HER2 regulatory control of angiopoietin-2 in breast cancer

Background. HER2 overexpression is a marker of aggressive breast cancer. Tumors that overexpress HER2 induce endothelial cell retraction and endothelial destabilization. Because angiopoietin-2 (Ang-2) also destabilizes microvessels, we postulated that HER2 signaling upregulates Ang-2 as a mechanism of angioinvasion. Methods. We tested human breast cancers and breast cancer cell lines for coexpression of HER2 and Ang-2 with Northern blot, reverse transcriptase-polymerase chain reaction, and enzyme-linked immunosorbent assay. Further, we manipulated HER2 signaling with 100 ng/mL MAbHu HER2 (Herceptin; Genentech, San Francisco, Calif) and Heregulin beta 1 (100 ng/mL; R&D Systems, Inc; Minneapolis, Minn) to test for HERB regulation of Ang-2 production. Results. Three of 4 breast cancer cell fines expressed HER2 protein and Ang-2 mRNA. HER cells, a stably transfected cell line that overexpresses HER2 6-fold, showed a 430% increase in Ang-2 mRNA compared to parental MCF-7 cells. Heregulin beta 1 stimulation of HER2 signaling in MCF-7 cells increased Ang-2 by 20% (P <.05). HER2 signaling blockade with 100 ng/mL Herceptin reduced Ang-2 mRNA 90% (P <.001). Five of 11 cancers expressed both HER2 and Ang-2; 2 cancers expressed only Ang-2. Conclusions. We conclude that human breast cancers express Ang-2. HER2 signaling appears to regulate Ang-2 expression, although other signaling pathways may also regulate Ang-2. Ang-2 may be a therapeutic target in these cancers and may define which patients would benefit from Herceptin therapy.