RNA-dependent phosphorylation of a nuclear RNA binding protein.
The human C1 heterogeneous nuclear ribonucleoprotein particle protein (hnRNP protein) undergoes a cycle of phosphorylation-dephosphorylation in HeLa cell nuclear extracts that modulates the binding of this protein to pre-mRNA. We now report that hyperphosphorylation of the C1 hnRNP protein is mediated by a kinase activity in nuclear extracts that is RNA-dependent. Although the basal phosphorylation of the C1 hnRNP protein in nuclear extracts reflects a casein kinase II-type activity, its RNA-dependent hyperphosphorylation appears to be mediated by a different kinase. This is indicated by the unresponsiveness of the RNA-stimulated hyperphosphorylation to casein kinase II inhibitors, and the distinct glycerol gradient sedimentation profiles of the basal versus RNA-stimulated C1 hnRNP protein phosphorylation activities from nuclear extracts. RNA-dependent phosphorylation was observed both for a histidine-tagged recombinant human C1 hnRNP protein added to nuclear extracts and also for the endogenous C1 hnRNP protein. Additional results rule out protein kinase A, protein kinase C, calmodulin-dependent protein kinase II, and double-stranded RNA-activated protein kinase as the enzymes responsible for the RNA-dependent hyperphosphorylation of the C1 hnRNP protein. These results reveal the existence in nuclear extracts of an RNA-dependent protein kinase activity that hyperphosphorylates a known pre-mRNA binding protein, and define an additional element to be integrated into the current picture of how nuclear proteins are regulated by phosphorylation.
Fung
P A
PA
Cell Biology Group, Worcester Foundation for Biomedical Research, Shrewsbury, MA 01545, USA.
Labrecque
R
R
Pederson
T
T
D047390:Casein Kinase II; D002467:Cell Nucleus / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D034482:Heterogeneous-Nuclear Ribonucleoprotein Group C; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D015138:RNA, Nuclear / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism*
C439788:C1 HNRNP; D004791:Enzyme Inhibitors; C503635:HNRNPC protein, human; D034482:Heterogeneous-Nuclear Ribonucleoprotein Group C; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D009687:Nuclear Proteins; D015138:RNA, Nuclear; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D011494:Protein Kinases; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases