Effects of cations on ceramide-activated protein phosphatase 2A.

Sehamuddin Galadari,Mahendra Patel,Abdulkadir Hago

doi:10.1038/emm.2001.39

Sehamuddin Galadari, Mahendra Patel + Show 1 more

Open Access

https://doi.org/10.1038/emm.2001.39

Copy DOI

Abstract

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.

Highlights

Sphingolipids constitute a diverse and ubiquitous group of membrane lipids with diverse molecular structures and multiple biological effects (Bell et al, 1993)
We investigated the effects of metal ions and chelators on metal ion-depleted ceramide-activated protein phosphatase 2A (CAPP)
In addition it was shown that CAPP activity was totally inhibited by Cr2+, but this cation appeared to be less effective in inhibiting the basal phosphatase activity

Summary

Introduction

Sphingolipids constitute a diverse and ubiquitous group of membrane lipids with diverse molecular structures and multiple biological effects (Bell et al, 1993) These lipids have been shown to be important for the understanding of a number of biological processes such as cell growth, differentiation, stress and apoptosis (Hannun and Bell, 1989; Hannun, 1996; Kolesnick and Kronke, 1998). Recent studies indicate that protein phosphatase 2A (PP 2A), like protein phosphatase 1 (PP 1), can exist in a metal ion-dependent form (Cai et al, 1995). This may represent a new mechanism for the regulation of PP2A. A quick one-step column method has been introduced for the partial purification of CAPP, allowing characterization of the role of metal cations on partially purified CAPP

Methods

Results

Conclusion