Abstract P1-05-03: A requirement for neural precursor cell-expressed developmentally downregulated gene 9 during the initiation of mammary tumorigenesis in MMTV-neu mice

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Abstract The Neural precursor cell-Expressed Developmentally Downregulated gene 9 (NEDD9; also HEF1, CAS-L) scaffolding protein regulates many signaling pathways associated with mitosis, survival, migration, and ciliary integrity. Within the last few years, elevated NEDD9 expression has been implicated in progression and metastasis of several types of cancer, including those of the lung, skin, and brain. We have investigated the consequences of introducing a Nedd9 genotype into the MMTV-neu mouse mammary tumor model, which in many respects recapitulates features of human HER2+ breast cancer. 80% of wild-type MMTV-Neu; Nedd9+/+ animals developed tumors with an average latency of 339 days, but only 18% of MMTV-Neu;Nedd9−/− animals developed tumors with an average latency of 416 days. This highly significant difference indicates that the Nedd9−/− genotype significantly prevents neu-dependent mammary tumor formation. HER2-positive human breast tumors and MMTV-neu-induced tumors originate from mammary luminal epithelial progenitor cells. We evaluated mammary progenitor cell populations from non-tumor bearing MMTV-neu;Nedd9−/− versus MMTV-neu;Nedd9+/+ 4-month old mice (2 months prior to appearance of tumors). Flow cytometry analysis indicated a significantly reduced CD24high;CD49flow luminal progenitor subpopulation in MMTV-neu;Nedd9−/− and Nedd9−/− mammary glands, that could be contributed to the tumorigenesis resistance in the MMTV-neu;Nedd9−/− model. The MMTV-neu;Nedd9−/−genotype negatively affected the Matrigel mammosphere colony-forming potential of luminal progenitor cells compared to MMTV-neu; Nedd9+/+cells, causing formation of fewer colonies with aberrant size and morphology. Quantification of mitotic division planes of MMTV-neu;Nedd9−/− mammospheres revealed no contribution to the observed defects. However, MMTV-neu;Nedd9−/− mammospheres had defective expression of signaling proteins governing cell attachment, with reduced levels of FAK and more cytoplasmic localization of SRC. The results reported above, together with other data, support three main conclusions. First, they revealed a very substantial requirement for Nedd9 during early stages of HER2/neu-dependent tumor formation. Second, these results are the first to demonstrate a role for Nedd9 in supporting the abundance and colony-forming potential of mammary luminal progenitor cells. Third, they indicate that the defects in mammosphere growth likely involve perturbation of crucial cellular attachment signaling pathways involving FAK and SRC. In sum, these data provide a strong justification for future analysis of NEDD9 in the defective signaling of transformed mammary epithelial progenitor cell populations that initiate human breast cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-03.