Osteolytic effects of tumoral estrogen signaling in an estrogen receptor-positive breast cancer bone metastasis model

Abstract

effects of tumoral estrogen signaling in an estrogen receptor-positive breast cancer bone metastasis model.

A Role for TGFβ Signaling in Preclinical Osteolytic Estrogen Receptor-Positive Breast Cancer Bone Metastases Progression

“…The E2 dependence of tumor-associated osteolysis in ER+ BMETs formed in vivo by MCF-7 cells and ER-mediated secretion of PTHrP from these same cells, has previously been reported [12]. Given the correlation documented here between in vivo osteolytic ER+ BMET formation and (1) tumoral Smad-mediated TGFβ signaling, as well as (2) TGFβinducible tumoral PTHrP secretion, additive to the stimulatory effects of E2, a possible contributing role for TGFβ in driving osteolytic estrogen-dependent ER+ BMET progression in vivo was assessed.…”

“…PTHrP secretion, which we previously demonstrated to be E 2 inducible via ERα in MCF-7 cells [12] and is TGFβ inducible via Smad signaling in some bone-tropic ERbreast cancer cell lines [13][14][15]43], was also induced by TGFβ in bone-tropic MCF-7 cells, demonstrating additive effects when combined with E 2 (Figure 5A, left panel). However, in ER+ cells that did not form osteolytic BMETs (T47D and ZR-75-1), PTHrP levels were near or at the limit of detection and were not altered by E 2 or TGFβ, alone or in combination (Figure 5A, middle and right panels).…”

“…Therefore, specific modeling of ER+ breast cancer BMET is clinically relevant due to its prevalence, and also due to the possibility that tumoral ER+ signaling could be a mediator, and not just a marker, specific to metastasis progression within the bone microenvironment. Recent experiments conducted by our laboratory support this postulate, providing what is, to the best of our knowledge, the first evidence of a possible causal role for tumoral ER signaling in mediating tumor-associated osteolysis in ER+ BMET [12]. In vivo peritumoral osteolysis, osteoclast formation, and osteolytic BMET progression all progressed in an estrogen (E 2 ) dose-dependent fashion in a human ER+ breast cancer cell (MCF-7) osteolytic BMET model, independent of direct estrogenic effects on the bone milieu or tumor cell proliferation, but in association with ER-mediated tumoral secretion of parathyroid hormone-related protein (PTHrP), an osteolytic factor expressed with greater prevalence in osseus vs. non-osseus metastases [13][14][15][16][17][18], providing a possible mechanistic basis for the E 2 -driven tumor-associated osteolysis documented in vivo.…”

“…When MCF-7 cells, MCF-7J (a MCF-7 subline transfected to express luciferase), T47D, or ZR-75-1 cells were inoculated into E 2 -supplemented female athymic nude mice, using methods previously established [12,41], only ER+ cells with TGFβ-inducible Smad signaling (MCF-7 and MCF-7J, Figure 1B) formed osteolytic BMETs. Osteolytic BMET lesions, confirmed by histology (MCF-7) or BLI (MCF-7J), reached maximal incidence by 3 weeks post tumor inoculation and were still increasing in size by the study's end at 6 weeks (Figure 2A,B).…”

“…Due to reports of antagonistic crosstalk between E 2 and Smad-mediated TGFβ signaling in breast cancer cells [34,35,[37][38][39][40] and our previous demonstration of the E 2dependency of osteolysis in ER+ MCF-7 BMETs [12], the time dependent effects of each agent on expression and/or activation of the opposing receptor were assessed in bonetropic ER+ tumor cells. Untreated control cells were included at each time point to account for possible changes in protein levels attributable to the addition of fresh media at the start of the experiment (Figure 3A).…”