Transcriptional profiling of MMTV-tTA/TOP-ICN1 tumor derived cell lines comparing untreated (ICN1-On) cells to 24-hour doxcycline treated (ICN1-Off) samples

NOTCH activation has been recently implicated in human basal-like breast cancers associated with a poor prognosis. To address the role of Notch1 in mammary transformation and mammary tumor initiating cell activity, we developed a doxycycline-regulated model of Notch1-mediated mammary transformation. These mice develop mammary adenocarcinomas that express cytokeratin (CK) 8/18 and contain rare cells that also express keratin 14. In vivo limiting dilution analyses reveal that these mammary tumors exhibit functional heterogeneity and harbor a rare (1/2978) mammary tumor initiating cell population. Using this dox-regulated Notch1 mammary tumor model, we demonstrate that Notch1 inhibition results in mammary tumor regression in vivo and prevents disease recurrence in 4 of 6 tumors tested. Consistent with the in vivo data, Notch1 inhibition reduces mammary tumorsphere forming activity in vitro. Using doxycycline-responsive tumor derived cell lines, we also identify the embryonic stem cell transcription factor Nanog as a novel Notch1-regulated gene in mammospheres. These data indicate that Notch1 contributes to mammary tumor initiating activity and raises the possibility that NOTCH therapeutics may have efficacy in human basal-like breast cancers associated with NOTCH activation.

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