Alternative Activation Mechanisms of Protein Kinase B Trigger Distinct Downstream Signaling Responses.
Protein kinase B (PKB/Akt) is an important mediator of signals that control various cellular processes including cell survival, growth, proliferation, and metabolism. PKB promotes these processes by phosphorylating many cellular targets, which trigger distinct downstream signaling events. However, how PKB is able to selectively target its substrates to induce specific cellular functions remains elusive. Here we perform a systematic study to dissect mechanisms that regulate intrinsic kinase activity versus mechanisms that specifically regulate activity toward specific substrates. We demonstrate that activation loop phosphorylation and the C-terminal hydrophobic motif are essential for high PKB activity in general. On the other hand, we identify membrane targeting, which for decades has been regarded as an essential step in PKB activation, as a mechanism mainly affecting substrate selectivity. Further, we show that PKB activity in cells can be triggered independently of PI3K by initial hydrophobic motif phosphorylation, presumably through a mechanism analogous to other AGC kinases. Importantly, different modes of PKB activation result in phosphorylation of distinct downstream targets. Our data indicate that specific mechanisms have evolved for signaling nodes, like PKB, to select between various downstream events. Targeting such mechanisms selectively could facilitate the development of therapeutics that might limit toxic side effects.
From the Structural Biology and Biocomputing Programme, Cell Signalling and Adhesion Group.
Deborah
D
Balzano
Cancer Cell Biology Programme, Growth Factors, Nutrients and Cancer Group.
Mohamad-Ali
MA
Fawal
From the Structural Biology and Biocomputing Programme, Cell Signalling and Adhesion Group.
Jose V
JV
Velázquez
Structural Biology and Biocomputing Programme, Spectroscopy and Nuclear Magnetic Resonance Unit, and.
Clara M
CM
Santiveri
From the Structural Biology and Biocomputing Programme, Cell Signalling and Adhesion Group.
Joshua
J
Yang
the Experimental Therapeutics Programme, Spanish National Cancer Research Centre, Madrid 28029, Spain.
Joaquín
J
Pastor
Structural Biology and Biocomputing Programme, Spectroscopy and Nuclear Magnetic Resonance Unit, and.
Ramón
R
Campos-Olivas
Cancer Cell Biology Programme, Growth Factors, Nutrients and Cancer Group.
Nabil
N
Djouder
From the Structural Biology and Biocomputing Programme, Cell Signalling and Adhesion Group, dlietha@cnio.es.
Daniel
D
Lietha
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D055162:Biocatalysis; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013379:Substrate Specificity; D013912:Threonine / Q000378:metabolism
D018129:Phosphatidylinositol Phosphates; C060974:phosphatidylinositol 3,4,5-triphosphate; D013912:Threonine; D007334:Insulin-Like Growth Factor I; D051057:Proto-Oncogene Proteins c-akt
Akt PKB; allosteric regulation; cell signaling; phosphoinositide; substrate specificity