Protein kinase C and membrane transport: divergent responses of Na+/K+/Cl- cotransport and sugar transport to exogenous diacylglycerol.
Even though the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) is known to bind to and activate protein kinase C (PKC), it is still not certain that all cellular responses to phorbol esters are necessarily mediated by PKC. In BALB/c 3T3 preadipose cells, TPA has previously been shown to rapidly inhibit Na+K+Cl- -cotransport activity, stimulate 2-deoxyglucose uptake and induce ornithine decarboxylase activity. The cell-permeable diacylglycerol sn-1,2-dioctanoylglycerol (DiC8) was used in order to distinguish between PKC-dependent and -independent responses of BALB/c 3T3 cells. DiC8 modulated 86Rb+ fluxes in BALB/c 3T3 cells in the same manner as TPA: furosemide-sensitive 86Rb+ influx and efflux was inhibited, while in cotransport-defective cells no effect was observed. In contrast, DiC8 did not stimulate 2-deoxyglucose uptake in either parental or cotransport-defective cell lines, even though TPA is a very effective inducer of this transport system in both cell types. Pretreatment of cells with DiC8 did not substantially alter the subsequent induction of 2-deoxyglucose uptake by TPA, although a slight but reproducible reduction in the magnitude of the response was observed in DiC8-pretreated cells. The PKC-dependent phosphorylation of an acidic 80-kDa protein was stimulated by both TPA and DiC8 in parental and cotransport-defective cell lines, suggesting that a gross defect in the primary effector system used by both TPA and diacylglycerols cannot explain any of our results. Ornithine decarboxylase was induced by DiC8 and the K1/2 was approximately the same as that for inhibition of Na+/K+/Cl- cotransport in these cells. Thus, our results suggest that PKC is clearly essential for some phorbol ester membrane transport responses (such as inhibition of Na+/K+/Cl- cotransport), but our results do not allow us to conclude that other responses (such as stimulation of 2-deoxyglucose uptake) necessarily require PKC activation.
O'Brien
T G
TG
Wistar Institute of Anatomy and Biology, Philadelphia, PA 19104.
George
K
K
Prettyman
R
R
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D004075:Diglycerides / Q000494:pharmacology*; D005989:Glycerides / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009955:Ornithine Decarboxylase / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002352:Carrier Proteins; D002712:Chlorides; D004075:Diglycerides; D005989:Glycerides; D009004:Monosaccharide Transport Proteins; D028021:Sodium-Potassium-Chloride Symporters; C044295:1,2-dioctanoylglycerol; D012964:Sodium; D011493:Protein Kinase C; D009955:Ornithine Decarboxylase; D012413:Rubidium; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium