Casein kinase I delta/epsilon phosphorylates topoisomerase IIalpha at serine-1106 and modulates DNA cleavage activity.
We previously reported that phosphorylation of topoisomerase (topo) IIalpha at serine-1106 (Ser-1106) regulates enzyme activity and sensitivity to topo II-targeted drugs. In this study we demonstrate that phosphorylation of Ser-1106, which is flanked by acidic amino acids, is regulated in vivo by casein kinase (CK) Idelta and/or CKIepsilon, but not by CKII. The CKI inhibitors, CKI-7 and IC261, reduced Ser-1106 phosphorylation and decreased formation of etoposide-stabilized topo II-DNA cleavable complex. In contrast, the CKII inhibitor, 5,6-dichlorobenzimidazole riboside, did not affect etoposide-stabilized topo II-DNA cleavable complex formation. Since, IC261 specifically targets the Ca(2+)-regulated isozymes, CKIdelta and CKIepsilon, we examined the effect of down-regulating these enzymes on Ser-1106 phosphorylation. Down-regulation of these isozymes with targeted si-RNAs led to hypophosphorylation of the Ser-1106 containing peptide. However, si-RNA-mediated down-regulation of CKIIalpha and alpha' did not alter Ser-1106 phosphorylation. Furthermore, reduced phosphorylation of Ser-1106, observed in HRR25 (CKIdelta/epsilon homologous gene)-deleted Saccharomyces cerevisiae cells transformed with human topo IIalpha, was enhanced following expression of human CKIepsilon. Down-regulation of CKIdelta and CKIepsilon also led to reduced formation of etoposide stabilized topo II-DNA cleavable complex. These results provide strong support for an essential role of CKIdelta/epsilon in phosphorylating Ser-1106 in human topo IIalpha and in regulating enzyme function.
Grozav
Adrian G
AG
Clinical Pharmacology Program, Taussig Cancer Institute, Cleveland, OH 44195, USA.
Chikamori
Kenichi
K
Kozuki
Toshiyuki
T
Grabowski
Dale R
DR
Bukowski
Ronald M
RM
Willard
Belinda
B
Kinter
Michael
M
Andersen
Anni H
AH
Ganapathi
Ram
R
Ganapathi
Mahrukh K
MK
D000951:Antigens, Neoplasm / Q000737:chemistry / Q000378:metabolism*; D048149:Casein Kinase 1 epsilon / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047389:Casein Kinase I / Q000235:genetics; D048148:Casein Kinase Idelta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053837:DNA Cleavage; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D015536:Down-Regulation; D005047:Etoposide / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D012694:Serine / Q000378:metabolism*; D014170:Transformation, Genetic
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D010455:Peptides; D047428:Protein Kinase Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D012694:Serine; D005047:Etoposide; D048149:Casein Kinase 1 epsilon; D047389:Casein Kinase I; D048148:Casein Kinase Idelta; C070775:HRR25 protein, S cerevisiae; D004250:DNA Topoisomerases, Type II