P4-05-01: Rab25 Alters Cellular Energetics and Growth Signaling during Breast Oncogenesis.

Abstract

Abstract Background: Conservation and consumption of cellular energy is centrally regulated by growth and metabolism of the whole organism. The cancer cell gains autonomy from this regulation to become an organism with indeterminate growth potential. Plasma membrane receptors including growth factors and nutrient receptors are sensors for microenvironmental cues that dictate the intracellular energetic pathways to recalibrate ATP production based on available resources. So altercations in both growth and metabolic pathways are common features of cancers. A unifying component between receptor mediated growth signaling and metabolic pathways within a cell could be the vesicular trafficking system that imports, transports and exports a wide array of cargo from both these pathways. In fact, derailed endocytosis is a hallmark of cancer. The endocytic pathway, as demonstrated by our laboratory, is a frequent target of genomic aberrations in cancer, and plays a critical role in maintenance of cellular polarity, stem cell fnction, bioenergetics, proliferation, motility, invasion, metastasis, apoptosis and autophagy. The Rab GTPases along with their effectors are critical regulators of this endocytic machinary and can have a huge impact on the cellular iterinary of growth and metabolism. Methods and results: A broad spectrum analysis of distribution of all the Rab family members across 52 breast cancer cell lines reflected a dichotomous distribution of Rab25, with higher mRNA and protein expression in ER+ cell lines. Rab 25 is of immense interest to us because of its unique substitution of leucine for glutamine at position 71which typically decreases the intrinsic GTPase activity, resulting in a dominant, constitutively active protein, akin to a transforming RAS mutation. Using high throughput mRNA data analysis, we report that Rab25 and its effector Rab Coupling Protein (RCP) are frequently coamplified and coordinately elevated in ER +ve breast cancers. Specifically in the luminal B subtypes, they are significantly associated with a markedly worsened outcome. In vitro, in MCF7 cell line, we observe an increased EGFR stability and MAPK signaling in Rab25 overexpressing stable clones which could be reversed with shRNA knockdown of Rab25. Loss of either Rab25 or RCP inhibited survival and growth of MCF7 lines under serum free conditions suggesting that Rab25 can potentially facilitate growth factor independence in cancer cells. Most importantly, we report that Rab25 enhances mitochondrial ATP production in breast and ***ovarian cancer cells and significantly reduces acidification of the ECM. Our ongoing experiments are directed towards understanding the mechanistic link between Rab25 mediated effects on EGFR/pERK signaling and its effects on cellular metabolism. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-05-01.