Biomedical subjects

G Lamson

Publications and source records attributed to G Lamson.

23 records · Page 2Linked to original sources

PubMed1990

Insulin-like growth factor binding proteins in maternal serum throughout gestation and in the puerperium: effects of a pregnancy-associated serum protease activity.

The cDNAs encoding three major insulin-like growth factor-binding proteins (IGFBPs) have been cloned and sequenced. We have examined, by Western ligand blotting, the profiles of these binding proteins in human female serum in the normal menstrual cycle, throughout pregnancy, and during the postpartum period. There was no change in the serum profile of any of the binding proteins in early pregnancy compared to that in the secretory phase of the menstrual cycle. However, there was a marked decrease in circulating levels of the main serum IGFBP, IGFBP-3, after 6 weeks of gestation, continuing progressively to term and returning to nonpregnant levels by 5 days postpartum. IGFBP-2 decreased steadily throughout gestation. In contrast, IGFBP-1 levels were found to rise by the second trimester. Endoglycosidase-F digestion did not enhance detection of IGFBP-3 by ligand blotting. Immunoprecipitations with two separate antibodies against IGFBP-3 and IGFBP-2, followed by Western ligand blotting, confirmed the marked decrease in IGFBP-3 levels after 6 weeks of gestation and the more gradual decrease in IGFBP-2. In contrast, immunoprecipitations with IGFBP-1 monoclonal antibodies confirmed the increase in IGFBP-1 during gestation. Endogenous serum IGFs were separated from serum IGFBPs by acid chromatography, and an 80% decrease in total IGF-binding activity in the IGFBP fraction of chromatographed pregnancy vs. nonpregnancy serum was detected by charcoal absorption assay. Furthermore, immunoprecipitations of IGF affinity cross-linked IGFBP fractions with IGFBP-3-specific antiserum confirmed a marked diminution of IGFBP-3 in pregnancy compared to nonpregnancy serum, and revealed, only in pregnancy serum, the concomitant appearance of a band with a mol wt of 34K and three less intense bands with mol wt between 20-26K on sodium dodecyl sulfate gels. Incubation of nonpregnancy serum with 6-week pregnancy serum at 37 C for 5 h, followed by Western ligand blotting, showed only a slight reduction in the amount of IGFBP-3 in the mixture compared to that in controls. However, incubation of term pregnancy with nonpregnancy serum at 37 C for 5 h revealed a marked reduction of IGFBP-3 in the mixture. When iodinated recombinant IGFBP-3 was incubated with term pregnancy serum under the same conditions, the appearance of a 29K protein was identified by gel electrophoresis and autoradiography, along with three less intense bands with mol wt between 17-22K.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1989

Developmental and muscle-specific changes in methylation of the myosin light chain LC1f and LC3f promoters during avian myogenesis.

The fast alkali myosin light chains LC1f and LC3f are two contractile protein isoforms encoded for by a single gene complex. Expression of these two isoforms is dependent upon differential initiation of transcription at either of two promoters encoding unique 5' exons for isoform-specific amino termini of these light chains. Studies of protein expression have shown that the two isoforms are first expressed at different stages of development and in the case of the LC3f isoform only in fast twitch muscle fiber types. The molecular mechanisms that regulate the differential transcription of the gene complex are unknown. Experiments reported here demonstrated the direct correlation of isoform protein and mRNA expression with the undermethylation of the DNA in the promoter regions of the gene for each of the expressed myosin light chain isoforms. We find that fast and slow muscles have different patterns of undermethylation of the two promoter regions of the gene. Moreover, changes in methylation of the promoter regions were shown to occur specifically in skeletal muscle tissue, to be developmentally regulated, and to only occur in the LC3f promoter of those muscle groups that express LC3f protein.

Age Factors↗

PubMed1989

Expression of the BRL-3A insulin-like growth factor binding protein (rBP-30) in the rat central nervous system.

The expression of the BRL 3A insulin-like growth factor binding protein (rBP-30) was characterized in rat brain, hypothalamus, and pituitary tissue and cultured neuronal and astroglial cells. The 27K BP expressed by BRL 3A cells (rBP-30) was found to also be expressed in conditioned media from newborn rat astrocytes and fetal neurons, but not in the medium from the neuroblastoma cell line, B104. Moreover, a polyclonal antibody, anti HEC1, specifically immunoprecipitated the BRL 3A BP from the same conditioned media, as well as from rat cerebrospinal and amniotic fluid and from conditioned medium of cells isolated from the neurointermediate lobe of adult rat pituitary. The same antibody also immunoprecipitated hBP-31 from human CSF. Northern blot analyses showed that rBP-30 mRNA was expressed in adult rat brain and pituitary, fetal brain and liver, and in fetal neurons and newborn astrocytes maintained in culture. We conclude that the BRL 3A BP (rBP-30) is the major insulin-like growth factor binding protein in the rat CNS and may be the rat analog of hBP-31, the predominant BP in human CSF.

Animals↗

PubMed1989

Expression of two insulin-like growth factor-binding proteins in a human endometrial cancer cell line: structural, immunological, and genetic characterization.

Insulin-like growth factors (IGFs) bind with high affinity to specific proteins in human serum, cerebrospinal fluid (CSF), and amniotic fluid. In serum, IGFs are bound to a complex with an apparent mol wt of 150K in which an acidstable binding protein of 53K, termed BP-53, is found. In amniotic fluid, a different binding protein with an apparent mol wt of 25K, termed hBP-25, has been identified. This binding protein is secreted by endometrial cells and has been shown to block the binding of IGFs to their membrane receptors and inhibit the mitogenic action of the IGFs on human choriocarcinoma cells. It has been proposed that hBP-25 modulates the action of IGFs on endometrial tissue, especially during pregnancy. We have identified two binding proteins produced by an endometrial adenocarcinoma, HEC 1A, neither of which is related structurally or genetically to hBP-25. One is present in two glycosylated forms with apparent mol wt of 37K and 40K, both of which are immunoprecipitated with an antiserum made to BP-53. Both forms are reduced to a core protein of 30K upon digestion with endoglycosidase-F. Furthermore, BP-53-specific RNA was detected in HEC 1A cells. A second binding protein with an apparent mol wt of 32K was also detected and did not increase in size upon treatment with endo glycosidase F. These two binding proteins were partially purified by a combination of wheat germ agglutinin and IGF affinity chromatography, and polyclonal antibodies were generated. The polyclonal antiserum specifically recognizes a 32K protein in human CSF, suggesting that the HEC 1A cells produce the same binding protein that is predominant in CSF. The findings suggest that IGF action in the endometrium may be modulated by more than a single binding protein, and that at least three structurally distinct human IGF binding proteins exist.

Blotting, Northern↗

PubMed1984

Changes in J chain and mu chain RNA expression as a function of B cell differentiation.

The time course of differentiative events in the pentamer IgM response was examined by following the expression of J chain and mu chain RNA and their protein products in mitogen-stimulated lymphocytes. The analyses showed that the shift to mus RNA synthesis begins shortly after stimulation and precedes proliferation of the cells and any increase in mu RNA levels. In contrast, expression of J chain RNA and the amplification of J chain and mus message are late events that coincide with a phase of rapid proliferation and with the secretion of pentamer IgM antibody. The kinetics of J and mu chain RNA expression observed in normal lymphocytes were supported by analyses of lymphoid cell lines. B lymphomas were found to display the RNA pattern characteristic of early-activated lymphocytes, i.e., a partial shift to mus RNA production and no J chain RNA, whereas IgM-secreting lines resembled late-activated lymphocytes in their expression of high levels of both mus and J chain mRNA. Moreover, the kinetics of J and mus chain RNA expression correlates with the sequential action of B cell lymphokines in the induction of the pentamer IgM response. This correlation suggests that the successive differentiative changes are triggered by successive membrane stimuli.

Animals↗