Akt-RSK-S6 kinase signaling networks activated by oncogenic receptor tyrosine kinases

Sci Signal. 2010 Aug 24;3(136):ra64. doi: 10.1126/scisignal.2000998.

Abstract

Receptor tyrosine kinases (RTKs) activate pathways mediated by serine-threonine kinases, such as the PI3K (phosphatidylinositol 3-kinase)-Akt pathway, the Ras-MAPK (mitogen-activated protein kinase)-RSK (ribosomal S6 kinase) pathway, and the mTOR (mammalian target of rapamycin)-p70 S6 pathway, that control important aspects of cell growth, proliferation, and survival. The Akt, RSK, and p70 S6 family of protein kinases transmits signals by phosphorylating substrates on an RxRxxS/T motif (R, arginine; S, serine; T, threonine; and x, any amino acid). We developed a large-scale proteomic approach to identify more than 300 substrates of this kinase family in cancer cell lines driven by the c-Met, epidermal growth factor receptor (EGFR), or platelet-derived growth factor receptor alpha (PDGFRalpha) RTKs. We identified a subset of proteins with RxRxxS/T sites for which phosphorylation was decreased by RTK inhibitors (RTKIs), as well as by inhibitors of the PI3K, mTOR, and MAPK pathways, and we determined the effects of small interfering RNA directed against these substrates on cell viability. Phosphorylation of the protein chaperone SGTA (small glutamine-rich tetratricopeptide repeat-containing protein alpha) at serine-305 was essential for PDGFRalpha stabilization and cell survival in PDGFRalpha-dependent cancer cells. Our approach provides a new view of RTK and Akt-RSK-S6 kinase signaling, revealing previously unidentified Akt-RSK-S6 kinase substrates that merit further consideration as targets for combination therapy with RTKIs.

MeSH terms

  • Amino Acid Motifs
  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism
  • Cell Line
  • Humans
  • Peptides / chemistry*
  • Peptides / metabolism
  • Phosphorylation
  • Proto-Oncogene Proteins c-akt / chemistry*
  • Proto-Oncogene Proteins c-akt / metabolism
  • Receptor, Platelet-Derived Growth Factor alpha / chemistry*
  • Receptor, Platelet-Derived Growth Factor alpha / metabolism
  • Ribosomal Protein S6 Kinases, 70-kDa / chemistry*
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Substrate Specificity
  • TOR Serine-Threonine Kinases / chemistry*
  • TOR Serine-Threonine Kinases / metabolism

Substances

  • Carrier Proteins
  • Peptides
  • SGTA protein, human
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Receptor, Platelet-Derived Growth Factor alpha
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases, 70-kDa