Mechanism of activation of choline acetyltransferase in a human neuroblastoma cell line.
In our previous report we have shown that the enzyme choline acetyltransferase (ChAT), responsible for the synthesis of the neurotransmitter acetylcholine, can be regulated in response to treatment by either retinoic acid or sodium butyrate. These responses were dose and time dependent, but the mechanism by which these agents were acting was not understood. We now report the results of studies aimed at elucidating the level at which both sodium butyrate and retinoic acid are able to increase ChAT activity. The effects of these agents on macromolecular synthesis appeared to be limited to small but statistically significant increases in the rate of RNA synthesis. However, inhibition of DNA, RNA and protein synthesis in these cells had no effect on the stimulation of ChAT activity by either sodium butyrate or retinoic acid. Several experiments appeared to rule out a role for cyclic AMP or protein kinase C in the regulation of ChAT activity, even though retinoic acid treatment could increase endogenous levels of cyclic AMP 3- to 4-fold over the time course of ChAT activity stimulation. Experiments performed to determine kinetic parameters of this enzyme demonstrated changes only in the Vmax, but not the Km of ChAT, suggesting that the affinity of enzyme for either of its substrates was not responsible for the increase in specific activity. Taken together, this evidence suggests that the activation of choline acetyltransferase in this human neuroblastoma cell line occurs at the post-translational level.
Casper
D
D
Department of Pathology, Albert Einstein College of Medicine, Bronx, NY 10461.
Davies
P
P
D002087:Butyrates / Q000494:pharmacology*; D020148:Butyric Acid; D002460:Cell Line; D002795:Choline O-Acetyltransferase / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D009447:Neuroblastoma; D009712:Nucleotides, Cyclic / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology*
D002087:Butyrates; D009712:Nucleotides, Cyclic; D012333:RNA, Messenger; D020148:Butyric Acid; D014212:Tretinoin; D003513:Cycloheximide; D002795:Choline O-Acetyltransferase