Heparin inhibits phorbol ester‐induced ornithine decarboxylase gene expression in endothelial cells

Abstract

Glycosaminoglycans regulate angiogenesis by affecting the availability of different growth factors for the endothelial cell (EC). However, little is known about the molecular and functional consequences resulting from direct interaction of these polyelectrolytes with the EC. Here we show that heparin markedly inhibited serum-stimulated DNA synthesis and ornithine decarboxylase (ODC) mRNA expression in human endothelial cells (HEC). About 50% of the serum effect on DNA synthesis and ODC gene expression was prevented by the selective protein kinase C (PKC) inhibitor chelerythrine or by PKC down-regulation. Heparin was ineffective in counteracting that part of the effect of serum that was resistant to PKC inhibition or down-regulation. In serum-free cultured HEC, heparin completely abolished the increase in DNA synthesis and ODC mRNA expression elicited by a number of PKC activators. Cell exposure to difluoromethylornithine, an irreversible inhibitor of ODC enzyme, dramatically antagonised both serum-and phorbol 12-myristate 13-acetate (PMA)-stimulated DNA synthesis. These results suggest that inhibition of PKC-mediated ODC gene expression by glycosaminoglycans may represent an important mechanism in the regulation of HEC proliferation.z 1998 Federation of European Biochemical Societies.

Inhibition of the MEK/ERK signaling pathway by the novel antimetastatic agent NAMI‐A down regulates c‐mycgene expression and endothelial cell proliferation

“…Finally, the cells were digested by the addition of 25 m formic acid (500 µL). Each formic acid digest was transferred with one rinse of NaCl/P i (1 mL) to a scintillation vial containing 3.5 mL of INSTA‐GEL scintillation fluid (Packard instrument Co., Meriden, CT, USA), and radioactivity was determined by liquid scintillation counting using a Wallac 1215 RackBeta liquid scintillation counter (LKB Instrument Inc., Gaithersburg, MD, USA) [16].…”

Heparin down‐regulates the phorbol ester‐induced protein kinase C gene expression in human endothelial cells: enzyme‐mediated autoregulation of protein kinase C‐α and ‐δ genes1

“…2C, D). We have previously shown that heparin failed to abolish completely the serum‐stimulated DNA synthesis in HEC and that the effect of the polyelectrolyte occurred by the inhibition of a serum‐activated PKC‐dependent pathway [21]. Here, we investigated whether such a signalling mechanism may also be involved in the induction of PKC genes.…”

“…Consonant with growth inhibition, heparin inhibits the expression of the early proto‐oncogenes c‐fos and c‐myc by acting selectively on a PKC‐dependent pathway [18–20]. The inhibition of this signalling pathway was also found to be the mechanism by which heparin down‐regulated the ODC gene expression and cell proliferation in EC [21]. It is increasingly becoming evident that PKC isoenzyme gene expression, besides enzyme activity, may elicit complex cellular responses.…”

“…Here, we assessed whether serum and/or PMA may affect the PKC gene expression in HEC and hypothesize that the growth inhibitory response elicited by heparin in HEC [21] may be associated with changes in the PKC gene expression. The current experimental data show that the exposure of HEC to serum or the treatment with PMA in a serum‐free medium enhanced the expression of both PKC‐α and ‐δ mRNA with a similar time course, suggesting that PKC is involved in serum stimulation of the PKC gene expression.…”

“…In particular, glycosaminoglycan‐mediated inhibition of cell proliferation [14–16] and angiogenesis [17] has been associated, at least in part, to the ability of heparin and heparan sulfate to counteract PKC‐mediated events [18–20]. In this regard, we have recently shown that heparin markedly reduced both the serum‐ and phorbol ester‐stimulated DNA synthesis in HEC by eliciting the down‐regulation of the PKC‐mediated ornithine decarboxylase gene expression (ODC) [21]. The elucidation of the effects induced by growth regulators on the expression of selected PKC genes is now becoming an area of inquiry.…”