Coordinated effects of electromagnetic field exposure on erythropoietin-induced activities of phosphatidylinositol-phospholipase C and phosphatidylinositol 3-kinase.
Initial studies with the erythropoietin-sensitive human hematopoietic cell line, TF1, demonstrated both multifarious effects of pulsed electromagnetic field (EMF) exposure on lipid signal transduction and antiproliferative effects of EMF. Stimulation of TF1 cells with erythropoietin resulted in increased phosphatidylinositol 3-kinase activity within 2 min. Addition of wortmannin, an inhibitor of phosphatidylinositol 3-kinase, produced a decrease in cell proliferation as measured by accumulation of cells in the G0/G1 phase of the cell cycle and suppression of erythropoietin-induced DNA synthesis. Similar effects on cell proliferation were seen under EMF treatment. Phosphatidylinositol 3-kinase activity in erythropoietin-stimulated TF1 cells, measured in whole-cell extracts, increased 34% within 2 min and remained above basal levels for at least 20 min. EMF decreased erythropoietin-stimulated phosphatidylinositol 3-kinase activity to lower than basal levels. Additionally, translocation of the 85-kDa regulatory subunit (p85) of phosphatidylinositol 3-kinase to the membrane was prevented by EMF. Phosphatidylinositol-specific phospholipase C was activated, as reflected by increases in diacylglycerol and inositol trisphosphate at 15-60 s after EMF treatment. These results provide the first evidence of subtle coordinated changes by EMF associated with loss of phosphatidylinositol 3-kinase activity, inhibition of the translocation of p85 to the membrane, and activation of phosphatidylinositol-phospholipase C.
Clejan
S
S
Department of Pathology and Laboratory Medicine, Tulane University School of Medicine, New Orleans, LA 70112-2699, USA. clejan@tmc.tulane.edu
Dotson
R S
RS
Ide
C F
CF
Beckman
B S
BS
D000730:Androstadienes / Q000494:pharmacology; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D002453:Cell Cycle; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D004261:DNA Replication / Q000187:drug effects; D004574:Electromagnetic Fields; D004789:Enzyme Activation; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*; D000077191:Wortmannin
D000730:Androstadienes; D000893:Anti-Inflammatory Agents; D004921:Erythropoietin; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D000077191:Wortmannin