Evidence that a protein kinase enhances amsacrine mediated formation of topoisomerase II-DNA complexes in murine mastocytoma cell nuclei.

Cytoplasmic extracts of K21 murine mastocytoma cells contain a protein factor, distinct from topoisomerases I and II, that facilitates formation of amsacrine-induced topoisomerase II-DNA complexes (PDC) in isolated K21 cell nuclei (Darkin, S.J. and Ralph, R.K. (1988) Biochim. Biophys. Acta 1007, 295-300). The PDC enhancing activity was shown to reside in a protein kinase with specificity for a casein kinase II substrate and sensitive to heparin and anti-casein kinase II antiserum. This appears to be the first direct evidence of a protein factor that modulates amsacrine-induced topoisomerase II action.