Differential effects of estrogen receptor b isoforms on glioblastoma progression

Abstract

The estrogen receptor b (ERb) functions as a tumor suppressor in glioblastoma (GBM) cells. However, the in vivo significance of endogenous ERb and the roles of its isoforms in GBM are incompletely understood. Using ERb isoform-specificPCR screening, we found that GBM cells predominantly express ERb1 and ERb5, along with low levels of ERb2 and ERb4. We observed greater ERb5 expression in higher grades of glioma than in lower grades. In CRISPR-based ERb knockout (KO) cells and ERb KO cells uniquely expressing ERb1 or ERb5 only, ERb1 significantly reduced proliferation. Compared with parental GBM cells, ERb KO cells exhibited high migratory and invasive potentials, and reexpression of ERb1 resulted in the reduction of this phenotype. Interestingly, ERb5 expression increased foci formation and anchorage-independent growth of NIH3T3 cells and increased motile structure formation, including filopodia and ruffles in GBM cells. Only ERb1-expressing tumors resulted in longer mouse survival. RNA-Seq analysis revealed unique pathways modulated by ERb1 and ERb5. Compared with ERb KO cells, ERb1 cells exhibited lower activation of mTOR signaling molecules, including p-mTOR, p-S6K, and p-S6, and ERb5-expressing cells had enhanced mTOR downstream signaling. Unique proteins including several that function as regulators of mTOR, immunomodulatory, and apoptosis pathways bound to ERb1 and ERb5 isoforms. Our work confirms the tumor-suppressive potential of ERb1 and reveals the acquired oncogenic ability of ERb5 in GBM cells. ERb isoform status and their unique interactions with oncogenic pathways may have important implications in GBM progression. Significance: These findings suggest that only ERb isoform 1 has tumor suppressor function in GBMand that ERb isoform switching contributes to GBM progression.