Phosphorylation is involved in the regulation of the taurine influx via the beta-system in Ehrlich ascites tumor cells.
The role of 3',5'-cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), protein kinase C (PKC) and phosphatases in the regulation of the taurine influx via the beta-system in Ehrlich ascites tumor cells has been investigated. The taurine uptake by the beta-system in Ehrlich cells is inhibited when PKC is activated by phorbol 12-myristate 13-acetate (PMA) and when protein phosphatases are inhibited by calyculin A (CLA). On the other hand, taurine uptake by the beta-system is stimulated by an increased level of cAMP or following addition of N6,2'-O-dibutyryl-3',5'-cyclic adenosine monophosphate (dbcAMP). The effect of dbcAMP is partially blocked by addition of the protein kinase inhibitor H-89, and suppressed in the presence of CLA. It is proposed that the beta-system in the Ehrlich cells exists in three states of activity: State I, where a PKC phosphorylation site on the transporter or on a regulator is phosphorylated and transport activity is low. State II, where the PKC phosphorylation site is dephosphorylated and transport activity is normal. State III, representing a state with high transport activity, induced by an elevated cellular cAMP level. Apparently, cAMP preferentially stimulates taurine transport when the beta-system is in State II.
Mollerup
J
J
August Krogh Institute, Biochemical Department, Copenhagen, Denmark.
Lambert
I H
IH
D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D003994:Bucladesine / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D048429:Cell Size; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008387:Marine Toxins; D008564:Membrane Potentials; D051379:Mice; D008954:Models, Biological; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D013654:Taurine / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D013654:Taurine; D003994:Bucladesine; C059041:calyculin A; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate