Differential Effects of Estrogen Receptor β Isoforms on Glioblastoma Progression

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The estrogen receptor β (ERβ) functions as a tumor suppressor in glioblastoma (GBM) cells. However, the in vivo significance of endogenous ERβ and the roles of its isoforms in GBM are incompletely understood. Using ERβ isoform-specific PCR screening, we found that GBM cells predominantly express ERβ1 and ERβ5, along with low levels of ERβ2 and ERβ4. We observed greater ERβ5 expression in higher grades of glioma than in lower grades. In CRISPR-based ERβ knockout (KO) cells and ERβ KO cells uniquely expressing ERβ1 or ERβ5 only, ERβ1 significantly reduced proliferation. Compared with parental GBM cells, ERβ KO cells exhibited high migratory and invasive potentials, and reexpression of ERβ1 resulted in the reduction of this phenotype. Interestingly, ERβ5 expression increased foci formation and anchorage-independent growth of NIH3T3 cells and increased motile structure formation, including filopodia and ruffles in GBM cells. Only ERβ1-expressing tumors resulted in longer mouse survival. RNA-Seq analysis revealed unique pathways modulated by ERβ1 and ERβ5. Compared with ERβ KO cells, ERβ1 cells exhibited lower activation of mTOR signaling molecules, including p-mTOR, p-S6K, and p-S6, and ERβ5-expressing cells had enhanced mTOR downstream signaling. Unique proteins including several that function as regulators of mTOR, immunomodulatory, and apoptosis pathways bound to ERβ1 and ERβ5 isoforms. Our work confirms the tumor-suppressive potential of ERβ1 and reveals the acquired oncogenic ability of ERβ5 in GBM cells. ERβ isoform status and their unique interactions with oncogenic pathways may have important implications in GBM progression.Significance: These findings suggest that only ERβ isoform 1 has tumor suppressor function in GBM and that ERβ isoform switching contributes to GBM progression. Cancer Res; 78(12); 3176-89. ©2018 AACR.