Induction of ubiquitin conjugating enzyme activity for degradation of topoisomerase II alpha during adenovirus E1A-induced apoptosis.

Topoisomerase (topo) II alpha is degraded via polyubiquitination during adenovirus E1A-induced apoptosis in MA1 cells, a derivative of the human epidermoid carcinoma cell line KB. Topo II alpha ubiquitination activity in MA1 cells increased nearly 10-fold after induction of E1A in response to dexamethasone. To identify a topo II alpha ubiquitination factor(s), the S100 fractions prepared from apoptosis-induced (42 h) and uninduced (0 h) MA1 cells were first fractionated by ubiquitin-Sepharose columns. The ubiquitination activity induced by E1A was predominantly eluted with 20 mM AMP. Further fractionation of the AMP eluates on Resource-Q columns and the thiolester formation of the proteins resolved by electrophoresis with biotinylated ubiquitin revealed that a species of E2 isozyme recovered in the QFT2 fraction increased markedly in MA1 cells after E1A expression. These results indicate that a ubiquitination factor(s) specific to topo II alpha is induced during E1A-induced apoptosis in MA1 cells.