PCR bias toward the wild-type k-ras and p53 sequences: implications for PCR detection of mutations and cancer diagnosis

PCR-based cancer diagnosis requires detection of rare mutations in k-ras, p53 or other genes. The assumption has been that mutant and wild-type sequences amplify with near equal efficiency, so that they are eventually present in proportions representative of the starting material. Work on factor IX suggests that this assumption is invalid for one case of near-sequence identity. To test the generality of this phenomenon and its relevance to cancer diagnosis, primers distant from point mutations in p53 and k-ras were used to amplify wild-type and mutant sequences from these genes. A substantial bias against PCR amplification of mutants was observed for two regions of the p53 gene and one region of k-ras. For k-ras and p53, bias was observed when the wild-type and mutant sequences were amplified separately or when mixed in equal proportions before PCR. Bias was present with proofreading and non-proofreading polymerases. Mutant and wild-type segments of the factor V, cystic fibrosis transmembrane conductance regulator and prothrombin genes were amplified and did not exhibit PCR bias. Therefore, the assumption of equal PCR efficiency for point mutant and wild-type sequences is invalid in several systems. Quantitative or diagnostic PCR will require validation for each locus, and enrichment strategies may be needed to optimize detection of mutants.

Analysis and application of an equilibrium model for in vitro bioassay systems with three components: receptor, hormone and hormone-binding-protein

A simple theoretical framework is presented for bioassay studies using three component in vitro systems. An equilibrium model is used to derive equations useful for predicting changes in biological response after addition of hormone-binding-protein or as a consequence of increased hormone affinity. Sets of possible solutions for receptor occupancy and binding protein occupancy are found for typical values of receptor and binding protein affinity constants. Unique equilibrium solutions are dictated by the initial condition of total hormone concentration. According to the occupancy theory of drug action, increasing the affinity of a hormone for its receptor will result in a proportional increase in biological potency. However, the three component model predicts that the magnitude of increase in biological potency will be a small fraction of the proportional increase in affinity. With typical initial conditions a two-fold increase in hormone affinity for its receptor is predicted to result in only a 33% increase in biological response. Under the same conditions an 11-fold increase in hormone affinity for receptor would be needed to produce a two-fold increase in biological potency. Some currently used bioassay systems may be unrecognized three component systems and gross errors in biopotency estimates will result if the effect of binding protein is not calculated. An algorithm derived from the three component model is used to predict changes in biological response after addition of binding protein to in vitro systems. The algorithm is tested by application to a published data set from an experimental study in an in vitro system (Lim et al., 1990, Endocrinology 127, 1287-1291). Predicted changes show good agreement (within 8%) with experimental observations.

Expression of growth hormone receptors by lymphocyte subpopulations in the human tonsil

The ability of human tonsillar lymphoid cells to express growth hormone receptor (hGH-N-R) was analyzed by flow cytometry. FITC-coupled recombinant human growth hormone (hGH-N) was used to reveal the receptors, in combination with phenotype markers. Unlike T cells, tonsillar B cells constitutively express the hGH-N receptor. Quiescent cells separated from activated cells by Percoll-gradient centrifugation bear fewer receptors than activated ones. Activated T cells express hGH-N-R, but the typical germinal centre CD4+ CD57+ T cells do not. These latter thus appear not to be fully activated. Inside the lymph follicles, the germinal centre CD38+ B-cell population and the mantle-zone CD39+ B-cell population display similar levels of hGH-N-R expression, but receptor density is lower on dividing dark-zone CD38+ CD10+ B cells. Different lymphoid-cell populations thus differ markedly in their ability to express the growth hormone receptor, in relation notably to their activation status. This highlights the link between the neuroendocrine system and the active immune defense.

Growth hormone-binding protein in normal and pathologic gestation: correlations with maternal diabetes and fetal growth

To date, measurements of GH-binding protein (GHBP) during human pregnancy have been carried out using assays susceptible to interference by the elevated levels of human placental GH typical of late gestation. We recruited a large cohort of pregnant women (n = 140) for serial measurements of GHBP and used the ligand immunofunctional assay for GHBP. For normal gravidas, GHBP levels fell throughout gestation. Mean levels were 1.07 nmol/L (SE = 0.18) in the first trimester, 0.90 nmol/L (SE = 0.08) at 18-20 weeks, 0.73 nmol/L (SE = 0.05) at 28-30 weeks, and 0.62 nmol/L (SE = 0.06) at 36-38 weeks. GHBP levels in the first trimester correlated significantly with maternal body mass index (r = 0.58; P < 0.01). GHBP levels in pregnancies complicated by noninsulin-dependent diabetes mellitus (NIDDM) were substantially elevated at all gestational ages. The mean value in the first quarter (2.29 nmol/L) was more than double the normal mean (P < 0.01). In contrast, patients with insulin-dependent diabetes mellitus (IDDM) showed reduced GHBP concentrations at 36-38 weeks. The correlation between body mass index and GHBP is consistent with a metabolic role for GHBP during pregnancy, as is the dramatic elevation in GHBP observed in cases of NIDDM. At 36 weeks gestation, GHBP was significantly elevated (P < 0.01) in those women whose neonates had low birth weight (< 10th percentile). In early gestation (< 14 weeks), GHBP tended to be higher in women whose fetuses were designated to be at risk of intrauterine growth retardation (1.39 nmol/L; n = 4; compared with 1.07 nmol/L in normals), but this did not reach statistical significance. Although both NIDDM and IDDM pregnancies are at risk of fetal macrosomia, their GHBP concentrations are markedly divergent. This paradox and the roles of glucose and insulin in the regulation of GHBP during gestation warrant further investigation.

Down-regulation of a novel form of fibroblast growth factor receptor 1 in human breast cancer

Monoclonal antibodies against two epitopes of FGFR-1 have been used to investigate FGFR-1 expression in the normal and neoplastic human breast. Different forms are detected in the different cell types constituting the normal breast. Moreover, breast cancer cells lack one form of FGFR-1. Western blot analysis showed 115-kDa and 106-kDa forms of FGFR-1 within the human breast. The 115-kDa band corresponds to the beta form of FGFR-1, whereas the 106-kDa band is truncated at the carboxyl terminus. The 106-kDa form of FGFR-1 is the major form present in breast fibroblasts and myoepithelial cells, whereas epithelial cells contain equal amounts of the 115-kDa and 106-kDa forms. Breast cancer cells, however, appear to contain only the 115-kDa form of FGFR-1. This expression pattern is reflected in malignant and non-malignant tissue samples. Using reverse transcription polymerase chain reaction (RT-PCR) analysis, we have shown that the 106-kDa FGFR-1 isoform is not the previously described alpha 2 receptor that arises from a 25-base pair insertion in the second kinase domain. It is probable that the 106-kDa FGFR-1 has different signalling properties to the full-length receptor, having lost at least one tyrosine at amino acid 766, which is required for phospholipase C activation. This form of FGFR-1 appears to be lost in all breast cancer cells analysed and its absence may have a bearing on malignancy.

AIDS and prehospital personnel: knowledge and prevention of occupational exposure

OBJECTIVES

Prehospital personnel, including law enforcement officers, paramedics, and fire-fighters, may be exposed to the human immunodeficiency virus (HIV) while working. This study of prehospital personnel sought to determine: 1) their knowledge of the acquired immune syndrome (AIDS) and HIV transmission; 2) the extent of AIDS training received; 3) self-assessment of risk for HIV infection; and 4) precautions adopted to reduce occupational risk of exposure to HIV.

METHODS

A survey was administered to pre-hospital personnel in a large Southern California jurisdiction. The response rate was 41% (n = 1,756) in 10 city and county departments where respondents were employed. Law enforcement officers (44%), firefighters (44%), and paramedics (12%) comprised the sample.

RESULTS

Respondents had accurate knowledge about AIDS, but incorrect perceptions about HIV transmission. A minority believed that HIV could be contracted from casual contact. Training relating to AIDS was not frequent. Preventive practices were infrequent in the work setting, with precautions used less than 50% of the time on eight of 10 measures. One-third of these prehospital personnel assessed their risk for HIV infection as medium to high, largely attributable to fear of occupational exposure.

CONCLUSIONS

Improved educational programs regarding HIV/AIDS are needed for prehospital personnel to increase the use of preventive occupational practices in the field.

Human growth hormone fragments 1-43 and 44-191: in vitro somatogenic activity and receptor binding characteristics in human and nonprimate systems

Human GH (hGH) fragments 1-43 and 44-191 have potent in vivo effects on glucose homeostasis in rodents but cannot stimulate body growth. To assess the in vitro bioactivity of these hGH fragments we tested their activity against GH-responsive FDC-P1 cell lines expressing full-length human (h), mouse (m), or rabbit (r) GH receptors (GHR). Binding specificity and affinity was tested using GHR-containing membrane preparations from three species and recombinant hGH binding protein (hGHBP). Recombinant hGH 1-43 and recombinant 44-191 stimulated proliferation of FDC-P1-hGHR cells with half-maximal effect at approximately 2000 and 100 nM, respectively, whereas intact hGH stimulates proliferation of FDC-P1-hGHR cells with ED50 of 0.02-0.03 nM. However, these fragments had minimal effect on cells expressing mGHR or rGHR. Although 44-191 did not stimulate proliferation of FDC-P1-rGHR cells, when added to these cells in the presence of 0.23 nM hGH, it antagonized hGH action in a dose-dependent manner (ED50 at 230 nM). Binding of these GH fragments was compared using membrane preparations from rabbit liver, rabbit and mouse adipose tissue, and recombinant hGHBP. Binding competition curves were consistent, with 44-191 having at least a 10-fold lower affinity for rabbit liver GHR and rabbit adipose GHR than bovine GH and a 61-fold lower affinity for hGHBP than hGH. Binding of hGH 1-43 could not be demonstrated to GHRs in rabbit liver microsomes, adipose microsomes, or to hGHBP. HGH 1-43 did not compete for insulin binding sites in adipose microsomes. In conclusion, hGH 44-191 binds with low affinity to the GHR and at supraphysiologic levels stimulates proliferation of FDC-P1-hGHR cells. At high doses, 44-191 can also antagonize GH action in FDC-P1-rGHR cells, presumably by blocking receptor dimerization. Binding of 1-43 to GHR could not be detected, and the basis for its weak in vitro mitogenic effect remains to be elucidated. The low affinity of the fragments for cloned GHRs and low biopotency in these systems suggests that the metabolic actions of these fragments are unlikely to be mediated by the cloned GHR. This raises the possibility of a separate receptor mediating metabolic effects of these fragments.

The effects of weight reduction to ideal body weight on body fat distribution

Obesity is a well-known health risk factor. Several studies have demonstrated that upper-body fat distribution plays a major role in the association between increased adiposity and metabolic disorders. The present study was undertaken to evaluate changes in intraabdominal and subcutaneous fat areas in obese subjects undergoing a weight reduction to their ideal body weight (IBW), as defined by a body mass index (BMI) no greater than 21 or body fat less than 30%, and compare the fat distribution at IBW with that of never-obese control subjects. We studied 33 obese women (151% +/- 1% of IBW; BMI, 31.6 +/- 2.5 [mean +/- SE]) before and after weight loss and a control group of 16 never-obese women (101.0% +/- 1.0% of IBW; BMI, 21.2 +/- 1.1). Eighteen obese women successfully achieved and stabilized at IBW for at least 2 months. Nonsuccessful obese subjects were significantly younger than reduced-weight subjects, but other physical characteristics were similar. In obese, reduced-obese, and never-obese groups, weight was 85 +/- 2.0, 62 +/- 1, and 58 +/- 1 kg; percent body fat was 41% +/- 1%, 24% +/- 2%, and 23% +/- 1%; intraabdominal fat area was 82 +/- 5, 28 +/- 3, and 25 +/- 4 cm2; waist subcutaneous fat area was 275 +/- 15, 120 +/- 9, and 81 +/- 7 cm2; hip subcutaneous fat area was 416 +/- 17, 204 +/- 10, and 195 +/- 7 cm2; and waist to hip ratio (WHR) was 0.84 +/- 0.02, 0.77 +/- 0.01, and 0.73 +/- 0.01, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Upregulation of GH receptor and GH binding protein during pregnancy in the GH deficient rat

During pregnancy there are dramatic changes in the endocrine and metabolic status of the mother: growth hormone (GH) is an important regulator of growth and development. A proportion of GH is bound by specific GH binding proteins (GHBP) that closely resemble the GH receptor (GHR). In the rodent both GHBP and the GHR are considered to be GH dependent, and consequently during pregnancy the increase in serum GH is associated with an increase in GHBP. To examine whether an increase in maternal GH is obligatory for elevation of maternal GHBP or GHR during pregnancy, we used a unique GH-deficient (GHD) strain of rats, to avoid the methodological complications of hypophysectomy and assessed serum GH, GHBP and hepatic GHR binding during the course of pregnancy. In GH normal rats, serum GH concentrations increased twofold and GHBP levels increased threefold; there was no change in hepatic GHR binding. In GHD rats, serum GH concentrations were low and did not increase during pregnancy. Nonetheless, levels of both serum GHBP and hepatic GHR binding increased to that measured in normal rats. Thus, an increase in maternal GH concentration is not required for the gestational upregulation of maternal GHBP or hepatic GHR binding, suggesting that other hormones may be essential in modulating the GH axis during pregnancy.

A growth hormone agonist produced by targeted mutagenesis at binding site 1. Evidence that site 1 regulates bioactivity

Growth hormone (GH) is believed to signal by dimerizing its receptor through two binding sites on the hormone. Previous attempts to increase the biopotency of GH by increasing its site 1 affinity have been unsuccessful, which has led to a bias toward engineering site 2 interactions in the quest for creation of super agonists. Here we report that increasing site 1 affinity can markedly increase proliferative bioactivity in FDC-P1 cells expressing full-length GHR. In contrast, we find three site 1 mutants with affinities for site one similar to or greater than wild type GH, which have markedly decreased bioactivity. Through crystal structure analysis of the receptor interactive regions of these GH analogues, we are able to suggest why previous mutagenesis on human GH failed to improve biopotency, and thus provide a new avenue for GH and cytokine agonist design.

Control of growth hormone (GH) binding protein release from human hepatoma cells expressing full-length GH receptor

In humans and rabbits, the circulating GH binding protein (GHBP) is released from the GH receptor by cleavage at a site proximal to the cell surface. There is evidence that GHBP status is predictive of GH responsiveness, presumably because it reflects GH receptor status. This assumes that GHBP release is not a regulated step. Here we report a model for study of GHBP release that provides some insight into this question. Human HepG2 cells were stably transfected with rabbit GH receptor and shown to be responsive to nonprimate (bovine) GH, indicating functionality of the transfected receptor. These cells released GHBP of the expected size, and this release could be increased by incubation with a phorbol ester, which stimulated receptor synthesis through the cytomegalovirus promoter. We surveyed a wide range of protease inhibitors both with and without streptolysin-O permeabilization, with the intention of defining the endogenous protease. Of 16 inhibitors, only benzamidine proved an effective inhibitor of release, indicating the existence of a novel protease. We could increase GHBP release with a membrane impermeable thiol blocker, suggesting activation of a membrane protease. We examined the ability of IGF-1, insulin, dexamethasone, sex steroids, and T4 to influence GHBP release. Although these agents are known to be effective in the parent hepatoma line, none were effective in modulating GHBP release, although GH itself decreased release by around 30% as assessed with a ligand immunofunctional assay. We conclude that GHBP release appears to be constitutive in this model and driven by receptor availability. This is consistent with an in vivo situation where circulating GHBP provides an index of hepatic receptor expression.

Measurement of growth hormone-binding protein in the rat by a ligand immunofunctional assay

We have developed a ligand immunofunctional assay (LIFA) for quantifying the circulating functional GH-binding protein (GHBP) in the rat. This two-site solid-phase assay uses a capture monoclonal antibody (4.3) specific to the hydrophilic C-terminal segment of rat GHBP (rGHBP), saturation of binding with human GH, and a detection system of rabbit antihuman GH polyclonal antibody and peroxidase-conjugated antirabbit immunoglobulin G antibody. Results were compared with Scatchard estimates derived by immuno-precipitation with monoclonal antibody 4.3. This assay was used to determine the GHBP levels in male and female rats and to investigate the diurnal properties and dynamics of GH and GHBP interaction in 15-min blood sampling over a 6-h period. The dynamic range of the rLIFA was 0.15-20.0 nM recombinant rGHBP, with intraassay and interassay coefficients of variation of 10.5% (n = 20) and 12.9% (n = 12), respectively. Serum GHBP levels determined by the rLIFA and those derived from Scatchard estimates were strongly correlated (n = 8; beta = 0.55; r2 = 0.89; P = 0.0005). Male rats had lower GHBP levels (6.5 +/- 0.7 nM; mean +/- SE; n = 14) than female rats (35.4 +/- 2.7 nM; n = 15; P = 0.0001). In the diurnal study, male rats had higher GH peaks (312.5 +/- 121.6 ng/ml; n = 7) than female rats (96.5 +/- 15.4 ng/ml; n = 9; P < 0.0001). In contrast to the pulsatile secretion of GH, GHBP levels in both sexes remained stable and showed no relationship to secretory pulses of GH. However, the GH bursts significantly altered the distribution of the GH-GHBP complex in male rats. By saturation and mass analysis, the greater GH pulsatile secretion in male rats resulted in occupancy of GHBP from less than 5% at nadir to about 80% at secretory peaks, in contrast to the less than 5-15% range of GHBP occupancy in female rats. In male rats, greater than 80% of GH at secretory peaks existed in the free form, whereas in female rats, 16-23% of GH existed in the free form during pulsatile secretion. In summary, the rLIFA shows good correlation to Scatchard analysis using an identical antibody. We conclude that this assay provides a rapid, sensitive, and accurate measurement of the circulating functional GHBP in the rat, and that it facilitates the study of GH and GHBP dynamics under a range of physiological conditions.

Serum growth hormone binding protein and hepatic GH binding sites in the Lewis dwarf rat: effects of IGF-I and GH

A radioimmunoassay (RIA) for the rat growth hormone binding protein (GHBP) was developed using a synthetic peptide (corresponding to the hydrophilic carboxyl-terminal sequence of mouse GHBP) as standard and a monoclonal antibody (MAb 4.3) reactive with this peptide as the primary antibody. The values for GHBP concentration obtained for normal rats using this assay compare favourably with those obtained by gel filtration and ELISA methods. The concentration of GHBP in normal male rats at 11 weeks of age (680 +/- 30 ng/ml, SEM, n = 9) was significantly less than the concentration in normal females (943 +/- 47 ng/ml, SEM, n = 25). In 11-week-old dwarf male rats the concentration of GHBP was 423 +/- 35 ng/ml (n = 8); less than in dwarf females (542 +/- 32, P < 0.05, n = 9) and normal males (680 +/- 30, P < 0.001, n = 9). The GHBP concentration in dwarf rats was not age-dependent, whereas in normal females the concentration of GHBP increased with age. The availability of an RIA which is not susceptible to interference by endogenous GH, will facilitate further studies on hormonal and nutritional regulation of the rat GHBP. The assay was applied to studying the effects of IGF-I infusion (240 micrograms/day for 1 week) and GH injection (65 micrograms/100 g body weight, twice daily for 1 week and 4 weeks) on the serum concentration of GHBP in 11-week-old Lewis dwarf rats. Hepatic GH binding sites were also measured in desaturated membranes from the same animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for involvement of the carboxy terminus of helix 1 of growth hormone in receptor binding: use of charge reversal mutagenesis to account for calcium dependence of binding and for design of higher affinity analogues

In this study we have demonstrated that the C-terminus of helix 1 of porcine GH (pGH) is a receptor-interactive region, thus extending the current binding site model of GH. This was achieved by introducing charge reversal mutations into this region of pGH, which influenced receptor affinity and Ca2+ dependence of binding. The first mutant (R34E pGH, conversion of Arg 34 to Glu) introduced a putative Ca2+ binding site which is present in human GH (hGH) [Barnard et al. (1989) J. Theor. Biol. 140, 355-367] and sits opposite E220 of receptor subunit 1. This mutant exhibited increased Ca2+ dependence of receptor binding but even at optimal Ca2+ did not display higher than wild-type affinity. Introduction of a second Ca2+ binding site adjacent to the first by a second charge reversal (K30E R34E pGH) further increased Ca2+ dependence of binding and also increased affinity for the rabbit GH receptor (2.4 +/- 0.4)-fold relative to wild-type pGH at optimal Ca2+. Equilibrium dialysis and Scatchard analysis of binding of 45Ca2+ to pGH and K30E R34E pGH revealed two Ca2+ binding sites on wild-type pGH and an additional two Ca2+ binding sites on the K30E R34E pGH mutant (Kd 0.5-0.8 mM), as predicted. A third partial charge reversal mutant in the fourth helix (H170D) also led to enhanced Ca2+ dependence of binding, supporting our proposal that E34 and D170 are responsible for the Ca2+ dependence of hGH binding to the rabbit GH receptor. Examination of the crystal structure shows that E34 and D170 are in close proximity and would interact repulsively with a cluster of acidic residues on the receptor consisting of E126, E127, and E220 unless neutralized by Ca2+ or an introduced basic residue. Accordingly, charge reversal at the adjacent pGH residue E33 (E33K pGH) led to a Ca2+ independent (3.0 +/- 0.4)-fold increase in affinity of binding. As well as extending the binding site model of GH, these studies provide a mechanistic explanation for the unique Ca2+ dependence of hGH binding to the rabbit GH receptor. They also indicate that charge reversal can be used to design higher affinity GH analogues and could assist in the mapping of interactive regions in ligand-receptor complexes generally.

Selective inhibition of mouse placental lactogen II secretion by tumour necrosis factor-alpha

The placental members of the prolactin-GH-placental lactogen (PL) gene family of the mouse include mPL-I, mPL-II, proliferin (PLF) and proliferin-related protein (PRP). The aim of the present study was to assess the effects of tumour necrosis factor-alpha (TNF-alpha) on the secretion of these proteins in primary cultures of placental cells from days 7, 9 and 12 of pregnancy. The effects of epidermal growth factor (EGF) on the secretion of PLF and PRP were also determined. EGF has previously been shown to stimulate mPL-I and inhibit mPL-II secretion. Incubation of placental cells from day 7 of pregnancy for 5 days with 10 nmol human (h)TNF-alpha/l did not affect the mPL-II concentration of the medium, but similar treatment of cells from days 9 or 12 of pregnancy resulted in a significant reduction in the mPL-II concentration of the medium by the second or third day of culture. The intracellular concentration of mPL-II, the number of cells that released mPL-II as assessed by reverse haemolytic plaque assay, and steady-state levels of mPL-II mRNA as assessed by Northern analysis were also reduced by hTNF-alpha treatment. The lowest concentration of hTNF-alpha that significantly inhibited mPL-II secretion by cells from day 12 of pregnancy was 0.01 nmol/l. hTNF-alpha treatment did not affect the secretion of mPL-I, PLF or PRP, as assessed by the concentrations of these proteins in the medium during a 5-day incubation. Incubation of the cells with 20 ng EGF/ml also did not affect the PLF or PRP concentration of the medium during 5 days of culture. To determine whether the effect of hTNF-alpha on mPL-II secretion was mediated by interleukin-6 (IL-6), the IL-6 concentration of the medium of control and hTNF-alpha-treated cells was determined. Bioactive and immunoreactive IL-6 could not be detected in medium from either treatment group. The presence of binding sites for hTNF-alpha was assessed in cells from day 12 of pregnancy. Scatchard analysis detected a single class of binding sites having a Kd of 1.61 +/- 0.34 nmol/l, with about 1350 sites per cell. The results of this study demonstrate that hTNF-alpha inhibits the secretion of mPL-II by placental cells from days 9 and 12 of pregnancy, suggesting that TNF-alpha may be one of the factors that regulate the production of this hormone in vivo.

Differential effect of insulin on whole-body proteolysis and glucose metabolism in normal-weight, obese, and reduced-obese women

The whole-body rate of proteolysis, as indicated by the postabsorptive appearance rate (Ra) of leucine, is increased in obese women. The present study was conducted to examine the hypothesis that the increased proteolysis is explained by insulin resistance, and to determine if proteolysis returns to normal when obese women reduce to normal weight. The mean basal leucine Ra was 21% higher in 31 obese women (> 135% ideal weight) than in 17 normal-weight women, and 9% higher per kilogram lean body mass ([LBM] P > .05). When 17 of the obese women reduced and stabilized at 100% to 116% of ideal weight, their mean basal leucine Ra decreased 17% (7%/kg LBM) and was not significantly different from that of the normal-weight control group. Insulin (40 mU/m2/min) was infused for 2 hours while maintaining euglycemia in eight normal-weight, 14 obese, and eight reduced-obese subjects. Glucose disposal per kilogram LBM was 29% lower in obese than in normal-weight subjects (P < .05) and was normal in the reduced-obese subjects. Insulin suppressed the leucine Ra an average of 18.4% in the control group, 20.4% in the obese group, and 24.1% in the reduced-obese group. Suppression of the leucine Ra by insulin did not correlate with the waist to hip ratio (WHR), glucose disposal rate, or basal leucine Ra. We conclude that the increased basal proteolysis of obese women is reversed by weight loss, and is not caused by insulin resistance.

Expression of growth hormone-binding protein with a hydrophilic carboxyl terminus by the mouse placenta: studies in vivo and in vitro

GH-binding protein (GHBP) or GH receptor is present in numerous extrahepatic tissues in the rodent. From mid- to late gestation in the mouse, the maternal serum concentration of GHBP increases 30- to 50-fold. We have investigated whether the placenta might synthesize GHBP and potentially contribute to this increase. RNA was isolated from placentas and subjected to Northern analysis using a cDNA probe to the shared region of GHBP and GH receptor-encoding mRNAs. From day 8 to day 18 of gestation, the GHBP-encoding mRNA (1.4 kb) increased 45-fold in quantity. The GH receptor-encoding mRNA (4.2 kb) increased sixfold by day 14 and then remained steady until day 18. These changes which were not co-ordinated parallel reported changes in the steady-state concentrations of 1.4 and 4.2 kb mRNAs in maternal liver, suggesting shared regulatory factors. Extracts of freshly isolated trophoblasts were assayed for GHBP with a radioimmunoassay specific for GHBP with a hydrophilic carboxyl terminus. The cytosolic content of immunoreactive GHBP increased fourfold from mid- to late gestation. Trophoblasts were isolated from placentas and cultured for 2 days on collagen gels in defined medium. Cultured cells were at least 90% viable and secreted mouse placental lactogen-II (mPL-II). Immunocytochemistry was carried out simultaneously on cells cultured from day 7 to day 17 of gestation using a monoclonal antibody (MAb 4.3), which recognizes the hydrophilic C-terminus of GHBP. Cell-localized GHBP was present in trophoblasts cultured for 2 days, but GHBP was not detectable by radioimmunoassay or by immunoprecipitation in concentrated culture media from cultures treated with 100 ng mouse GH/ml or 100 ng mPL-II/ml or from untreated cultures. RNA was isolated from cells cultured in an identical manner to those analysed by immunocytochemistry. Three GH receptor/GHBP mRNA species of 8, 4.2 and 1.4 kb were observed. The quantity of 4.2 and 1.4 kb mRNAs did not change significantly in cultures from day 7 to day 15 of gestation but, in cultures from day 17 of gestation, the amount of 1.4 kb mRNA dropped significantly, while that of the 4.2 kb mRNA remained unchanged. GHBP- and GH receptor-encoding mRNAs are not co-ordinately regulated in vivo or in vitro. Although mPL-II was secreted into the medium by cultured trophoblasts, secretion of GHBP could not be detected. The culture medium may not contain the specific factors required for secretion of placental GHBP, or placental GHBP may not be destined for secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

O6-alkylguanine-DNA alkyltransferase activity in schistosomiasis-associated human bladder cancer

O6-Alkylguanine-DNA-alkyltransferase (ATase) activity was measured in extracts of 55 bladder tissue samples (46 tumour and nine uninvolved mucosal tissue) from Egyptian patients with schistosome-associated bladder carcinoma. Activity varied from 2.0 to 16.2 fmole ATase/microgram DNA (mean +/- S.D.; 5.6 +/- 4.0) or from 28 to 351 fmole ATase/mg (117 +/- 71). ATase levels in schistosome-associated bladder cancer tissues (5.6 +/- 4.0 fmole ATase/microgram DNA) tended to be lower than those observed in normal human bladder mucosal tissue (8.5 +/- 4.4 fmole ATase/microgram DNA). In a previous study (Badawi et al., Carcinogenesis, 1992, 13, 877-881) DNA-alkylation damage (O6-methyldeoxyguanosine) was found in 44/46 of these schistosome-associated bladder cancer samples at levels ranging from 0.012 to 0.485 mumole O6-MedG/mole deoxyguanosine. We now report an inverse correlation between the levels of methylation damage and ATase activity (r = -0.67; P < 0.001). These observations encourage further investigations of the possible role of environmental alkylating agents in the aetiology of early bladder cancer associated with schistosomiasis.

Growth hormone receptor and growth hormone-binding protein messages in mouse placenta contain the exon analogous to human exon 3

Growth hormone receptor (GHR)-encoding messages from the human placenta and other tissues have been recently characterized by several investigators. Of particular interest is the finding that exon 3 is deleted from the mRNA encoding GHR in human placenta, but not in maternal tissues. We have used a reverse transcriptase-polymerase chain reaction (RT-PCR) technique to amplify the distinct mRNAs encoding GHR and GH-binding protein (GHBP) in the mouse placenta and liver, followed by restriction analysis, to determine whether an analogous deletion exists in these mRNAs. The restriction analysis and sequencing of the PCR products shows that the mRNAs encoding GHBP and GHR in the mouse placenta do not have a deletion analogous to that found in human placental GHR mRNA.

Localization and ontogeny of growth hormone receptor gene expression in the central nervous system

There is literature evidence that both growth hormone (GH) and its mediator, insulin-like growth factor 1 (IGF-1), are able to act upon neuronal and glial cells in the brain. We report here the location of the GH receptor in the brain of the rat and rabbit. Receptor distribution was determined by immunohistochemistry with GH receptor/binding protein (BP) specific monoclonal antibodies and by in situ hybridization with a [35S]riboprobe. GH receptor/BP immunoreactivity in the rat was most prominent in the neonate and declined with postnatal age. Receptor immunoreactivity was generalised with variation in immunoreactivity in regional areas. In the rat, strongest immunoreactivity was seen in layers 2, 3, 5 and especially layer 6 of the cerebral cortex, in neurones of the thalamus and hypothalamus, in Purkinje cells of the cerebellum, in neurones of the trapezoid body of the brainstem, and in retinal ganglion cells. Glial cells, notably astrocytes were also strongly reactive, along with ependyma of the choroid plexus, ventricular lining and pia mater. In the neonatal rabbit, strongest immunoreactivity was evident in layers 2 and 3 of the cerebral cortex, in pyramidal cells of the hippocampus, and in neurones of the inferior and superior colliculi, brain stem reticular formation, dorsal thalamus and hypothalamus. A similar distribution of GH receptor mRNA was seen by in situ hybridization. The ontogeny of GH receptor/BP mRNA in whole rat brain was quantified by solution hybridization-RNAse protection assay. Contrary to its ontogeny in the liver (Endocrinology, 113 (1983) 1325-1329) receptor mRNA decreased with postnatal age.(ABSTRACT TRUNCATED AT 250 WORDS)