Expression data from Control and Six1 expressing MCF7 derived xenograft tumors

Although an important association between lymph node metastasis and poor prognosis in breast cancer was observed decades ago, an active role for the lymphatic system in metastatic dissemination has only recently been examined. We demonstrate that the Six1 homeoprotein promotes peri- and intra-tumoral lymphangiogenesis, lymphatic invasion, and distant metastasis of breast cancer cells. We identify the pro-lymphangiogenic factor, VEGF-C, as required for this process, and demonstrate transcriptional induction as the mechanism of regulation of VEGF-C expression by Six1. Using a different, but complementary animal model, we show that while required, VEGF-C is not sufficient for the pro-metastatic effects of Six1. Verifying the clinical significance of this pro-metastatic Six1-VEGF-C axis, we demonstrate co-expression of Six1 and VEGF-C in human breast cancer. Two Control and two Six1 expressing MCF7 clones were orthotopically injected into NOD/Scid mice forming a total of 3 Control and 3 Six1 tumors that were allowed to grow to 2 cm^3 . The tumors were dissected and total RNA was isolated from each tumor and hybridized to Affymetrix arrays