Nitrotyrosination of endothelial α-tubulin:: Potential effects on binding of the tumour vascular-targeting agent, combretastatin A-4-P

The intrinsic ability of endothelial cells to add or remove tyrosine and 3-nitrotyrosine to/from a-tubulin was investigated as a potential modulator of the anti-vascular action of the tubulin-binding agent, combretastatin A4-phosphate (CA-4-P). Both substrates were incorporated into a-tubulin proficiently. Subsequent incubation in deficient medium resulted in the loss of tyrosine but not 3-nitrotyrosine from endothelial tubulin. Incorporation of 3-nitrotyrosine, but not tyrosine, resulted in increased permeability of endothelial cell monolayers with similar magnitude to that evoked following tubulin-depolymerisation by CA-4-P. Immuno-histochemical 3-nitrotyrosine was present in a tumour type that responds to CA-4-P. We conclude that nitrotyrosination of a-tubulin in endothelial cells may contribute to the susceptibility of tumours to CA-4-P.