TNBC is an aggressive
breast cancer subtype that does not express
hormone receptors (estrogen and
progesterone receptors, ER and PR) or amplified human
epidermal growth factor receptor type 2 (HER2), and there currently exist no targeted
therapies effective against it. Consequently, finding new molecular targets in
triple negative breast cancer (TNBC) is critical to improving patient outcomes. Previously, we have detected the expression of metabotropic
glutamate receptor-1 (gene: GRM1;
protein:
mGluR1) in TNBC and observed that targeting glutamatergic signaling inhibits TNBC growth both in vitro and in vivo. In this study, we explored how
mGluR1 contributes to TNBC progression, using the isogenic MCF10 progression series, which models breast
carcinogenesis from nontransformed epithelium to malignant basal-like
breast cancer. We observed that
mGluR1 is expressed in human
breast cancer and that in MCF10A cells, which model nontransformed mammary epithelium, but not in MCF10AT1 cells, which model
atypical ductal hyperplasia,
mGluR1 overexpression results in increased proliferation, anchorage-independent growth, and invasiveness. In contrast,
mGluR1 knockdown results in a decrease in these activities in malignant MCF10CA1d cells. Similarly, pharmacologic inhibition of glutamatergic signaling in MCF10CA1d cells results in a decrease in proliferation and anchorage-independent growth. Finally, transduction of MCF10AT1 cells, which express c-Ha-ras, using a lentiviral construct expressing GRM1 results in transformation to
carcinoma in 90% of resultant xenografts. We conclude that
mGluR1 cooperates with other factors in hyperplastic mammary epithelium to contribute to TNBC progression and therefore propose that glutamatergic signaling represents a promising new molecular target for TNBC
therapy.