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Biomedical subjects

H M Kronenberg

Publications and source records attributed to H M Kronenberg.

At least 91 records · Page 5Linked to original sources
PubMed1989

Regions of the rat osteocalcin gene which mediate the effect of 1,25-dihydroxyvitamin D3 on gene transcription.

We have cloned the genomic DNA encoding rat osteocalcin and have isolated fragments in the 5' flanking region which mediate the effects of 1,25-(OH)2D3 (1,25-dihydroxyvitamin D3) on osteocalcin gene transcription. Approximately 3 kilobase pairs of the osteocalcin gene's 5' flanking region, including the promoter and transcription start site, were fused to the reporter gene chloramphenicol acetyltransferase. Transfection into ROS 17/2.8 rat osteosarcoma cells demonstrated low level basal expression of the chloramphenicol acetyltransferase gene. The expression increased markedly in the presence of 1,25-(OH)2D3; induction was observed at doses as low as 10(-11) M 1,25-(OH)2D3. Chloramphenicol acetyltransferase activity increased as early as 16 h after stimulation with 10(-9) M 1,25-(OH)2D3. Basal chloramphenicol acetyltransferase activity in ROS 24/1 and 25/1 cells was much lower than in ROS 17/2.8 cells. In these two cell lines, there was little induction of chloramphenicol acetyltransferase activity in the presence of 10(-9) M 1,25-(OH)2D3. Deletion studies of the 5' flanking region demonstrated two regions that contribute to the induction by 1,25-(OH)2D3. Deletion of a 650-base pair fragment ending 1.4 kilobase pairs upstream from the initiator ATG led to an 80% decrease in responsiveness. Removal of an additional 1.1 kilobase pairs, leaving a 300-base pair promoter containing fragment obliterated responsiveness to 1,25-(OH)2D3.

Animals↗
PubMed1989

Molecular cloning and chromosomal mapping of DNA rearranged with the parathyroid hormone gene in a parathyroid adenoma.

Parathyroid adenomas are common benign neoplasms for which no chromosomal defects have been described. We recently found two parathyroid adenomas bearing clonal restriction fragment abnormalities involving the PTH locus, and now show that in one of these tumors: (a) a DNA rearrangement occurred at the PTH locus; (b) the rearrangement separated the PTH gene's 5' flanking region from its coding exons, conceivably placing a newly adjacent gene under the influence of PTH regulatory elements; (c) the DNA that recombined with PTH normally maps to 11q13, the known chromosomal location of several oncogenes and the gene for multiple endocrine neoplasia type I; and (d) the rearrangement was a reciprocal, conservative recombination of the locus on 11q13 (Human Gene Mapping Library assignment D11S287) with PTH (on 11p15). These data provide molecular cytogenetic evidence for the clonal occurrence of a major chromosome 11 aberrancy in this benign parathyroid tumor. The D11S287 clone could prove useful in genetic linkage analyses, in determining precise 11q13 breakpoints in other neoplasms, and in identifying a gene on chromosome 11 that may participate in parathyroid tumor development.

Adenoma↗
PubMed1989

Inhibition of parathyroid hormone responsiveness in clonal osteoblastic cells expressing a mutant form of 3',5'-cyclic adenosine monophosphate-dependent protein kinase.

PTH activates multiple acute intracellular signals within responsive target cells, but the importance of cAMP vs. other second messenger signals in mediating different biological responses to PTH is not known. To address these questions, we developed a genetic approach to block activation of the cAMP-dependent protein kinase (PK-A) in PTH-responsive cell lines. Clonal rat osteosarcoma cells (UMR 106-01) were stably transfected with REV-I, a plasmid that directs synthesis of a mutant cAMP-resistant form of the type I regulatory subunit of PK-A. In the transfected bone cells, most of the catalytic subunits of PK-A were associated with the mutant regulatory subunit, and activation of PK-A by cAMP was correspondingly inhibited. We have characterized one such mutant (UMR 4-7) that expressed large amounts of mutant mRNA and exhibited inducible blockade of PK-A via the REV-1 metallothionein promoter. In the absence of metallothionein induction, these cells exhibited nearly normal PTH responsiveness, but after REV-1 induction by Zn2+, they were resistant to PTH-induced activation of PK-A and regulation of membrane phospholipid synthesis by both PTH and cAMP analogs. The mutant UMR 4-7 cell provides a model system in which the consequences of cAMP production by PTH or other agonists that activate adenylate cyclase in osteoblasts may be specifically inhibited by brief exposure to Zn2+. Such mutant cell lines will facilitate further investigation of the linkage between early signalling events and subsequent biological responses in the action of PTH and other agonists on target cells in bone.

Animals↗
PubMed1989

Mutations in signal sequence cleavage domain of preproparathyroid hormone alter protein translocation, signal sequence cleavage, and membrane-binding properties.

Signal sequences, known to mediate the targeting of nascent secreted proteins to membranes, share common structural domains: a positively charged amino-terminus, a hydrophobic core, and a signal cleavage domain. Mutations have been introduced into the cDNA encoding the signal sequence of the mammalian protein preproparathyroid hormone to analyze the roles played by the signal cleavage domain in secretion. Two mutant genes were constructed missing the entire six-residue propeptide sequence and several residues of the signal cleavage domain. The effects of these mutations on signal function were assessed after expression in clonal cell lines and in a transcription-linked translation system. Alterations in the signal cleavage domain resulted in reduced translocation and signal cleavage. Furthermore, in one mutant, the removal of the signal cleavage domain converted the signal into a membrane anchor sequence. The nonhydrophobic sequences at the end of the signal sequence thus crucially affect the translocation, cleavage, and membrane-binding properties of signal sequences.

Amino Acid Sequence↗
PubMed1988

Importance of the propeptide sequence of human preproparathyroid hormone for signal sequence function.

The function of amino-terminal pro-specific peptides (propeptides), sequences often found on intermediate precursor forms of secreted proteins, is poorly understood. Human preproparathyroid hormone (prepro-PTH), a precursor protein containing such a propeptide, is initially synthesized as a precursor containing a 25-amino acid signal sequence, a 6-amino acid propeptide, and the 84-amino acid mature secreted peptide. Cloned cDNA encoding prepro-PTH and synthetic oligonucleotides were used to generate a mutant missing precisely the pro-specific sequences. The effects of this deletion on signal sequence function and on secretion per se were assessed after expression of the mutant cDNA in intact cells and in a cell-free translation system using synthetic mRNA in the presence of microsomal membranes. The mutant precursor protein was inefficiently translocated and cleaved, and cleavage occurred both at the normal site and within the signal sequence. Thus, for the eukaryotic protein prepro-PTH, sequences immediately downstream and separate from the classically defined signal sequence facilitate accurate and efficient signal function.

Amino Acid Sequence↗
PubMed1988

Monoclonality and abnormal parathyroid hormone genes in parathyroid adenomas.

Previous work based on the relative tissue content of glucose-6-phosphate dehydrogenase isoenzymes suggested that parathyroid adenomas, like primary hyperplasia, may be multicellular (not clonal) in origin. We have reexamined this issue by using two independent molecular genetic methods. We report tumor-cell-specific restriction-fragment-length alterations involving the parathyroid hormone gene from two human parathyroid adenomas. These abnormal restriction fragments indicate that in each case a clonal proliferation of cells was present and also suggest that DNA alterations involving the parathyroid hormone locus may be important in the tumorigenesis or clonal evolution of some parathyroid adenomas. In addition, we used a restriction-fragment-length polymorphism in an X-linked gene (hypoxanthine phosphoribosyltransferase) to examine the clonality of eight parathyroid adenomas in women. Of these eight adenomas, six had the DNA hybridization pattern of monoclonality, and two had an equivocal pattern. None of five hyperplastic parathyroid glands had a monoclonal pattern. We conclude that some (and perhaps many) single parathyroid adenomas are monoclonal neoplasms. Our observations suggest that there is a fundamental biologic difference between parathyroid adenomas and primary hyperplasia--a difference that could prove useful in distinguishing these entities clinically.

Adenoma↗
PubMed1988

5'-flanking region of the parathyroid hormone gene mediates negative regulation by 1,25-(OH)2 vitamin D3.

To study the effects of 1,25-(OH)2 vitamin D3 on the transcription of the human parathyroid hormone (PTH) gene, 684 base pairs of the 5'-flanking portion of the human PTH gene were fused to the bacterial neo gene. The fusion gene was transfected into rat pituitary cells, and mixed populations of colonies were selected using the neomycin analog, G418. The level of RNA initiated from the human PTH gene promoter region in these cells was suppressed by 1,25-(OH)2 vitamin D3. Synthesis of the same transcript under control of a viral promoter was not regulated by 1,25-(OH)2 vitamin D3. The effect of 1,25-(OH)2 vitamin D3 was detected within 24 h at physiologic doses of 1,25-(OH)2 vitamin D3, and was not influenced by addition of cycloheximide. Thus 1,25-(OH)2 vitamin D3 acts on the 5'-flanking portion of the PTH gene to decrease the rate of transcription by a mechanism that requires no new protein synthesis.

Animals↗
PubMed1988

Nucleotide sequence of cloned cDNAs encoding chicken preproparathyroid hormone.

In order to characterize an avian parathyroid hormone gene, a lambda gt10 cDNA library constructed from chicken parathyroid gland mRNA was screened with a human preproparathyroid hormone (preproPTH) cDNA probe. Nucleotide sequence analysis of three independent clones confirmed that they encoded chicken preproPTH. This analysis, complemented by primer extension and Northern blot analysis of mRNA, demonstrated a 5'-untranslated region for chicken preproPTH of 127 nucleotides, a coding region of 357 nucleotides, and a 3'-untranslated region of approximately 2500 nucleotides. The coding sequence predicts a mature chicken PTH of 88 amino acids in contrast to the 84 amino acids of the mammalian hormones. Comparison of the avian and the mammalian hormones shows striking homology in the region of amino acids 1-32. The middle and carboxyl-terminal portions of chicken PTH, however, differ considerably from the mammalian hormones and include deletions of sequences conserved in mammalian PTH and insertions of novel peptide sequences. Comparison of the avian and mammalian structures suggests potential alterations of the mammalian sequences that may lead to altered bioactivity and/or hormone metabolism.

Amino Acid Sequence↗
PubMed1988

Inhibition of parathyroid hormone bioactivity by human parathyroid hormone (PTH)-(3-84) and PTH-(8-84) synthesized in Escherichia coli.

Human PTH (hPTH)-(3-84) and hPTH-(8-84) were synthesized in Escherichia (E.) coli when the cells were transformed with a multicopy plasmid in which the transcription of human preproPTH cDNA is directed by the E. coli lac promoter. PTH fragments were extracted from cells and purified by reverse phase HPLC. PTH bioactivity and PTH antagonist activity were estimated in a renal cytochemical bioassay. hPTH-(3-84) and hPTH-(8-84) exhibited less than 1% and less than 0.1%, respectively, of the biological activity of synthetic hPTH-(1-84). hPTH-(8-84) had 1% of the PTH inhibitory activity of synthetic [Nle8,18,Tyr34]bovine PTH-(3-34)amide, whereas hPTH-(3-84) was 100 times more active as a PTH inhibitor than the synthetic bovine PTH-(3-34) analog. The latter has so far been recognized as the most potent PTH antagonist in vitro. A 5-fold molar excess of hPTH-(3-84) over hPTH-(1-84) completely blocked the biological action of intact hPTH-(1-84) in the renal cytochemical bioassay. These findings suggest that the carboxyl-terminal portion of the intact hPTH-(1-84) molecule contributes importantly to inhibitor potency.

Animals↗
PubMed1987

Signal sequence of human preproparathyroid hormone is inactive in yeast.

The biosynthesis of human preproparathyroid hormone (hpreproPTH) and the processing to mature parathyroid hormone (hPTH) was investigated in yeast. Cells were transformed with a plasmid that carried a fusion gene made of the yeast pyruvate kinase promoter, complementary DNA (cDNA) encoding a slightly modified form of hpreproPTH and the transcription termination signal from yeast triosephosphate-isomerase. In transformed yeast cells we identified a protein that was recognized by a PTH antiserum and, on gel electrophoresis, comigrated with hpreproPTH marker. The amino-terminal sequence of the protein was consistent with that of hpreproPTH, indicating that the hormone precursor is not processed. It was localized inside the cell, when analyzed in pulse-chase experiments by trypsin accessibility in intact and lysed spheroplasts. In contrast, when mRNA from these yeast cells and from human parathyroid tissue was translated into preproPTH in a reticulocyte lysate supplemented with canine pancreatic microsomes, the preproPTHs from both mRNAs were transported and cleaved with identical efficiencies. We conclude that hpreproPTH is synthesized in yeast but not recognized and processed like a precursor of a secreted protein by the yeast secretory apparatus.

Animals↗
PubMed1987

Human preproparathyroid hormone synthesized in Escherichia coli is transported to the surface of the bacterial inner membrane but not processed to the mature hormone.

cDNA encoding human preproPTH (hpreproPTH) was expressed in Escherichia coli to study the processing of the precursor to hPTH and its secretion by the bacterial secretory apparatus. We first constructed hybrid genes that differed randomly in the distance between the E. coli lac promoter's ribosomal binding site and DNA encoding a fusion protein with beta-galactosidase activity and the prepro sequence of hpreproPTH on the aminoterminus. Starting with clones identified as efficient producers of beta-galactosidase on indicator agar plates, the coding sequence for hpreproPTH was reconstituted intact. In a different construction we placed the hpreproPTH coding sequence downstream from the lac promoter at a distance of 12 base pairs from the ribosomal binding site. PTH immunoreactive proteins from multiple clones were identified by protein gel electrophoresis and by protein microsequencing. PTH-related proteins encoded by different plasmids were shown to be hpreproPTH with amino-terminal extensions of either two or four amino acids and as authentic hpreproPTH. Two hPTH fragments, hPTH(3-84) and hPTH(8-84), were also observed. The trypsin accessibility of hpreproPTH and of the two hPTH fragments in pulse-chase, cell-fractionation experiments using intact and lysed spheroplasts lets us conclude that the mammalian signal sequence directs hpreproPTH to the surface of the spheroplast membrane but is not appropriately cleaved by the signal peptidase.

Animals↗
PubMed1987

Consequences of amino-terminal deletions of preproparathyroid hormone signal sequence.

PTH is initially synthesized as a larger precursor, containing a 25 amino acid signal sequence. Modification of cDNA encoding the hormone precursor resulted in the synthesis of proteins whose signal sequences were shortened at their amino termini. The effects of these mutations were analyzed using a cell-free translation system and rat pituitary GH4 cells in culture. Removal of the first six amino acids of the signal sequence had no effect on the efficiency or kinetics of protein processing as measured in the two assay systems. Mutants lacking 10 or 13 amino acids were not processed efficiently in the cells, nor were they translocated across microsomes in the cell-free translation system. These studies suggest that a modest change in the hydrophobic domain of the signal sequence, which might not have been predicted to alter function, led to a dramatic decline in signal activity.

Amino Acid Sequence↗
PubMed1986

Tissue and gene specific hypomethylation of the human parathyroid hormone gene: association with parathyroid hormone gene expression in parathyroid glands.

An association between decreased cytosine methylation at specific sites adjacent to or within eukaryotic genes and increased gene expression has been described. To determine if tissues secreting PTH show hypomethylation within the vicinity of the PTH gene, we compared the degree of cytosine methylation in DNA from parathyroid glands and control tissues (leukocytes, anterior pituitary, posterior pituitary, and placenta). We digested DNA with HpaII (which cleaves only unmethylated CCGG sequences) and MspI [which cleaves CCGG and C 5-methyl cytosine GG], hybridized the DNA fragments to a PTH complementary DNA probe, and scanned autoradiograms of Southern blots. After MspI digestion all tissues yielded equivalent amounts of a single hybridizing fragment of 6.7 kilobases. The degree of hypomethylation at sites within and flanking the PTH gene was determined as the ratio of the amount of hybridizing fragments obtained by methylation-sensitive digestion (HpaII) relative to methylation-insensitive digestion (MspI). DNA from all parathyroid glands showed significantly greater hypomethylation of the PTH gene than did DNA from control tissues that did not express the PTH gene. Despite variability in the levels of secretory activity of the different parathyroid glands, we found no significant differences in the degree of hypomethylation of the PTH gene. In contrast to the PTH gene studies, hypomethylation was not seen using GH probe on the same blots. Our findings thus suggest that tissue and gene specific hypomethylation of the PTH gene is associated with expression of the gene.

Adenoma↗
PubMed1986

Familial isolated hypoparathyroidism: a molecular genetic analysis of 8 families with 23 affected persons.

Abnormalities in the parathyroid hormone (PTH) gene as a cause of hypoparathyroidism were evaluated by linkage analysis with DNA polymorphisms adjacent to the PTH gene in 8 families in which members were affected with familial isolated hypoparathyroidism (FIH). We found that in none of the 23 affected individuals was there absence of the parathyroid hormone gene or abnormal restriction patterns to suggest recognizable deletions, insertions, or rearrangements. To determine if subtle mutations within the PTH gene were associated with hypoparathyroidism in these families, we used the Pst I and Taq I restriction-site polymorphisms in linkage analysis as markers to differentiate between PTH alleles. In 4 families, affected sibs inherited different PTH gene alleles, implying that hypoparathyroidism was not due to an abnormality in the PTH gene. In 2 other families, linkage analysis was uninformative because of inability to differentiate between PTH alleles. In 2 families, concordance was found between the inheritance of hypoparathyroidism and specific PTH alleles in affected members, suggesting that in these families, hypoparathyroidism may be due to an alteration in or near the PTH structural gene. We conclude that FIH is a diverse group of disorders and is characterized by genetic and molecular heterogeneity. In some forms of FIH the mutation that leads to PTH deficiency does not lie within the region of the structural gene for PTH. Linkage analysis using DNA polymorphisms within the PTH gene is of benefit in identifying individuals with disorders of PTH secretion or synthesis in whom DNA sequencing and expression studies of the PTH gene might succeed in establishing the molecular basis of the disease.

Cloning, Molecular↗
PubMed1985

Chromosome mapping of genes on the short arm of human chromosome 11: parathyroid hormone gene is at 11p15 together with the genes for insulin, c-Harvey-ras 1, and beta-hemoglobin.

The human parathyroid hormone gene (PTH) was mapped to the 11p15 chromosomal band by in situ hybridization. Using the same procedures and cells, the closely linked beta-hemoglobin gene (HBB), the Harvey-ras 1 proto-oncogene (HRAS1), and the insulin gene (INS) were also mapped to this same region. Some reports have demonstrated differences in regional localization of the latter three genes, and linkage and molecular studies have not resolved how far this linkage group extends from p15 toward the centromere on the physical gene map. Our results show that all of these genes are localized at 11p15, a region of one chromosomal band that appears to comprise a genetic distance of more than 20 cM.

Chromosome Mapping↗