Angiopoietin-1 is inversely related to thymidine phosphorylase expression in human breast cancer, indicating a role in vascular remodeling

Purpose: Angiogenesis is essential for tumor growth and metastasis. It is a complex, dynamic process that is coordinated by several classes of angioge nic factors. One candidate family is the Tie2 tyrosine kinase, whose expres sion is restricted largely to endothelial cells. Tie2 has three known ligan ds, angiopoietin (Ang)-1, Ang-2, and Ang-4, that have different functional effects but play a requisite role in embryonic vessel remodeling. Because t here are only limited data on the Tie2 pathway in human breast cancer, and our previous data have suggested that breast tumors establish a blood suppl y by vascular remodeling, we have investigated the expression of Ang-l, Ang -2, Ang-4, and Tie2 in a series of normal and neoplastic human breast tissu es. Experimental Design: We examined mRNA expression by reverse transcription-P CR in 6 normal and 52 malignant breast tissues and correlated expression wi th clinicopathological and angiogenic variables. We also examined the effec t of physiological levels of estrogen on Ang expression. Results: Ang-l, Ang-2, Ang-4, and Tie2 were detected in 19%, 52%, 35%, and 65%, respectively, of tumor samples. There was a significant reduction in e xpression of tumor Ang-1 (P = 0.03), Ang-2 (P = 0.01), Ang-4 (P = 0.004), a nd Tie2 (P = 0.02) compared with that in normal breast tissues. There was a significant relationship in tumors between ah Angs and between each ligand and Tie2. In a multivariate analysis, there were significant positive corr elations between Ang-4 and estrogen receptor (P = 0.016) and a significant inverse correlation between Ang-l and thymidine phosphorylase expression (P = 0.01). No significant associations were observed between the other membe rs of the Ang/Tie2 gene family and patient age, tumor size, lymph node stat us, tumor grade, vascular invasion, tumor vascularity, vascular maturation, thymidine phosphorylase, or vascular endothelial growth factor A expressio n (P > 0.05 for all). The potential regulation of Ang-4 by estrogen was fur ther investigated in vitro. Addition of physiological concentrations of 17 beta -estradiol (1 nM) to hormone-free media caused no significant change i n Ang-4 mRNA abundance (P = 0.75) in the estrogen receptor-positive cell li ne MCF-7 after either 2 or 18 h, despite demonstrating induction for the es trogen response gene pS2. Conclusions: These findings suggest that the Ang/Tie2 pathway plays a signi ficant role in human breast tumor angiogenesis but provide no initial evide nce for direct regulation of the pathway by estrogen.