Biomedical subjects

T Quertermous

Publications and source records attributed to T Quertermous.

At least 55 records · Page 3Linked to original sources

PubMed1992

Tumor necrosis factor increases transcription of the heparin-binding epidermal growth factor-like growth factor gene in vascular endothelial cells.

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a recently identified, potent vascular smooth muscle cell (SMC) mitogen of macrophage origin. To determine whether this gene is transcribed and regulated in vascular endothelial cells, we measured HB-EGF mRNA levels in human umbilical vein endothelial cells (HUVEC) by RNA blot analysis with an HB-EGF cDNA probe. The base-line level of HB-EFG mRNA in HUVEC in culture was low. However, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta markedly increased HB-EGF mRNA levels in HUVEC by 12- and 7-fold, respectively, and induction of the gene by TNF-alpha was both dose- and time-dependent. In response to TNF-alpha, HB-EGF mRNA levels quickly increased and peaked at 1 h, indicating that HB-EGF belongs to the family of immediate early genes. In nuclear run-off experiments, TNF-alpha increased the rate of HB-EGF gene transcription by 3.2-fold. To our knowledge this is the first demonstration that the HB-EGF gene is transcribed in vascular endothelial cells. The inducible transcription of this potent SMC mitogen gene in endothelial cells suggests that HB-EGF may have an important role in the pathogenesis of atherosclerosis.

Base Sequence↗

PubMed1991

Stimulation of endothelin-1 gene expression by insulin in endothelial cells.

The present study characterized the regulation of the genetic expression of the vasoactive peptide endothelin-1 (ET-1) by insulin in bovine aortic endothelial cells. By RNA blot analysis, insulin (1.67 x 10(-8) M) increased ET-1 mRNA levels by 2.3-fold over the basal within 10 min and attained a maximum (5.3-fold increase) in 2 h. Dose-response studies showed that a maximum effect of insulin was reached at 1.67 x 10(-8) M although a significant increase can be observed at 1.66 x 10(-9) M. Radioligand receptor studies indicated that the affinity constant for insulin receptors on endothelial cells correlated closely with the dose response observed for ET-1 mRNA. The ET-1 mRNA half-life was estimated with actinomycin D studies to be 20 min in control cells and was not affected by insulin treatment. Moreover, the effects of phorbol 12-myristate 13-acetate (PMA) and insulin were additive in the induction of ET-1 gene expression. When protein kinase C in the bovine aortic endothelial cells was down-regulated by preincubation with 8 x 10(-7) M PMA for 24 or 48 h, insulin was still able to increase ET-1 mRNA levels whereas PMA was ineffective. Using a chloramphenicol acetyltransferase (CAT) fusion plasmid containing the CAT gene and the 5'-flanking region of the ET-1 gene (Lee, M. E., Bloch, K. D., Clifford, J. A., and Quertermous, T. (1990) J. Biol. Chem. 265, 10446-10450), we observed that 1.67 x 10(-8) M insulin increased CAT enzyme activity and mRNA levels. The insulin dose-response curve observed for CAT activity correlated with that observed for ET-1 mRNA levels. These results suggest that insulin stimulates expression of the ET-1 gene at the transcriptional level via its own receptors. This effect is mediated mostly through a protein kinase C-independent pathway, suggesting the existence of an insulin-responsive element in the ET-1 gene 5'-flanking sequence.

Amino Acid Sequence↗

PubMed1991

A recombinant chimeric plasminogen activator with high affinity for fibrin has increased thrombolytic potency in vitro and in vivo.

A recombinant plasminogen activator with high fibrin affinity and specificity was expressed by transfecting hybridoma cells with a plasmid that combines sequence coding for low molecular mass (32 kDa) single-chain urokinase-type plasminogen activator [scuPA(32kDa)] and anti-fibrin monoclonal antibody 59D8. The expression of the recombinant molecule [r-scuPA(32kDa)-59D8] was optimized by replacing the 3' untranslated region (initially that of high molecular mass scuPA) in the plasmid with the 3' untranslated region of either beta-globin or mouse immunoglobulin. This modification resulted in a greater than 100-fold improvement in the level of protein expression. The 103-kDa r-scuPA(32kDa)-59D8 protein displayed catalytic activity indistinguishable from that of high molecular mass scuPA and fibrin binding comparable to that of native antibody 59D8. r-scuPA(32kDa)-59D8 was 6 times more potent than high molecular mass scuPA in lysing a human plasma clot in vitro and was 20 times more potent than high molecular mass scuPA in the rabbit jugular vein model of thrombolysis. Molecules of this type may serve as prototypes for highly specific, antibody-targeted enzymes suitable for human use.

Animals↗

PubMed1991

Regulation of endothelin-1 gene expression by Fos and Jun.

The endothelin peptides constitute a family of potent vasoconstrictor molecules. Endothelin-1 (ET1) is secreted by vascular endothelial cells and may have a role in the regulation of vascular tone. To better understand the function of ET1, we have investigated the transcriptional regulation of the ET1 gene. Utilizing reporter gene transfection experiments, we have previously identified two promoter regions, located at base pairs -148 to -117 (Region A) and -117 to -98 (Region B) of the ET1 gene. Both regions are necessary for high level ET1 transcription in endothelial cells. A nuclear protein binding to the GATA motif in Region A has been identified and proven to be necessary for expression of the ET1 gene. However, the cis-acting sequences and their cognate binding proteins for Region B have not been investigated. To identify protein binding motifs in Region B we performed DNase I footprinting and gel mobility shift assays using a DNA fragment encoding base pairs -204 to -94 of the ET1 gene. Results from these studies indicated that the AP1 consensus sequence (GTGACTAA) in Region B as the only protein-binding motif. Site-directed mutagenesis of the ET1 AP1 site resulted in a 30-fold reduction in promoter activity, establishing the functional significance of this sequence. Additional experiments investigated the role of Jun and Fos in ET1 transcription. By employing antisera to Jun and Fos in gel mobility shift assays, both of these proteins were identified as endothelial cell nuclear proteins binding to the ET1 AP1 sequence. In trans-activation experiments, we showed that cotransfection of c-fos and c-jun expression plasmids markedly increased the transcription rate of chloramphenicol acetyltransferase reporter plasmids containing three synthetic ET1 AP1 sites. Taken together, these data indicate the importance of the AP1 recognition sequence, and the role of Fos and Jun proteins in the regulation of ET1 gene transcription.

Base Sequence↗

PubMed1991

Cloning of the GATA-binding protein that regulates endothelin-1 gene expression in endothelial cells.

Previously, we have identified two regions (A and B) of the endothelin-1 promoter that are important for the expression of this gene in cultured vascular endothelial cells. The cis-acting sequence in one of these regions (Region A) includes the core binding motif GATA, raising the possibility that this region of DNA mediates binding of a member of the GATA-binding protein family. In this report, we describe the use of polymerase chain reaction in conjunction with cDNA cloning to characterize the GATA-binding protein expressed in endothelial cells. The nucleotide sequence of endothelial cell cDNA clones is highly homologous to that of the chicken GATA-2 (NF-E1b) gene, indicating that our clones encode the human GATA-2 gene transcript. By RNA blot analysis, this gene is expressed in cultured cell lines derived from a number of different tissues. Transactivation experiments utilizing human GATA-2 eukaryotic expression vectors indicate that the GATA-2 protein interacts with the endothelin-1 GATA sequence to increase transcription of reporter genes in both BAEC and HeLa cells. These data provide the first evidence for a non-erythroid target gene regulated by GATA-2 and indicate that GATA-2 may have a more broad role in transcriptional regulation than the erythroid-specific GATA-1 protein.

Amino Acid Sequence↗

PubMed1991

Effect of chemical conjugation of recombinant single-chain urokinase-type plasminogen activator with monoclonal antiplatelet antibodies on platelet aggregation and on plasma clot lysis in vitro and in vivo.

The murine monoclonal antiplatelet antibodies MA-TSPI-1 (directed against human thrombospondin) and MA-PMI-2, MA-PMI-1, and MA-LIBS-1 (directed against ligand-induced binding sites [LIBS] on human platelet glycoprotein IIb/IIIa) were conjugated with recombinant single-chain urokinase-type plasminogen activator (rscu-PA) using the cross-linking reagent N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). The conjugates (rscu-PA/MA-TSPI-1, rscu-PA/MA-PMI-2, rscu-PA/MA-PMI-1, and rscu-PA/MA-LIBS-1), purified by immunoadsorption and gel filtration, were obtained with recoveries of 34% to 45%, with an average stoichiometry of 1.6 to 1.8 IgG molecules per rscu-PA molecule, and with unaltered specific activities and affinities. Preincubation of human platelet-rich plasma with rscu-PA/MA-PMI-2, rscu-PA/MA-PMI-1, or unconjugated rscu-PA resulted in partial inhibition of ADP-induced aggregation; 25% inhibition was obtained with 63 micrograms/mL rscu-PA and with 6 micrograms u-PA/mL rscu-PA/MA-PMI-2 or 1.2 micrograms u-PA/mL rscu-PA/MA-PMI-1. In an in vitro system composed of a 125I-fibrin-labeled platelet-rich human plasma clot immersed in normal human plasma, the conjugates had threefold to greater than 15-fold less fibrinolytic potency than unconjugated rscu-PA. The thrombolytic potency of rscu-PA/MA-PMI-1 and rscu-PA/MA-LIBS-1 was compared with that of rscu-PA and that of a control conjugate rscu-PA/MA-1C8 in a pulmonary embolism model in the hamster, using clots prepared from platelet-poor or platelet-rich human plasma. Lysis was measured 30 minutes after the end of a 60-minute intravenous infusion of the thrombolytic agents. rscu-PA, rscu-PA/MA-PMI-1, rscu-PA/MA-LIBS-1, as well as rscu-PA/MA-1C8 had comparable thrombolytic potencies (percent lysis per dose administered) towards platelet-poor human plasma clots. In contrast, the thrombolytic potency of rscu-PA/MA-PMI-1 and of rscu-PA/MA-LIBS-1 towards platelet-rich clots was 2.3- to 3-fold higher than that of rscu-PA (P less than .005) and fivefold to sevenfold higher than that of the control conjugate (P less than .01).

Adenosine Diphosphate↗

PubMed1991

cDNA cloning and chromosomal assignment of the endothelin 2 gene: vasoactive intestinal contractor peptide is rat endothelin 2.

Four members of the endothelin family of vasoactive and mitogenic peptides have been identified: human endothelins 1, 2, and 3 (ET1, ET2, and ET3, respectively) and mouse vasoactive intestinal contractor (VIC). To characterize the mRNA encoding ET2, a 192-bp fragment of the ET2 gene, amplified by the polymerase chain reaction from human genomic DNA, was used to screen cell lines and tissues for ET2 gene expression. ET2 mRNA was detected in a cell line (HTB119) derived from a human lung small cell carcinoma, and an ET2 cDNA was cloned from a cDNA library prepared from HTB119 mRNA. DNA prepared from human-mouse somatic hybrid cell lines was used to assign the gene encoding ET2 (EDN2) to the 1p21----1pter region of chromosome 1, demonstrating that EDN2 is not linked to genes encoding ET1 (EDN1; chromosome 6) and ET3 (EDN3; chromosome 20). Southern blot hybridization revealed a single gene in human and rat genomes that hybridized with the ET2 gene fragment, and the rat gene was cloned. The endothelin peptide encoded by the rat gene differed from ET2 at 1 of 21 residues and was identical to mouse VIC. We conclude that VIC is the mouse and rat analogue of the human ET2 gene.

Amino Acid Sequence↗

PubMed1991

Hybrid molecules: insights into plasminogen activator function.

Hybrid molecules containing the catalytic domain of either tissue plasminogen activator (tPA) or single chain urokinase-type plasminogen activator (scuPA), and the fibrin binding domain of a murine antifibrin monoclonal antibody were constructed using either cDNA or genomic DNA encoding the plasminogen activator and genomic DNA encoding antifibrin monoclonal antibody 59D8. In order to optimize expression of these fusion proteins in hybridoma cells, we compared plasminogen activator 3' UT domains (which decrease mRNA stability) with immunoglobulin and beta globin 3' UT domains (which increase mRNA stability). The presence of the plasminogen activator 3' UT domain resulted in approximately tenfold lower steady-state mRNA levels, and 300 to 500-fold lower levels of expressed functional protein. The initial goal of these studies was to increase the fibrinolytic potency and selectivity of tPA or scuPA. Fusion proteins comprising an antifibrin antibody domain and the catalytic domain of either tPA or scuPA were expressed and shown to have very different properties. The fusion protein that comprised the Fab portion of an antifibrin antibody and the catalytic domain of tPA, while displaying antigen binding properties indistinguishable from those of the parent antibody and amidolytic activity similar to that of tPA, was not more efficient than tPA in an in vitro clot lysis assay. In contrast, it had been shown that tPA chemically coupled to the same antibody was four- to sixfold more efficient in fibrinolysis both in vitro and in vivo. A recombinant scuPA-antifibrin antibody hybrid, however, was sixfold more potent than scuPA in vitro and 20-fold more potent in a rabbit thrombolysis model. An explanation for this apparent discrepancy may relate to the requirement for stimulation by fibrin in order for tPA to achieve its maximal catalytic activity, a property that was demonstrated to have been lost in the antifibrin-tPA fusion protein. In contrast, the activity of urokinase is independent of the presence of fibrin. This may explain the greater success achieved in enhancing catalytic activity in the urokinase-antifibrin fusion protein. It is of additional interest that fibrin or soluble fibrin fragments stimulate the catalytic activity of both tPA and the isolated tPA B chain, demonstrating that at least part of the enhanced catalytic activity of tPA observed in the presence of fibrin is independent of fibrin binding either by the tPA kringles or finger domain (or any heavy chain domain). These data indicate that it is possible to construct recombinant hybrid molecules in which both plasminogen activator catalytic function and antibody binding are preserved.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

PubMed1990

Polymerase chain reaction cloning of L-type calcium channel sequences from the heart and the brain.

The sequences of the highly conserved S4 regions of voltage-sensitive ion channels were used to design oligonucleotide primers for the polymerase chain reaction. Specific fragments of the cDNA encoding L-type calcium channels from the heart, brain, and skeletal muscle were amplified and cloned. The nucleotide sequences of the cardiac and brain calcium channels obtained are identical over this region, and share 78% homology with the skeletal muscle calcium channel. Comparison of the predicted amino acid sequences of our clones with those of other calcium channels reveals unexpected patterns of conservation which suggest alternative exon use.

Amino Acid Sequence↗

PubMed1990

Functional analysis of the endothelin-1 gene promoter. Evidence for an endothelial cell-specific cis-acting sequence.

Endothelin-1 (ET-1) is a peptide synthesized by endothelial cells both in culture and in vivo. ET-1 induces contraction of smooth muscle cells and stimulates growth in a variety of mesenchymal cell types. We have previously characterized the genomic organization of the ET-1 gene and described its chromosomal localization and promoter region sequence. In this report, we describe the use of fusion plasmids containing ET-1 5'-flanking sequence and the chloramphenicol acetyltransferase gene to identify cis-acting sequences that direct transcription of the ET-1 gene. When transfected into bovine aortic endothelial cells, constructs containing 143 base pairs of ET-1 5'-flanking sequence allowed maximal transcription, whereas constructs containing 129 base pairs of sequence had 40-fold lower rates of transcription. A synthetic DNA fragment encoding the region delineated by these deletion mutants was found to have a positive effect on transcription when placed in either orientation upstream of short inactive ET-1 promoter constructs. However, this increase in transcription was noted only when a second region containing an AP1 consensus sequence was also included in the constructs. In experiments with a heterologous promoter and a 119-base pair DNA fragment containing these two functional regions, this 119-base pair sequence acted in a positive and endothelial cell-specific fashion. Taken together, these data localize cis-acting sequences important in determining the rate and tissue specificity of ET-1 gene transcription and should allow the study of protein-DNA interactions which mediate transcription of this gene in endothelial cells.

Animals↗

PubMed1990

Binding of tissue-type plasminogen activator with human endothelial cell monolayers. Characterization of the high affinity interaction with plasminogen activator inhibitor-1.

The formation and release of covalent complexes between tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) limits the application of equilibrium radioligand binding analysis to characterize the interaction between t-PA and human umbilical vein endothelial cell (HUVEC) monolayers. To avoid this difficulty, we used a recombinant mutant of t-PA, S478A rt-PA, in which alanine has been substituted for the active-site serine. Although the mutant is incapable of covalently reacting with PAI-1, 125I-labeled S478A rt-PA binding to HUVEC monolayers is specific and reversible and is characterized by a high affinity (Kd of 1.5 nM) and a large number of sites (1.5 x 10(6)/cell). This binding was shown to occur through noncovalent interaction with PAI-1 in the HUVEC monolayer by the fact that a monoclonal anti-PAI-1 antibody (MA-7D4) completely blocked S478A rt-PA binding. Two solution-phase assays with recombinant PAI-1 (rPAI-1) confirmed this noncovalent interaction: complexes between 125I-S478A rt-PA and rPAI-1 could be isolated by immunoprecipitation with anti-PAI-1 antibodies, and S478A rt-PA competed with rt-PA for inactivation by rPAI-1. In contrast diisopropylphosphate rt-PA (in which the active site serine is chemically modified) showed minimal binding to HUVEC monolayers, as a result of impaired interaction with PAI-1, in the two assays. Thus, both wild-type rt-PA and S478A rt-PA interact with the HUVEC monolayer through PAI-1. With rt-PA this results in the formation of covalent rt-PA.PAI-1 complexes that are released from the monolayer into the supernatant. With S478A rt-PA this results in the formation of noncovalent complexes that remain associated with the HUVEC monolayer, thereby identifying a large pool of reactive PAI-1 molecules in the monolayer.

Alanine↗

PubMed1990

Expression of the potent vasoconstrictor endothelin in the human central nervous system.

Endothelin is a potent vasoconstrictive peptide initially characterized as a product of endothelial cells. To examine the potential role of endothelin as a neuropeptide, we studied its distribution in the human central nervous system. RNA blot hybridization provided evidence of endothelin gene transcription in a variety of functional regions of the brain. In situ hybridization confirmed the widespread pattern of endothelin transcription and indicated that the highest density of cells containing endothelin mRNA is in the hypothalamus. This technique localized endothelin transcription to cells of the nervous system as well as the vascular endothelium. Immunocytochemical studies detected endothelin immunoreactivity in neurons, providing evidence of the synthesis of the peptide in this cell type and confirming that endothelin is a neuropeptide. Although the prominent expression of endothelin in the hypothalamus may indicate a central vasoregulatory role for the peptide, the widespread distribution of endothelin in neurons in other areas of the brain implies a more fundamental role in the regulation of nervous system function.

Blotting, Northern↗

PubMed1990

Antibody-targeted thrombolytic agents.

Plasminogen activator therapy for acute myocardial infarction has become standard medical practice. Bleeding complications, however, limit the utility of the currently available agents. This article reviews how the tools of immunology, molecular biology and protein engineering are being used to develop safer and more effective plasminogen activators.

Fibrinolysis↗

PubMed1989

cDNA cloning and chromosomal assignment of the gene encoding endothelin 3.

The vasoactive peptide endothelin 1 (ET1) is encoded by a well characterized gene located on human chromosome 6. Recently, two human genomic fragments were isolated which potentially encode related vasoconstrictor peptides, endothelin 2 (ET2) and endothelin 3 (ET3) (Inoue, A., Yanagisawa, M., Kimura, S., Kasuya, Y., Miyauchi, T., Goto, K., and Masaki, T. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 2863-2867). Inoue et al. were unable to detect transcripts of the ET2 and ET3 genes and observed ET1 gene expression exclusively in endothelial cells. In this study, we document transcription of the ET3 gene by isolating from a hypothalamic cDNA library DNA clones complementary to human ET3 mRNA. ET3 mRNA encodes a 238-amino acid precursor that includes ET3 and a 15-amino acid homologous segment, the ET3-like sequence. On the basis of DNA isolated from human-mouse somatic hybrid cell lines, we assigned the ET3 gene to human chromosome 20. The ET3 and ET1 genes are, therefore, not genetically linked. RNA blot hybridization with restriction fragments derived from cDNAs revealed that the ET3 and ET1 genes are both expressed in lung, pancreas, and spleen. Cultured endothelial cells and cardiac tissues express the ET1 but not the ET3 gene. Observations that genes encoding endothelin-related peptides are expressed in a variety of human tissues suggest that these peptides may participate in complex vasoregulatory mechanisms.

Amino Acid Sequence↗

PubMed1989

Modulation of mRNA levels for urinary- and tissue-type plasminogen activator and plasminogen activator inhibitors 1 and 2 in human fibroblasts by interleukin 1.

Plasminogen activators and their inhibitors are thought to play an important role in the regulation of a variety of pathologic processes including inflammation and wound healing. IL-1 is one inflammatory mediator which has been shown to increase release of plasminogen activator (PA) Ag and activity by mesenchymal cells such as chondrocytes and synoviocytes. We have found that rIL-1 beta induces a rapid and significant accumulation of both tissue-and urinary-type plasminogen activator (t-PA and u-PA) mRNA and type 1 and 2 plasminogen activator inhibitor (PAI-1 and PAI-2) mRNA in MRC-5 fetal lung fibroblasts. An SV40 transformed fibroblast cell line, XP12RO, showed an identical response of PAI-1 and t-PA message levels but revealed no change in PAI-2 or u-PA mRNA levels with rIL-1 beta stimulation. Treatment with the transcriptional inhibitor actinomycin D blocked accumulation of t-PA, u-PA, PAI-1, and PAI-2 mRNA, suggesting that RNA synthesis is required for accumulation of all four transcripts. Cycloheximide (CHX) treatment altered the rate of PAI-1 and t-PA mRNA accumulation, but both were able to increase in the absence of protein synthesis. CHX blocked the rIL-1 beta-induced increase in PAI-2 mRNA levels normally observed at 8 h, indicating that protein synthesis is required for this response to IL-1. The increase in u-PA message level was augmented in a synergistic fashion by CHX. These data for PAI-2 and u-PA provide evidence for short-lived proteins which act either to modulate transcription of these genes or regulate mRNA stability. Thus plasminogen activators and their inhibitors are regulated in a positive and complex fashion in the fibroblast by IL-1, suggesting an important role for these molecules and this cell type in the response to inflammation.

Cell Line, Transformed↗

PubMed1989

Structural organization and chromosomal assignment of the gene encoding endothelin.

Endothelin is a 21-amino acid vasoconstrictor synthesized and secreted by vascular endothelial cells. The human peptide is derived from a 212-amino acid precursor, preproendothelin. A nearly full length clone containing DNA complementary to human preproendothelin mRNA was isolated, and its nucleotide sequence was determined. Using this cDNA as a probe, the genomic organization of the human endothelin gene was determined and the promoter region delineated. The gene contains five exons and four intervening sequences. Nucleotide sequences encoding endothelin are contained within the second exon, and the third exon specifies a portion of preproendothelin that is homologous to endothelin. The second and third exons may represent descendants of a common progenitor exon. The 3'-untranslated portion of the gene contains a 250-base pair region that is highly conserved between human and porcine genomes and may have an important role in endothelin mRNA stability. On the basis of DNA isolated from human-mouse somatic hybrid cell lines, the endothelin gene was assigned to human chromosome 6.

Amino Acid Sequence↗

PubMed1989

Innovative approaches to plasminogen activator therapy.

Plasminogen activator therapy for acute myocardial infarction has become standard medical practice. Bleeding complications, however, limit the utility of the currently available agents. This article reviews how the tools of molecular biology and protein engineering are being used to develop safer and more effective plasminogen activators.

Humans↗

PubMed1989

Variability in messenger RNA levels in human umbilical vein endothelial cells of different lineage and time in culture.

Levels of seven messenger RNA species were compared in human umbilical vein endothelial cells of different lineage and time in culture. Specifically, cells obtained from the American Type Culture Collection (ATCC) and subcultured were compared to early passage cells from cultures produced in our laboratory. Messenger RNA for tissue plasminogen activator, plasminogen activator inhibitor 1, urokinase, and thrombomodulin were expressed at higher levels in the ATCC cells. Thrombospondin, von Willebrand's Factor, and protein S messenger RNA were expressed at higher levels in the cells that we isolated. In addition, in the ATCC cells a shift in the proportion of plasminogen activator inhibitor messenger RNA from the 3.4 to the 2.4 kilobase species was found. We conclude that specific messenger RNA levels can vary considerably between cultured human umbilical vein endothelial cells. The large variation in mRNA levels which we describe has important implications for experiments involving gene expression in cultured endothelium.

Cell Division↗