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Biomedical subjects

D Prager

Publications and source records attributed to D Prager.

At least 37 records · Page 2Linked to original sources
PubMed1995

Pituitary disorders during pregnancy.

A number of morphologic and physiologic changes accompany pregnancy such as an increase in lactotrophs and prolactin production, and a decrease in gonadotropins and GH. The hormonal milieu can affect patients with prolactinomas, especially macroadenomas, to cause an increase in size in a minority of patients. Complications are treated with bromocryptine. Enlargement of GH-secreting tumors with acromegaly may respond to bromocryptine and possibly to octreotide. Pituitary tumors causing Cushing's syndrome may need removal if major complications develop. Hypopituitarism during pregnancy may be the result of lymphocytic hypophysitis or antepartum pituitary necrosis, and in the postpartum period may be because of postpartum hemorrhage and pituitary necrosis. These abnormalities need prompt recognition and hormonal replacement therapy with neurosurgical decompression to avoid serious morbidity and mortality. Posterior pituitary problems in pregnancy usually manifest by diabetes insipidus, with a pregnancy-specific variety resulting from excessive degradation of AVP by placental vasopressinase. The condition is treated with an analogue dDAVP, which is resistant to vasopressinase.

Female↗
PubMed1994

Human insulin-like growth factor I receptor internalization. Role of the juxtamembrane domain.

Cytoplasmic submembrane domains of the insulin-like growth factor I (IGF-1) receptor ranging from glycine 940 to proline 959 were investigated for their role in endocytosis of the IGF-1 ligand in rat pituitary GC cells stably expressing mutant human IGF-1 receptors. Replacement of each of three tyrosine residues within the juxtamembrane domain reduced the internalization rate (Ke) by 33% (943Y-->A), 47% (950Y-->A), and 41% (957Y-->A), respectively. Other substitutions within the submembrane region variably retarded receptor-mediated IGF-1 ligand endocytosis. Thus, each amino acid appears to independently contribute to the overall ligand-stimulated IGF-1 receptor internalization rate. The effect of receptor occupancy on IGF-1 receptor endocytosis was also tested. The rate of 125I-labeled IGF-1 internalization by transfectants overexpressing the wild type IGF-1 receptor was rapid but decreased markedly in the presence of increasing unlabeled IGF-1 (ED50 = 44,000 receptors/cell). Substitution by alanine for any of the three submembrane tyrosines increased the ED50 to > 56,000 receptors/cell, decreased the slope (Kic), and had a variable effect on Vmax in the presence of increasing unlabeled IGF-1. In contrast, 125I-labeled IGF-1 endocytosis by the mutant kinase-deficient 952STOP cells was slow and not further retarded by unlabeled IGF-1. These results suggest that ligand-mediated internalization of the human IGF-I is consistent with saturable interactions between the IGF-I receptor juxtamembrane region (glycine 940-tyrosine 957) and components of the endocytic apparatus.

Amino Acid Sequence↗
PubMed1994

Dominant negative inhibition of tumorigenesis in vivo by human insulin-like growth factor I receptor mutant.

Although insulin-like growth factor I (IGF-I) is a mitogenic growth factor, its role in tumorigenesis is unclear. We therefore transfected wild-type and truncated beta-subunit mutant (952STOP) human IGF-I receptor cDNAs into Rat-1 fibroblasts. Rat-1 transfectants expressed 2.5- to 7-fold increased IGF-I receptor mass, while the Kd for IGF-I binding was unchanged. The Rat-1 cells transfected with wild-type receptor cDNA responded to in vitro IGF-I treatment by increased proliferation and DNA synthesis. Cells overexpressing wild-type receptors were also transformed as evidenced by ligand-dependent colony proliferation in soft agar. After injection into athymic nude mice, all wild-type transfectants formed solid sarcomas within 3 weeks, and ex vivo tumor cell assays confirmed continued overexpression of human IGF-I receptors. In contrast, both DNA synthesis and proliferation of 952STOP-transfected cells were attenuated below that of untransfected cells. 952STOP cells were nonresponsive to IGF-I in vitro and were unable to sustain anchorage-independent growth. No tumors were induced for up to 8 weeks after injection of 952STOP transfectants into athymic mice, despite the presence of demonstrable endogenous IGF-I receptors on the 952STOP-transfected cells. Therefore, 952STOP behaves as a dominant negative inhibitor of endogenous IGF-I receptor function, probably by assembling nonfunctional hybrid rat/mutant human receptor tetramers.

Animals↗
PubMed1994

Grouping of porcine enteroviruses by indirect immunofluorescence and description of two new serotypes.

Porcine enteroviruses (PEV) types 1-11 were assigned to three serologic groups by indirect immunofluorescence (IIF). Serotype group I consists of PEV types 1-7 and 11 and is correlated with CPE-type I. Serotype group II is represented by PEV type 8, producing CPE-type II, while PEV types 9 and 10 are classified as serotype group III and cause CPE-type III. Three PEV isolates from the central nervous system of pigs with polioencephalomyelitis were assigned to serotype group I by IIF but to none of the established 11 serotypes by cross-neutralization. It is concluded that these isolates are representatives of two new PEV types for which the designation PEV12 and 13 is suggested.

Animals↗
PubMed1994

H-ras mutations in human pituitary carcinoma metastases.

Molecular mechanisms of pituitary tumorigenesis were studied using Polymerase chain reaction-single stranded conformational polymorphism with DNA sequencing to identify potential mutations in the ras protooncogenes and the tumor suppressor gene p53 in invasive pituitary adenomas and carcinomas. Sequencing of exons 5 through 8 of the p53 gene revealed no mutations, nor were mutations detected in the N- or K-ras protooncogenes in four of the carcinomas and their respective metastatic deposits. Point mutations of H-ras however, were identified in three distant metastatic pituitary tumor secondaries, but not in their respective primary pituitary carcinomas, or in six invasive adenomas. Two of the mutations included a G to C substitution at codon 12, and a G to A substitution at codon 18, resulting in a glycine to arginine, and an alanine to threonine change at these amino acids, respectively. A third mutation involved a single base pair (adenine) deletion in codon 3 of H-ras which causes a frame shift, resulting in a termination signal at codon 19. These results suggest that point mutations in p53 and ras are not associated with pituitary tumorigenesis, however, point mutations of the H-ras gene may be important in the formation and or growth of pituitary metastases. This observed genomic instability will be of value in predicting the potential metastatic behavior of these aggressive pituitary tumors.

Adenoma↗
PubMed1994

Insulin-like growth factor-1 activation of extracellular signal-related kinase-1 and -2 in growth hormone-secreting cells.

Intracellular pathways mediating feedback regulation by insulin-like growth factor-1 (IGF-1) of pituitary GH gene expression remain incompletely understood. Extracellular signal-related kinases (ERKs), a family of serine/threonine kinases, are activated by tyrosine kinase-associated growth factor receptors. To further define the IGF-1 postreceptor events occurring in GH-secreting cells, we investigated the activity of ERKs in response to IGF-1 in GC cells following stable transfection with either wild type human IGF-1 receptor cDNA (WT cells) or a mutant cDNA encoding a truncated, kinase-defective IGF-1 receptor with a dominant negative effect on endogenous receptor function (952STOP cells). Zymography of immunoprecipitated ERKs in myelin basic protein (MBP)-containing polyacrylamide gels demonstrated dose-dependent induction of ERK-1 and -2 activity by IGF-1 in GC cells with maximal activity occurring at 6 min. IGF-1-induced ERK activity in WT-transfected cells was up to 80-fold basal and 4-fold that observed in GC cells. 952STOP cells expressing the tyrosine kinase-deficient receptor were refractory to IGF-1 action, demonstrating minimal ERK induction. In contrast, 12-O-tetradecanoylphorbol 13-acetate stimulated ERK activity to the same degree in all three cell types regardless of their IGF-I receptor status. Forskolin (50 microM), isobutylmethylxanthine (0.5 mM), and forskolin/isobutylmethylxanthine in combination attenuated IGF-1-induced ERK activity in WT cells by 54, 55, and 75% respectively. The rapid, dose-dependent, and IGF-1 receptor-dependent activation of ERKs and the attenuation of this effect by cAMP suggest an interrelated role for both molecules in IGF-1 signal transduction in GH-secreting cells.

Animals↗
PubMed1994

Hypercalcemia, parathyroid hormone-related protein expression and human T-cell leukemia virus infection.

Adult T-cell leukemia (ATL) associated with HTLV-1 infection is characterized by the development of hypercalcemia in over two thirds of patients. Dysregulation of cellular gene transcription by viral proteins is an emerging paradigm for molecular pathogenesis of disease. A recent example is the parathyroid hormone-related protein (PTHrP) gene, which has been implicated in the hypercalcemia of ATL, and is transactivated by the HTLV-1 tax and HTLV-11 tax proteins. PTHrP is expressed at high levels in leukemia cells derived from ATL patients, as well as in asymptomatic HTLV-1 positive carriers. This article reviews the interaction of the HTLV-1 transcriptional regulator tax with the PTHrP promoter. Tax mediates its effects on PTHrP via cellular transcription factors AP-2 and AP-1, and transactivation via an AP-2 motif represents a novel interaction of tax with a cellular transcription factor.

Deltaretrovirus Infections↗
PubMed1994

[Typing of 17 porcine enterovirus isolates from polio encephalomyelitis cases during the years 1983-1991].

Seventeen strains of porcine enteroviruses (PEV) were isolated from organs of 119 pigs with symptoms of polioencephalomyelitis submitted to the State Veterinary Institute Arnsberg/Westphalia between 1983 and 1991. 15 isolates originated from the central nervous system and 2 from organ suspensions made up of a brain-spleen-pool and a lung-spleen-lymph node-pool, respectively. Isolates were assigned to 7 PEV types which were present at the following frequencies: PEV1: 2x; PEV2: 6x; PEV4: 3x; PEV5: 1x; PEV6: 2x; PEV 12: 1x; PEV 13: 2x. Mortality rates of affected groups exhibited an age-dependent curvilinear relationship suggesting that the PEV involved possessed a rather similar low to medium grade neurovirulence, irrespective of type. Exceptions were 1 herd with 100% mortality at the age of 10-18 weeks from which PEV2 strain 6793/83 was isolated (described earlier) and a second herd with 18% mortality at the age of 14-18 weeks from which PEV types 1, 2 and 4 were recovered. Sensitivity of 5 cell lines for the isolation of PEV was compared. Rates of isolation from organ suspensions which had proved positive in any of the cell lines tested were as follows: PS-EK: 77%; IB-RS-2: 63%; ST: 56%; PK-15: 47%; BHK21 (CT): 10%.

Animals↗
PubMed1993

Cell-type-specific transactivation of the parathyroid hormone-related protein gene promoter by the human T-cell leukemia virus type I (HTLV-I) tax and HTLV-II tax proteins.

The human T-cell leukemia virus type I (HTLV-I) and HTLV-II Tax proteins are potent transactivators of viral and cellular gene expression. Using deletion mutants, the downstream parathyroid hormone-related protein (PTHrP) promoter is shown to be responsive to both HTLV-I and HTLV-II Tax as well as the AP1/c-jun proto-oncogene. Transactivation of PTHrP by Tax was seen in T cells but not in B-cell lines or fibroblasts. A carboxy terminal Tax deletion mutant was deficient in transactivation of both the PTHrP and IL2R alpha promoters but not the HTLV-I long terminal repeat (LTR). Exogenous provision of NFkB rescued IL2R alpha expression but not the PTHrP promoter. Thus, HTLV-I Tax, HTLV-II Tax, and c-jun transactivate PTHrP and may contribute to the pathogenesis of hypercalcemia in adult T-cell leukemia.

Animals↗
PubMed1993

A review of the clinical indications for the plasma heparin assay.

The basis for the clinical indications for the use of the plasma heparin assay for anticoagulation control are reviewed, and alternatives for currently used laboratory methods of monitoring heparin therapy in selected clinical situations are recommended. Many literature references support the role of plasma heparin assay with combined heparin and warfarin therapy, with combined heparin and recombinant tissue plasminogen activator therapy, in situations in which heparin resistance is noticed in the presence of a circulating anticoagulant, and in patients receiving heparin in an unrecognized manner, as well as with the use of the low molecular weight heparins. For now, however, in the absence of any prospective clinical trials establishing the superiority of the plasma heparin assay compared with the APTT, the recommendations outlined are presented as guidelines for the more specific monitoring of heparin therapy using currently available techniques.

Blood Coagulation Disorders↗
PubMed1993

Rat pituitary GC cell insulin-like growth factor-I receptor regulation.

Exposure of rat GC pituitary cells to insulin-like growth factor-I (IGF-I) resulted in a time- and concentration-dependent reduction in cell surface IGF-I receptor binding. Preincubation of cells with 6.5 nM IGF-I for 24 h caused an approximately 50% reduction of the number of cell surface receptors. Scatchard analysis revealed that the number of IGF-I cell surface receptors decreased from 18,500 to 9,100 sites/cell, with no apparent alteration in the affinity of IGF-I receptor for its ligand. The level of IGF-I receptor mRNA, however, was not altered by preincubating cells for up to 24 h with 6.5 nM IGF-I. The sequestered IGF-I receptors reappeared on the cell membrane and return to their preincubation surface distribution within 3 h after removal of IGF-I. These results support the notion that down-regulation of somatotroph IGF-I receptors involves translocation of cell surface receptors to the intracellular pool, and this effect is reversed by removal of IGF-I ligand.

Animals↗
PubMed1993

Structure-function of the human insulin-like growth factor-I receptor: a discordance of somatotroph internalization and signaling.

Insulin-like growth factor-I (IGF-I), a GH-dependent growth factor, suppresses GH secretion by pituitary cells. To clarify the role of ligand-mediated receptor internalization for IGF-I signaling to GH, human IGF-I receptor (IGF-IR) cDNAs mutated in the beta-subunit were stably transfected into GC rat pituitary cells. Overexpression of wild-type IGF-IR markedly enhanced IGF-I suppression of GH 4-fold (P < 0.005) compared to that of untransfected cells. A mutant IGF-IR with a 943Tyr-->Ala substitution in the IGF-IR submembrane domain only partially suppressed GH (73% of IGF-IR wild type), while replacement of 957Tyr-->Ala or 940Gly-->Ala produced IGF-IRs that retained enhanced IGF-I signaling to GH. Substitution of 950Tyr-->Ala or 1003Lys-->Ala in the human IGF-IR beta-subunit failed to enhance IGF-I signaling to GH above that of untransfected cells. Intracellular phosphorylation of insulin-responsive substrate-I by these mutant IGF-IRs paralleled the observed IGF-I suppression of GH, with no phosphorylation of IRS-I by 950Tyr-->Ala. Ligand-mediated receptor internalization, however, was not reduced by substitution of either 943Tyr-->Ala or 950Tyr-->Ala. In contrast, substitution of 957Tyr-->Ala reduced the internalization of labeled IGF-I to 35% that of wild-type IGF-IR. Substitution of 1003Lys-->Ala abolished IGF-IR internalization, as expected. These results demonstrate that both 950Tyr and 943Tyr are important for IGF-I signaling to GH and that IGF-IR internalization is discordant for IGF-I signaling to the GH gene.

Animals↗
PubMed1993

Interaction between insulin and thyroid hormone in rat pituitary tumour cells: insulin attenuates tri-iodothyronine-induced growth hormone mRNA levels.

Insulin has previously been shown to inhibit basal and stimulated rat GH (rGH) secretion as well as basal GH transcription in rat pituitary cells. The effect of physiological doses of insulin on tri-iodothyronine (T3)-stimulated GH mRNA levels in rat pituitary tumour cells was therefore examined. Insulin (7 nmol/l) suppressed T3-stimulated GH mRNA levels in GC and GH3 rat pituitary tumour cells by 58%. This inhibitory effect of insulin on T3-stimulated GH mRNA levels was already present after 24 h of treatment, and persisted for at least 48 h after insulin treatment was withdrawn. The effect of insulin on GH mRNA was selective, as rat prolactin mRNA was stimulated by insulin and T3 in the same cells. Treatment of cells with cycloheximide (10 mumol/l) did not alter the attenuation of GH mRNA levels by insulin, indicating that the insulin effect is independent of new protein synthesis. When de-novo mRNA synthesis was blocked with actinomycin D (4 micrograms/ml) for up to 7 h, an additional decrease in the relative amount of GH mRNA levels was observed after 24, 48 and 72 h of insulin treatment, indicating that an effect of insulin on GH mRNA stability is likely. The results show that physiological doses of insulin selectively attenuate the stimulatory effect of T3 on GH mRNA levels. This suppressive effect of insulin occurs independently of protein synthesis and is presumably mediated both at a transcriptional and post-transcriptional level.

Animals↗
PubMed1992

Human insulin-like growth factor I receptor 950tyrosine is required for somatotroph growth factor signal transduction.

Insulin-like growth factor I (IGF-I), a growth hormone (GH)-dependent growth factor exerts feedback regulation of GH by inhibiting GH gene expression. IGF-I inhibition of GH secretion is enhanced 3-5-fold in GC rat pituitary cells overexpressing the wild type 950Tyr human IGF-I receptor which autophosphorylates appropriately. To determine the critical amino acid sequence responsible for IGF-I signaling, insertion, deletion, and site-directed mutants were constructed to substitute for 950Tyr in exon 16 of the human IGF-I receptor beta-subunit transmembrane domain. All mutant transfectants bound IGF-I with a similar Kd to untransfected cells but had markedly increased (7-34-fold) IGF-I-binding sites. GH responsiveness to IGF-I was tested in mutant transfectants. Overexpressed site-directed and insertion mutant IGF-I receptors exhibited a modest suppressive effect on GH in response to the IGF-I ligand, similar to that observed in untransfected cells. Deletion mutant (IG-FIR delta 22) (amino acid 944-965) did not transduce the IGF-I signal to the GH gene. Site-directed and insertion mutants therefore did not enhance the IGF-I response of the endogenous rat receptor, unlike the 950Tyr wild type transfectants which enhanced the IGF-I signal. All mutant transfectants, except the deletion mutant, internalized radioactive ligand similarly to 950Tyr wild type transfectants. 950Tyr of the human IGF-I receptor is therefore required for IGF-I signal transduction in the pituitary somatotroph, but not for IGF-I-mediated internalization.

Amino Acid Sequence↗