ERK2-topoisomerase II regulatory axis is important for gene activation in immediate early genes
The transcription of stress-inducible genes requires synchronized and robust activation, which is critical for organismal survival and homeostasis. The function of the mitogen-activated protein kinase (MAPK) signaling pathway is required for the activation of immediate early genes (IEGs), including EGR1 and FOS, for cell growth and proliferation1-3. In addition, recent studies have identified topoisomerase II (TOP2) as one of the important regulators of the transcriptional activation of IEGs4-6. However, the mechanism underlying transcriptional regulation involving TOP2 in IEG activation has remained unknown. Here, we demonstrate that ERK2, but not ERK1, is important for IEG transcriptional activation and report a critical ELK1 binding sequence for ERK2 function at the EGR1 gene. Our data indicate that both ERK1 and ERK2 extensively phosphorylate the C-terminal domain of TOP2B at mutual and distinctive residues. Although both ERK1 and ERK2 enhance the catalytic rate of TOP2B required to relax positive DNA supercoiling, ERK1 can relax the DNA by itself and produces a semi-relaxed DNA, which is apparently resistant to TOP2B catalysis. Inhibition of ERK2 kinase activity or ERK2 knock-down interferes with transcription and deregulates TOP2B in IEGs. Furthermore, we obtained the first cryo-EM structure of the human cell-purified TOP2B and etoposide together with the EGR1 transcriptional start site (50 nt; -30 to +20) that has the strongest affinity to TOP2B within -423 to +332. The structure elucidated in our studies showed TOP2B-mediated breakage and dramatic bending of the double-stranded DNA, comparable to previously reported structures of TOP2. Our cell-based analyses showed transcriptional activation by etoposide and transcriptional inhibition by ICRF193 at EGR1 and FOS, suggesting that TOP2B-mediated DNA break to favor transcriptional activation. Taken together, this study suggests that activated ERK2 phosphorylates TOP2B to regulate TOP2-DNA interactions and favor transcriptional activation in IEGs. We propose that TOP2B association, catalysis, and dissociation on its substrate DNA are important processes for regulating transcription and that ERK2-mediated TOP2B phosphorylation may be key for the catalysis and dissociation steps.