Ceramide starves cells to death by downregulating nutrient transporter proteins

Abstract

Ceramide induces cell death in response to many stimuli. Its mechanism of action, however, is not completely understood. Ceramide induces autophagy in mammalian cells maintained in rich media and nutrient permease downregulation in yeast. These observations suggested to us that ceramide might kill mammalian cells by limiting cellular access to extracellular nutrients. Consistent with this proposal, physiologically relevant concentrations of ceramide produced a profound and specific downregulation of nutrient transporter proteins in mammalian cells. Blocking ceramide-induced nutrient transporter loss or supplementation with the cell-permeable nutrient, methyl pyruvate, reversed ceramide-dependent toxicity. Conversely, cells became more sensitive to ceramide when nutrient stress was increased by acutely limiting extracellular nutrients, inhibiting autophagy, or deleting AMP-activated protein kinase (AMPK). Observations that ceramide can trigger either apoptosis or caspase-independent cell death may be explained by this model. We found that methyl pyruvate (MP) also protected cells from ceramide-induced, nonapoptotic death consistent with the idea that severe bioenergetic stress was responsible. Taken together, these studies suggest that the cellular metabolic state is an important arbiter of the cellular response to ceramide. In fact, increasing nutrient demand by incubating cells in high levels of growth factor sensitized cells to ceramide. On the other hand, gradually adapting cells to tolerate low levels of extracellular nutrients completely blocked ceramide-induced death. In sum, these results support a model where ceramide kills cells by inducing intracellular nutrient limitation subsequent to nutrient transporter downregulation.autophagy ͉ caspase-independent cell death ͉ daunorubicin ͉ bioenergetics ͉ sphingolipid C eramide and related sphingolipids play an evolutionarily conserved role in the cellular response to stress by regulating cell growth, differentiation, senescence, and survival (1). Uncovering the mechanisms by which ceramide regulates these processes is of paramount importance given the wide range of human diseases that result from altered ceramide metabolism including cancer, type II diabetes, and neurodegenerative disease (2-4). Ceramide plays a particularly well-established role in cancer. Decreasing cellular ceramide levels increases tumor growth and metastasis and can lead to multidrug resistance, a major cause of cancer treatment failure (2, 5, 6). The ability of ceramide to trigger programmed cell death in response to growth factor withdrawal, death receptor ligation, hypoxia, and chemotherapeutic drugs is likely integral to its role in suppressing cancer initiation and progression. Although many of the downstream, executioner pathways that are activated by ceramide are known, how ceramide triggers these pathways is not completely understood.Autophagy, a process by which cells catabolize their own components, is induced in ceramide-treated cells (7-9). Autophagy has been conserved through...

Compound C sensitizes Caki renal cancer cells to TRAIL-induced apoptosis through reactive oxygen species-mediated down-regulation of c-FLIPL and Mcl-1

“…Moreover, its activation by AICAR has been shown to sensitize human cancer cells to tert-Butylhydroxyquinone (t-BHQ), TRAIL, and TNFinduced apoptosis [10,11]. On the other hand, some reports demonstrated the activity of AMPK to protect cells from ischemia, hyperglycemia, glucose deprivation, fatty acids and ceramide [12][13][14][15]. In accordance with this report, treatment of MCF-7 cells with AMPK inhibitor compound C resulted in apoptosis.…”

Horizontal gene transfer of an entire metabolic pathway between a eukaryotic alga and its DNA virus

“…Wilson et al (2005) originally proposed that the viral enzymes would be part of a viral lysis strategy to kill the host cell. This hypothesis was based on the role of ceramide as an inducer of cell death in mammalian and yeast cells (Guenther et al 2008). The presence of eight protease genes in the EhV-86 genome (Wilson et al 2005) parallels the known connection between protease activation and ceramide-induced programmed cell death in mammalian cells (Susin et al 1997;Siskind 2005).…”

“…Despite these recent efforts to characterize the EhV sphingolipid biosynthesis genes, their function in the virus replication cycle remains unknown. Based on the role of ceramide as an inducer of cell death in mammalian and yeast cells (Susin et al 1997;Siskind 2005;Guenther et al 2008), several investigators proposed that the viral sphingolipid/ceramide pathway may activate host cell death, thus helping disseminate newly generated virions in the host population (Wilson et al 2005;Bidle et al 2007).…”

“…Sphingolipid metabolism has been mostly studied in mammalian and yeast cells, where it was found to play key roles in signal transductions (Hannun et al 2001). The de novo sphingolipid biosynthesis leads to the production of ceramide (Merrill 2002), which serves as the backbone for all complex sphingolipids and has a fundamental role in coordinating eukaryotic cell stress responses, including activation of apoptosis (Hannun 1996;Yang et al 2004;Guenther et al 2008).…”

AMPK-independent down-regulation of cFLIP and sensitization to TRAIL-induced apoptosis by AMPK activators

“…Moreover, its activation by AICAR has been shown to sensitize human colon adenocarcinoma cells to TRAIL and TNF-induced apoptosis [21]. Against these data, AMPK has been proposed as an anti-apoptotic molecule to protect cells from ischemia, hyperglycemia, glucose deprivation, fatty acids and ceramide [22][23][24] .…”