Recurrence of metastatic breast cancer stemming from acquired endocrine and chemotherapy resistance remains a health burden for women with luminal (ER+) breast cancer. Disseminated ER+ tumor cells can remain viable but quiescent for years to decades. Contributing factors to metastatic spread include the maintenance and expansion of breast cancer stem cells (CSCs). Breast CSCs frequently exist as a minority population in therapy resistant tumors. In this study, we show that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, modulate breast CSC expansion through upregulation of the HIF-activated metabolic target genes PFKFB3 and PFKFB4 . Seahorse metabolic assays demonstrated that cytoplasmic PELP1 influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. PELP1 interacts with PFKFB3 and PFKFB4 proteins, and inhibition of PFKFB3 and PFKFB4 kinase activity blocks PELP1-induced tumorspheres and protein-protein interactions with SRC-3. PFKFB4 knockdown inhibited in vivo emergence of circulating tumor cell (CTC) populations in mammary intraductal (MIND) models. Application of PFKFB inhibitors in combination with ER targeted therapies blocked tumorsphere formation in multiple models of advanced breast cancer including tamoxifen (TamR) and paclitaxel (TaxR) resistant models, murine tumor cells, and ER+ patient-derived organoids (PDxO). Together, our data suggest that PELP1, SRC-3, and PFKFBs cooperate to drive ER+ tumor cell populations that include CSCs and CTCs. Identifying non-ER pharmacological targets offers a useful approach to blocking metastatic escape from standard of care ER/estrogen (E2)-targeted strategies to overcome endocrine and chemotherapy resistance.
Recurrence of metastatic breast cancer stemming from acquired endocrine and chemotherapy resistance remains a health burden for women with luminal (ER+) breast cancer. Disseminated ER+ tumor cells can remain viable but quiescent for years to decades. Contributing factors to metastatic spread include the maintenance and expansion of breast cancer stem cells (CSCs). Breast CSCs frequently exist as a minority population in therapy resistant tumors. In this study, we show that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, modulate breast CSC expansion through upregulation of the HIF-activated metabolic target genes PFKFB3 and PFKFB4. Seahorse metabolic assays demonstrated that cytoplasmic PELP1 influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. PELP1 interacts with PFKFB3 and PFKFB4 proteins, and inhibition of PFKFB3 and PFKFB4 kinase activity blocks PELP1-induced tumorspheres and protein-protein interactions with SRC-3. PFKFB inhibitors exhibited combinatorial effects in conjunction with ER targeted therapies in breast cancer cells, including tamoxifen resistant (TamR) and paclitaxel resistant (TaxR) models and ER+ patient-derived organoids (PDxO). Finally, PFKFB4 knockdown resulted in decreased circulating tumor cell (CTC) populations in mammary intraductal (MIND) models. Together, our data suggest that PELP1, SRC-3, and PFKFBs cooperate to drive ER+ tumor cell populations that include CSCs and CTCs. Identifying non-ER pharmacological targets offers a useful approach to blocking metastatic escape from standard of care ER/estrogen (E2)-targeted strategies to overcome endocrine and chemotherapy resistance.
Late recurrence of metastatic disease stemming from acquired therapy resistance remains a significant health burden for women with estrogen receptor (ER) positive breast cancer. Disseminated ER+ tumor cell populations can remain quiescent for years to decades, and contributing factors include breast cancer stem cells (CSCs), which are non-proliferative and frequently exist as a minority population in recurrent therapy-resistant tumors. Progesterone receptors (PR) are known drivers of both normal stem and breast CSC outgrowth. Our objective was to define novel signaling pathways governing cell fate transitions involved in driving therapy resistance in ER+ breast cancer. We reported that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, drive breast CSC outgrowth. SRC-3 knockdown abrogated cytoplasmic PELP1-induced CSC expansion and target genes required for cell survival, suggesting an essential role for PELP1/SRC-3 complexes in breast CSC outgrowth. PELP1 also forms a signaling and transcriptional complex with ERα and PR-B. Phospho-PR species are key mediators of stemness in ER+ breast cancer models. Accordingly, PR knockdown and antiprogestins disrupted PELP1/SRC-3 complexes and blocked PELP1-induced breast CSC outgrowth. Moreover, mammary stem cell (MaSC) populations were increased in vivo in MMTV-tTA;TRE-cyto-PELP1 transgenic mouse models as well as in MMTV-tTA;TRE-hPR-B mice. To better understand PELP1-mediated pathways, we performed RNA-seq on MCF-7 PELP1+ models grown in tumorsphere conditions to enrich for breast CSC populations (ALDH+, CD44+/CD24-). Cytoplasmic PELP1-expressing cells had a different global gene profile relative to cells expressing WT PELP1 (i.e. nuclear). Gene sets associated with stem cell biology, hypoxic stress, and cancer metabolism were differentially regulated, including members of the glycolytic bi-functional kinase/phosphatase PFKFB family. Seahorse metabolic phenotyping demonstrated that cytoplasmic PELP1 influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. Cytoplasmic PELP1 interacted strongly with PFKFB3 and PFKFB4, and inhibition of PFKFB3 or PFKFB4 kinase activity blocked PELP1-induced tumorsphere formation and protein-protein interactions with SRC-3. Additionally, antiprogestin and PFKFB inhibitors were synergistic when combined with ER+ targeted therapies. These aspects of PELP1/SRC-3 biology were phenocopied in therapy resistant models (tamoxifen resistant [TamR], paclitaxel resistant [TaxR]). Together, our data suggest that PELP1, SRC-3, PR, and PFKFBs form signaling complexes that reprogram cellular metabolism to drive expansion of breast CSCs. Identifying the molecular mechanisms that regulate recurrent ER+ tumor cell populations will enable specific targeting within heterogeneous breast tumors. Our work may lead to the development of non-ER targets that can be used in combination with current endocrine treatments and PR-targeting strategies to overcome therapy resistance in ER+ breast cancer. Citation Format: Julie Hanson Ostrander, Thu H. Truong, Elizabeth Benner, Amy R. Dwyer, Carol A. Lange. Steroid receptor co-activator complexes cooperate to reprogram metabolic pathways and drive therapy resistance in luminal breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3782.
Recurrence of metastatic breast cancer stemming from acquired endocrine and chemotherapy resistance remains a health burden for women with luminal (ER+) breast cancer. Disseminated ER+ tumor cells can remain viable but quiescent for years to decades. Contributing factors to metastatic spread include the maintenance and expansion of breast cancer stem cells (CSCs). Breast CSCs are poorly proliferative and frequently exist as a minority population in therapy resistant tumors. Our objective is to define novel signaling pathways that govern therapy resistance in ER+ breast cancer. In this study, we show that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, modulate breast CSC expansion through upregulation of the HIF-activated metabolic target genes PFKFB3 and PFKFB4. Seahorse metabolic assays demonstrated that cytoplasmic PELP1 influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. PELP1 interacts with PFKFB3 and PFKFB4 proteins, and inhibition of PFKFB3 and PFKFB4 kinase activity blocks PELP1-induced tumorspheres and protein-protein interactions with SRC-3. PFKFB4 knockdown inhibited in vivo emergence of circulating tumor cell (CTC) populations in ER+ mammary intraductal (MIND) xenografts. Application of PFKFB inhibitors in combination with ER targeted therapies blocked tumorsphere formation in multiple models of advanced breast cancer, including tamoxifen (TamR) and paclitaxel (TaxR) resistant models and ER+ patient-derived organoids (PDxO). Together, our data suggest that PELP1, SRC-3, and PFKFBs cooperate to drive ER+ tumor cells that include CSCs and CTCs. Identifying non-ER pharmacological targets offers a useful approach to blocking metastatic escape from standard of care ER/estrogen (E2)-targeted strategies to overcome endocrine and chemotherapy resistance in ER+ breast cancer.
Recurrence of metastatic breast cancer stemming from acquired endocrine and chemotherapy resistance remains a health burden for women with luminal (ER+) breast cancer. Disseminated ER+ tumor cells can remain viable but quiescent for years to decades. Contributing factors to metastatic spread include the maintenance and expansion of breast cancer stem cells (CSCs). Breast CSCs are poorly proliferative and frequently exist as a minority population in therapy resistant tumors. Our objective is to define novel signaling pathways that govern therapy resistance in ER+ breast cancer. In this study, we show that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, modulate breast CSC expansion through upregulation of the HIF-activated metabolic target genes PFKFB3 and PFKFB4. Seahorse metabolic assays demonstrated that cytoplasmic PELP1 influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. PELP1 interacts with PFKFB3 and PFKFB4 proteins, and inhibition of PFKFB3 and PFKFB4 kinase activity blocks PELP1-induced tumorspheres and protein-protein interactions with SRC-3. PFKFB4 knockdown inhibited in vivo emergence of circulating tumor cell (CTC) populations in ER+ mammary intraductal (MIND) xenografts. Application of PFKFB inhibitors in combination with ER targeted therapies blocked tumorsphere formation in multiple models of advanced breast cancer, including tamoxifen (TamR) and paclitaxel (TaxR) resistant models and ER+ patient-derived organoids (PDxO). Together, our data suggest that PELP1, SRC-3, and PFKFBs cooperate to drive ER+ tumor cells that include CSCs and CTCs. Identifying non-ER pharmacological targets offers a useful approach to blocking metastatic escape from standard of care ER/estrogen (E2)-targeted strategies to overcome endocrine and chemotherapy resistance in ER+ breast cancer. Citation Format: Thu Ha Truong, Elizabeth Benner, Kyla M. Hagen, Nuri A. Temiz, Carlos Perez Kerkvliet, Ying Wang, Emilio Cortes-Sanchez, Chieh-Hsiang Yang, Thomas Pengo, Katrin P. Guillen, Bryan E. Welm, Sucheta Telang, Carol A. Lange, Julie H. Ostrander. Steroid receptor co-activators regulate metabolic kinases to drive therapy resistant ER+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3085.
Recurrence of metastatic breast cancer stemming from acquired endocrine and chemotherapy resistance remains a health burden for women with luminal (ER+) breast cancer. ER+ tumor cells can remain viable but quiescent for years to decades. Contributing factors to metastatic spread include the survival and expansion of breast cancer stem cells (CSCs). Breast CSCs are poorly proliferative and frequently exist as a minority population in recurrent tumors. Our objective is to define novel signaling pathways that govern therapy resistance in ER+ breast cancer. We previously showed that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, modulate breast CSC expansion through upregulation of the HIF-activated metabolic target genes PFKFB3 and PFKFB4. PELP1 interacts with PFKFB proteins, and inhibition of PFKFB3 and PFKFB4 kinase activity blocks PELP1-induced tumorspheres and protein-protein interactions with SRC-3. PFKFB inhibitors in combination with ER targeted therapies blocked proliferation and tumorsphere formation in multiple models of advanced breast cancer, including paclitaxel (TaxR) and tamoxifen (TamR) resistant models and ER+ patient-derived organoids (PDxO). Chemotherapy and endocrine therapy resistant models contained increased levels of cytoplasmic PELP1, PELP1/SRC-3 complexes, and phenocopied PELP1/SRC-3/PFKFB biology and CSC behavior. To better understand CSC-mediated pathways in the context of therapy resistance, we performed RNA-seq on 3D-cultured TaxR tumorspheres to enrich for CSCs. Pathway analysis revealed that TaxR tumorspheres upregulate stem (Sox2-Oct4-Nanog), HIF, and progesterone mediated pathways. Progesterone receptor (PR) is a known contributor to CSC populations, and we observed increased PR mRNA and protein expression in TaxR cells grown as tumorspheres. Additionally, in vivo emergence of circulating tumor cell (CTC) populations was observed in ER+ TaxR mammary intraductal (MIND) xenografts. Together, our data suggest that PELP1, SRC-3, and PFKFBs cooperate to drive ER+ tumor cells that include CSCs and CTCs. Our findings are applicable to therapy resistant models, indicating that SR co-activator complexes are a key mediator of resistance in ER+ breast cancer and may cooperate with PR to promote therapy resistant CSCs. Identifying non-ER pharmacological targets offers a useful approach to blocking metastatic escape from standard of care ER/estrogen (E2)-targeted strategies to overcome endocrine and chemotherapy resistance in ER+ breast cancer. Presentation: Sunday, June 12, 2022 11:15 a.m. - 11:30 a.m.
Late recurrence of metastatic disease stemming from acquired therapy resistance remains a significant health burden for women with ER+ breast cancer. Disseminated ER+ tumor cell populations can remain quiescent for years to decades, and contributing factors include breast cancer stem cells (CSCs), which are non-proliferative and frequently exist as a minority population in recurrent therapy-resistant tumors. Progesterone receptors (PR) are known drivers of normal stem and breast CSCs. Our objective was to define novel signaling pathways governing cell fate transitions involved in driving therapy resistance in ER+ breast cancer. We reported that cytoplasmic complexes composed of steroid receptor (SR) co-activators, PELP1 and SRC-3, drive breast CSC outgrowth. SRC-3 knockdown abrogated PELP1-induced CSC expansion and target genes required for cell survival, suggesting an essential role for PELP1/SRC-3 complexes. PELP1 also forms a signaling and transcriptional complex with ER and PR-B. Phospho-PR species are key mediators of stemness in ER+ breast cancer models. Accordingly, PR knockdown and antiprogestins disrupted PELP1/SRC-3 complexes and blocked PELP1-induced breast CSC outgrowth. Mammary stem cell (MaSC) populations were increased in vivo in MMTV-tTA;TRE-cyto-PELP1 transgenic mice as well as in MMTV-tTA;TRE-hPR-B mice. To better understand PELP1-mediated pathways, we performed RNA-seq on MCF-7 PELP1+ models grown in tumorsphere conditions to enrich for CSC populations (ALDH+, CD44+/CD24-). Cytoplasmic PELP1-expressing cells had a different global gene profile relative to WT PELP1 (i.e. nuclear). Gene sets associated with stem cell biology, hypoxic stress, and cancer metabolism were differentially regulated, including members of the glycolytic bi-functional kinase/phosphatase PFKFB family. Seahorse metabolic phenotyping demonstrated cytoplasmic PELP1 influences metabolism by increasing both glycolysis and mitochondrial respiration. Cytoplasmic PELP1 interacted strongly with PFKFB3 and PFKFB4, and inhibition of PFKFB3 or PFKFB4 kinase activity blocked PELP1-induced tumorspheres and protein-protein interactions with SRC-3. Additionally, antiprogestin and PFKFB inhibitors were synergistic when combined with ER+ targeted therapies. These aspects of PELP1/SRC-3 biology were phenocopied in therapy resistant models (tamoxifen resistant [TamR], paclitaxel resistant [TaxR]). Together, our data suggest that PELP1, SRC-3, PR, and PFKFBs form complexes that reprogram cellular metabolism to drive breast CSC expansion. Identifying the mechanisms that regulate recurrent ER+ tumor cell populations will enable specific targeting within heterogeneous breast tumors and may lead to the development of non-ER targets that can be used in combination with endocrine treatments to overcome therapy resistance.
Despite highly effective treatments for breast cancer (BC), recurrence remains a significant risk among node-positive patients. Breast cancer stem or stem-like progenitor cells (BCSCs herein) are non-proliferative, evade first-line therapies in resistant breast tumors, and account for high mortality among patients with advanced disease. Our objective is to define the signaling pathways that drive cell fate transitions associated with endocrine resistance and the survival and expansion of BCSCs, with the goal of blocking these pathways to impact breast cancer survival. Filling this knowledge gap will pave the way for interventions that increase endocrine therapy duration and specifically target BCSC populations within heterogeneous luminal tumors. We recently defined the steroid receptor (SR) co-regulator, PELP1, as a mediator of BCSC expansion. Utilizing mass spectrometry, we identified steroid receptor coactivator-3, SRC-3, as a novel and preferential interactor with cytoplasmic PELP1. Notably, cytoplasmic PELP1 elevated SRC-3 activation, as measured by SRC-3 phosphorylation at Thr24 and Ser857. SRC-3 knockdown blocked cytoplasmic PELP1-induced BCSC expansion measured using tumorsphere assays, suggesting an essential role for PELP1/SRC-3 complexes in BCSC outgrowth. To better understand PELP1-regulated pathways we performed RNA-seq on MCF7 models grown in tumorsphere conditions to enrich for BCSC populations. We found that cells expressing cytoplasmic PELP1 have a dramatically different global gene profile relative to cells expressing wt-PELP1 (i.e. nuclear). Stem cell biology, metabolic, and hypoxic gene signatures were differentially upregulated, including members of the bi-functional kinase/phosphatase family (PFKFBs). Seahorse metabolic phenotype tests demonstrate that cytoplasmic PELP1 expression influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. Recent studies have implicated pSer857 SRC-3 as a key substrate of PFKFB4 in lung and breast cancer metastases. Furthermore, we found that cytoplasmic PELP1 interacts with PFKFB3 and PFKFB4, and inhibition of PFKFB3 kinase activity blocks PELP1-induced tumorsphere formation. Together, our data suggests that PELP1, SRC-3, and PFKFBs form cytoplasmic signaling complexes that reprogram cellular metabolism to promote BCSC expansion. Our work will lead to the development of targeted therapies against BCSCs that can be used in combination with current treatments to overcome endocrine therapy resistance.
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