ERRβ Splice Variants Differentially Regulate Cell Cycle Progression
Heckler, Mary Mazzotta
Orphan receptors comprise nearly half of all members of the nuclear receptor superfamily. Despite having broad structural similarities to the classical estrogen receptors, estrogen-related receptors (ERRs) have their own unique DNA response elements and functions. In this study, we focus on two ERRβ splice variants, short form ERRβ (ERRβsf) and ERRβ2, and identify their differing roles in cell cycle regulation. Using the acyl hydrazone DY131 (a synthetic agonist of ERRβ) as a tool to modulate endogenous ERRβ function, splice-variant selective shRNA, and exogenous ERRβsf and ERRβ2 cDNAs, we differentiate between splice variant function in cell cycle regulation. We demonstrate the role of ERRβsf in mediating the G1/S checkpoint through p21. We also show ERRβsf is required for DY131-induced cellular senescence. A key novel finding of this study is that ERRβ2 can mediate a G2/M arrest. Furthermore, in the absence of ERRβ2, the G2/M arrest is reversed and ERRβsf now induces p21 and initiates a G1/S arrest. These data imply a potential dominant inhibitory role for ERRβ2 on ERRβsf. Furthermore, we demonstrate DY131 cytotoxic sensitivity is dependent on p53 status. In the absence of wild-type p53 (null or mutated), activated ERRβ2 initiates an apoptotic response. In wild-type p53, ERRβsf induces p21 in a cytoprotective response and the magnitude of cell death is lessened. This study illustrates both novel functions for ERRβ splice variants as well as evidence for splice variant interaction.
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