Hyperactivation of MAPK Induces Tamoxifen Resistance in SPRED2-Deficient ERα-Positive Breast Cancer

Abstract

Breast cancer is the number one cause of cancer-related mortality in women worldwide. Most breast tumors depend on the expression of the estrogen receptor a (ERα) for their growth. For this reason, targeting ERα with antagonists such as tamoxifen is the therapy of choice for most patients. Although initially responsive to tamoxifen, about 40% of the patients will develop resistance and ultimately a recurrence of the disease. Thus, finding new biomarkers and therapeutic approaches to treatment-resistant tumors is of high significance. SPRED2, an inhibitor of the MAPK signal transduction pathway, has been found to be downregulated in various cancers. In the present study, we found that SPRED2 is downregulated in a large proportion of breast-cancer patients. Moreover, the knockdown of SPRED2 significantly increases cell proliferation and leads to tamoxifen resistance of breast-cancer cells that are initially tamoxifen-sensitive. We found that resistance occurs through increased activation of the MAPKs ERK1/ERK2, which enhances the transcriptional activity of ERα. Treatment of SPRED2-deficient breast cancer cells with a combination of the ERK 1/2 inhibitor ulixertinib and 4-hydroxytamoxifen (4-OHT) can inhibit cell growth and proliferation and overcome the induced tamoxifen resistance. Taken together, these results indicate that SPRED2 may also be a tumor suppressor for breast cancer and that it is a key regulator of cellular sensitivity to 4-OHT.

CRISPR/Cas9 screen reveals a role of purine synthesis for estrogen receptor α activity and tamoxifen resistance of breast cancer cells

“…1, B and C). We have recently shown that SPRED2 deficiency is an important indicator of tamoxifen resistance because of ERα hyperactivation through the MAPK signaling pathway ( 37 ).…”

Network-informed discovery of multidrug combinations for ERα+/HER2-/PI3Kα-mutant breast cancer

“…The approach is based on a phenotypic assay of the cellular ATP levels, which reflect the metabolic activity, and hence, the viability of cells. We initially screened drug combinations using the three ERα+ breast cancer cell lines, MCF7 (tamoxifen-sensitive), MCF7-V (a more tamoxifen-tolerant variant of MCF7) (Vafeiadou et al , 2022; Mohammadi Ghahhari et al , 2022), and MCF7/LCC2 (tamoxifen-resistant) (Brünner et al , 1993). In parallel, we used MCF10A, a non-malignant breast epithelial cell line, to monitor the relative toxicity, and to calculate the therapeutic window (TW), which represents the difference in efficacy between cancerous and non-cancerous cells.…”

“…In addition, ERα can be activated in an estrogen- independent manner by a large panel of factors, including epidermal growth factor (EGF) (Ignar-Trowbridge et al , 1992; Ignar-Trowbridge et al , 1993), insulin and insulin-like growth factors (IGF) (Newton et al , 1994), PI3K (Campbell et al , 2001), Akt (Campbell et al , 2001; Martin et al , 2000), and hypoxia-inducible factor 1 α (HIF1α) (Cho et al , 2006; Bennesch & Picard, 2015) (see detailed list at https://www.picard.ch/downloads/Factors.pdf). Through various domains, ERα can interact with a plethora of proteins that regulate its activity, such as the MAPKs ERK1/ERK2 (ERK1/2) (Chen et al , 2002; Kato et al , 1995; Kim et al , 2021; Vafeiadou et al , 2022; Li et al , 2012; Mueller et al , 2000; Bunone et al , 1996), mTOR (Alayev et al , 2016), cyclin-dependent kinase inhibitor 1 (p21) (Fritah et al , 2005; Redeuilh et al , 2002; Abukhdeir et al , 2008), and poly (ADP-ribose) polymerase 1 (PARP1) (Schiewer & Knudsen, 2014; Zhang et al , 2013; Pulliam et al , 2019; Gadad et al , 2021) (see the updated list of ERα interactors at https://www.picard.ch/downloads).…”

“…Resistance to tamoxifen can be attributed to multiple mechanisms, including loss of ERα expression or function due to genetic mutations, alterations in the levels of co-regulatory factors (Osborne et al , 2003), upregulation of oncogenic signal transduction pathways, and ligand-independent activation of ERα (Kato et al , 1995; Shim et al , 2000; Coutts & Murphy, 1998; Gee et al , 2001; Clark et al , 2002; Gutierrez et al , 2005; Bennesch & Picard, 2015). For example, ERK1/2 play a critical role in breast cancer and their hyperactivation is associated with tamoxifen resistance and poor prognosis (Gee et al , 2001; Coutts & Murphy, 1998; Shim et al , 2000; Chen et al , 2002; Kato et al , 1995; Kim et al , 2021; Vafeiadou et al , 2022; Li et al , 2012; Mueller et al , 2000; Bunone et al , 1996). ERK1/2 can stimulate cell growth independently of ERα or through signaling crosstalk with ERα.…”

The Predictive and Prognostic Role of RAS–RAF–MEK–ERK Pathway Alterations in Breast Cancer: Revision of the Literature and Comparison with the Analysis of Cancer Genomic Datasets

“…NF1-knockout MCF7 cells showed increased levels of phospho-ERK and resistance to fulvestrant, which could be reverted by ERK inhibitors [ 85 ]. Similarly, downregulation of Sprouty-related EVH1 domain containing 2 (SPRED2), a member of the Sprouty family of RAS inhibitors, frequently altered in breast cancer due to deletion or promoter methylation, leads to tamoxifen resistance, which can be overcome in breast cancer cell lines by a combination of the ERK 1/2 inhibitor ulixertinib with tamoxifen [ 112 ]. RAS mutations have been identified in circulating tumor DNA in 15% of patients who had disease progression under aromatase inhibitors, potentially mediating resistance [ 113 ].…”