PREX1 drives spontaneous bone dissemination of ER+ breast cancer cells

Abstract

A significant proportion of breast cancer patients develop bone metastases, but the mechanisms regulating tumor cell dissemination from the primary site to the skeleton remain largely unknown. Using a novel model of spontaneous bone metastasis derived from human ER+ MCF7 cells, molecular profiling revealed increased PREX1 expression in a cell line established from bonedisseminated MCF7 cells (MCF7b), which were more migratory, invasive, and adhesive in vitro compared to parental MCF7 cells, and this phenotype was mediated by PREX1. MCF7b cells grew poorly in the primary tumor site when re-inoculated in vivo, suggesting these cells are primed to grow in the bone, and were enriched in skeletal sites of metastasis over soft tissue sites. Skeletal dissemination from the primary tumor was reversed with PREX1 knockdown, indicating that PREX1 is a key driver of spontaneous dissemination of tumor cells from the primary site to the bone marrow. In breast cancer patients, PREX1 levels are significantly increased in ER+ tumors and associated with invasive disease and distant metastasis. Together, these findings implicate PREX1 in spontaneous bone dissemination and provide a significant advance to the molecular mechanisms by which breast cancer cells disseminate from the primary tumor site to bone.

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

“…This presents a challenge when studying murine models of human ER+ BMETs given the responsiveness of both tumor and bone cells to E 2 [29][30][31][32][33] and the absence of syngeneic models of murine ER+ breast cancer BMET. Indeed, the E 2 doses required to promote ER+ breast cancer growth in osteolytic xenograft models also increase murine bone mass [18,20,21,26,28,34] and furthermore, can induce osteolytic murine osteosarcomas in some animals, as previously demonstrated by our laboratory [34] .…”

“…The possible mechanistic importance of tumoral PTHrP secretion in promoting tumor-associated osteolysis and, in turn, osteolytic BMET progression, has already been established in one commonly studied pre-clinical ER-human BMET model, where osteolytic BMET progression does not occur in the absence of tumoral PTHrP bioactivity [8,42] . Also of particular relevance to the current studies, while E 2 -regulation of PTHrP expression in ER+ MCF7 cells has not, to our knowledge, been examined by laboratories other than our own [74] , overexpression of PTHrP by stable transfection in MCF-7 cells has been demonstrated to increase osteolysis specifically, in concert with a significant increase in osteolytic BMET progression (as compared to wild-type cells) [26] . Thus, existing evidence supports the postulate that enhanced secretion of PTHrP mediated by ERα in ER+ tumor cells disseminated to bone, as documented here, may be one specific pathway driving E 2 dose-dependent tumor osteolysis and osteolytic ER+ BMET progression documented in vivo.…”

“…Because mice, unlike humans, lack aromatase expression in mammary tissue and bone cells [14,15] and also have 10-fold lower circulating 17β-estradiol (E 2 ) levels than humans [16] , the optimal growth of human ER+ breast cancer orthotopic tumors and osteolytic BMETs in preclinical murine models is dependent on exogenous E 2 supplementation [17,18,[19][20][21][22][23][24][25][26]27,28] . This presents a challenge when studying murine models of human ER+ BMETs given the responsiveness of both tumor and bone cells to E 2 [29][30][31][32][33] and the absence of syngeneic models of murine ER+ breast cancer BMET.…”

“…Taken together, these ERbreast cancer xenograft studies suggest that both induction of bone formation by E 2 -treatment [35,36] and bone resorption by E 2 -deprivation [via ovariectomy (OVX)] [28,37,38] promote ER-BMET progression. In ER+ BMET models, E 2 bone-microenvironmental effects have often not been considered [19,[21][22][23][24][25][26]39,40] and are rarely documented [18,20,28] , while a role of tumor ERα signaling in driving tumor-associated osteolysis has not, to our knowledge, previously been studied.…”

In vitro Models of Breast Cancer Metastatic Dormancy

“…injection (Harrell et al, 2006;Holen et al, 2016;Wright et al, 2016;Gawrzak et al, 2018). Recently, bone metastatic versions of MCF7 cell line have been developed (Pavlovic et al, 2015;Clements and Johnson, 2019).…”