Regulated interaction of protein kinase Cdelta with the heterogeneous nuclear ribonucleoprotein K protein

J Biol Chem. 1999 May 21;274(21):15101-9. doi: 10.1074/jbc.274.21.15101.


The heterogeneous nuclear ribonucleoprotein (hnRNP) K protein recruits a diversity of molecular partners that are involved in signal transduction, transcription, RNA processing, and translation. K protein is phosphorylated in vivo and in vitro by inducible kinase(s) and contains several potential sites for protein kinase C (PKC) phosphorylation. In this study we show that K protein is phosphorylated in vitro by PKCdelta and by other PKCs. Deletion analysis and site-directed mutagenesis revealed that Ser302 is a major K protein site phosphorylated by PKCdelta in vitro. This residue is located in the middle of a short amino acid fragment that divides the two clusters of SH3-binding domains. Mutation of Ser302 decreased the level of phosphorylation of exogenously expressed K protein in phorbol 12-myristate 13-acetate-treated COS cells, suggesting that Ser302 is also a site for PKC-mediated phosphorylation in vivo. In vitro, PKCdelta binds K protein via the highly interactive KI domain, an interaction that is blocked by poly(C) RNA. Mutation of Ser302 did not alter the K protein-PKCdelta interaction in vitro, suggesting that phosphorylation of this residue alone is not sufficient to alter this interaction. Instead, binding of PKCdelta to K protein in vitro and in vivo was greatly increased by K protein phosphorylation on tyrosine residues. The ability of PKCdelta to bind and phosphorylate K protein may serve not only to alter the activity of K protein itself, but K protein may also bridge PKCdelta to other K protein molecular partners and thus facilitate molecular cross-talk. The regulated nature of the PKCdelta-K protein interaction may serve to meet cellular needs at sites of active transcription, RNA processing and translation in response to changing extracellular environment.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cells, Cultured
  • Heterogeneous-Nuclear Ribonucleoprotein K
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Isoenzymes / metabolism*
  • Mice
  • Mutation
  • Phosphorylation
  • Protein Kinase C / metabolism*
  • Protein Kinase C-delta
  • RNA / genetics
  • RNA, Heterogeneous Nuclear / genetics
  • RNA, Heterogeneous Nuclear / metabolism*
  • Ribonucleoproteins / genetics
  • Ribonucleoproteins / metabolism*
  • Serine / genetics
  • Serine / physiology


  • Heterogeneous-Nuclear Ribonucleoprotein K
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Isoenzymes
  • RNA, Heterogeneous Nuclear
  • Ribonucleoproteins
  • Serine
  • RNA
  • Prkcd protein, mouse
  • Protein Kinase C
  • Protein Kinase C-delta