Accumulating literature implicates pathological angiogenesis and lymphangiogenesis as playing key roles in tumor progression. Autocrine human growth hormone (hGH) is a wild-type orthotopically expressed oncogene for the human mammary epithelial cell. Herein we demonstrate that autocrine hGH expression in the human mammary carcinoma cell line MCF-7 stimulated the survival, proliferation, migration, and invasion of a human microvascular endothelial cell line (HMEC-1). Autocrine/paracrine hGH secreted from mammary carcinoma cells also promoted HMEC-1 in vitro tube formation as a consequence of increased vascular endothelial growth factor-A (VEGF-A) expression. Semiquantitative RT-PCR analysis demonstrated that HMEC-1 cells express both hGH and the hGH receptor (hGHR). Functional antagonism of HMEC-1-derived hGH reduced HMEC-1 survival, proliferation, migration/invasion, and tube formation in vitro. Autocrine/paracrine hGH secreted by mammary carcinoma cells increased tumor blood and lymphatic microvessel density in a xenograft model of human mammary carcinoma. Autocrine hGH is therefore a potential master regulator of tumor neovascularization, coordinating two critical processes in mammary neoplastic progression, angiogenesis and lymphangiogenesis. Consideration of hGH antagonism to inhibit angiogenic processes in mammary carcinoma is therefore warranted.

Deregulated PAX5 expression has been associated with metastatic mammary carcinoma, although the precise role of PAX5 in cancer progression is unclear. Stable forced expression of PAX5α in the mammary carcinoma cell lines MCF-7 and MDA-MB-231 reduced cell cycle progression, cell survival, and anchorage-independent cell growth. In xenograft studies, forced expression of PAX5α was associated with a significant reduction in tumor volume. Furthermore, forced expression of PAX5α in mammary carcinoma cells resulted in altered cell morphology with resultant enhancement of epithelial cell characteristics. Morphologic changes were associated with localization of β-CATENIN at cell-cell junctions and with altered mRNA expression of mesenchymal markers in mammary carcinoma cells. In addition, forced expression of PAX5α in MCF-7 and MDA-MB-231 cells significantly reduced cell migration and invasion. Concomitantly, small interfering RNA-mediated depletion of PAX5α increased MCF-7 total cell number, cell motility, migration, and invasion. These studies show that PAX5α enhances the epithelial characteristics of mammary carcinoma cells, reminiscent of mesenchymal to epithelial transition. Mol Cancer Res; 8(3); 444-56. ©2010 AACR.