Radiation-induced angiogenic signaling pathway in endothelial cells obtained from normal and cancer tissue of human breast.

Despite strong possibility that endothelial cells (ECs) of tumors and normal tissues may differ in various aspects, most previous studies on ECs have used normal cells. Here, we purified ECs from tumorous and normal human breast tissues, and studied the effect of radiation on angiogenesis and relevant molecular mechanisms in these cells. We found that in normal tissue-derived ECs (NECs), 4 Gy irradiation increased tube formation, matrix metalloproteinase 2 (MMP-2) expression and extracellular signal-regulated kinase (ERK) pathway activation. In cancer-derived ECs (CECs), however, 4 Gy irradiation significantly reduced tube formation, increased the production of angiostatin and interleukin-6 (IL-6), and upregulated AKT and c-Jun N-terminal kinase (JNK) pathway activation. Knockdown experiments showed that siMMP-2 efficiently inhibited tube formation by irradiated NECs, whereas siPlasminogen effectively attenuated the radiation-induced suppression of tube formation and the upregulation of angiostatin in CECs. Moreover, siIL-6 clearly inhibited the radiation-induced generation of angiostatin in CECs. Inhibition of ERK with a pharmacological inhibitor or small interfering RNAs (siRNAs) markedly suppressed the radiation-induced tube formation and MMP-2 upregulation in NECs, whereas the inhibition of either AKT or JNK with pharmacological inhibitor or siRNA treatment of CECs markedly attenuated the inhibition of tube formation and the upregulation of angiostatin and IL-6 caused by 4 Gy irradiation. These observations collectively demonstrate that there are distinct differences in the radiation responses of NECs and CECs, and might provide important clues for improving the efficacy of radiation therapy.