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Biomedical subjects

T L Jones

Publications and source records attributed to T L Jones.

At least 73 records · Page 4Linked to original sources
PubMed1993

Increased palmitoylation of the Gs protein alpha subunit after activation by the beta-adrenergic receptor or cholera toxin.

The alpha subunit of the heterotrimeric Gs protein that couples the beta-adrenergic receptor to adenylyl cyclase undergoes post-translational palmitoylation. We examined the dynamics of this modification of alpha s by metabolic labeling of COS and S49 lymphoma cells under different conditions. The endogenous alpha s proteins were immunoprecipitated with a peptide-specific antibody, separated by SDS-polyacrylamide gel electrophoresis, and analyzed by fluorography and densitometry. A pulse-chase study of COS cells incubated with [3H]palmitate or [35S]methionine showed that for alpha s the palmitate turnover (t1/2 approximately 50 min) was significantly faster than the protein degradation. Treatment of cells with 10 microM isoproterenol, a beta-adrenergic receptor agonist, in the presence of [3H]palmitate led to a rapid 4-10-fold increase in the palmitoylation of alpha s. This increase in palmitoylation was concentration-dependent (EC50 approximately 0.9 microM) and blocked by the antagonist propranolol. The mutant alpha s proteins in the unc and H21a S49 cell lines did not show an increase in [3H]palmitate incorporation with isoproterenol treatment. Cholera toxin treatment of COS cells increased the [3H]palmitate incorporation into the alpha s subunits. These data indicate that palmitoylation of the alpha s subunit is dynamic and regulated by activation of the alpha s subunit.

Animals↗
PubMed1993

The G protein alpha s subunit incorporates [3H]palmitic acid and mutation of cysteine-3 prevents this modification.

We investigated whether alpha s could be acylated by palmitate by transfecting COS cells with the cDNA for the wild-type, long form of alpha s and metabolically labeling with [3H]palmitate or [35S]methionine. Cells were separated into particulate and soluble fractions and immunoprecipitated with a specific peptide antibody. [3H]Palmitate was incorporated into both endogenous and transfected alpha s. Inhibition of protein synthesis with cycloheximide did not block the radiolabeling of alpha s with [3H]palmitate. Hydroxylamine treatment caused a release of the tritium radiolabel, demonstrating that the incorporation was through a thioester bond. The tritium radiolabel was base-labile and comigrated with [3H]palmitate on thin-layer chromatography. The third residue of the wild-type alpha s was mutated from a cysteine to an alanine by site-directed mutagenesis. This mutant was expressed in COS cells and localized to the particulate fraction as determined by immunoprecipitation of the [35S]methionine-labeled cells. The cysteine-3 mutant did not undergo radiolabeling with [3H]palmitate, indicating that this residue is crucial for the modification.

Animals↗
PubMed1993

In vivo pulse labeling of proteins in attached leaves with radioactive amino acids.

The pulse labeling of proteins in attached leaves by the incorporation of radioactive amino acids can be a valuable approach to study a wide range of topics pertaining to plant gene expression. Transient changes in the rate of net protein synthesis can be measured since pulse labeling permits discrimination between proteins actively synthesized during the labeling interval from those accumulated at earlier times. Specific procedures for a rapid and convenient method of in vivo pulse labeling are outlined which we believe could be broadly useful in plant biological research. A particularly important technical feature of the protocol is electroblotting of radioactive proteins from the sodium dodecyl sulfate acrylamide resolving gel matrix to polyvinylidene difluoride transfer membrane. This step permits a single polyacrylamide slab gel to be used for autoradiography, immunoblot analysis, and protein staining, thereby greatly facilitating comparison among these complementary techniques and resulting in a significant savings in time and radioactive sample. Central considerations concerning the quantitation and interpretation of in vivo pulse labeling data are discussed.

Amino Acids↗
PubMed1993

Baculovirus expression and purification of a soluble, mutant G-protein alpha subunit.

The cDNA for the alpha i1 protein that had undergone site-directed mutagenesis to change glycine-2 to alanine was ligated into a baculovirus transfer vector. A recombinant virus was obtained by transfecting Sf9 cells with both the wild-type baculovirus DNA and the transfer vector and screening for recombinant plaques. Infection with the recombinant virus led to a high level of expression of the mutated alpha i1 protein in the soluble fraction of the cell. The protein was purified by ammonium sulfate precipitation, gel filtration, and immobilized dye chromatography. The typical yield was 7.5 mg from two 800-ml cultures. The protein showed immunoreactivity to three different alpha i-specific antibodies. It bound guanosine 5'-(gamma-thio)triphosphate (GTP gamma S) with a stoichiometry of 0.63 to 0.91 mol/mol and with a rate constant (kGTP gamma S) of binding of 0.126 min-1. When GTP gamma S bound, the protein was protected from complete tryptic cleavage. The recombinant protein was able to undergo pertussis toxin-catalyzed ADP ribosylation and bind beta gamma subunits but with a reduced affinity compared to that of alpha transducin. Thus using a recombinant baculovirus, a nonmyristylated G protein alpha subunit was abundantly expressed in Sf9 cells and milligram quantities of a functional protein were easily purified.

Amino Acid Sequence↗
PubMed1993

Selection bias from differential residential mobility as an explanation for associations of wire codes with childhood cancer.

Several studies of childhood cancer, especially leukemia, in residential areas have reported an association with wire configuration codes. These codes were suggested to be surrogates of electromagnetic field exposure. However, the selection criteria used in several of the studies caused the case and control populations to be non-comparable, especially with respect to residential mobility. Specifically, controls were required to be residentially stable but cases were not. Thus, an artificial association between residential mobility and cancer was created by the subject selection procedure. The present study of 5721 residences in Columbus, Ohio was conducted to learn if bias due to differences in residential mobility, rather than electromagnetic fields, could explain the reported association between wire configuration codes and childhood cancer. It was found that the proportion of homes classified as "high" wire code in the non-stable population was 31% greater than the corresponding proportion in the stable population. This finding shows that high wire codes are associated with homes in which the residents are mobile and low wire codes are associated with homes occupied by stable residents. Thus, as a consequence of this association between residential mobility and high wire codes, studies that created an artificial association between residential mobility and childhood cancer will also produce a false association between high wire codes and cancer.

Case-Control Studies↗
PubMed1993

Oocyte maturation in starfish is mediated by the beta gamma-subunit complex of a G-protein.

The stimulation of meiotic maturation of starfish oocytes by the hormone 1-methyladenine is mimicked by injection of beta gamma subunits of G-proteins from either retina or brain. Conversely, the hormone response is inhibited by injection of the GDP-bound forms of alpha i1 or alpha t subunits, or by injection of phosducin; all of these proteins should bind free beta gamma. alpha-subunit forms with reduced affinity for beta gamma (alpha i1 or alpha t bound to hydrolysis-resistant GTP analogs, or alpha i1-GMPPCP treated with trypsin to remove the amino terminus of the protein) are less effective inhibitors of 1-methyladenine action. These results indicate that the beta gamma subunit of a G-protein mediates 1-methyladenine stimulation of oocyte maturation.

Adenine↗
PubMed1992

Differential isoprenylation of carboxy-terminal mutants of an inhibitory G-protein alpha-subunit: neither farnesylation nor geranylgeranylation is sufficient for membrane attachment.

To determine the effect of protein isoprenylation with farnesyl vs geranylgeranyl groups on membrane association in vivo, COS cells were transfected with cDNAs encoding the wild-type G-protein alpha i1 (WT) subunit, the soluble nonmyristoylated G-protein alpha i1 glycine to alanine mutant (GA), a double mutant in which the carboxy-terminal residues CGLF of GA were mutated to CVLS (GA-CVLS), and a double mutant in which the carboxy terminus of GA was mutated to CALL (GA-CALL). As opposed to the WT and GA proteins, the GA-CVLS and GA-CALL proteins were not pertussis toxin substrates nor were they recognized by antibodies that recognize the nonmutated alpha i1 carboxy terminus. Only the GA-CVLS and GA-CALL proteins incorporated [3H]mevalonate in the form of a farnesyl and a geranylgeranyl moiety, respectively. Subcellular localization, as assessed by immunoblotting and immunoprecipitation, revealed that the WT protein localizes almost exclusively to the membrane fraction, whereas the GA, GA-CVLS, and GA-CALL proteins localize predominantly to the soluble fraction. The soluble GA-CVLS and GA-CALL proteins were not carboxyl methylated, but the small amount localized to the membrane was partially carboxyl methylated. These results indicate that neither farnesylation nor geranylgeranylation is sufficient alone to lead to membrane association.

Amino Acid Sequence↗
PubMed1992

Quantitative determination of the induction of apoptosis in a murine B cell line using flow cytometric bivariate cell cycle analysis.

WEHI-231 cells have been used extensively as a model of tolerance induction in B cells. Recent evidence has shown that anti-IgM treatment of WEHI-231 cells resulted in the induction of apoptosis. In this study, using acridine orange staining and flow cytometric analysis, we demonstrated that apoptotic cells are detected as a distinct population of cells separate from the cells in normal cell cycle progression. The validity of analysis gates was confirmed by cell sorting of the apoptotic population versus normal cells and subsequent gel analysis. Using this technique, we have demonstrated that F(ab')2 anti-mu, A23187, or PMA induced apoptosis in the WEHI-231 cells. The addition of LPS reversed apoptotic induction as seen previously with the WEHI-231 cell line. In contrast, however, PMA did not prevent the induction of apoptosis in anti-mu-treated cells. Additionally, we were interested in determining if the induction of apoptosis was restricted to a specific phase of cell cycle. Since growth inhibition results in most cells arresting in the G1 phase of cell cycle, we wanted to demonstrate apoptosis as a G1-dependent event. This was examined with WEHI-231 cells treated with known cell cycle inhibitors. Interestingly, inhibition of cells in each phase of cycle resulted in the induction of apoptosis. LPS was able to inhibit the induction of apoptosis with each of the cell cycle inhibitors except actinomycin D. Furthermore, we have demonstrated that the WEHI-231 cells contain a Ca(2+)-Mg(2+)-dependent preexisting endonuclease.

Acridine Orange↗
PubMed1992

Amino- and carboxy-terminal deletion mutants of Gs alpha are localized to the particulate fraction of transfected COS cells.

To elucidate the structural basis for membrane attachment of the alpha subunit of the stimulatory G protein (Gs alpha), mutant Gs alpha cDNAs with deletions of amino acid residues in the amino and/or carboxy termini were transiently expressed in COS-7 cells. The particulate and soluble fractions prepared from these cells were analyzed by immunoblot using peptide specific antibodies to monitor distribution of the expressed proteins. Transfection of mutant forms of Gs alpha with either 26 amino terminal residues deleted (delta 3-28) or with 59 amino terminal residues deleted (delta 1-59) resulted in immunoreactive proteins which localized primarily to the particulate fraction. Similarly, mutants with 10 (delta 385-394), 32 (delta 353-384), or 42 (delta 353-394) amino acid residues deleted from the carboxy terminus also localized to the particulate fraction, as did a mutant form of Gs alpha lacking amino acid residues at both the amino and carboxy termini (delta 3-28)/(delta 353-384). Mutant and wild type forms of Gs alpha demonstrated a similar degree of tightness in their binding to membranes as demonstrated by treatment with 2.5 M NaCl or 6 M urea, but some mutant forms were relatively resistant compared with wild type Gs alpha to solubilization by 15 mM NaOH or 1% sodium cholate. We conclude that: (a) deletion of significant portions of the amino and/or carboxyl terminus of Gs alpha is still compatible with protein expression; (b) deletion of these regions is insufficient to cause cytosolic localization of the expressed protein. The basis of Gs alpha membrane targeting remains to be elucidated.

Amino Acid Sequence↗
PubMed1992

The electrical effect of two commonly used clinical stimulators on traumatic edema in rats.

The purposes of this study were to determine the effect of electrical stimulation on traumatic rat hind-paw edema and to establish whether there would be a difference in edema reduction when two types of stimulators were used. The animals were divided into a control group (n = 15) and two experimental groups, one group receiving monophasic pulsed current (MPC group, n = 15) and the other group receiving symmetrical biphasic pulsed current (SBPC group, n = 14). The right hind-paw volume of all groups was measured prior to traumatization and at 24, 48, 72, and 96 hours posttrauma. Following the 24-, 48-, and 72-hour measurements, 1 hour of electrical stimulation was administered to the experimental groups. The control group received sham treatment. Results revealed significant edema reduction in all groups over the 96-hour period, with each group's greatest change in paw volume occurring 48 hours posttrauma. At the final paw volume measurement, there was no significant difference between the MPC and control groups or between the MPC and SBPC groups. The SBPC group, however, showed less reduction in edema than did the control group. One hour of electrical stimulation per day over 3 consecutive days failed to demonstrate significant edema reduction in either the MPC group or the SBPC group as compared with the control group. The results of this study demonstrated that the electrical stimulation characteristics and procedures currently used in the clinic do not significantly reduce extant edema caused by trauma in rat hind limbs.

Analysis of Variance↗
PubMed1991

The G protein connection: molecular basis of membrane association.

Two distinct types of lipid modification, myristoylation and isoprenylation, are critical for membrane association of heterotrimeric G proteins. Elucidation of the molecular basis for G protein membrane association has important implications for understanding G protein structure and function, and is relevant to potential therapeutic approaches to AIDS and cancer.

Amino Acid Sequence↗
PubMed1990

Isoprenylation of an inhibitory G protein alpha subunit occurs only upon mutagenesis of the carboxyl terminus.

We transfected COS cells with expression vectors for the wild-type G protein alpha i1 subunit (pWT) and for mutated alpha i1 subunits, including the nonmyristylated glycine 2 to alanine mutant (pGA) and mutants in which the carboxyl termini of pWT and pGA were changed from CGLF to CVLS (pCVLS and pGA-CVLS, respectively). Immunoblot analysis of transfected COS cells with an antibody to residues 159-168 of the alpha i1 protein indicated that all four proteins were expressed. Unlike the WT and GA proteins, both CVLS mutant proteins failed to react with an antibody specific for the carboxyl terminus and failed to undergo pertussis toxin-catalyzed ADP-ribosylation. Analysis of COS cell lysates after [3H]mevalonic acid labeling indicated that specific incorporation of radioactivity occurred only in the alpha i1 subunits with the CVLS mutation. Immuno-precipitation of COS cell fractions after labeling with [35S]methionine indicated that both WT and CVLS mutant proteins were localized predominantly in the particulate fraction, whereas GA and GA-CVLS mutant proteins were found primarily in the soluble fraction. These results directly demonstrate that the carboxyl-terminal sequence, CGLF, is incapable of leading to isoprenylation but that alteration of two residues (glycine to valine, phenylalanine to serine) is sufficient to promote isoprenylation.

Adenosine Diphosphate Ribose↗
PubMed1990

Myristoylation of an inhibitory GTP-binding protein alpha subunit is essential for its membrane attachment.

We transfected COS cells with cDNAs for the alpha subunits of stimulatory and inhibitory GTP-binding proteins, alpha s and alpha i1, respectively, and immunoprecipitated the metabolically labeled products with specific peptide antibodies. Cells were separated into particulate and soluble fractions before immunoprecipitation; [35S]methionine-labeled alpha s and alpha i were both found primarily in the particulate fraction. [3H]Myristate was incorporated into endogenous and transfected alpha i but could not be detected in alpha s even when it was overexpressed. We converted the second residue, glycine, of alpha i1 into alanine by site-directed mutagenesis. Upon transfection of the mutant alpha i1 into COS cells, the [35S]methionine-labeled product was localized primarily to the soluble fraction, and, also unlike normal alpha i1, the mutant failed to incorporate [3H]myristate. The unmyristoylated mutant alpha i1 could still interact with the beta-gamma complex, since purified beta gamma subunits promoted pertussis toxin-catalyzed ADP-ribosylation of both the normal and mutant alpha i1 subunits. These results indicate that myristoylation is critical for membrane attachment of alpha i but not alpha s subunits.

Adenosine Diphosphate Ribose↗
PubMed1990

Antibodies as probes of G-protein receptor-effector coupling and of G-protein membrane attachment.

The specificity of antisera raised against synthetic decapeptides corresponding to the C-terminus of G-protein alpha-subunits was rigorously defined. Antisera raised against alpha-subunit C-terminal decapeptides proved capable of immuno-precipitating their cognate G-proteins, as well as recognizing these proteins in native cell membranes. Thus the alpha s-specific antiserum could block agonist-stimulated adenylyl cyclase activity in native membranes and also immuno-precipitate an activated alpha s-adenylyl cyclase complex. The alpha i 2-, but not alpha i 3- and alpha z-specific antiserum could block agonist-mediated inhibition of adenylyl cyclase in human platelet membranes. These results indicate that the C-terminal decapeptide is involved in G-protein receptor, but not effector, coupling. These antisera also proved useful in immunoprecipitation of endogenous and transfected alpha-subunits in COS cells. Using this approach, we were able to show that both alpha s and alpha i are membrane associated, but only the latter is myristylated. A mutant alpha i 1 (second residue Gly changed to Ala) fails to incorporate myristate and is localized in the soluble fraction. Myristylation is thus essential for membrane attachment of alpha i, but not alpha s.

Amino Acid Sequence↗
PubMed1989

Acute effects of cycloheximide on the translocation of glucose transporters in rat adipose cells.

Insulin's rapid action to increase glucose transport is believed to occur primarily through the translocation of glucose transporters from an intracellular pool to the plasma membrane. To better understand the mechanism involved, we studied the role of protein synthesis in glucose transporter translocation by using the protein synthesis inhibitor, cycloheximide. Isolated rat epididymal adipose cells were incubated in the presence or absence of cycloheximide (10 micrograms/ml) for a total of 120 min. Insulin (7 nM) was added to half of the cells from both groups for the final 30 min. Protein synthesis was inhibited by approximately 90%, as measured by [14C]leucine incorporation, in the cells exposed to cycloheximide. The 3-O-methylglucose uptake in intact cells was slightly increased in the basal state with cycloheximide treatment, but the insulin-stimulated 3-O-methylglucose uptake was unchanged by cycloheximide. The distribution of glucose transporters in the different subcellular membrane fractions, as measured by the cytochalasin B binding assay, was unchanged by cycloheximide. These results suggest that insulin's stimulation of glucose transport and translocation of glucose transporters can occur without acute protein synthesis.

3-O-Methylglucose↗
PubMed1989

The clear-cell variant of uterine epithelioid leiomyoma. An immunohistologic and ultrastructural study.

A case of a rare uterine clear-cell epithelioid leiomyoma is presented, emphasizing immunohistologic and ultrastructural findings. The presence of actin, vimentin, desmin, muscle-specific antigen, and smooth-muscle-specific actin in tumor cells indicates a smooth-muscle origin, confirmed by electron microscopy. Numerous vacuolated mitochondria produced the cytoplasmic "clearing" on light microscopy.

Actins↗