DNA-dependent protein kinase (DNA-PK) phosphorylates nuclear DNA helicase II/RNA helicase A and hnRNP proteins in an RNA-dependent manner.

Department of Biochemistry, Institute of Molecular Biotechnology, Postfach 100 813, D-07708 Jena, Germany.
An RNA-dependent association of Ku antigen with nuclear DNA helicase II (NDH II), alternatively named RNA helicase A (RHA), was found in nuclear extracts of HeLa cells by immunoprecipitation and by gel filtration chromatography. Both Ku antigen and NDH II were associated with hnRNP complexes. Two-dimensional gel electrophoresis showed that Ku antigen was most abundantly associated with hnRNP C, K, J, H and F, but apparently not with others, such as hnRNP A1. Unexpectedly, DNA-dependent protein kinase (DNA-PK), which comprises Ku antigen as the DNA binding subunit, phosphorylated hnRNP proteins in an RNA-dependent manner. DNA-PK also phosphorylated recombinant NDH II in the presence of RNA. RNA binding assays displayed a preference of DNA-PK for poly(rG), but not for poly(rA), poly(rC) or poly(rU). This RNA binding affinity of DNA-PK can be ascribed to its Ku86 subunit. Consistently, poly(rG) most strongly stimulated the DNA-PK-catalyzed phosphorylation of NDH II. RNA interference studies revealed that a suppressed expression of NDH II altered the nuclear distribution of hnRNP C, while silencing DNA-PK changed the subnuclear distribution of NDH II and hnRNP C. These results support the view that DNA-PK can also function as an RNA-dependent protein kinase to regulate some aspects of RNA metabolism, such as RNA processing and transport.
Mesh Terms:
Adenosine Triphosphatases, Antigens, Nuclear, Autoantigens, Cell Extracts, DEAD-box RNA Helicases, DNA Helicases, DNA-Activated Protein Kinase, DNA-Binding Proteins, HeLa Cells, Heterogeneous-Nuclear Ribonucleoproteins, Humans, Macromolecular Substances, Membrane Proteins, Neoplasm Proteins, Nuclear Proteins, Phosphorylation, Precipitin Tests, Protein Binding, Protein-Serine-Threonine Kinases, RNA, RNA Helicases, RNA Interference, RNA, Small Interfering, RNA-Binding Proteins
Nucleic Acids Res. Jan. 06, 2004; 32(1);1-10 [PUBMED:14704337]
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