The protein kinase C-eta isoform induces proliferation in glioblastoma cell lines through an ERK/Elk-1 pathway.
Glioblastoma multiforme (GBM) is the highest grade of astrocytoma. GBM pathogenesis has been linked to receptor tyrosine kinases and kinases further down signal-transduction pathways - in particular, members of the protein kinase C (PKC) family. The expression and activity of various PKC isoforms are increased in malignant astrocytomas, but not in non-neoplastic astrocytes. This suggests that PKC activity contributes to tumor progression. The level of PKC-eta expressed correlates with the degree of phorbol-12-myristate-13-acetate (PMA)-induced proliferation of two glioblastoma cell lines, U-1242 MG and U-251 MG. Normally, U-1242 cells do not express PKC-eta, and PMA inhibits their proliferation. Conversely, PMA increases proliferation of U-1242 cells that are stably transfected with PKC-eta (U-1242-PKC-eta). PMA treatment also stimulates proliferation of U-251 cells, which express PKC-eta. Here, we determined that extracellular signal-regulated kinase (ERK) and Elk-1 are downstream targets of PKC-eta. Elk-1-mediated transcriptional activity correlates with the PKC-eta-mediated mitogenic response. Pretreatment of U-1242-PKC-eta cells with inhibitors of PKC or MAPK/ERK kinase (MEK) (bisindolyl maleimide (BIM) or U0126, respectively) blocked both PMA-induced Elk-1 transcriptional activity and PMA-stimulated proliferation. An overexpressed dominant-negative PKC-eta reduced the mitogenic response in U-251 cells, as did reduction of Elk-1 by small interfering RNA. Taken together, these results strongly suggest that PKC-eta-mediated glioblastoma proliferation involves MEK/mitogen-activated protein (MAP) kinase phosphorylation, activation of ERK and subsequently of Elk-1. Elk-1 target genes involved in GBM proliferative responses have yet to be identified.
Uht
R M
RM
Department of Pathology, School of Medicine, University of Virginia, Charlottesville, VA 22908, USA. ruht@virginia.edu
Amos
S
S
Martin
P M
PM
Riggan
A E
AE
Hussaini
I M
IM
D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism / Q000502:physiology*; D016762:Genes, fos / Q000502:physiology; D016758:Genes, jun / Q000502:physiology; D005909:Glioblastoma / Q000473:pathology*; D006801:Humans; D007527:Isoenzymes / Q000502:physiology; D008954:Models, Biological; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection; D050807:ets-Domain Protein Elk-1 / Q000502:physiology*
D007527:Isoenzymes; D018808:Transcription Factor AP-1; D050807:ets-Domain Protein Elk-1; D004815:Epidermal Growth Factor; C081975:protein kinase C eta; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D013755:Tetradecanoylphorbol Acetate