Heat shock alters the distribution and in vivo interaction of major nuclear structural proteins, lamin and DNA topoisomerase II, with nucleic acids

Lamins and topoisomerases play a critical role in the structural support of cell nuclei, in the regulation of chromatin structure, chromatin distribution, topology of DNA, gene expression, transcription, splicing and transport. Here, we report the role of lamins and Top2 during transition from normal conditions (N), in heat shock (HS) and recovery (R) in Drosophila since the fly genome contains a single gene for B-type lamin (lamin Dm), for A-type lamin (lamin C) and Top2. Heat shock increases transient phosphorylation of lamin Dm on S25, induces changes in solubility of lamin Dm, Top2, HSF, HDAC1 and HP1 proteins, especially in S2 cells and relocates Top2 and chromatin closer to the nuclear lamina with induction of granular staining for Top2 in Kc, S2 and embryonic cells. Lamin Dm interacts with Top2 protein and HS increases the interaction. In vivo photocrosslinking and immunoprecipitation revealed a significant increase in binding to chromatin and nucleic acids upon HS induction for Top2 and lamin Dm. All the detected changes in the properties and location of proteins returned to "normal" after recovery from heat shock. This suggests an important role for lamin Dm, Top2 and their complexes in nuclear functions during HS and recovery. We propose a model in which relocation of Top2 chromatin complexes closer to the nuclear lamina and lamin Dm may help to rearrange the gene expression pattern by tethering HS inactivated genes to nuclear lamina and NPCs which might also help to bind nuclear fraction of non-HS-related transcripts at the nuclear lamina/NPCs area.