Irradiation induces upregulation of CD31 in human endothelial cells

Radiation-induced vascular injury is believed to be a major factor contributing to parenchymal atrophy, fibrosis and necrosis in normal tissue after radiotherapy. In this study irradiation of human umbilical vein endothelial cells (HUVECs) significantly increased adherence of U-937 cells in a time-dependent manner. Given the potential multifunctional role of CD31 in the vasculature we have examined the possible effects of irradiation on levels of CD31 expression in HUVECs. Irradiation upregulated CD31 expression on HUVECs, independently of initial plating density and radiation-induced changes such as cell number, cell cycle stage, or cell size. CD31 mRNA levels were raised in irradiated HUVECs relative to controls. Both CD31 mRNA and surface protein showed similar changes, suggesting that the increase in mRNA in irradiated HUVECs is responsible for the elevation in cell surface protein. A semi-quantitative study of tissue specimens from patients who had received radiotherapy indicated that CD31 staining in the blood vessels from irradiated tissues was increased compared with controls. Endothelial CD31 is important in the transmigration of leukocytes. We have demonstrated that the incorporation of monoclonal antibody to CD31 significantly inhibited the transmigration of human peripheral blood leukocytes through a monolayer of irradiated HUVECs. Taken together these data strongly suggest that irradiation induces a marked increase in CD31 expression on endothelial cells as part of a general response to irradiation. Its upregulation may play an important role in the development of radiation-induced normal tissue damage and thus is a possible target for therapeutic intervention.

Transcriptional activation of vesicular monoamine transporter 2 in the pre-B cell line Ea3.123

Uptake and storage of monoamines in secretory granules is accomplished by vesicular monoamine transporters, and it is likely that vesicular monoamine transporter 2 (VMAT2) is important for histamine transport in vivo. In the present study we have used the pre-B-cell line Ea3.123 to investigate the mechanisms involved in the transcriptional activation of the VMAT2 gene. In Ea3.123 cells, VMAT2 mRNA abundance was increased following mobilization of intracellular calcium, and this increased mRNA expression was paralleled by changes in l-histidine decarboxylase mRNA, suggesting that VMAT2 may be responsible for sequestration of histamine into secretory vesicles in this cell line. We cloned the 5'-flanking region of the VMAT2 gene and determined its transcriptional start site by primer extension of rat VMAT2 mRNA. There was no TATA or TATA-like sequence upstream of this region; instead there were GC-rich elements, Ca2+/cAMP-response-element- and SP1-binding motifs. Approx. 900 bp upstream of the transcriptional start site was a purine-pyrimidine repeat sequence that may form a Z-DNA structure. A series of 5'-deletional VMAT2-promoter segments cloned upstream of a luciferase reporter were capable of driving transcription and indicated the presence of multiple regulatory elements, while stimulation with ionomycin or PMA resulted in an increased level of the transcriptional activity of the 5'-promoter segments studied.

Regulation by gastric acid of the processing of progastrin-derived peptides in rat antral mucosa

1. Inhibition of gastric acid secretion by proton pump inhibitors like omeprazole increases the synthesis and secretion of the pyloric antral hormone gastrin. We report here how omeprazole influences the conversion of the gastrin precursor to its final products, and the abundance of mRNAs encoding proteins associated with progastrin processing in rat antral mucosa. 2. Progastrin processing was studied using a pulse-chase protocol in antral mucosa, incubated in vitro, from rats treated with omeprazole for up to 5 days. Labelled peptides were detected by on-line scintillation counting after immunoprecipitation and HPLC. The mRNAs encoding prohormone-processing enzymes were identified by Northern blot, polymerase chain reaction or ribonuclease protection assay, and their cellular origins identified by immunocytochemistry. 3. Cleavage of [3H]- and [35S]-labelled progastrins at Arg-94-95 or Arg-57-58, and amidation at Phe-92 were not influenced by pretreatment with omeprazole. In contrast, cleavage of G34 (the thirty-four amino acid amidated gastrin) at Lys-74-75 to give G17 (the seventeen amino acid amidated gastrin), and of G34-Gly to G17-Gly (G34 and G17 with COOH-terminal glycine), was increased 3-fold after treatment with omeprazole for either 1 or 5 days. 4. Approximately 20% of newly synthesized amidated and Gly-extended gastrins were secreted within 240 min of the labelling period in omeprazole-treated samples, but secretion of labelled gastrins from control tissue was undetectable over a comparable period. 5. The amidating enzyme, peptidyglycine alpha-amidating mono-oxygenase (PAM), the prohormone convertases PC1/3, PC2, PC5 and the PC2 chaperone 7B2 were localized to rat antral gastrin cells by immunocytochemistry. The relative abundance of mRNA species encoding 7B2, PC5 and PAM were unchanged after treatment with omeprazole for 5 days, whereas gastrin, PC1/3 and PC2 mRNAs are known to increase at this time. 6. The main consequence of increased cleavage at Lys-74-75 is the production of G17 and G17-Gly at the expense of G34 and G34-Gly, respectively. The latter have longer plasma half-lives, and so their increased cleavage may serve to limit the rise in plasma gastrin concentration after inhibition of acid secretion. Changes in the abundance of mRNAs encoding prohormone-processing enzymes cannot account for the rapidity of the changes in cleavage of progastrin at Lys residues after omeprazole.

Identification and expression of prohormone-converting enzymes in the rat stomach

The conversion of regulatory peptide precursors to their active forms usually involves limited proteolysis that may be mediated by subtilisin-like prohormone convertases (PC). We have examined the representation of this enzyme family in rat gastric mucosa. With the use of polymerase chain reaction, employing primers to conserved sequences, we identified from rat antrum clones corresponding to PC1/3, PC2, PC5, and furin. Northern blots indicated that the mRNAs for PC1/3 and PC2 were substantially more abundant in mucosa compared with muscle, and that there were differences in expression in antrum and corpus. In the antrum a PC1/3 probe identified hands of 3 and 4.5 kb that were of equal intensity and were both increased in fasted rats; in corpus, the latter mRNA species predominated and did not change with fasting. In rats treated with omeprazole, there was a preferential increase in the antral 3-kb band. In both antrum and corpus, a PC2 probe hybridized with a band of 2.8 kb that increased in omeprazole-treated rats. The data suggest that 1) PC1/3 and PC2 are expressed in antral mucosa and so are candidates for gastric regulatory peptide processing, 2) there is selective processing of the mRNAs encoding prohormone convertases in different gastric cell populations, and 3) the expression of these enzymes is physiologically regulated.

Transformation of the filamentous fungus Gibberella fujikuroi using the Aspergillus niger niaD gene encoding nitrate reductase

A transformation system for Gibberella fujikuroi based on the Aspergillus niger nitrate reductase gene (niaD) was developed. A strain (designated SG140) carrying a non-reverting niaD mutation (niaD11) was generated by screening mutagenised cells for non-growth on nitrate as sole nitrogen source. Transformation frequencies of 1-2 transformants per microgram DNA were observed when strain SG140 was transformed to nitrate utilisation. Southern blot analyses of niaD+ transformants showed that the vector DNA sequences were integrated into the chromosomal DNA. The results demonstrate that the A. niger niaD gene is expressed in G. fujikuroi.

Improved transformation efficiency of Aspergillus niger using the homologous niaD gene for nitrate reductase

Aspergillus niger transformation frequencies of up to 1,176 transformants per micrograms DNA were achieved using the plasmid vector pSTA10 containing the A. niger nitrate reductase structural gene. Analysis of genomic endonuclease cleaved DNA from nitrate utilising transformants by DNA hybridisation, showed that most integration events are as a result of homologous recombination. The niaD transformation system was used successfully for the introduction of the unselected Escherichia coli fusion genes lacZ, encoding beta-galactosidase, and uidA, for beta-glucuronidase, as well as the Neurospora crassa tub-2 gene, for beta-tubulin. pSTA10 was also capable of transforming niaD mutants of other filamentous fungi such as A.nidulans, A. oryzae and Penicillium chrysogenum.