Radiation-Induced Notch Signaling in Breast Cancer Stem Cells

Abstract

Purpose Breast cancers are thought to be organized hierarchically with a small number of breast cancer stem cells able to self-renew and to regrow the entire tumor. Importantly, breast cancer stem cells are resistant to established chemotherapeutic agents and relatively resistant to radiation. Self-renewal of breast cancer stem cells is under control of the Notch signaling pathway, which suggests that targeting this pathway could be a novel way of eliminating breast cancer stem cells. The γ-secretase complex controls the final intramembranous cleavage step that activates Notch receptors upon binding of its ligands and specific inhibitors of γ-secretase, which prevent Notch activation, are currently clinically tested against solid cancers in combination with radiotherapy. Radiation activates Notch signaling and therefore, we sought to explore patterns of Notch receptor and ligand expression in response to radiation that could be crucial in defining optimal dosing schemes for γ-secretase inhibitors if combined with radiation. Methods and Materials Using MCF-7 and T47D breast cancer cell lines we used realtime RT-PCR to study the Notch pathway in response to radiation. Results We show that Notch receptor and ligand expression during the first 48 hours after irradiation followed a complex radiation dose-dependent pattern and was most pronounced in mammospheres, enriched for breast cancer stem cells. Additionally, radiation activated the Notch pathway. Treatment with a γ-secretase inhibitor prevented radiation-induced Notch family gene expression and led to a significant reduction in the size of the breast cancer stem cell pool. Conclusions Our results indicate that, if combined with radiation, γ-secretase inhibitors may prevent up-regulation of Notch receptor and ligand family members and thus reduce the number of surviving breast cancer stem cells.

Radiation-Induced Dedifferentiation of Head and Neck Cancer Cells Into Cancer Stem Cells Depends on Human Papillomavirus Status

“…Previous reports demonstrated the use of the ZsGreen-cODC protein-reporter in identifying cells with increased in vivo tumorigenicity in breast and glioma cells (14, 28). We investigated whether the ZsGreen-cODC-neg and ZsGreen-cODC-pos cells sorted from two different HPV-negative HNSCC lines (Cal33 and Fadu) differed in their tumorigenicity in an in vivo limiting dilution assay.…”

Metabolic differences in breast cancer stem cells and differentiated progeny

“…We have demonstrated that this fluorescent reporter identifies breast cancer cells with a stem cell phenotype [7, 8, 11] and that breast cancer cells with low proteasome activity overlap with cells expressing high levels of ALDH1 and cells with a CD24 −/low /CD44 high phenotype, markers commonly used for identifying BCSCs [11]. Furthermore, more recent data indicate that breast cancer cells with low proteasome activity (ZsGreen-cODC-pos) are significantly more tumorigenic compared to the ZsGreen-cODC-neg cells [12], and are necessary for tumor initiation and maintenance [13]. Initially, we characterized the intrinsic numbers of cells with low proteasome activity (ZsGreen-cODC-pos) in four different breast cancer cell lines: two luminal cell lines, MCF-7 and T47D, a basal cell line MDA-MB-231 and the claudin-low cell line, SUM159PT.…”

The “virgin birth”, polyploidy, and the origin of cancer

“…Potential normalization targets in spontaneous TP53 mutant tumour revertants lead to, among others, presenilin1 activating Notch1 substrate γ-secretase, up-stream of c-myc stress signaling [117]. In turn, Notch1, which directly regulates c-myc is co-operating with Wnt in enhancing tumorigenesis [128] enriches mammospheres induced in breast cancer by irradiation [129]. In addition, it was also found that p21CIP1, involved in regulation of cellular senescence, functions as a negative transcriptional regulator of WNT4 downstream of Notch 1 [130] and that p21CIP1 potentially reorganizes the nucleus during tumour reversion [117].…”