GENE EXPRESSION PROFILES IN EPITHELIAL AND STROMAL CELLS FROM MURINE MAMMARY TUMORS WITH DIFFERENT HORMONE DEPENDENCE

SEBASTIAN GIULIANELLI; JASON I. HERSCHKOWITZ; VYOMESH PATEL; ALFREDO MOLINOLO; SILVIO GUTKIND; CHARLES M. PEROU; CLAUDIA LANARI

San Diego, California. USA

Congreso; 99th AACR Annual Meeting; 2008

AACR

The mechanisms by which hormone dependent (HD) tumors start growing without hormone supply has been a topic of study in our laboratory. We have developed an experimental model of breast cancer in BALB/c female mice in which metastatic ductal mammary carcinomas transit through different stages of hormone dependence. HD tumors (C4-HD) need the exogenous administration of medroxyprogesterone acetate (MPA) to grow in vivo, while the hormone-independent (HI) variants (C4-HI) are able to grow in untreated female mice without hormone supply. Both tumor types express high levels of estrogen and progesterone receptors (PR). In vitro, however, both tumor types have the same hormone or growth factor requirements, thus suggesting the involvement of host factors regulating in vivo tumor growth. We have also demonstrated that in vitro, carcinoma associated fibroblasts from HI tumors were different than those from HD tumors. The former induce a higher increase in epithelial cell proliferation than the latter. Thus, our hypothesis is that the stromal compartment has a pivotal role in the acquisition of the HI phenotype. To address this premise, and to broaden the scope of our in vitro observations, we have used DNA microarrays to compare gene expression profiles of C4-HD (+ MPA: n=5, - MPA: n=4) and C4-HI (n=7) using whole tumor samples or purified cells obtained by Laser Capture Microdissection (LCM) from the stroma or from the tumor parenchyma (n=3).  The RNA from each sample was isolated, amplified, labeled (Cy5) and co-hybridized with a common reference sample (C57Bl6/J and 129 male and female Day1 pups - Cy3) to Agilent Mouse Oligo Microarrays (G4121B). We used Significance Analysis for Microarrays (SAM), with a false discovery rate <5%, to find genes differentially expressed between tumors. This non redundant list (6418 genes) was used to find specific genes expressed only in stromal (411 genes) or in the parenchymal compartment (1098 genes). We could identify 348 genes that were up regulated in the stroma from HI tumors, and 63 that were down regulated, respect to HD stroma. Whereas 319 genes were up regulated in HI tumor parenchyma and 779 genes were down regulated respect to HD parenchyma. These results confirm our in vitro data indicating that the stroma from HD and HI tumors are different and it is the first report focused in stromal differences between HD and HI mammary carcinomas. Understanding the molecular mechanisms related to the acquisition of hormone independence is essential in order to design rationale treatments to delay the onset of hormone resistance.