PKC-eta mediates glioblastoma cell proliferation through the Akt and mTOR signaling pathways.
We previously demonstrated that protein kinase C-eta (PKC-eta) mediates a phorbol 12-myristate-13-acetate (PMA)-induced proliferative response in human glioblastoma (GBM) cells. In this report, we show that PMA-stimulated activation of PKC-eta in U-251 GBM cells resulted in activation of both Akt and the mammalian target of rapamycin (mTOR) signaling pathways and an increase in cell proliferation. Expression of a kinase dead PKC-eta (PKC-etaKR) construct reduced the basal and PMA-evoked proliferation of PKC-eta-expressing U-251 GBM cells, as well as abrogated the PMA-induced activation of Akt, mTOR, and the mTOR targets 4E-BP1 and STAT-3. Treatment of cells with the PI-3 kinase inhibitor LY294002 (10 muM) or the mTOR inhibitor rapamycin (10 nM) also reduced PMA-induced proliferation and cell-cycle progression. Expression of a constitutively active PKC-eta (PKC-etaDeltaNPS) construct in a GBM cell line with no endogenous PKC-eta (U-1242) also provided evidence that PKC-eta targets the Akt and mTOR signaling pathways. Moreover, activation of 4E-BP1 and STAT-3 in both PMA-treated U-251 and PKC-etaDeltaNPS-expressing U-1242 GBM cells was inhibited by rapamycin. However, activation of Akt, but not mTOR was inhibited by the PI-3 kinase inhibitor LY294002. This study identifies Akt and mTOR as downstream targets of PKC-eta that are involved in GBM cell proliferation.
Department of Pathology and Neurology, University of Virginia, Charlottesville, VA 22908, USA. sea4s@virginia.edu
Sean E
SE
Aeder
Patrick M
PM
Martin
Jae-Won
JW
Soh
Isa M
IM
Hussaini
D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005909:Glioblastoma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D011518:Proto-Oncogene Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D011494:Protein Kinases; C081975:protein kinase C eta; C546842:MTOR protein, human; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D020123:Sirolimus