Abstract P4-06-19: Role of Caveolin-1 and PDGFR in Inflammatory Breast Cancer

Inflammatory breast cancer is a highly metastatic form of locally advanced breast cancer. Its uniqueness lies in the fact that it is found to be highly metastatic from the inception. Given the clinical differences between IBC and non-IBC, it is hypothesized that IBC has a characteristic molecular profile. Microarray data reveals interesting differences in the genetic makeup of these two cancer types. Caveolin-1, 2 proteins typically have much reduced expression in other breast cancers; however, this is not the case in inflammatory breast cancer. Caveolins, primarily caveolin-1 and 2 are over-expressed in IBC cells SUM 149. Caveolin-1 is membrane-associated protein located in lipid rafts called ‘caveolae9. Its unique scaffolding domain is known to concentrate several signaling molecules including PDGFR, Rho GTPases etc. leading to unique signaling cascades. Due to this characteristic feature, caveolin-1 has become one of the potential regulators of many cellular signaling and trafficking pathways that control cell growth and migration. Previously, our laboratory demonstrated that RhoC GTPase is responsible for the invasive phenotype of IBC. However, the mechanism of RhoC activation has not been elucidated yet. Preliminary data from Translational cancer research group Antwerp, Belgium shows over-expression of PDGFR alfa at mRNA level in IBC patient samples. Therefore, primary objectives of our study are to determine whether the highly invasive phenotype of IBC is due to increased PDGFR signaling through Akt1 leading to increased RhoC activation and what role does caveolin-1 play in regulating the interaction of PDGFRA and RhoC GTPase in Inflammatory breast cancer. We first determined the down-regulation of caveolin-1 at the mRNA level using varying doses of caveolin-1-specific siRNA in the inflammatory breast cancer cell line, SUM 149. QPCR showed a maximum down regulation of 50% at the mRNA level 72 h post siRNA treatment; bringing caveolin-1 mRNA levels close to the levels in normal human mammary epithelial cells. Next we quantitatively analyzed the effect of caveolin-1 down-regulation on SUM 149 cell invasiveness through a Matrigel coated filter. After 72 h caveolin-1 siRNA treatment, the percent invasion of SUM149 IBC cells was significantly reduced to 10% as compared to the control SUM 149 cells. We also determined that siRNA treatment does not affect cell viability or proliferation. This data supports our hypothesis that over-expression of caveolin-1 is involved in the invasive phenotype of IBC and is possibly due to interactions with RhoC GTPase. We are particularly interested in PDGFR that is found to be associated with caveolin-1 at plasma membrane. So far, we have found mRNA and protein expression of PDGFR in SUM 149 cells. However, instead of doublet at 150 and 180kDa in control NIH3T3 cells, SUM 149 cells produce only single band at 140-150kDa. Data from our lab shows that SUM 149 cells express high levels of active Akt1 and selective downregulation of Akt1 significantly reduces SUM 149 cells invasion. These results support our hypothesis that high levels of PDGFR in SUM 149 cells act through Akt1 causing RhoC activation at caveolin-1 and thus regulate invasive and metastatic behavior of IBC. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-06-19.