Irradiation induces up-regulation of E9 protein (CD105) in human vascular endothelial cells

The use of MAb E-9 raised against tissue-cultured endothelial cells (EC) has shown marked heterogeneity in vascular EC lining the blood vessels of normal and tumour tissues. MAb E-9 is human EC-specific and the protein recognized by it is a homodimer with a molecular mass of 97 kDa. The E-9 protein is resistant to treatment by 3 mM sodium periodate, but is sensitive to 10% trichloroacetic acid and 70% ethanol. E-9 protein has been assigned to a new cluster, CD105, and mapped to human chromosome 9q3. It has approximately 70% homology with type-III cell-surface receptor for transforming growth factor beta (TGF-beta). Recently CD105 has been reported to be the gene in patients with hereditary haemorrhagic telangiectasia. We have examined the effects of radiation on its expression in normal human umbilical-vein endothelial cells (HUVEC) and brain-tumour-derived endothelial cells (BTEC). Irradiation induced dose- and time-dependent up-regulation in the expression of the E-9 protein on the plasma membranes of EC, and also resulted in greater increase in the expression of the E-9 protein in semi-confluent (proliferating) as compared with confluent (non-proliferating) EC. It may well be that, following radiotherapy in cancer patients, E-9 protein is also up-regulated. The presence of increased amounts of E-9 protein in EC makes it an attractive target in the control of angiogenesis, especially after radiotherapy in cancer patients. The time scale involved in the up-regulation of E-9 protein following irradiation has led us to suggest that it may be a secondary event, the primary being the production and release of mitogenic factors (such as basic fibroblast growth factor) from irradiated EC.

Irradiation of bovine aortic endothelial cells enhances the synthesis and secretion of sulphated glycosaminoglycans

The effect of X-irradiation on the synthesis of heparan sulphate (HS) and chondroitin/dermatan sulphate (CS/DS) by bovine aortic endothelial cells (BAEC), was studied by measuring the incorporation of [35S]sulphate and [3H]glucosamine into newly synthesized glycosaminoglycan (GAG) chains. Medium extracts from irradiated cultures (5Gy) were found to contain approx. 130% more HS and 200% more CS/DS than unirradiated controls. Smaller increases were observed in cellular extracts, irradiated cultures (5Gy) containing approx. 60% more HS and 100% more CS/DS than unirradiated controls. Structural studies showed no significant changes occurred upon irradiation in either the amounts or distribution of N- and O-sulphate groups in the HS molecule. Values for N-sulphation of 41.1% control and 41.5% irradiated (5Gy) were obtained, the corresponding values for O-sulphation being 19.9% control and 20.2% irradiated. Isotope incorporation data indicated that sulphation of CS/DS may decrease after irradiation, however, analysis of chondroitin ABC lyase derived disaccharides showed no changes in the proportion of non-sulphated and O-sulphated disaccharides. The present study indicates that X-irradiation stimulates the synthesis and secretion of HS and CS/DS proteoglycans (PGs) by BAEC. This could be relevant to many features which are found to be indicative of radiation-induced damage.

The multifactorial role of ATP in repair processes and radioprotection

Endogenous ATP as a source of energy appears to play an important role associated with repair processes after ionising radiation damage in living organisms. Also exogenous ATP can play a central part in radioprotection. This paper considers interaction between the multifactorial roles of ATP in radioprotection and metabolic provision for repair processes, which can depend on its physiological regulatory function as a neuromodulator via cell membrane receptors. It is hypothesised that all these complex functions reflect an adaptive defence mechanism, against radiation insults, in which ATP plays a pivotal role to maintain homeostasis.