Note for: Molecular mechanisms of etoposide
Note for: Molecular mechanisms of etoposide (doi: 10.17179/excli2015-561) TopoII - introducing transient breaks in the DNA molecule. involved in fundamental biological processes such as DNA replication, transcription, DNA repair and chromatin remodeling. A tyrosine in the active site of the enzyme initiates the first transesterification and forms a covalent adduct with the phosphate in the backbone of the DNA molecule. TopoII can perform three kinds of reactions while DNA relaxation is in common to TopoI, catenation/decatenation and knotting/unknotting are TopoII specific. Etoposide poisons the TopoII cleavage complexes (TopoIIcc) and inhibits the second step of the reaction (i.e. DNA religation). Mammals have two TopoII isoenzymes, TopoIIa and beta that are differently regulated during cell growth. TopoIIalpha is a proliferation marker and is greatly elevated in tumor cells, beta isoenzyme is present in proliferating as well as postmitotic cells (cell not devide anymo...