Ceramide Induces Bcl2 Dephosphorylation via a Mechanism Involving Mitochondrial PP2A

Abstract

). The potent apoptotic agent ceramide can activate a PP2A, suggesting that one potential component of the ceramide-induced death signal may involve the inactivation of Bcl2. Results indicate that C2-ceramide but not inactive C2-dihydroceramide, was found to specifically activate a mitochondrial PP2A, which rapidly and completely induced Bcl2 dephosphorylation and correlated closely with ceramide-induced cell death. Using a genetic approach, the gain-of-function S70E Bcl2 mutation, which mimics phosphorylation, fails to undergo apoptosis even with the addition of high doses of ceramide (IC 50 > 50 M). In contrast, cells overexpressing exogenous wild-type Bcl2 were sensitive to ceramide at dosages where PP2A is fully active and Bcl2 would be expected to be dephosphorylated (IC 50 ‫؍‬ 14 M). These findings indicate that in cells expressing functional Bcl2, the mechanism of death action for ceramide may involve, at least in part, a mitochondrial PP2A that dephosphorylates and inactivates Bcl2.

Akt2 and acid ceramidase cooperate to induce cell invasion and resistance to apoptosis

“…25 Furthermore, a major role of ceramide is to activate the protein phosphatases PP2A and PP1, [43][44][45][46] and the upregulation of ASAH1 often seen in cancer would decrease ceramide and, therefore, PP1/PP2A activities. PP2A is known to act as a tumor suppressor via dephosphorylating T308 in Akt, 47,48 RalA, 49 SPHK1, 50 but also anti-apoptotic Bcl-2 51 and pro-apoptotic Bax. 52 Similarly, PP1 plays anti-proliferative and (ASAH1 α subunit, #612302), Covance (GAPDH, #MMS-580S) and SigmaAldrich (vinculin, #V9131).…”

True

“…67,68 Recently, we discovered that ceramide can also activate a mitochondrial PP2A responsible for Bcl2 dephosphorylation in association with cell death. 69 Since expression of S70E Bcl2, a non-phosphorylatable, activated form of Bcl2, can protect cells from ceramide-induced apoptosis, one likely mechanism by which ceramide induces cell death is by functionally inactivating Bcl2. 69 Thus, dynamic phosphorylation-dephosphorylation of Bcl2 may serve as a 'survival sensor' during stress stimuli.…”

“…69 Since expression of S70E Bcl2, a non-phosphorylatable, activated form of Bcl2, can protect cells from ceramide-induced apoptosis, one likely mechanism by which ceramide induces cell death is by functionally inactivating Bcl2. 69 Thus, dynamic phosphorylation-dephosphorylation of Bcl2 may serve as a 'survival sensor' during stress stimuli. 69 If favorable growth and survival conditions are achieved, Bcl2 is phosphorylated.…”

“…69 Thus, dynamic phosphorylation-dephosphorylation of Bcl2 may serve as a 'survival sensor' during stress stimuli. 69 If favorable growth and survival conditions are achieved, Bcl2 is phosphorylated. As death-inducing conditions are encountered, however, ceramide (and possibly other negative regulators) is likely produced and Bcl2 dephosphorylated in association with cell death.…”

“…66 Importantly, ceramide may also promote a decrease in Bcl2's anti-apoptotic function by activating mitochondrial PP2A and dephosphorylating Bcl2. 69 Further, the opposite effects of DAG and ceramide on cell signaling and survival appear to be cumulative and where Bcl2 regulation is involved, may result in diverse outcomes for post-translational modification of Bcl2 that can act as a cell's 'survival sensor'.…”