title: Roles of protein kinase C and alpha-tocopherol in regulation of signal transduction for GATA-4 phosphorylation in HL-1 cardiac muscle cells.
abstract: Our previous study demonstrated that endothelin-1 induced a phosphorylation of GATA-4 transcription factor, which plays important roles in cardiac hypertrophy and failure. The goal of the present study was to determine whether protein kinase C (PKC) is involved in the signaling pathway, and, if so, whether alpha-tocopherol inhibits the GATA-4 phosphorylation. Treatment of HL-1 adult mouse cardiac muscle cells with PMA, a known activator of PKC, induced a transient phosphorylation of GATA-4. PMA also phosphorylated MEK and ERK, and PMA-induced GATA-4 phosphorylation was blocked by an MEK inhibitor, PD98059, suggesting that PMA phosphorylates GATA-4 via the MEK-ERK pathway. Treatment of HL-1 cells with 1 microM PMA for 24 h resulted in a downregulation of PKC. In PKC-downregulated cells, PMA- or ET-1-induced GATA-4 phosphorylation was suppressed, suggesting the role of PKC in GATA-4 phosphorylation. However, alpha-tocopherol (5--100 microM) did not inhibit the phosphorylation of GATA-4 or ERK in HL-1 cells. In contrast, alpha-tocopherol potently inhibited the PMA-induced ERK activation in smooth muscle cells. Our studies in HL-1 cells showed that PKC inhibitors, such as calphostin C and chelerythrin, failed to inhibit the PMA signaling. Furthermore, HL-1 cells appear to possess a unique PKC-signaling mechanism as PKC is constitutively phosphorylated and PMA did not cause further phosphorylation. Thus, in HL-1 cardiac muscle cells, PMA activates the MEK-ERK-GATA-4 pathway, apparently via a PKC-independent mechanism.
authors.affiliation: Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA.
authors.forename: Sophie A
authors.initials: SA
authors.lastname: Clément
authors.forename: Chia Chi
authors.initials: CC
authors.lastname: Tan
authors.forename: Jianli
authors.initials: J
authors.lastname: Guo
authors.forename: Kazumi
authors.initials: K
authors.lastname: Kitta
authors.forename: Yuichiro J
authors.initials: YJ
authors.lastname: Suzuki
mesh_terms: D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005609:Free Radicals; D050991:GATA4 Transcription Factor; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009206:Myocardium / Q000166:cytology*; D009281:Naphthalenes / Q000378:metabolism; D010617:Phenanthridines / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D024502:alpha-Tocopherol / Q000378:metabolism*
chemical_list: D000470:Alkaloids; D053119:Benzophenanthridines; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005609:Free Radicals; D050991:GATA4 Transcription Factor; D009281:Naphthalenes; D010617:Phenanthridines; D014157:Transcription Factors; C016299:chelerythrine; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D024502:alpha-Tocopherol; C058819:calphostin C