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Biomedical subjects

D J Peters

Publications and source records attributed to D J Peters.

51 records · Page 3Linked to original sources
PubMed1992

Lithium, an inhibitor of cAMP-induced inositol 1,4,5-trisphosphate accumulation in Dictyostelium discoideum, inhibits activation of guanine-nucleotide-binding regulatory proteins, reduces activation of adenylylcyclase, but potentiates activation of guanylyl cyclase by cAMP.

Li+ drastically alters pattern formation in Dictyostelium by inhibiting cAMP-induced prespore-gene expression and promoting cAMP-induced prestalk-gene expression. We reported previously that Li+ inhibits inositol monophosphatases in this organism and strongly reduces basal and cAMP-stimulated inositol 1,4,5-trisphosphate levels. We show here that Li+ also reduces cAMP-induced accumulation of cAMP, but promotes cAMP-induced accumulation of cGMP. This effect is not due to inhibition of cGMP hydrolysis or inhibition of adaptation and may therefore reflect stimulation of guanylyl-cyclase activation. Li+ does not affect the binding of cAMP to surface receptors but interferes with the interaction between receptors and guanine-nucleotide-binding regulatory (G) proteins. These effects are complex; in the absence of Mg2+, Li+ increases guanosine 5'-[gamma-thio]triphosphate(GTP[S])-binding activity to similar levels as 1 mM Mg2+. However, while Mg2+ potentiates cAMP-induced stimulation of GTP[S]-binding activity, Li+ effectively inhibits stimulation. Li+ also inhibits cAMP-stimulated, but not basal high-affinity GTP-ase activity, indicating an inhibitory effect on cAMP-induced activation of G-proteins. Our data suggest that in addition to inositolphosphate metabolism, the activation of G-proteins may be a second biochemical target for Li+ effects on pattern formation and signal transduction in Dictyostelium.

Adenylyl Cyclases↗
PubMed1991

Selective induction of gene expression and second-messenger accumulation in Dictyostelium discoideum by the partial chemotactic antagonist 8-p-chlorophenylthioadenosine 3',5'-cyclic monophosphate.

During development of the cellular slime mold Dictyostelium discoideum, cAMP induces chemotaxis and expression of different classes of genes by means of interaction with surface cAMP receptors. We describe a cAMP derivative, 8-p-chlorophenylthioadenosine 3',5'-cyclic monophosphate (8-CPT-cAMP), which inhibits cAMP-induced chemotaxis at low concentrations but induces chemotaxis at supersaturating concentrations. This compound, moreover, selectively activates expression of aggregative genes but not of postaggregative genes. 8-CPT-cAMP induces normal cGMP and cAMP accumulation but in contrast to cAMP, which increases inositol 1,4,5-trisphosphate levels, 8-CPT-cAMP decreases inositol 1,4,5-trisphosphate levels. The derivative induces reduced activation of guanine nucleotide regulatory proteins, which may cause its defective activation of inositol 1,4,5-trisphosphate production. Our data suggest that disruption of inositolphospholipid signaling impairs chemotaxis and expression of a subclass of cAMP-regulated genes.

Journal Article↗
PubMed1991

Control of cAMP-induced gene expression by divergent signal transduction pathways.

A compilation of literature data and recent experiments led to the following conclusions regarding cyclic adenosine 3':5' monophosphate (cAMP) regulation of gene expression. Several classes of cAMP-induced gene expression can be discriminated by sensitivity to stimulation kinetics. The aggregation-related genes respond only to nanomolar cAMP pulses. The prestalk-related genes respond both to nanomolar pulses and persistent micromolar stimulation. The prespore specific genes respond only to persistent micromolar stimulation. The induction of the aggregation- and prestalk-related genes by nanomolar cAMP pulses may share a common transduction pathway, which does not involve cAMP, while involvement of the inositol 1,4,5-trisphosphate (IP3)/Ca2+ pathway is unlikely. Induction of the expression of prespore and prestalk-related genes by micromolar cAMP stimuli utilizes divergent signal processing mechanisms. cAMP-induced prespore gene expression does not involve cAMP and probably also not cyclic guanosine 3'.5' monophosphate (cGMP) as intracellular intermediate. Involvement of cAMP-induced phospholipase C (PLC) activation in this pathway is suggested by the observation that IP3 and 1,2-diacylglycerol (DAG) can induce prespore gene expression, albeit in a somewhat indirect manner and by the observation that Li+ and Ca2+ antagonists inhibit prespore gene expression. Cyclic AMP induction of prestalk-related gene expression is inhibited by IP3 and DAG and promoted by Li+, and is relatively insensitive to Ca2+ antagonists, which indicates that PLC activation does not mediate prestalk-related gene expression. Neither prespore nor prestalk-related gene expression utilizes the sustained cAMP-induced pHi increase as intracellular intermediate.

Cyclic AMP↗
PubMed1991

Abberant chemotaxis and differentiation in Dictyostelium mutant fgdC with a defective regulation of receptor-stimulated phosphoinositidase C.

Dictyostelium cells use extracellular cyclic AMP both as a chemoattractant and as a morphogen inducing cell-type-specific gene expression. Cyclic AMP binds to surface receptors, activates one or more G-proteins, and stimulates adenylate cyclase, guanylate cyclase and phosphoinositidase C. Mutant fgdC showed aberrant chemotaxis, and was devoid of cyclic AMP-induced gene expression and differentiation. Both the receptor- and G-protein-mediated stimulation of adenylate cyclase and guanylate cyclase were unaltered in mutant fgdC as compared to wild-type cells. In wild-type cells phosphoinositidase C was activated about twofold by the cyclic AMP receptor. In mutant fgdC cells, however, the enzyme was inhibited by about 60%. These results suggest that phosphoinositidase C is regulated by a receptor-operated activation/inhibition switch that is defective in mutant fgdC. We conclude that activation of phosphoinositidase C is essential for Dictyostelium development.

Animals↗
PubMed1990

In vivo phosphorylation and membrane association of the fyn proto-oncogene product in IM-9 human lymphoblasts.

The protein product of the src-related proto-oncogene, fyn, was isolated from IM-9 cells with antibodies specific for the amino-terminal 22 residues of the fyn protein. Peptide mapping demonstrated that the fyn protein was distinct from the closely related c-src and c-fgr proteins. The fyn protein from IM-9 cells incorporated [3H]myristate in vivo and was found to be membrane associated. Phosphoamino acid analysis demonstrated that the fyn protein from IM-9 cells was phosphorylated in vivo predominantly on tyrosine and threonine with only a small amount of phosphoserine detected. the major chymotryptic phosphopeptide of the fyn protein was phosphorylated exclusively on tyrosine. This peptide was specifically precipitated by antibodies directed against a peptide modeled on the closely related carboxy termini of the c-src and fyn proteins. These results provide direct evidence for phosphorylation of tyrosine-531 in the carboxy-terminal chymotryptic peptide of the fyn protein. Phosphorylation of the corresponding site in the closely related c-src protein (tyrosine-527) represses src kinase activity and transforming ability. Loss of the phosphorylation site at tyrosine-531 may similarly contribute to the transforming abilities of carboxy-terminal deletion mutants of the fyn protein.

Antibodies, Monoclonal↗
PubMed1989

Lithium ions induce prestalk-associated gene expression and inhibit prespore gene expression in Dictyostelium discoideum.

We investigated the effect of Li+ on two types of cyclic AMP-regulated gene expression and on basal and cyclic AMP-stimulated inositol 1,4,5-triphosphate (Ins(1,4,5)P3) levels. Li+ effectively inhibits cyclic AMP-induced prespore gene expression, half-maximal inhibition occurring at about 2 mM-LiCl. In contrast, Li+ (1-3 mM) promotes the cyclic AMP-induced increase of cysteine proteinase-2 mRNA levels, and induces the expression of this prestalk-associated gene in the absence of cyclic AMP stimuli. At concentrations exceeding 4-5 mM, LiCl inhibits cysteine proteinase-2 gene expression. LiCl reduces basal Ins(1,4,5)P3 levels and decreases the cyclic AMP-induced accumulation of Ins(1,4,5)P3; both effects occur half-maximally at 2-3 mM-LiCl. These results indicate that the induction of the cysteine proteinase-2 gene by Li+ is not due to elevated levels of Ins(1,4,5)P3. It is, however, possible that inhibition of prespore gene expression by Li+ is caused by Li+-induced reduction of basal and/or stimulated Ins(1,4,5)P3 levels.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1988

Signal transduction, chemotaxis, and cell aggregation in Dictyostelium discoideum cells without myosin heavy chain.

Dictyostelium discoideum cells have been generated that lack myosin heavy chain (MHC) due to antisense RNA inactivation of the endogenous mRNA or to insertional mutagenesis of the myosin gene. These cells retain chemotactic movement in gradients of the chemoattractant cAMP. Furthermore, cAMP does induce many biochemical and physiological responses in aggregative cells, including binding of cAMP to surface receptors, modification, and down-regulation of the receptor; activation of adenylate and guanylate cyclase, secretion of cAMP; and the association of actin to the Triton-insoluble cytoskeleton. Cells lacking MHC were found to have a requirement for bivalent cations in the medium for optimal chemotaxis and cell aggregation.

Actins↗
PubMed1986

Biochemical analyses of the crustacean hyperglycemic hormone of the crayfish Astacus leptodactylus.

A biochemical analysis was made of the crustacean hyperglycemic hormone (CHH) of the crayfish Astacus leptodactylus, as present in the CHH-producing perikarya, in the axonal tract and in the sinus gland, respectively. Hyperglycemic material was analyzed by polyacrylamide gel electrophoresis (PAGE and SDS-PAGE) and high-pressure liquid chromatography (HPLC) in combination with a dotting immunobinding assay (DIA) and a bioassay for hyperglycemic activity. After electrophoretic analyses, the predominant biologically as well as immunologically detectable product present in all parts of the cell has an apparent molecular radius of approximately 7000 Da. In the perikarya extract, a second factor with lower electrophoretic mobility was found, which may represent the prohormone or precursor of CHH. The analyses by means of HPLC showed two predominant immunopositive peaks with an elution time of 28-29 and 52-54 min, respectively. For both HPLC peaks, electrophoretic analyses indicate a molecular weight of 7000 Da.

Animals↗
PubMedDate not supplied

Expression and purification of active recombinant platelet factor 4 from a cleavable fusion protein.

A synthetic gene for human platelet factor 4 (hPF4) has been expressed at high levels as a fusion protein in Escherichia coli. The hPF4 sequence has been cleaved from the fusion protein by cyanogen bromide treatment and purified by column chromatography. Like hPF4, our recombinant hPF4 (rhPF4) is tetrameric under physiological conditions, binds heparin, and inhibits angiogenesis. Extensive purification to remove trace amounts of uncleaved fusion protein completely from the desired product rhPF4 was difficult. We have exploited recombinant DNA technology by modifying the fusion moiety to accomplish separation. This type of modification, which did not affect expression level, could be applied to other recombinant fusion proteins.

Amino Acid Sequence↗
PubMedDate not supplied

Human experience in disablement: the imperative of the ICIDH.

The ICIDH recognizes that the perspectives of people whose lives are personally shaped by disablement are critical to improving our understanding of disease consequences. However, this 'insider's perspective' has received comparatively little attention in medical research. This article suggests that the weight of medical history mitigates against human experience as a focus of investigation, traces the history of the International Classification of Diseases (ICD) from this perspective, and suggests that these historical influences are still operative in disablement studies. The ICIDH's inclusion of the insider's perspective represents a significant departure from traditional ways of thinking in medical science, and allows for important changes in the discourse about disablement. This article uses phenomenological theory to show how the insider's perspective might be more fully integrated into clinical research and theory development. Finally, this article suggests modifications to the ICIDH that would help to include more explicitly the insider's perspective in its structure.

Attitude to Health↗