We measured the activities of UDP-galactose:globotriaosylceramide α1–3-galactosyltransferase (α-GalTase) and protein kinase C (PKC) in PC12D pheochromocytoma (PC12D) cells which were induced to differentiation by nerve growth factor (NGF), forskolin (FRK), staurosporine (STP), retinoic acid (RA), 2-chloroadenosine (ClAd), and/or galactosylceramide (GalCer). NGF, STP, FRK, and RA were found to be stimulators for the PKC activity, whereas ClAd appeared to be an inhibitor of the enzyme. At the concentration of 25 µM, GalCer having normal fatty acids was found to be a stimulator, whereas GalCer having hydroxy fatty acids was ineffective in modulating the PKC activity. Interestingly, all stimulators of PKC activities, including GalCer having normal fatty acids, appeared to be activators for the α-GalTase activity. On the other hand, GalCer having α-hydroxy fatty acids had no effect and ClAd was found to be a potent inhibitor for the α-GalTase activity. These data suggest that α-GalTase activity during PC12D cell differentiation may be regulated by a PKC-dependent process.
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