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Biomedical subjects

M Vaughan

Publications and source records attributed to M Vaughan.

At least 91 records · Page 5Linked to original sources
PubMed1993

Effects of brefeldin A and accessory proteins on association of ADP-ribosylation factors 1, 3, and 5 with Golgi.

ADP-ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins initially identified by their ability to enhance in vitro cholera toxin-catalyzed ADP-ribosylation and subsequently shown to participate in vesicular transport in the Golgi and other cellular compartments. By cDNA and genomic cloning, at least six mammalian ARFs were identified. Brefeldin A (BFA) disrupts Golgi membranes and inhibits binding of soluble high molecular weight proteins to Golgi fractions. We examined the effects of BFA on binding of ARF1, -3, and -5 to a Golgi fraction in the presence of an ATP-regenerating system and a fraction of soluble, high molecular weight, accessory proteins (SAP), presumably containing complexes identified by others as coatomers that are involved in vesicular transport. ARF binding in all instances was dependent on guanosine 5'-O-(3-thiotriphosphate) and increased by the ATP-regenerating system. Binding of ARF1 and -3, but not ARF5, was enhanced by SAP. BFA inhibited the SAP-dependent, but not the SAP-independent, binding of ARF1 and -3. It had no effect on the increment in binding produced by an ATP-regenerating system. B36, an inactive derivative of BFA, did not inhibit SAP-dependent binding of ARF1 and -3. Binding of ARF5, which was SAP-independent, was not affected by BFA. These observations are consistent with the conclusion that mammalian ARFs differ in their dependence on accessory proteins for interaction with Golgi and, perhaps, other cellular membranes and that BFA specifically inhibits SAP-dependent ARF binding.

ADP-Ribosylation Factor 1↗
PubMed1993

Characterization of the human ADP-ribosylation factor 3 promoter. Transcriptional regulation of a TATA-less promoter.

The 5'-flanking region of the human ADP-ribosylation factor 3 gene contains the features of a housekeeping gene. It lacks a TATA or CAAT box, has several GC boxes within a highly GC-rich region, and utilizes multiple transcription initiation sites. The cis-acting elements involved in regulating expression of the gene were identified by transient transfections of IMR-32 neuroblastoma cells. Reporter plasmids were modified to facilitate construction of defined promoter deletions linked to chloramphenicol acetyltransferase or luciferase using ligation-independent cloning. Transfection analyses indicated that sequences within 58 base pairs of the transcription initiation site were necessary for full expression, in particular a sequence containing the 10-base pair palindrome TCTCGCGAGA. Electrophoretic mobility shift assays performed with IMR-32 nuclear extracts demonstrated that a DNA-binding protein, termed TLTF, bound to an oligonucleotide containing this palindrome. Competition experiments showed that mutations within the core of the palindrome abolished in vitro binding and that the same protein bound to a 5'-proximal sequence. Expression of the promoter containing a mutated palindrome was reduced dramatically, consistent with the conclusion that this region functions in vivo to control expression of the ARF3 gene.

ADP-Ribosylation Factors↗
PubMed1993

ARD 1, a 64-kDa guanine nucleotide-binding protein with a carboxyl-terminal ADP-ribosylation factor domain.

Clones referred to as ARD 1 were isolated from human and rat cDNA libraries. ARD 1 genes encode a putative 64-kDa protein that contains an 18-kDa ADP-ribosylation factor (ARF) domain at the carboxyl terminus and is much larger than the other monomeric approximately 20-kDa guanine nucleotide-binding ARF proteins thus far identified. ARD 1 mRNAs of 3.7 and 4.1 kilobases were detected in all rat tissues as well as in mouse and rabbit brain, human fibroblasts, and human neuroblastoma cells but not in HL-60 cells. Based on sequence identities, ARD 1 is highly conserved between rat and human. The ARF domain of ARD 1 contains the consensus sequences believed to be involved in guanine nucleotide binding, which are conserved in the ARFs and other GTP-binding proteins. Recombinant ARD 1 or the ARF domain of ARD 1, which lacks the 15 amino acids corresponding to the amino-terminal regions of ARFs stimulated, in a GTP-dependent manner, cholera toxin ADP-ribosyltransferase activity in the presence of 0.3% Tween 20. It had no effect in the presence of SDS, dimyristoylphosphatidylcholine/cholate, or cardiolipin. These observations are consistent with the conclusion that the amino-terminal region of ARF proteins is not required for activation of cholera toxin. In addition, the characteristic features of ARF proteins may be found as domains of larger mammalian proteins.

ADP-Ribosylation Factors↗
PubMed1993

Effect of myristoylation on GTP-dependent binding of ADP-ribosylation factor to Golgi.

ADP-ribosylation factors (ARFs), a family of approximately 20-kDa guanine nucleotide-binding proteins that activate cholera toxin ADP-ribosyltransferase in vitro, have been implicated in intracellular protein trafficking and are thought to cycle between cytosolic and membrane compartments. Although isolated predominantly as soluble proteins, ARFs associate with membranes and phospholipids in a GTP-dependent manner. In contrast to other small GTP-binding proteins, ARFs are NH2 terminally myristoylated. Using a bacterial expression system, recombinant myristoylated and non-myristoylated human ARF5 were produced to investigate the role of myristoylation in its association with Golgi. The recombinant ARFs (myristoylated and non-myristoylated) exhibited similar biochemical activity as measured by GTP binding and in vitro activation of cholera toxin. Myristoylated ARF5, however, demonstrated a temperature- and GTP-dependent association with Golgi membranes, whereas non-myristoylated ARF did not bind to Golgi under any of the experimental conditions. These data indicate that myristoylation is necessary, although not sufficient, for membrane attachment, but is not necessary for activation of cholera toxin.

ADP-Ribosylation Factors↗
PubMed1993

Interaction of ADP-ribosylation factor with Escherichia coli enterotoxin that contains an inactivating lysine 112 substitution.

Cholera toxin and Escherichia coli heat-labile enterotoxin (LT) exert their effects on cells through ADP-ribosylation of guanine nucleotide-binding proteins. Both toxins consist of one A subunit, which is an ADP-ribosyltransferase, and five B (or binding) subunits. Their enzymatic activities are latent; activation requires reduction and proteolysis, resulting in a catalytically active A1 protein and a much smaller A2 protein. These ADP-ribosyltransferases are activated by GTP-dependent 20-kDa ADP-ribosylation factors or ARFs. To determine if proteolysis plus reduction is required for appearance of the ARF allosteric site as well as for catalytic activity, an inactive mutant of LT, LT(E112K), with replacement of glutamate by lysine at position 112 of its A subunit, was utilized as a competitor in cholera toxin ADP-ribosyltransferase assays containing limiting amounts of ARF. LT(E112K) required trypsinization and reduction to become a potent, concentration-dependent inhibitor. Inhibition was reversed by increasing concentrations of ARF. Reduction or trypsinization alone did not generate an inhibitory form of LT(E112K). These studies are consistent with the conclusion that the ARF site is not expressed in the latent toxin. Both trypsinization and reduction are required for expression of a functional ARF binding site as well as for catalytic activity.

ADP-Ribosylation Factors↗
PubMed1993

Characterization of the gene for ADP-ribosylation factor (ARF) 2, a developmentally regulated, selectively expressed member of the ARF family of approximately 20-kDa guanine nucleotide-binding proteins.

ADP-ribosylation factors (ARFs) are a family of approximately 20-kDa guanine nucleotide-binding proteins that stimulate the ADP-ribosyltransferase activities of cholera toxin in vitro and function in protein trafficking in vivo. The six cloned mammalian ARFs can be grouped into three classes based on size and sequence identity. ARF 2 is a class I ARF, whose approximately 2.6-kilobase mRNA exhibits species and tissue selective expression and is developmentally regulated in rat brain. Here we report the sequence, structure, and functional promoter region of the bovine ARF 2 gene, which was facilitated by constructing a composite cDNA. The ARF 2 cDNA, constructed from a partial cDNA clone and polymerase chain reaction-amplified fragments from reverse-transcribed poly(A)+ RNA, was approximately 2270 base pairs (bp) (minus the poly(A) tail). In the 3'-untranslated region, there are two potential polyadenylation signals, ATTAAA and AATAAA, at positions 1064 and 2232, respectively, and two ATTTA motifs, believed to signal mRNA degradation, at positions 2115 and 2165. The ARF 2 gene, represented in three overlapping genomic clones, spans approximately 20 kilobase pairs with five exons and four introns. Consensus sequences for guanine nucleotide-binding and GTP hydrolysis are in separate exons, except for the NKXD sequence, which is divided by intron 4. There are multiple transcriptional initiation sites. Transient transfection of embryonic trachea cells with deletion constructs defined the functional promoter region to be within 400 bp upstream of the most 5' site of transcription initiation. This 400-bp region lacks a TATA-like sequence but contains six inverted CCAAT boxes, four potential Sp1-binding sites, and a potential AP-2-binding site. Although the pattern of expression of ARF 2 is unique among the ARFs, the structures of the class I ARF genes are conserved among its members and across species.

ADP-Ribosylation Factors↗
PubMed1993

Effects of temperature on ADP-ribosylation factor stimulation of cholera toxin activity.

The effects of cholera toxin, a secretory product of Vibrio cholerae, result from ADP-ribosylation of the stimulatory guanine nucleotide-binding (Gs) protein of the adenylyl cyclase system. Cholera toxin A subunit (CTA) also uses agmatine, a simple guanidino compound, several proteins unrelated to Gs, and CTA itself as alternative ADP-ribose acceptors. The effects of toxin occur in the jejunum presumably at body core temperature. With agmatine as a model substrate, the optimal temperature for CTA-catalyzed ADP-ribosylation was 25-30 degrees C, and that for CTA-catalyzed auto-ADP-ribosylation was 20-25 degrees C. Both activities were significantly less at 37 degrees C, reflecting lower initial velocities, not heat-inactivation of the toxin. All the transferase activities of CTA are enhanced by ADP-ribosylation factors (ARFs), approximately 20-kDa guanine nucleotide-binding proteins that are ubiquitous in mammalian cells. Phospholipids and a soluble brain ARF, in a GTP-dependent manner, activated toxin NAD:agmatine ADP-ribosyltransferase activity; their simultaneous effect was maximal at physiological temperatures (approximately 37 degrees C). At lower temperatures, the stimulation by ARF was much less. There were similar effects on other toxin-catalyzed reactions, notably, the ADP-ribosylation of Gs alpha and the hydrolysis of NAD. Thus, host factors, such as ARF and phospholipid, synergistically increase cholera toxin activity at 37 degrees C and may be important in toxin action in the mammalian gut.

ADP-Ribosylation Factors↗
PubMed1993

Rapid prenatal diagnosis of Patau's syndrome in a fetus with an abdominal wall defect by 72 hour culture of cells from amniotic fluid.

A woman in the 32nd week of pregnancy was referred for investigation because of fetal abnormalities, including an abdominal wall defect, detected by ultrasonography. In view of the increased risk of chromosome abnormality, amniocentesis was performed to enable informed decisions about the management of the pregnancy and delivery to be taken. Cells from the liquor were inoculated into standard lymphocyte culture medium and incubated for 72 h. Slides with a high mitotic index and good quality metaphases, comparable to those from a blood culture, were obtained after harvesting. Cytogenetic analysis showed the karyotype to be 46,XY, - 14,+t(13q14q), which is consistent with Patau's syndrome. This technique appears to be an option for rapid karyotyping in cases of abdominal wall defect, where a chromosomal abnormality is suspected.

Abdominal Muscles↗
PubMed1992

Human and Giardia ADP-ribosylation factors (ARFs) complement ARF function in Saccharomyces cerevisiae.

ADP-ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins that stimulate the ADP-ribosyltransferase activity of cholera toxin in vitro. ARFs are highly conserved, ubiquitously expressed in eukaryotic cells and appear to be involved in vesicular protein transport. The two yeast ARFs are > 60% identical to mammalian ARFs and are essential for cell viability (Stearns, T., Kahn, R. A., Botstein, D., and Hoyt, M. A. (1990) Mol. Cell. Biol. 10, 6690-6699). Although the two yeast ARF proteins are 96% identical in amino acid sequence, the yeast ARF1 gene is constitutively expressed, whereas the ARF2 gene is repressed by glucose. Human ARF5 and ARF6 and a Giardia ARF differ substantially in size and amino acid identity from other mammalian and eukaryotic ARFs but will, as befits their designation, activate cholera toxin. Expression of human ARF5, ARF6, or Giardia ARF cDNA rescued the lethal yeast ARF double mutant (arf1, arf2). Strains rescued by human ARF5, ARF6, or Giardia ARF grew much more slowly than wild-type yeast or strains rescued with yeast ARF1. We infer from the impaired growth of these rescued strains that the homologous ARFs may have specific targeting information that does not interact effectively or efficiently with the yeast protein membrane trafficking system.

ADP-Ribosylation Factor 1↗
PubMed1992

Regulation of ADP-ribosylation factor (ARF) expression. Cross-species conservation of the developmental and tissue-specific alternative polyadenylation of ARF 4 mRNA.

ADP-ribosylation factors (ARFs), approximately 20-kDa guanine nucleotide-binding proteins, are involved in protein trafficking and enhance cholera toxin ADP-ribosyltransferase activity. Expression of six ARF genes was examined in mammalian tissues; only ARF 4 mRNA was detected in rat testis in forms considerably shorter than those in other tissues. Testis-specific expression of short forms of ARF 4 mRNA was observed in several mammalian species. On Northern analysis of the developmental expression of rat ARF 4 mRNA, appearance of the shorter species was consistent with its involvement in a late stage of spermatogenesis. Sequences of products of rapid amplification of cDNA ends (RACE-polymerase chain reaction) of rat ARF 4 mRNA revealed that different mRNAs resulted from the use of three polyadenylation signals, one AUUAAA and two AAUAAA. Sequences of 3'-untranslated regions of rat and human ARF 4 mRNA were very similar with identical polyadenylation signals at similar positions. Of the ARF 4 mRNAs identified by RACE-PCR, with sizes of 1.1, 1.3, and 1.8 kb, the 1.1-kb mRNA was predominant in adult testis. By in situ hybridization, the 1.1-kb mRNA was identified primarily in mature sperm, consistent with the developmental studies. Shorter mRNAs, thought to be more stable, may compensate for cessation of transcription at late stages of spermatogenesis.

ADP-Ribosylation Factors↗
PubMed1992

Differential interaction of ADP-ribosylation factors 1, 3, and 5 with rat brain Golgi membranes.

Six mammalian ADP-ribosylation factors (ARFs) identified by cDNA cloning were expressed as recombinant proteins (rARFs) that stimulated cholera toxin ADP-ribosyltransferase activity. Microsequencing of soluble ARFs I and II (sARFs I and II), purified from bovine brain, established that they are ARFs 1 and 3, respectively. Rabbit antibodies (IgG) against sARF II reacted similarly with ARFs 1, 2, and 3 (class I) on Western blots. ARFs 1 and 3 were distinguished by their electrophoretic mobilities. Antiserum against rARF 5 cross-reacted partially with rARF 4 but not detectably with rARF 6 and minimally with class I ARFs. Guanosine 5'-O-(3-thiotriphosphate) (GTP[gamma S]) increased recovery of ARF activity and immunoreactivity in organelle fractions separated by density gradient centrifugation, after incubation of rat brain homogenate with ATP and a regenerating system. ARF 1 accumulated in microsomes plus Golgi and Golgi fractions, whereas ARF 5 seemed to localize more specifically in Golgi; the smaller increment in ARF 3 was distributed more evenly among fractions. On incubation of Golgi with a crude ARF fraction, GTP[gamma S], and an ATP-regenerating system, association of ARF activity with Golgi increased with increasing ATP concentration paralleled by increases in immunoreactive ARFs 1 and 5 and, to a lesser degree, ARF 3. Golgi incubated with GTP[gamma S] and purified ARF 1 or 3 bound more ARF 1 than ARF 3. Based on immunoreactivity and assay of ARF activity, individual ARFs 1, 3, and 5 appeared to behave independently and selectively in their GTP-dependent association with Golgi in vitro.

ADP-Ribosylation Factors↗
PubMed1992

Effects of phospholipid and GTP on recombinant ADP-ribosylation factors (ARFs). Molecular basis for differences in requirements for activity of mammalian ARFs.

ADP-ribosylation factors (ARFs) are highly conserved approximately 20-kDa guanine nucleotide-binding proteins that were first identified based on their ability to stimulate the cholera toxin-catalyzed ADP-ribosylation of Gs alpha and thus activate adenylyl cyclase. Proteins with ARF activity have been characterized from different mammalian tissues and exhibited different requirements for activity, stability, and phospholipid. Based on molecular cloning and mRNA distribution, at least six mammalian ARFs, which fall into three classes, have been identified. To test whether individual ARFs might have different requirements for optimal activity, as judged by their ability to enhance cholera toxin ADP-ribosyltransferase activity, four ARFs from classes I, II, and III were produced as recombinant proteins in Escherichia coli and characterized. Recombinant bovine ARF 2 (rARF 2) and human ARF 3 (rARF 3) (class I), human ARF 5 (rARF 5, class II), and human ARF 6 (rARF 6, class III) differed in the effects of phospholipid and detergent on their ability to enhance cholera toxin activity; rARFs 2, 3, and 5 required dimyristoylphosphatidylcholine (DMPC) and cholate, whereas rARF 6 did not require phospholipid/detergent for activity. Further characterization of two of the more divergent ARFs (ARFs 2 and 6) showed that both exhibited guanosine 5'-O-(3-thio)triphosphate binding which was enhanced by DMPC/cholate. In the transferase assay, rARF 2 required approximately 4 microM GTP for half-maximal stimulation of toxin activity, whereas rARF 6 required 0.05 microM GTP. rARF 6 exhibited a delay in activation of toxin not detected with rARF 2 that may be related to a requirement for guanine nucleotide exchange and/or GTP binding. These findings are consistent with the conclusion that the highly conserved members of the ARF family have different requirements for optimal activity.

ADP-Ribosylation Factor 6↗
PubMed1992

Pertussis toxin-catalyzed ADP-ribosylation of G(o) alpha with mutations at the carboxyl terminus.

The guanine nucleotide-binding protein G(o alpha) has been implicated in the regulation of Ca2+ channels in neural tissues. Covalent modification of G(o alpha) by pertussis toxin-catalyzed ADP-ribosylation of a cysteine (position 351) four amino acids from the carboxyl terminus decouples G(o alpha) from receptor. To define the structural requirements for ADP-ribosylation, preparations of recombinant G(o alpha) with mutations within the five amino acids at the carboxyl terminus were evaluated for their ability to serve as pertussis toxin substrates. As expected, the mutant in which cysteine 351 was replaced by glycine (C351G) was not a toxin substrate. Other inactive mutants were G352D and L353 delta/Y354 delta. Mutations that had no significant effect on toxin-catalyzed ADP-ribosylation included G350D, G350R, Y354 delta, and L353V/Y354 delta. Less active mutants were L353G/Y354 delta, L353A/Y354 delta, and L353G. ADP-ribosylation of the active mutants, like that of wild-type G(o alpha), was enhanced by the beta gamma subunits of bovine transducin. It appears that three of the four terminal amino acids critically influence pertussis toxin-catalyzed ADP-ribosylation of G(o alpha).

Adenosine Diphosphate Ribose↗
PubMed1992

Guanine nucleotide-binding proteins in the intestinal parasite Giardia lamblia. Isolation of a gene encoding an approximately 20-kDa ADP-ribosylation factor.

Giardia lamblia is a protozoan intestinal parasite that has characteristics of both eukaryotes and prokaryotes. To determine whether genes for guanine nucleotide-binding proteins are present in Giardia, genomic DNA and cDNA libraries were screened by polymerase chain reaction and by hybridization with mixed oligonucleotide probes complementary to sequences encoding conserved GTP-binding domains. A gene with a high degree of sequence identity with mammalian ADP-ribosylation factors (ARFs), believed to be important in vesicular transport, was identified. The Giardia ARF gene had a 573-base open reading frame encoding 191 amino acids which are 63-70% identical with known mammalian and yeast ARFs. Sequence conservation among ARFs was greatest in putative GTP-binding domains. A single ARF mRNA species of approximately 750 bases was found in two different Giardia isolates. Primer extension and RNA sequencing of the Giardia ARF transcript revealed a short (6-base) 5'-untranslated region similar in size to those found in other Giardia transcripts. Giardia extracts contained ARF activity, as shown by stimulation of cholera toxin-catalyzed ADP-ribosylation and a Giardia ARF expressed in Escherichia coli as a fusion protein likewise exhibited biochemical activity. Its presence in Giardia is consistent with the view that ARF emerged before the divergence of this protozoan from other eukaryotes (approximately 1.5 billion years ago), and that an ARF-like protein may have been the ancestor of several other classes of signal-transducing guanine nucleotide-binding proteins, including the alpha subunits of the heterotrimeric G proteins.

ADP-Ribosylation Factors↗
PubMed1992

Characterization of the human gene encoding ADP-ribosylation factor 1, a guanine nucleotide-binding activator of cholera toxin.

Mammalian ADP-ribosylation factors (ARFs), approximately 20-kDa guanine nucleotide-binding proteins that stimulate cholera toxin ADP-ribosyltransferase activity, were grouped into three classes based on deduced amino acid sequence. Human ARF 1, a class I ARF, is identical with its bovine counterpart, has a distinctive pattern of tissue and developmental expression, and is encoded by a approximately 1.9-kilobase mRNA. ARF 1 cDNAs were isolated from a human fibroblast cDNA library; one arose via an alternative polyadenylation signal (AA-TACA) 84 nucleotides 5' to the polyadenylation signal (AATAAA) used in the 1815-base pair cDNA. The polyadenylation signals, their respective locations, and the surrounding nucleotide sequences are conserved in human and rat. The human ARF 1 gene, with four introns, spans approximately 16.5 kilobases. Exon 1 (46 base pairs) contains only untranslated sequence. Translation initiates in exon 2, which encodes the sequence GXXXXGK involved in phosphate binding (GTP hydrolysis). The sequence DVGG is encoded in exon 3, and NKQD, which is involved in the interaction with the guanine ring, is interrupted following the codon for Q by intron 4. The carboxyl-terminal 53 amino acids and greater than 1110 base pairs of 3'-untranslated region are encoded in exon 5. Primer extension and mung bean and S1 nuclease mapping indicated multiple transcription initiation sites and were consistent with Northern analyses. The 5'-flanking region has a high GC content but no TATA or CAAT box, as found in housekeeping genes. In addition, the two human class I ARF genes, ARF 1 and ARF 3, have similar exon/intron organizations and use GC-rich promoters.

ADP-Ribosylation Factors↗
PubMed1992

GTP but not GDP analogues promote association of ADP-ribosylation factors, 20-kDa protein activators of cholera toxin, with phospholipids and PC-12 cell membranes.

ADP-ribosylation factors (ARFs) are a family of approximately 20-kDa guanine nucleotide-binding proteins initially identified by their ability to enhance cholera toxin ADP-ribosyltransferase activity in the presence of GTP. ARFs have been purified from both membrane and cytosolic fractions. ARF purified from bovine brain cytosol requires phospholipid plus detergent for high affinity guanine nucleotide binding and for optimal enhancement of cholera toxin ADP-ribosyltransferase activity. The phospholipid requirements, combined with a putative role for ARF in vesicular transport, suggested that the soluble protein might interact reversibly with membranes. A polyclonal antibody against purified bovine ARF (sARF II) was used to detect ARF by immunoblot in membrane and soluble fractions from rat pheochromocytoma (PC-12) cell homogenates. ARF was predominantly cytosolic but increased in membranes during incubation of homogenates with nonhydrolyzable GTP analogues guanosine 5'-O-(3-thiotriphosphate), guanylyl-(beta gamma-imido)-diphosphate, and guanylyl-(beta gamma-methylene)-diphosphate, and to a lesser extent, adenosine 5'-O-(3-thiotriphosphate). GTP, GDP, GMP, and ATP were inactive. Cytosolic ARF similarly associated with added phosphatidylserine, phosphatidylinositol, or cardiolipin in GTP gamma S-dependent fashion. ARF binding to phosphatidylserine was reversible and coincident with stimulation of cholera toxin-catalyzed ADP-ribosylation. These observations may reflect a mechanism by which ARF could cycle between soluble and membrane compartments in vivo.

ADP-Ribosylation Factors↗