Status of topoisomerase-2β protein in all-trans retinoic acid-treated human neuroblastoma (SK-N-SH) cells

Of the mammalian topoisomerase (Topo)-2 isozymes (alpha and beta), Topo-2 beta protein has been reported to regulate neuronal development and differentiation. However, the status of Topo-2 beta in all-trans retinoic acid (ATRA)-treated human neuroblastoma (SK-N-SH) cells is not understood. More information about the effects of ATRA on SK-N-SH cells is needed to reveal the role of ATRA in the regulation of Topo-2 beta levels and spontaneous regression of SK-N-SH cells to predict the clinical activity. This study was proposed to investigate the status and role of Topo-2 beta protein in ATRA-induced survival and neuronal differentiation of SK-N-SH cells. Microscopic, sodium dodecyl sulfate polyacrylamide gel electrophoresis after immunoprecipitations and Western blot analysis were used to study and compare Topo-2 beta protein among 10 mu M ATRA-treated SK-N-SH cells and controls at different time points. The level of Topo-2 beta protein increased in the initial days of treatment but markedly decreased upon induction of differentiation by ATRA in later stages. Upon ATRA treatment, SK-N-SH cells stretched, exhibited neurite extensions, and acquired a neuronal phenotype. Both treated and untreated SK-N-SH cells were able to migrate, occupy the scratched area, and completely recolonized 24 hours later. These results suggest an indirect role of Topo-2 beta protein in regulation of genes involved in cell migration and differentiation of ATRA-treated SK-N-SH cells. This study suggests that Topo-2 beta may be part of activation/repression of protein complexes activated by epigenetic modifying agents, differentiating signals, and inducible locus. However, detailed studies are needed to explore the ATRA-downstream genes leading to Topo-2 beta regulation and regulatory proteins of neuronal differentiation.