A casein kinase type II (CKII)-like nuclear protein kinase associates with, phosphorylates, and activates topoisomerase I.
Topoisomerase I (Topo I) is involved in many cellular functions that involve unwinding of supercoiled DNA, such as transcription and replication. Topo I is also the target of autoimmune antibodies in progressive systemic sclerosis (scleroderma), and abnormal regulation of Topo I may influence the excessive production of collagen found in scleroderma. Topo I is phosphorylated in vivo at serine residues and, in vitro, the activity of Topo I is increased by phosphorylation by casein kinase type II (CKII) and protein kinase C (PKC). In this study, a protein kinase activity from rat liver nuclei is shown to copurify with Topo I during Bio-Rex 70 cation exchange chromatography. The kinase can phosphorylate Topo I at serine residues, resulting in a threefold increase in topoisomerase activity. A relatively tight association between this kinase and Topo I is demonstrated by the ability to coprecipitate the kinase with scleroderma autoimmune anti-Topo I antibodies. The kinase activity is similar to CKII since it is Ca2+ and cyclic nucleotide independent, it can utilize either ATP or GTP as phosphate donor, and it can phosphorylate casein and phosvitin, but not histones. However, unlike typical CKII, the Topo I-associated kinase could utilize Mn2+ almost as well as Mg2+, it is not stimulated by polyamines, and it does not appear to undergo autophosphorylation. In conclusion, we demonstrate that rat liver Topo I is relatively tightly associated with a CKII-like protein kinase that can phosphorylate and activate Topo I. These findings provide corroborative evidence that CKII, or a CKII-like protein kinase, is a physiologic regulator of Topo I.
Turman
M A
MA
Department of Biochemistry, University of Colorado Health Sciences Center, Denver 80262.
Douvas
A
A
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D047390:Casein Kinase II; D002413:Cations, Divalent / Q000494:pharmacology; D002467:Cell Nucleus / Q000201:enzymology*; D004264:DNA Topoisomerases, Type I / Q000276:immunology / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000502:physiology; D007074:Immunoglobulin G / Q000276:immunology / Q000302:isolation & purification; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000648:ultrastructure; D010766:Phosphorylation; D010774:Phosvitin / Q000378:metabolism; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D013379:Substrate Specificity
D000596:Amino Acids; D002413:Cations, Divalent; D007074:Immunoglobulin G; D010774:Phosvitin; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D004264:DNA Topoisomerases, Type I