Tyrosine phosphorylation modulates the vascular responses of mesenteric arteries from human colorectal tumors

Abstract

The aim of this study was to analyze whether tyrosine phosphorylation in tumoral arteries may modulate their vascular response. To do this, mesenteric arteries supplying blood flow to colorectal tumors or to normal intestine were obtained during surgery and prepared for isometric tension recording in an organ bath. Increasing tyrosine phosphorylation with the phosphatase inhibitor, sodium orthovanadate produced arterial contraction which was lower in tumoral than in control arteries, whereas it reduced the contraction to noradrenaline in tumoral but not in control arteries and reduced the relaxation to bradykinin in control but not in tumoral arteries. Protein expression of VEGF-A and of the VEGF receptor FLT1 was similar in control and tumoral arteries, but expression of the VEGF receptor KDR was increased in tumoral compared with control arteries. This suggests that tyrosine phosphorylation may produce inhibition of the contraction in tumoral mesenteric arteries, which may increase blood flow to the tumor when tyrosine phosphorylation is increased by stimulation of VEGF receptors.

Figure 1

Contraction in response to sodium orthovanadate (10⁻⁴–10⁻²M) of mesenteric arteries supplying colorectal tumours (tumor, n = 10) and those supplying normal colon (control, n = 9), in the absence or in the presence of genistein (10⁻⁴M, n = 4). Values are represented as mean ± SEM. *P < 0.05 statistically significant versus control.

Figure 2

Contraction in response to noradrenaline (10⁻⁹–10⁻⁴M) of mesenteric arteries supplying colorectal tumours (tumour, n = 6) and those supplying normal colon (control, n = 6), untreated or treated (n = 6-7) with sodium orthovanadate (10⁻³M). Values are represented as mean ± SEM. **P < 0.01; *P < 0.05 statistically significant versus untreated segments.

Figure 3

Relaxation in response to bradykinin (10⁻⁹–10⁻⁵M) of mesenteric arteries supplying colorectal tumours (tumour, n = 7) and those supplying normal colon (control, n = 7), precontracted with U46619 and untreated or treated (n = 8) with sodium orthovanadate (10⁻³M). Values are represented as mean ± SEM. *P < 0.05 statistically significant versus untreated segments.

Figure 4

RT-PCR analysis of mRNA expression for VEGF-A, FLT1, and KDR in mesenteric arteries supplying colorectal tumours (tumour, n = 6) and those supplying normal colon (control, n = 6). Values were normalized to GAPDH mRNA expression. Data are presented as mean ± SEM. *P < 0.05 statistically significant versus control samples.

Figure 5

Protein expression in mesenteric arteries supplying colorectal tumours (T, n = 10) and those supplying normal colon (C, n = 10). VEGF-A, FLT1, KDR, and α-tubuline expression was determined by western blot. Data are presented as means ± SEM. *P < 0.05 statistically significant versus control samples.