Effects of cations on ceramide-activated protein phosphatase 2A.
Characterization of ceramide-effector(s), which includes protein phosphatase 2A (PP2A) is an important prelude to understanding the molecular basis of sphingolipid-mediated biological effects such as cell growth, differentiation and apoptosis. Recently, the existence of a metal-dependent form of PP2A has been reported (Cai et al., 1995). In this study, we investigated the effects of metal ions and chelators on ceramide-activated PP2A (CAPP). Our study demonstrates that at 0.5 mM concentration, Mg2+ appears to have no significant effect on either basal or ceramide-stimulated phosphatase activities, whereas Ca2+ stimulated the basal phosphatase activity, but was inhibitory towards CAPP. Moreover, the divalent cations Cr2+, Mn2+, Fe2+, Ni2+, Cu2+ and Zn2+ were tested and all were found to be inhibitory towards both CAPP and basal phosphatase activities. By contrast, Cs+ and Li+ had almost no effect on CAPP, although both stimulated basal phosphatase activity. The effects of EDTA and EGTA were tested and it was observed that EDTA decreased CAPP activity in a dose-dependent fashion, but had no effect upon basal phosphatase activity. These results suggest that CAPP is a metal-dependent protein, but, because Ca2+ inhibitied CAPP and EGTA was much less potent than EDTA in inhibiting CAPP, Ca2+ is unlikely to be its metal cofactor.
Galadari
S
S
Department of Biochemistry, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain. sehamuddin@uaeu.ac.ae
Hago
A
A
Patel
M
M
D002413:Cations, Divalent / Q000494:pharmacology*; D002460:Cell Line; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D008214:Lymphocytes / Q000166:cytology; D010749:Phosphoprotein Phosphatases / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D054648:Protein Phosphatase 2
D002413:Cations, Divalent; D004533:Egtazic Acid; D004492:Edetic Acid; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2