Biomedical subjects
Publications and source records attributed to R K Craig.
A cDNA clone complementary to the mRNA encoding human alpha-lactalbumin (ALA) has been used as a probe in the analysis of DNA from panels of rodent/human somatic cell hybrids. The presence of the ALA gene correlates with the presence of chromosome 12. In situ hybridization localizes the ALA gene to 12q13.
The content of GSH transferase mRNAs in poly(A)-containing RNA isolated from eight rat tissues was examined by immunoprecipitation of cell-free translation products and by Northern blotting. Considerable tissue-specific distribution and heterogeneity of immunoprecipitable GSH transferase subunits 1 and 2 synthesized in vitro was observed. These results were confirmed by Northern blotting using a 32P-labelled subunit 1 cDNA probe. The same probe, used in a Southern blot analysis of genomic DNA, provided confirmation that GSH transferase subunits 1 and 2 comprise a multigenic family in the rat. The results show that the selection of cDNA clones coding for chosen subunits can be made easier by making use of qualitative and quantitative tissue differences in GSH transferase mRNAs.
In the anaesthetised rat, human and rat CGRP (calcitonin gene-related peptide) which differ by 4 out of 37 amino acids, when given intravenously, lowered blood pressure and increased heart rate. The effects of human CGRP were unaltered by either propranolol or by mepyramine plus cimetidine. In the rat isolated perfused heart the peptides decreased coronary perfusion pressure and evoked a tachycardia. The latter effect was not seen in the rabbit isolated heart, although human CGRP increased coronary flow. The two peptides were equipotent at increasing the rate and force of contraction in the rat isolated right atrium, effects unaltered by propranolol. In the guinea-pig isolated atrium, rat CGRP was 10 times as potent as a chronotropic agent than as an inotrope, unlike human CGRP which was equipotent. In conclusion, human and rat CGRP probably acted directly on the cardiovascular system to produce their qualitatively similar effects.
A single gene encodes both calcitonin and the calcitonin gene-related peptide (CGRP). Human and rat alpha-CGRP were compared with sodium nitroprusside in the rat and rabbit isolated mesenteric vascular preparation perfused at constant flow. In the presence of the vasoconstrictor noradrenaline (10(-5) M), rat alpha-CGRP was about 10 times as potent as either human alpha-CGRP or sodium nitroprusside as a vasodilator in the rat mesenteric vasculature. In the rabbit mesenteric vasculature the order of potency was rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. Human and salmon calcitonin showed no vasodilator activity at doses 100 times greater than human alpha-CGRP. These results show that human and rat alpha-CGRP are potent vasodilators in the mesenteric vasculature, an effect not mimicked by the alternative gene product, the plasma calcium lowering hormone calcitonin.
Cloning and nucleotide sequence analysis of the human calcitonin mRNA from the BEN lung carcinoma cell line, a cell line known to secrete high-Mr forms of calcitonin, showed no difference in the coding region at the nucleotide level compared with calcitonin mRNA isolated from medullary thyroid carcinoma which secretes calcitonin monomer. Therefore, the secretion of high-Mr forms of calcitonin reflects the absence or limited activity of proteolytic processing enzymes within the secretory pathway of this cell line. In all other respects, as judged by RNA blotting and S1 mapping, calcitonin/alpha-CGRP expression was identical to that found in medullary thyroid carcinoma, including the differential use of an alternative splice donor site within intron 1. The BEN cell line also produces low levels of alpha-CGRP mRNA and secretes CGRP antigenic determinants. Analysis of plasma CGRP levels in 12 patients with anaplastic lung carcinoma showed elevated levels in 11 of these, suggesting that CGRP may be an important diagnostic marker for this disease.
We describe the isolation and characterisation of a full-length cDNA sequence (pZH-21) of a human ribosomal protein (rp) mRNA isolated from a cDNA library constructed from the human ZR-75-1 mammary tumour cell-line. The predicted protein is highly basic and shows 72% homology at the amino acid (aa) level with yeast rp L44. Comparative RNA blotting of ZR-75-1 poly(A)+ RNA isolated from cells cultured in the presence of the anti-oestrogen tamoxifen demonstrates the presence of a number of mRNA species whose concentration is elevated co-ordinately 5-6-fold in the presence of 17beta-oestradiol. Insulin in the presence of tamoxifen, also enhanced rp mRNA levels suggesting increased levels are a reflection of cell proliferation as opposed to specific hormonal regulation. Genomic analysis demonstrates the presence of a family of related human sequences, and homology with rat and guinea pig rp genes, but not yeast DNA. The conservation of rp aa sequence, in the absence of detectable homology at the nucleotide (nt) level, points to an important common functional role of the L44 protein in ribosome structure and function in man and yeast.
We have investigated the levels of serum calcitonin and calcitonin-gene related peptide (CGRP) in 35 patients with well-documented medullary thyroid carcinoma (MTC). Immunohistochemical investigations for calcitonin and CGRP have been performed on tumour tissue from 9 patients to clarify the cellular pattern of production. In four patients with aggressive disease, serum calcitonin and CGRP values have been monitored in relation to progression of disease after surgery. All 35 patients with MTC have elevated calcitonin and 26 elevated CGRP levels. Generally calcitonin values were found to be higher than those of CGRP, although the ratio of the two peptides varied from patient to patient. The immunohistochemical investigations corresponded with these findings, generally showing diffuse staining for calcitonin in MTC tumour-cells and only a small number of CGRP positive cells. Calcitonin and CGRP are produced by alternative processing of the common precursor gene transcript. Our results suggest that absolute values of either calcitonin or CGRP in serum have no direct relationship to aggressiveness of disease. Thus whilst serum CGRP measurements appear to be a useful additional marker for the disease, they can be considered to be only a useful adjunct to serum calcitonin as a marker for tumour progression.
The effects of rat and human alpha-calcitonin gene-related peptide (CGRP) were compared in the mouse and rabbit isolated vas deferens preparation contracted by either field stimulation or acetylcholine. The peptides were about equipotent at inhibiting twitch responses of the mouse vas deferens to field stimulation at 0.2 Hz (IC50 12 +/- 4 nM and 15 +/- 3 nM, rat and human alpha-CGRP respectively). Rat alpha-CGRP was less potent at inhibiting responses to 10 Hz than to either 0.2 Hz or 1.0 Hz stimulation. The potency of rat alpha-CGRP at 1.0 Hz was unaltered by halving the calcium concentration of the Krebs solution. The inhibitory effect of human alpha-CGRP was not antagonized by either propranolol (300 nM) or idazoxan (300 nM), although in the same tissues these latter two drugs reduced responses to isoprenaline and clonidine respectively. Rat alpha-CGRP (100 nM) and human alpha-CGRP (1.0 microM) did not alter the uptake of [3H]-noradrenaline (30 nM) into mice isolated vasa deferentia. Rat alpha-CGRP (3-100 nM) did not alter the fractional release per pulse (1.0 Hz, 100 pulses) of tritium from vasa preloaded with [3H]-noradrenaline, although at the same time the peptide inhibited responses of the smooth muscle to field stimulation. Rat and human alpha-CGRP were equipotent at inhibiting contractions of the mouse vas deferens evoked by acetylcholine although the peptides were less potent than against twitch responses. In the rabbit vas deferens neither rat nor human alpha-CGRP (3 nM-1 microM) inhibited either twitch responses or acetylcholine contractions. 7 These results suggest that rat and human alpha-CGRP inhibit contractor responses of the mouse vas deferens not by interference with adrenergic mechanisms, but through postjunctional (possibly CGRP) receptors. A similar mechanism may underlie effects ofCGRP in other tissues. The rabbit vas deferens appears to lack the CGRP 'receptors'.
Studies on the structure and expression of the rat and human calcitonin gene provide a remarkable example by which a combination of molecular, immunocytochemical and pharmacological techniques have led to the identification of a novel gene product, the calcitonin gene-related peptide, a peptide of unexpected tissue distribution and biological activity. Future studies at the molecular level will provide insight into post-transcriptional mechanisms by which a single gene can give rise to discrete mRNAs in a tissue-specific manner. The isolation and characterization of the CGRP receptor, and hence the site(s) and mechanism(s) of action of the CGRP family within the vasculature, will also add significantly to our understanding of molecular mechanisms involved in the modulation of cardiovascular function in man. Furthermore, the role and mechanism of action of the CGRP peptide family in the central and peripheral nervous systems remains to be elucidated. It is also apparent that measurement of circulating plasma levels of CGRP may be of diagnostic and prognostic value, providing information concerning the onset and progression of lung and thyroid carcinoma. Our analysis of the structure and expression of the calcitonin/alpha-CGRP gene also demonstrates, for the first time, the molecular basis of large calcitonin secretion by lung carcinoma cells. Whether the expression of this gene in lung carcinoma cell-lines can truly be described as 'ectopic' is however questionable, in the light of recent immunocytochemical evidence which demonstrates that the lung is a major source of CGRP producing cells in the rat (see Springall et al., 1984).
RNA complexity analyses of total cellular polyadenylate-containing RNA isolated from lactating human breast tissue, human breast tumor tissue, and a mixture of established cell lines of mammary origin demonstrate extensive homology between the tissue RNA populations but suggest a decrease in the complexity of cell line nuclear RNA populations, with the exception of an early-passage MCF-7 cell line. Cell-free protein synthesis and two-dimensional gel electrophoresis also show quantitative and qualitative differences in gene expression between human mammary tumor tissue and reduction mammoplasty or established mammary cell lines of early and late passage number. The results demonstrate a major role for transcriptional and posttranscriptional mechanisms in the regulation of gene expression in the human mammary gland and show that studies on mammary gland gene expression using established cell lines of mammary origin reflect only in part gene expression in normal lactating human breast or breast tumor tissues.
A serine-specific casein kinase, an integral membrane protein of the lactating guinea-pig mammary gland, has been purified from a Golgi-enriched membrane fraction, using a combination of sucrose gradient centrifugation and chromatography on ATP-agarose. The enzyme comprises a polypeptide of estimated Mr 74 000 as judged by sodium dodecyl sulphate/polyacrylamide gel electrophoresis, compared with a monomer Mr of 50 000 as determined by sucrose gradient centrifugation in the presence of 500 mM NaCl and 0.1% Triton X-100. Kinetic studies show that the purified enzyme exhibits kinetic constants distinctly different from the rabbit reticulocyte casein kinases I and II, whilst polyclonal antisera raised against the mammary gland enzyme did not cross-react with soluble liver or reticulocyte protein kinase activities. Immunoblotting and immunocytochemical analyses demonstrate the mammary gland enzyme's apparently unique location in lactating mammary gland tissue. Comparative studies with polyclonal antisera raised against bovine galactosyltransferase, show that casein kinase and galactosyltransferase have a similar intracellular localisation in the lactating mammary gland as judged by immunocytochemistry at the light level, but that casein kinase was unique to mammary gland whereas galactosyltransferase could be found in other tissues. The results extended our earlier observations which suggest a Golgi location for casein kinase, and demonstrate that future studies using this enzyme may well prove advantageous for the study of intracellular mechanisms involved in the biogenesis of organelles, in this instance the Golgi apparatus.
Alpha 1-Antitrypsin and albumin mRNA levels of 4 human livers were assessed using a newly sequenced cDNA clone of the carboxyterminal third of alpha 1-antitrypsin and a previously cloned albumin cDNA sequence. The relative concentration of alpha 1-antitrypsin mRNA was the same in poly(A)-containing RNA isolated from acute phase (MM) and alpha1-antitrypsin deficient (ZZ) individuals. In the acute phase liver relative to the normal (MM) liver, total RNA extracts showed a marked decrease in albumin mRNA concentration but no increase in alpha 1-antitrypsin mRNA. The ZZ liver showed decreased total and poly(A)-containing RNA content but the same proportion of alpha 1-antitrypsin to albumin mRNA as in the normal (MM) liver. This supports other evidence that ZZ alpha 1-antitrypsin deficiency is due to a defect in polypeptide processing (secretion) rather than a deficiency in mRNA accumulation.
Nucleotide sequence analysis of a partially processed polyadenylated precursor RNA transcript shows that the human calcitonin gene in common with the rat calcitonin gene, encodes calcitonin and the calcitonin gene related peptide (CGRP). Using hybridisation probes specific to calcitonin mRNA, intron, coding and non-coding regions of the CGRP mRNA, we demonstrate by Southern blotting the existence of a second human CGRP gene, and by RNA blotting and S1 mapping, the differential expression of calcitonin and CGRP in medullary thyroid carcinoma and human lung tumour cell-lines. These studies implicate the requirement for separate post-transcriptional events in the differential expression of calcitonin and CGRP from a single gene, the preferential use of splice acceptor sites for the synthesis of CGRP mRNA, and post-transcriptional cleavage modulated by a trans-acting gene product for the synthesis of calcitonin mRNA. Studies using antisera raised against CGRP and calcitonin, demonstrate elevated circulating levels of plasma CGRP in medullary thyroid carcinoma which do not parallel calcitonin levels, and the presence of CGRP in secretions from lung tumour cell-lines. These studies indicate that CGRP is a tumour marker of diagnostic and possibly prognostic value in the management of lung and thyroid tumours.
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The lactating guinea-pig mammary gland synthesizes and secretes four major milk proteins, i.e., three caseins and alpha-lactalbumin. Of these, the caseins are highly phosphorylated, a post-translational event which in the mammary gland involves a specific casein kinase, which is an integral membrane protein probably of Golgi origin. The microinjection of milk protein mRNA into Xenopus oocytes in the presence of [35S]methionine leads to the synthesis, sequestration, and secretion of proteins which coelectrophorese with alpha-lactalbumin and with partially processed caseins. That the secreted caseins were not phosphorylated was shown by the use of 32P. Either the oocytes were injected with mammary gland mRNA followed by incubation with [32P]phosphate containing media or the mRNA was co-injected with [gamma-32P]ATP and the oocytes were then incubated. In neither case were 32P-labeled caseins secreted. Golgi-rich fractions, identified by the marker enzyme galactosyltransferase, were isolated from the postnuclear supernatant of both oocytes and lactating mammary gland by sucrose density gradient fractionation. In contrast to the mammary gland fractions those derived from the oocytes contained no detectable casein kinase activity. Homogenates of oocytes do effect the phosphorylation of casein but the enzyme activity appears to be present in the soluble fraction and is not membrane bound. It is concluded that the Xenopus oocyte lacks the specific kinase that in the mammary gland phosphorylates sequestered caseins and that the phosphorylation of the caseins is not a prerequisite for their secretion by the oocyte.
Nucleotide sequence analysis of cloned guinea-pig casein B cDNA sequences has identified two casein B variants related to the bovine and rat alpha s1 caseins. Amino acid homology was largely confined to the known bovine or predicted rat phosphorylation sites and within the 'signal' precursor sequence. Comparison of the deduced nucleotide sequence of the guinea-pig and rat alpha s1 casein mRNA species showed greater sequence conservation in the non-coding than in the coding regions, suggesting a functional and possibly regulatory role for the non-coding regions of casein mRNA. The results provide insight into the evolution of the casein genes, and raise questions as to the role of conserved nucleotide sequences within the non-coding regions of mRNA species.
Golgi and endoplasmic-reticulum fractions were prepared from the lactating guinea-pig mammary gland. The endoplasmic-reticulum fraction was highly active in the processing and sequestration of milk-protein primary translation products. Explants from the lactating gland in organ culture were used to identify milk-protein intermediates present in the secretory pathway, and the timing of the events leading to their post-translational modification. With [35S]methionine, the milk proteins labelled after a short pulse (3 min) were represented by the partially processed (but not phosphorylated) caseins and alpha-lactalbumin sequestered within membrane-bound vesicles. After a 30 min labelling period, higher-Mr caseins with electrophoretic mobilities identical with those of the phosphorylated caseins isolated from milk were identified in the incubation medium, and sequestered within membrane-bound vesicles. Pulse-chase experiments established a precursor-product relationship between these forms. Secretion is apparent approx. 30 min after sequestration. Caseins are highly phosphorylated; removal of the phosphate residues with acid phosphatase results in proteins with increased electrophoretic mobility, similar to those of the partially processed early casein intermediates found sequestered in explants after a 3 min pulse with [35S]methionine, and those sequestered within microsomal membranes after mRNA-directed cell-free protein synthesis. A comparison of the proteins labelled during both short (5 min) and long (30 min) pulses with [35S]methionine and [32P]Pi shows that, in contrast with the 35S-labelled caseins, those labelled with [32P]Pi exhibit only electrophoretic mobilities identical with those of the mature caseins isolated from milk and those identified after long labelling periods with [35S]methionine. No phosphorylated early intermediate forms of caseins were identified. We conclude that the synthesis and post-translational modification of guinea-pig caseins occurs in two stages, (i) an early event involving synthesis and sequestration within the endoplasmic reticulum, an event that involves signal-peptide removal, followed (ii) 10-20 min later by phosphorylation at a different point in the secretory pathway, probably in the Golgi complex. Secretion of the phosphorylated caseins occurs 10-20 min later.
Free polyribosomal poly(A)-containing RNA isolated from normal rat liver was used to prepare a complementary DNA plasmid library in the Pst1 site of the plasmid pAT153 . A plasmid pGSTr155 complementary to mRNA coding for a glutathione transferase Ya subunit was selected by differential hybridization in situ and preliminary characterization was performed by hybrid-selected mRNA translation, immunoprecipitation and polyacrylamide-gel electrophoresis of the product synthesized in vitro. The nucleotide sequence of the complementary DNA contained within pGSTr155 was determined and shown to contain a single open reading frame corresponding to the first 129 amino acids of the N-terminus of the Ya subunit and a further 63 nucleotides upstream of the initiating methionine codon.