Ceramide regulation of the tumor suppressor phosphatase PTEN in rafts isolated from neurotumor cell lines

Abstract

The neutral sphingolipid ceramide has been implicated in the apoptotic death of cells by a number of different mechanisms, including activation of protein kinase B (Akt) phosphatase. Here we present evidence that ceramide recruits the tumor suppressor PTEN (phosphatase and tensin homolog deleted from chromosome 10) into membrane microdomains (rafts), where it could act to reduce the levels of polyphosphoinositides necessary for the activation of Akt. A PTEN construct with a red-fluorescent protein (RFP) tag was overexpressed in both a human cell line derived from oligodendroglioma (HOG) and a rat pheochromocytoma cell line (PC12) by means of an inducible promoter system (Tet-Off). Induction of PTEN by removal of doxycycline enhanced both capsase-3 and cell death with staurosporine, wortmannin, or C2-ceramide, whereas antisense PTEN had the reverse effect. Overexpression of PTEN also increased acid sphingomyelinase (ASMase) activity. PTEN normally has a generalized (cytosolic/membrane) distribution, but treatment with C2-ceramide translocated a fraction of the PTEN to the plasma membrane, showing a plasma membrane distribution similar to that observed for a prenylated green-fluorescent (GFP) construct. PTEN was then shown to translocate to the detergent-resistant membrane microdomain fraction (raft) of the plasma membrane. The colocalization of sphingomyelinases, ceramide, polyphosphoinositides, and PTEN in the raft fraction further suggests that the association of these lipids is critical for regulating cell death.

Sphingolipids: agents provocateurs in the pathogenesis of insulin resistance

“…In addition to promoting the recruitment of PKB and aPKC1/z, ceramide exposure can also significantly elevate levels of phosphatase and tensin homologue deleted on chromosome ten (PTEN) in caveolin-enriched DRM fractions [53,60]. The tumour suppressor PTEN acts as a phosphoinositide phosphatase and its increased abundance in CEMs would likely result in reduced localised levels of 3′-phosphoinositides.…”

Cholesterol Depletion Reduces Entry of Campylobacter jejuni Cytolethal Distending Toxin and Attenuates Intoxication of Host Cells

“…This idea is supported by the finding that the A. actinomycetemcomitans CdtB subunit exhibits phophatidylinositol-3,4,5-triphosphate (PIP3) phosphatase activity similar to that of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) (30,52). A previous study found that PTEN normally has a generalized cytosolic and membrane distribution but is recruited into membrane rafts when cells are treated with ceramide (18). We found that both CdtA and CdtC interact with lipid rafts (predominantly localized in cholesterol-rich microdomains) to enhance the association of CdtB with the cell membrane and its subsequent delivery into the cells.…”

Targeting the sphingolipid metabolism to defeat pancreatic cancer cell resistance to the chemotherapeutic gemcitabine drug

“…Ceramide is indeed able, by directly promoting the recruitment into lipid raft of phosphatase and tensin homologue (43) and/or by indirectly activating ceramide-activated protein phosphatase 2A (43,44), to inhibit specifically this pathway, conducting to NF-κB inactivation and to decreased Bcl-xL expression. Conversely, both SphK1 and, indirectly, S1P by acting in an autocrine loop via its S1PR/Edg receptors are able to stimulate this same pathway (45,46).…”