p70 S6 kinase is regulated by protein kinase Czeta and participates in a phosphoinositide 3-kinase-regulated signalling complex

Mol Cell Biol. 1999 Apr;19(4):2921-8. doi: 10.1128/MCB.19.4.2921.

Abstract

p70 S6 kinase (p70S6K) is an important regulator of cell proliferation. Its activation by growth factor requires phosphorylation by various inputs on multiple sites. Data accumulated thus far support a model whereby p70S6K activation requires sequential phosphorylations at proline-directed residues in the putative autoinhibitory pseudosubstrate domain, as well as threonine 389. Threonine 229, a site in the catalytic loop is phosphorylated by phosphoinositide-dependent kinase 1 (PDK-1). Experimental evidence suggests that p70S6K activation requires a phosphoinositide 3-kinase (PI3-K)-dependent signal(s). However, the intermediates between PI3-K and p70S6K remain unclear. Here, we have identified PI3-K-regulated atypical protein kinase C (PKC) isoform PKCzeta as an upstream regulator of p70S6K. In coexpression experiments, we found that a kinase-inactive PKCzeta mutant antagonized activation of p70S6K by epidermal growth factor, PDK-1, and activated Cdc42 and PI3-K. While overexpression of a constitutively active PKCzeta mutant (myristoylated PKCzeta [myr-PKCzeta]) only modestly activated p70S6K, this mutant cooperated with PDK-1 activation of p70S6K. PDK-1-induced activation of a C-terminal truncation mutant of p70S6K was also enhanced by myr-PKCzeta. Moreover, we have found that p70S6K can associate with both PDK-1 and PKCzeta in vivo in a growth factor-independent manner, while PDK-1 and PKCzeta can also associate with each other, suggesting the existence of a multimeric PI3-K signalling complex. This work provides evidence for a link between a phorbol ester-insensitive PKC isoform and p70S6K. The existence of a PI3-K-dependent signalling complex may enable efficient activation of p70S6K in cells.

Publication types

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

MeSH terms

  • 3-Phosphoinositide-Dependent Protein Kinases
  • Enzyme Activation
  • Epidermal Growth Factor / pharmacology
  • Isoenzymes / metabolism
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Protein Binding
  • Protein Kinase C / metabolism*
  • Protein Serine-Threonine Kinases / metabolism
  • Ribosomal Protein S6 Kinases / genetics
  • Ribosomal Protein S6 Kinases / metabolism*
  • Sequence Deletion
  • Signal Transduction

Substances

  • Isoenzymes
  • Epidermal Growth Factor
  • 3-Phosphoinositide-Dependent Protein Kinases
  • Protein Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases
  • protein kinase C zeta
  • Protein Kinase C