of hCGbeta gene expression. Total RNA from 27 first trimester placentas varying in age from 6-16 weeks was reverse transcribed into complementary DNA. The complementary DNA was amplified by PCR, and the amount of DNA representative of each hCGbeta gene was quantified by Genescan analysis. In 14 of the 27 placentas, hCGbeta gene 5 accounted for 50% or more of the total beta messenger RNA expressed. Beta gene 3 was expressed at levels ranging from 1-42% of the total, and beta gene 8 expression ranged from 12-32% of the total. Gene 7 expression was less than 3% of the total beta expression in all 27 placentas. Although there appeared to be a trend toward lower expression of beta gene 3 in placentas beyond 10 weeks gestational age, there was no correlation of the pattern of beta expression with placental age. Beta gene expression was also examined in two blighted ova, a spontaneous abortion sample, and a hydatidiform mole as well as in cultured JAR choriocarcinoma cells. With the exception of JAR cells, these abnormal tissues had low levels of gene 3 expression, but these levels were within the range of the patterns observed in normal placentas. These data suggest that it is the total amount of hCGbeta gene expression rather than the expression of individual beta genes that is important for the maintenance of normal pregnancy.

Tetramerization domain of human butyrylcholinesterase is at the C-terminus

Butyrylcholinesterase (BChE) in human serum consists predominantly of tetramers. Recombinant BChE, however, expressed in Chinese hamster ovary (CHO) cells, consists of approx. 55% dimers, 10-30% tetramers and 15-40% monomers. To determine the origin of the monomer species we added the FLAG epitope (epitope tag, amino acid sequence DYKDDDDK) to the C-terminus of the enzyme, and expressed BChE-FLAG in CHO cells. We found that secreted, active monomers had lost their FLAG epitope, suggesting that the monomers were made by proteolysis of dimers or tetramers at the C-terminus. To estimate the number of amino acids that could be deleted from the C-terminus without losing BChE activity, we expressed deletion mutants. We found that deletion of up to 50 amino acids from the C-terminus yielded active monomers, but that deletion of 51 amino acids destroyed BChE activity and caused the inactive protein to remain within the cell. Deletion of eight or more amino acids from the N-terminus also resulted in inactive protein that remained inside the cell. Monomeric BChE had wild-type Km and kcat values (8 microM and 24000 min-1 for butyrylthiocholine) and showed substrate activation. The Cys-571-->Ala mutant, though incapable of forming the interchain disulphide bond, had nearly the same amount of tetrameric BChE as recombinant wild-type BChE. These results support the conclusion that the tetramerization domain of BChE is at the C-terminus, within the terminal 50 amino acids, and that the interchain disulphide bond is not essential for tetramerization. Molecular modelling suggested that the tetramerization domain was a four-helix bundle, stabilized by interactions of seven conserved aromatic amino acids.

Novel covalent chaperone complexes associated with human chorionic gonadotropin beta subunit folding intermediates

Molecular chaperones facilitate the folding of proteins in the endoplasmic reticulum (ER) of mammalian cells. The glycoprotein hormone chorionic gonadotropin beta subunit is a secretory protein whose folding in the ER has been demonstrated (Huth, J. R., Mountjoy, K., Perini, F., and Ruddon, R. W.(1992) J. Biol. Chem. 267, 8870-8879). Because folding of wild type hCG-beta subunit occurs in the ER with a t1/2 = 4-5 min, stable association of ER chaperones with hCG-beta have been difficult to detect probably because they have a short half-life. However, beta-chaperone complexes containing the ER chaperones BiP, ERp72, and ERp94 have been detected in slow folding mutants of hCG-beta subunit that lack both of the N-linked oligosaccharides (Feng, W., Matzuk, M. M., Mountjoy, K., Bedows, E., Ruddon, R. W., and Boime, I. (1995) J. Biol. Chem. 270, 11851-11859). The questions addressed here are 1) whether the detection of chaperone-containing complexes is related to the absence of carbohydrate or to the rate of hCG-beta subunit folding, 2) whether such complexes are dead-end or whether they lead to formation of a secreted, mature hCG-beta form, and 3) what the nature of the hCG-beta-chaperone binding is. The data obtained indicate that the amount of detectable hCG-beta-chaperone complexes correlates with the rate or extent of folding, that the complexes of hCG-beta with ER chaperones lead to the formation of secretable beta, and that the complexes of hCG-beta with chaperones involve the formation of intermolecular disulfide bonds.

Protein folding in the endoplasmic reticulum: lessons from the human chorionic gonadotropin beta subunit

There have been few studies of protein folding in the endoplasmic reticulum of intact mammalian cells. In the one case where the in vivo and in vitro folding pathways of a mammalian secretory protein have been compared, the folding of the human chorionic gonadotropin beta subunit (hCG-beta), the order of formation of the detected folding intermediates is the same. The rate and efficiency with which multidomain proteins such as hCG-beta fold to native structure in intact cells is higher than in vitro, although intracellular rates of folding of the beta subunit can be approached in vitro in the presence of an optimal redox potential and protein disulfide isomerase. Understanding how proteins fold in vivo may provide a new way to diagnose and treat human illnesses that occur due to folding defects.

The asparagine-linked oligosaccharides of the human chorionic gonadotropin beta subunit facilitate correct disulfide bond pairing

The role of asparagine (N)-linked oligosaccharide chains in intracellular folding of the human chorionic gonadotropin (hCG)-beta subunit was determined by examining the kinetics of folding in Chinese hamster ovary (CHO) cells transfected with wild-type or mutant hCG-beta genes lacking one or both of the asparagine glycosylation sites. The half-time for folding of p beta 1 into p beta 2, the rate-determining step in beta folding, was 7 min for wild-type beta but 33 min for beta lacking both N-linked glycans. The p beta 1-->p beta 2 half-time was 7.5 min in CHO cells expressing the beta subunit missing the Asn13-linked glycan and 10 min for the beta subunit missing the Asn30-linked glycan. The inefficient folding of hCG-beta lacking both N-linked glycans correlated with the slow formation of the last three disulfide bonds (i.e. disulfides 23-72, 93-100, and 26-110) to form in the hCG-beta-folding pathway. Unglycosylated hCG-beta was slowly secreted from CHO cells, and beta subunit-folding intermediates retained in cells for more than 5 h were degraded into a hCG-beta core fragment-like protein. However, coexpression of the hCG-alpha gene enhanced folding and formation of disulfide bonds 23-72, 93-100, and 26-110 of hCG-beta lacking N-linked glycans. In addition, the molecular chaperones BiP, ERp72, and ERp94, but not calnexin, were found in a complex with unglycosylated, unfolded hCG-beta and may be involved in the folding of this beta form. These data indicate that N-linked oligosaccharides assist hCG-beta subunit folding by facilitating disulfide bond formation.

Misfolded human chorionic gonadotropin beta subunits are secreted from transfected Chinese hamster ovary cells

There are six intramolecular disulfide (S-S) bonds that form during intracellular folding of the human chorionic gonadotropin (hCG)-beta subunit. Site-directed mutagenesis of every pair of Cys residues involved in the formation of each S-S bond was used to examine the roles that S-S bonds play in beta subunit folding and secretion. Tryptic maps of secreted hCG-beta showed that only one S-S bond formed in all S-S bond mutants that failed to fold from the earliest detectable beta folding intermediate, p beta 1, into a second major intermediate, p beta 2 (C34A-C88A, C38A-C57A or C9A-C90A mutants), whereas all 5 remaining S-S bonds formed in mutants when p beta 1-->p beta 2 conversion occurred (C23A-C72A, C93A-C100A, or C26A-C110A mutants). Nonreducing SDS-polyacrylamide gel electrophoresis showed that beta multimers were secreted from cells expressing S-S bond mutations where the folding of p beta 1-->p beta 2 was blocked. However, for mutations where p beta 1-->p beta 2 conversion was efficient, beta monomers rather than multimers were secreted. For all cell lines studied, secreted hCG-beta migrated as monomeric beta during reducing SDS-polyacrylamide gel electrophoresis, indicating that hCG-beta multimers formed via intermolecular cross-linking of unpaired thiols. Tryptic maps of hCG-beta isolated from mutants lacking the 34-88 bond, where > 80% turnover occurs, showed that only the 38-57 S-S bond formed. beta Subunits lacking the 9-90 linkage also have only S-S bond 38-57 formed, but < 10% turnover of C9A-C90A hCG-beta occurs. Thus, subtle conformational differences between partially folded or misfolded beta subunits may determine whether hCG-beta is degraded, or undergoes intracellular translocation and secretion.

Protein folding and assembly in vitro parallel intracellular folding and assembly. Catalysis of folding and assembly of the human chorionic gonadotropin alpha beta dimer by protein disulfide isomerase

Although purified proteins will refold and assemble in vitro, it is not known if cellular factors change the mechanisms of these processes. Based on the gel migration of folding intermediates, the kinetic relationships between these intermediates, and on the order of formation of six disulfide bonds, we have found that the in vitro folding pathway of the human chorionic gonadotropin beta subunit (hCG-beta) is indistinguishable from the intracellular folding pathway. The same rate-limiting event was found in both folding environments; however, the t1/2 for this step in a cell is 4 min, whereas in vitro the t1/2 was > or = 80 min. Protein disulfide isomerase (PDI) increased the in vitro rate of this event (t1/2 = 25 min) without changing the order of disulfide bond formation. PDI also catalyzed the in vitro rate of assembly of hCG subunits. In intact cells, assembly of the alpha beta heterodimer occurs before all of the intramolecular disulfide bonds of beta are formed. In vitro, assembly was increased after reduction of two of the carboxyl-terminal disulfide bonds of hCG-beta by PDI. These results strongly suggest that both in intact cells and in vitro, partially unfolded hCG-beta is more assembly-competent than is fully folded hCG-beta. The comparison of in vitro and intracellular hCG-beta folding and hCG subunit assembly which is shown in this report indicates that the assisted folding and assembly pathway that occurs in cells, where proteins such as PDI play a role, differs only in rate but not in the order of disulfide bond formation or in the precursor-product relationships among the folding intermediates.

Disulfide bond mutations affect the folding of the human chorionic gonadotropin-beta subunit in transfected Chinese hamster ovary cells

Previous kinetic studies have characterized the intracellular folding pathway of the human chorionic gonadotropin (hCG)-beta subunit in which each of the folding intermediates can be biochemically identified based on the formation of disulfide (S-S) bonds: p beta 1-early--> p beta 1-late--> p beta 2-free--> p beta 2-combined--> native hCG-alpha beta. Based on these data, we postulated that hCG-beta folding coincides with the formation of specific S-S bonds. We have now tested this hypothesis employing Chinese hamster ovary cells transfected with mutated hCG-beta genes in which the Cys residues required for the formation of the final four (of six total) S-S bonds were replaced by Ala. When the Cys residues required for the third hCG-beta S-S linkage to form (bond 9-90) were substituted, folding did not proceed beyond the earliest detectable folding intermediate (p beta 1-early). In the absence of the subsequently formed S-S bond (bond 23-72), p beta 1-early was converted into a second folding intermediate (p beta 1-late), but conversion to the next intermediate (p beta 2-free) was inhibited. When either of the final two S-S bonds (the carboxyl-terminal 93-100 or 26-110 bonds) were removed, conversion of p beta 1-late to p beta 2-free was detected, but conversion of p beta 2-free to the last folding intermediate (p beta 2-combined) was not observed. These data support the hypothesis that individual S-S bonds are involved in discrete steps in the hCG-beta folding pathway.

Domain-dependent protein folding is indicated by the intracellular kinetics of disulfide bond formation of human chorionic gonadotropin beta subunit

We have measured the intracellular rates of formation of the six disulfide bonds in the human chorionic gonadotropin beta subunit (hCG-beta) to determine whether the folding pathway of this molecule can be described by a simple sequential model. If such a model is correct, the formation of disulfide bonds, which is indicative of tertiary structural changes during protein folding, should occur in a discrete order. The individual rates of disulfide bridging were determined by identifying the extent of disulfide bond formation in hCG-beta intermediates purified from choriocarcinoma cells that had been metabolically labeled for 40 to 120 s and chased for 0 to 25 min. The results of these kinetic studies describe a folding pathway in which the disulfide bonds between cysteines 34-88, 38-57, 9-90 and 23-72 stabilize, in a discrete order, the putative domain(s) involving amino acids 1-90 of hCG-beta. However, the S-S bonds 93-100 and 26-110 begin to form before the complete formation of the disulfide bonds that stabilize the amino acid 1-90 domain(s), and continue to form after complete formation of these disulfide bonds, suggesting that hCG-beta does not fold by a simple sequential pathway. The order of completion of each of the six disulfide bonds of hCG-beta is: 34-88 (t1/2 = 1-2 min), 38-57 (t1/2 = 2-3 min), 9-90 and 23-72, 93-100, and 26-110. Moreover, 60-100% of each of the six disulfide bonds form posttranslationally, and nonnative disulfide bonds do not form in detectable amounts during intracellular folding of hCG-beta.

Kinetics of folding and assembly of the human chorionic gonadotropin beta subunit in transfected Chinese hamster ovary cells

We have employed Chinese hamster ovary (CHO) cell lines transfected with either the wild type human chorionic gonadotropin beta (hCG-beta) gene alone (CHO beta cells) or in conjunction with the gene expressing the alpha subunit (CHO alpha,beta cells) to study the folding pathway of the hCG-beta subunit. In both CHO beta and CHO alpha,beta cells, the earliest detectable hCG-beta precursor, p beta 1, which had two of six potential disulfide bonds (34-88 and 38-57) formed, was converted to p beta 2, a form that, following the formation of disulfide bonds between cysteines 9-90 and 23-72, migrated more slowly than p beta 1 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. The t1/2 for the conversion of p beta 1 to p beta 2 in CHO alpha,beta and CHO beta cells was 5 min, demonstrating that the alpha subunit had no effect on the rate of this conversion. Furthermore, the tryptic-releasable peptides generated from nonreduced p beta 1 or p beta 2 were the same in both CHO alpha,beta and CHO beta cells. Thus, both the rate and order of disulfide bond formation during the conversion of the folding intermediate p beta 1 into p beta 2 were the same whether or not the alpha subunit was present. A comparison between cell types expressing different alpha/beta subunit ratios revealed that the higher the glycoprotein hormone alpha subunit to beta subunit ratio, the greater the rate and extent of hCG heterodimer assembly.

Characterization of a halothane-resistant strain of measles virus

A strain of measles virus (MVr) whose replication demonstrated increased resistance to halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) exposure compared with the susceptible parental strain (MVs) is described. After exposure to a 1.2% halothane concentration, substantial amounts of the measles virus H protein were detected in MVr-infected Vero cell lysates by immunoprecipitation and polyacrylamide gel electrophoresis or by quantitative immunofluorescence staining. The protein was barely detectable in identically treated MVs-infected lysates, however. The recovery of all other measles virus proteins studied was the same in MVr- and MVs-infected cells at this anesthetic concentration. Thus, the altered expression of a single gene product appears to be responsible for the observed halothane resistance.

Inhibition of herpes simplex virus type 1 replication by halothane

Halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) inhibited herpes simplex virus type 1 (HSV-1) replication, although HSV-1 DNA was synthesized at normal levels in Vero cells. Viral capsids and extracellular virions were inhibited, and HSV-1 protein synthesis decreased by 50%, although no specific HSV-1 protein failed to be synthesized. Hyperbaric pressure failed to reverse the halothane-induced inhibition of HSV-1 replication.

Search for virus nucleic acid sequences in postmortem human brain tissue using in situ hybridization technology with cloned probes: some solutions and results on progressive multifocal leukoencephalopathy and subacute sclerosing panencephalitis tissue

In order to obtain a useful and readily applicable in situ hybridization (ISH) protocol for progressive central nervous system (CNS) diseases of unknown etiology that are possibly due to persistent viral infection, known and well described diseases were studied, namely, progressive multifocal leukoencephalopathy (PML) and subacute sclerosing panencephalitis (SSPE). The procedures described were validated by confirming results obtained by other investigators using histology, immunocytochemistry, electron microscopy, and ISH. A number of frequently encountered problems of tissue preparation are addressed as well as techniques to reduce autoradiography exposure times. A multi-staged specific, sensitive, reliable, and valid procedure for detection of viral genomes, mRNA and proteins is approached. Formalin-fixed and paraffin-embedded (FFPE) brain material from six patients who died with PML and one patient who died from SSPE were studied using ISH with a tritium-labeled cloned JC virus DNA probe and a measles-cloned nucleocapsid (NC) gene cDNA probe, respectively. This report constitutes a methodological framework as well as a detailed neuropathological analysis of identified brain cell populations within which in situ hybridization was detected. In early PML lesions, swollen nuclei or oligodendrocytes were the predominant cells labeled, whereas older lesions revealed increased numbers of reactive and bizarre hypertrophic astrocytes hybridized at the outer periphery of the demyelinated lesions. The hybridization varied greatly in intensity in different cells. Intense hybridization was noted very rarely in microglial cells, including rod cells and rarely in venular pericytes, intravascular mononuclear cells, or in vascular endothelial cells. These results, considered together with previous findings, indicate that in PML the viral infection runs different courses in the various cells: in astrocytes the viral genome persists for a long time inducing pathological changes in some cells. In oligodendrocytes the infection rapidly lyses the cells. There was a good correlation between chromatic changes observable in routinely stained sections and virus presence. In addition, in situ hybridization using a measles-NP-cloned probe in white matter from FFPE SSPE brain is presented confirming earlier results in SSPE cryopreserved brain.

Hyperbaric pressure of 51 atmospheres is without effect on the depression of oxygen uptake in kidney tissue culture produced by halothane

Although anesthetized animals are awakened when subjected to increased pressure, compression does not result in antagonism of all phenomena associated with these drugs. It has recently been demonstrated that halothane's inhibition of respiration of isolated rat liver mitochondria is not reversed by hydraulic compression to 51 atmospheres. In order to determine whether this phenomenon can be extrapolated to the whole cell, we have investigated the effect of hydraulic compression of intact renal cells equilibrated with halothane, and conclude that pressure does not overcome the inhibitory effect of this anesthetic.

Effect of general anesthetics and pressure on aerobic metabolism of monkey kidney cells

The authors examined the inhibition of aerobic metabolism in monkey kidney cell cultures exposed to halothane, enflurane, and isoflurane. The ability of hyperbaric pressure to reverse the halothane-induced metabolic inhibition also was examined. Incubation of two monkey kidney cell lines for 24 h with clinically equipotent concentrations (2.6 MAC) of halothane, enflurane, or isoflurane vapors increased the concentration of lactate in the media by 126 to 244% relative to nonexposed control cultures. The increased rate of lactate accumulation was proportional to the concentration of halothane and was accompanied by a decrease in media pH. Removal of halothane restored the normal rate of lactate production. Hyperbaric pressures of 25, 50, and 100 atmospheres did not alter the halothane-stimulated rate of lactate production relative to non-anesthetic-treated controls, although pressure alone did depress the rate of lactate accumulation in all cultures. The stimulation of lactate production likely reflects the known ability of halothane to inhibit mitochondrial respiration. The failure of pressure to reverse the stimulation of lactate production by halothane suggests that inhibition of mitochondrial metabolism cannot be reversed by pressure.

Effect of halothane on the replication of animal viruses

Five RNA- and two DNA-containing viruses were propagated in Vero cells and tested for their ability to replicate in the presence of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane), a commonly used inhalational anesthetic. Halothane did not affect poliovirus replication at any anesthetic concentration tested, but all other viruses were either partially or totally inhibited by clinical doses of the anesthetic. Replication of Sendai virus, simian virus 40, vesicular stomatitis virus, and herpes simplex virus type 1 were moderately inhibited by halothane exposure. At concentrations of 2.2% (vol/vol) halothane, peak virus titers were reduced by ca. 2 orders of magnitude for vesicular stomatitis virus and simian virus 40, 3.5 orders of magnitude for Sendai virus, and 4 orders of magnitude for herpes simplex virus. Newcastle disease virus and measles virus were the most susceptible to exposure to halothane. Total inhibition of the replication of these viruses occurred at 1.6 to 2.0% halothane. All of the viruses whose replication was susceptible to the action of halothane were inhibited in a concentration-dependent manner. Furthermore, with the exception of simian virus 40, the inhibition of the replication of all viruses was reversible after halothane removal, although total recovery of virus synthesis was not observed unless the culture medium was changed or the pH was adjusted after anesthetic removal.

Pressure reversal of halothane's antiviral effect

The authors have studied the effects that hyperbaric pressure and halothane had on measles virus replication. Two per cent halothane at one atmosphere of air (ATA) reduced the number of infectious measles virus particles produced in cultured Vero cells by greater than four orders of magnitude (P less than 0.001) relative to virus produced in untreated cultures at 1 ATA. The same concentration of halothane at 100 ATA still reduced the amount of virus synthesized but only by 1 1/2 orders of magnitude (P less than 0.01) as compared with control cultures. Pressure (100 ATA) alone reduced virus production insignificantly. Thus, it appears that the antiviral effects of halothane on measles virus replication in cultured Vero cells is reversible at least partially by pressure.

Fate of microfilaments in vero cells infected with measles virus and herpes simplex virus type 1

In herpes simplex virus type 1-infected Vero cells, reorganization of microfilaments was observed approximately 4 h postinfection. Conversion of F (filamentous) actin to G (globular) actin, as assessed by a DNase I inhibition assay, was continuous over the next 12 to 16 h, at which time a level of G actin of about twice that observed in uninfected cells was measured. Fluorescent localization of F actin, using 7-nitrobenz-2-oxa-1,3-diazole (NBD)-phallacidin, demonstrated that microfilament fibers began to diminish at about 16 to 18 h postinfection, roughly corresponding to the time that G actin levels peaked and virus-induced cytopathology was first observable. In measles virus-infected cells, no such disassembly of microfilaments occurred. Rather, there was a modest decrease in G actin levels. Fluorescent localization of F actin showed that measles virus-infected Vero cells maintained a complex microfilament network characterized by fibers which spanned the entire length of the newly formed giant cells. Disruption of microfilaments with cytochalasin B, which inhibits measles virus-specific cytopathology, was not inhibitory to measles virus production at high multiplicities of infection (MOI) but was progressively inhibitory as the MOI was lowered. The carbobenzoxy tripeptide SV-4814, which inhibits the ability of Vero cells to fuse after measles virus infection, like cytochalasin B, inhibited measles virus production at low MOI but not at high MOI. Thus, it appears that agents which affect the ability of Vero cells to fuse after measles virus infection may be inhibitory to virus production and that the actin network is essential to this process.

Alterations in influenza virus pulmonary pathology induced by diethyl ether, halothane, enflurane, and pentobarbital anesthesia in mice

Three-week-old CD-1 mice infected with the PR-8 (mouse-adapted) strain of influenza virus while exposed to enflurane demonstrated a decrease in virus titers from the lungs of infected animals, less abnormality of lung histology, and an increase in survival in animals as compared with those receiving the other anesthetics tested. Greater than 90% mortality occurred in groups of mice which inhaled aerosolized virus and received no anesthesia, pentobarbital, diethyl ether, or halothane anesthesia 96 h following infection. Infected mice anesthetized with enflurane 96 h post-infection had significantly lower mortality rate (68%) when compared with the other groups. Halothane-anesthetized mice receiving intranasal influenza virus during anesthesia demonstrated increased survival and a delay in the mean day of death when compared with animals receiving either diethyl ether of pentobarbital anesthesia. Animals receiving enflurane during virus inoculation had an even lower mortality rate and a later mean day of death when compared with infected animals receiving day of the other three anesthetics. Examination of lungs from animals infected during anesthesia demonstrated influenza virus titers significantly less in the animals that received enflurane anesthesia when compared with the other groups. Histologic sections of lungs revealed extensive spread of the disease process into the alveoli and interstitium of the lungs of animals infected while receiving pentobarbital or diethyl ether anesthesia. Animals infected during halothane demonstrated pathologic characteristics similar to pentobarbital- and diethyl-ether-treated groups; however, the changes were not as extensive. Mice infected during exposure to enflurane revealed only a mild bronchopneumonia.

An investigation of the antiviral activity of Podophyllum peltatum

The antiviral activity of an aqueous extract of Podophyllum peltatum was investigated. The extract was fractionated by reversed-phase chromatography, and podophyllotoxin was found to be the most active component in inhibiting the replication of measles and herpes simplex type I viruses. beta-Peltatin and desoxypodophyllotoxin produced marginal antiviral effects, while alpha-peltatin and picropodophyllotoxin were inactive at the levels tested.

Enrichment of measles virus-like RNA in the nucleocapsid fraction isolated from subacute sclerosing panencephalitis brains

A procedure has been developed which facilitates the detection of measles virus RNA sequences in human brains. The procedure involves isolating subviral components (nucleocapsids) from brain tissues prior to RNA purification, followed by hybridization of these RNAs to cDNA synthesized from measles virus 50 S RNA template. Using these techniques we were able to obtain an RNA fraction which was manyfold enriched in measles virus-specific RNA, relative to unfractionated subacute sclerosing panencephalitis (SSPE) brain RNAs 70-100% of the measles virus-specific RNA present these SSPE brain samples were recovered in this enriched fraction.

Inhibiting effects of enflurane and isoflurane anesthesia on measles virus replication: comparison with halothane

Replication of measles virus in BSC cells was studied in the presence of enflurane (2-chloro-1,1,2-trifluoroethyl difluoromethyl ether), a commonly used volatile anesthetic agent, and its isomer, isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether). At clinical concentrations of the anesthetics (up to 4%), cell division was retarded, whereas only minimal toxic cellular effects were observed. The appearance of progeny virus from the cell cultures exposed to these anesthetics was decreased in a dose-related manner. Incorporation of [(3)H]uridine into measles virus nucleocapsids also decreased progressively with increasing anesthetic concentrations. In comparing the inhibition of measles virus replication in the presence of halothane (2-bromo-2-chloro,1,1,1-trifluoroethane), enflurane, or isoflurane, it was found that both inhibition of the appearance of infectious virus at 48 h postinfection and incorporation of [(3)H]uridine into measles virus nucleocapsids were proportional to the anesthetic concentrations. An equivalent degree of effect was produced by anesthetically equivalent concentrations of the three anesthetics (minimal alveolar concentration) but not by absolute concentrations. In addition, recovery of infectious virus synthesis from the inhibition encountered during exposure of infected BSC cells to halothane or isoflurane was also investigated. In cultures exposed to halothane or enflurane, recovery of infectious virus synthesis was rapid and complete. Recovery of virus synthesis was slower after isoflurane removal and did not reach the peak control titers of infected cultures not exposed to the anesthetic. Treatment with halothane resulted in the formation of a preponderance of slowly sedimenting virus nucleocapsid particles which contained less than full-length ribonucleic acids after anesthetic removal. Neither enflurane nor isoflurane treatment of BSC cultures resulted in the formation of significant levels of these slowly sedimenting particles with short genomes after anesthetic removal.

Host cell factors involved in the production of slowly sedimenting nucleocapsids in measles virus-infected cells

A decrease in the sedimentation rates of the measles virus nucleocapsid, and the RNA contained within, were observed during acute measles virus infection when the growth conditions of Vero cells were altered. The change in sedimentation rates of virus nucleocapsids in these experiments was apparently due to the physiological state of the cell and was independent of the history of the measles virus used for infection since: (i) the same virus stock was used to infect cells from which nucleocapsids were prepared, (ii) nucleocapsid sedimentation rates were rapid when Vero cells freshly revived from liquid nitrogen were infected, but nucleocapsid profiles showed no decrease in the amount of slowly sedimenting material using the same cells and changing the virus preparation used for infection. Frequent cell splittings and numerous medium changes were among the growth factors which appeared to correlate to slowly sedimenting particle production. Changes in the amount of self-complementarity of the measles virus RNA were also observed under these conditions.

Anesthetic action and virus replication: inhibition of measles virus replication in cells exposed to halothane

Replication of measles virus in BSC cells was studied in the presence of halothane, a commonly used volatile anesthetic. At clinical concentrations of the anesthetic, appearance of progeny virus was decreased in a dose-related manner. This inhibition was reversible as the removal of halothane allowed virus replication to be resumed. Studies attempting to elucidate the mechanism of action of the anesthetic inhibition of virus replication revealed that halothane did not directly inactivate the virus particle or prevent viral adsorption to the cell. Infectious virus and nucleocapsid production were decreased or stopped, depending on the anesthetic dosage used. Direct immunofluorescent staining for measles virus antigen was negative in cells treated at the higher concentrations of halothane. Recovery of nucleocapsid production started within a few hours after removal of halothane. Furthermore, the combined inhibitory effects on viral ribonucleic acid synthesis of 5-azacytidine and halothane were additive. This evidence suggests that inhibition of measles virus replication occurs at or before ribonucleic acid synthesis.

L cell DNA ligase joins RNA to DNA on a DNA template

L cell DNA ligase catalyzes a covalent linkage between 5'-hosphoryl oligodeoxyribonucleotides and 3'-hydroxyl oligoribonucleotides on a complementary polydeoxyribonucleotide template. This reaction occurs to a substantially lesser extent than does the sealing of DNA to DNA. The joining of [5'32P]d(pA)12-18 to (Ap)11A on poly[d(T)] or of [5'-32P]d(pG)12-18 to 5'-hydroxyl, 3'-hydroxyl oligo(I) ON POLY[D(C)] was demonstrated by the formation of alkaline phosphatase resistant radioactivity. The 32P of the hybrid reaction products became sensitive to the action of alkaline phosphatase after treatment with alkali. Furthermore, hydrolysis of the products of the linkage of [5'-32P]d(pG)12-18 to 5'-hydroxyl, 3'-hydroxyl oligo(I) on poly[d(C)] with micrococcal nuclease and spleen phosphodiesterase resulted in the formation of [3'-32P]IMP. Attempts to seal [5'-32p[-(pA)12 to d(Ap)11-17A on poly[d(T) or [5'-32P]oligo(pI) to d(Gp)11-17G on poly[d(C)] were unsuccessful.

T4-induced RNA ligase joins single-stranded oligoribonucleotides

RNA ligase isolated from Escherichia coli infected with bacteriophage T4 will catalyze the formation of an intermolecular 3' leads to 5' phosphodiester linkage between an oligoribonucleotide with a free 3'-hydroxyl and another oligoribonucleotide with a 5'-phosphate. Upon reaction with (Ap)5C, nearly quantitative conversion of the hexamer [5'-32P]p(Up)5U to the dodecamer (Ap)5C[3' leads to 5'-32P]p(Up)5U was observed. The product was identified by its mobility on RPC-5 column chromatography, its resistance to alkaline phosphatase, and the appearance of the expected radiolabeled products on hydrolysis with alkali, ribonuclease A, snake venom phosphodiesterase, and spleen phosphodiesterase. The coupling of other pairs of single-stranded oligoribonucleotides has also been demonstrated. The intermolecular joining reaction is probably mechanistically similar to the intramolecular cyclization activity previously reported for Tr RNA ligase. It is expected that this enzyme will be useful for the synthesis of RNA fragments of defined sequence.