"DNA topoisomerase IIβ (TOP2B) is a type II topoisomerase that changes DNA topology by an ATP-dependent strand-passage reaction. Mechanistically, one duplex DNA segment (G-DNA, gate) is transiently cleaved to create an enzyme-bridged break, and a second duplex (T-DNA, transported) is passed through; the G-DNA is then religated, and ATP hydrolysis resets the enzyme cycle. "

"The N-terminal ATPase domain has a Bergerat/GHKL fold; E103 acts as a catalytic base for ATP hydrolysis (E103A abolishes ATP hydrolysis). Reported ATPase kinetic parameters (construct-dependent): e.g., Km ~0.115 mM for ATP for a 45-444 ATPase-domain construct. "

"TOP2B is primarily a nuclear enzyme. Structural work on human TOP2B states that the C-terminal domain contains nuclear localization signals and many phosphorylation sites, consistent with nuclear chromatin-associated function. "

"Experimental trapping condition: etoposide 50 μM for 30 min. Genome-wide called peaks: n = 35,505. Distribution: TOP2B catalytic engagement is relatively depleted at promoters/TSSs and enriched across gene bodies and active chromatin/transcription states. "

"Agreement with occupancy mapping: TOP2Bcc-seq correlated with prior TOP2B ChIP-seq (Spearman 0.64) but shows distinct distribution emphasizing catalytic engagement rather than mere binding. These results support a model where TOP2B's catalytic function is frequently deployed within transcribed regions to manage topological constraints rather than being limited to promoter-localized binding. "

"TOP2B catalytic engagement and/or binding has been reported to occur in open chromatin and at architectural protein sites (CTCF/cohesin) in neurons. The 2024 mapping study reports TOP2B activity correlates with chromosomal compartment organization and nucleosome configuration. "

"A 2024 review synthesizing the field notes that neuronal stimulation can increase TOP2B association/activation at immediate early genes, with a reported five-fold increase in IEG-bound TOP2B upon NMDA stimulation in cited work; the same review also describes calcineurin-dependent regulation (Ca2+ influx → calcineurin → TOP2B dephosphorylation) of activity-induced breaks. "

"AD brains contained 19.9× more PAR peaks than non-demented brains. Yet adaptive breaks at nervous-system genes were "profoundly lost" and gene expression downregulated. TOP2B-positive cells by IHC quantification (3 ND vs 3 AD): 82.4 ± 7.0 (ND) vs 21.7 ± 9.3 (AD), p < 0.05. "

"The paper notes that TOP2B is essential for cardiotoxicity in mouse models and that disruption of TOP2B in iPSC-CMs can reduce doxorubicin sensitivity (reported as background/interpretive context). "

"Human topoisomerase II beta (TOP2B) modulates DNA topology using energy from ATP hydrolysis. "

"Mutagenesis demonstrated residue E103 as essential for ATP hydrolysis in TOP2B. "

"Biochemical characterization revealed the N-terminal strap reduces the rate of ATP hydrolysis. "

"We trapped catalytically engaged topoisomerase IIβ (TOP2B) in covalent DNA cleavage complexes (TOP2Bccs) and mapped their positions genome-wide in cultured mouse cortical neurons. "

"TOP2Bcc distribution varies with both nucleosome and compartmental chromosome organization. While TOP2Bccs in gene bodies correlate with their level of transcription. "

"Promoters with high RNA polymerase II occupancy show elevated TOP2B chromatin immunoprecipitation sequencing signals but low TOP2Bccs, indicating that TOP2B catalytic engagement is curtailed at active promoters. "

"Surprisingly, either poisoning or inhibiting TOP2B increases nascent transcription at most genes and enhancers but reduces transcription within long genes. These effects are independent of transcript length and instead correlate with the presence of intragenic enhancers. "

"AD brains contained 19.9× more PAR peaks than non-demented brains. Yet adaptive breaks at nervous-system genes were "profoundly lost" and gene expression downregulated. "

"TOP2B-positive cells by IHC quantification (3 ND vs 3 AD): 82.4 ± 7.0 (ND) vs 21.7 ± 9.3 (AD), p < 0.05. "

"A 2024 review synthesizing the field notes that neuronal stimulation can increase TOP2B association/activation at immediate early genes, with a reported five-fold increase in IEG-bound TOP2B upon NMDA stimulation in cited work; the same review also describes calcineurin-dependent regulation (Ca2+ influx → calcineurin → TOP2B dephosphorylation) of activity-induced breaks. "

"The paper notes that TOP2B is essential for cardiotoxicity in mouse models and that disruption of TOP2B in iPSC-CMs can reduce doxorubicin sensitivity (reported as background/interpretive context). "

"Median LD50 (μM): DOX 14.02, DNR 0.98, EPI 3.79, MTX 0.98. "

"Cumulative doxorubicin thresholds and risks: ~5% cardiomyopathy/CHF at 400 mg/m², and elevated incidence at higher cumulative doses; the review also cites >35% incidence of dilated cardiomyopathy at 650 mg/m² and notes thresholds ~550 mg/m² (or 450 mg/m² with additional risks). "