MPA-induced gene expression and stromal and parenchymal gene expression profiles in luminal murine mammary carcinomas with different hormonal requirements.

Over the past several years, we have been interested in understanding the mechanisms by which mammary carcinomas acquire hormone independence. We demonstrated that carcinoma associated fibroblasts participate in the ligand-independent activation of progesterone receptors inducing tumor growth. In this study, we used DNA microarrays to compare the gene expression profiles of tumors from the MPA mouse breast cancer model, one hormone-dependent (C4-HD) and one hormone-independent (C4-HI), using whole tumor samples or laser-captured purified stromal and epithelial cells obtained from the same tumors. The expression of selected genes was validated by immunohistochemistry and immunofluorescence assays. We identified 413 genes specifically expressed in tumor stroma. Eighty-five percent of these genes were upregulated, whereas the remaining 15% were downregulated in C4-HI relative to their expression in the C4-HD tumor stroma. Several matrix metallopeptidases were overexpressed in the C4-HI tumor microenvironment. On the other hand, 1100 genes were specifically expressed in the tumor parenchyma. Among them, the 29% were upregulated, whereas the remaining 71% were downregulated in C4-HI relative to C4-HD tumor epithelium. Steap, Pdgfc, Runx2, Cxcl9, and Sdf2 were among the genes with high expression in the C4-HI tumor parenchyma. Interestingly, Fgf2 was one of the few genes upregulated by MPA in C4-HD tumors, confirming its pivotal role in regulating tumor growth in this model. In conclusion, we demonstrate herein a gene expression profile that distinguishes both the epithelial and the stromal cells in mammary tumors with different hormone dependence, supporting the hypothesis that the tumor-associated stroma may contribute to hormone-independent tumor growth.