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

Cell Signaling Technology Inc., Danvers, MA 01923, USA.
Science Signaling (Impact Factor: 7.65). 08/2010; 3(136):ra64. DOI: 10.1126/scisignal.2000998
Source: PubMed

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.

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    • "MS analysis of in vitro phosphorylated MBP-RacGAP1 and FLAG-RacGAP1 immunoprecipitated from 293T cells identified a single predominant PKB/Akt phosphorylation site in RacGAP1 but could not distinguish between T249 (within the sole PKB/Akt consensus within RacGAP1, previously reported in MS analysis; Moritz et al., 2010) and T251 (unpublished data). In vitro phosphorylation using recombinant active PKB/Akt, with either putative phosphorylation site mutated to alanine, revealed T249 to be the predominant PKB/Akt phosphorylation site within RacGAP1 (Fig. 3 A). "
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    The Journal of Cell Biology 09/2013; 202(6). DOI:10.1083/jcb.201302041 · 9.69 Impact Factor
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    • "The EGFR, an RTK, is activated by ligands, such as transforming growth factor-a (TGF-a) [8] [9] and epidermal growth factor (EGF). Binding EGFR with a ligand stimulates the intrinsic tyrosine kinase activity of the receptors and triggers the autophosphorylation of specific tyrosine residues, thereby phosphorylating and activating the downstream pathways [7] [8] [10] [11], which include the Ras/MAPK [12] [13] and PI3K/Akt [14] pathways. The EGFR plays an important role in regulating cell proliferation, differentiation, and transformation, and is a critical target in cancer therapy [7] [11] [13] [15]. "
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    Biochemical pharmacology 09/2013; 86(10). DOI:10.1016/j.bcp.2013.08.066 · 4.65 Impact Factor
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    • "The consequences of RTKs such as PDGFRa high expression in ESCC are tumor cell proliferation, dissemination or angiogenesis [Gockel et al., 2008]. According to Moritz et al. [Moritz et al., 2010] the protein chaperone SGTA at Ser 305 is essential for PDGFRa stabilization and cell survival in PDGFRa‐dependent cancer cells. They highlighted the importance of pathways regulating RTK abundance on survival of cancer cells. "
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