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Ceramide mediates tumor-induced dendritic cell apoptosis
T Kanto1, P Kalinski, O C Hunter
1Department of Surgery, Division of Biologic Therapeutics and Surgical Oncology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Abstract:
Induction of apoptosis in dendritic cells (DC) is one of the escape mechanisms of tumor cells from the immune surveillance system. This study aimed to clarify the underlying mechanisms of tumor-induced DC apoptosis. The supernatants (SN) of murine tumor cell lines B16 (melanoma), MCA207, and MCA102 (fibrosarcoma) increased C16 and C24 ceramide as determined by electrospray mass spectrometry and induced apoptosis in bone marrow-derived DC. N-oleoylethanolamine or D-L-threo 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), which inhibits acid ceramidase or glucosylceramide synthase and then increases endogenous ceramide, enhanced DC apoptosis and ceramide levels in the presence of tumor SN. Pretreatment with L-cycloserine, an inhibitor of de novo ceramide synthesis, or phorbol ester, 12-O-tetradecanoylphorbol-13-acetate reduced endogenous ceramide levels and protected DC from tumor-induced apoptosis. However, other DC survival factors, including LPS and TNF-alpha, failed to do so. The protective activity of 12-O-tetradecanoylphorbol-13-acetate is abrogated by pretreatment with phosphoinositide 3-kinase (PI3K) inhibitor, LY294002. Therefore, down-regulation of PI3K is the major facet of tumor-induced DC apoptosis. Tumor SN, N-oleoylethanolamine, or PDMP suppressed Akt, NF-kappaB, and bcl-x(L) in DC, suggesting that the accumulation of ceramide impedes PI3K-mediated survival signals. Taken together, ceramide mediates tumor-induced DC apoptosis by down-regulation of the PI3K pathway.
Insights
Tumor cells induce dendritic cell (DC) apoptosis by increasing ceramide levels, which inhibits survival signals. This ceramide accumulation down-regulates the phosphoinositide 3-kinase (PI3K) pathway, leading to DC death and immune evasion.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Tumor cells evade immune surveillance partly by inducing apoptosis in dendritic cells (DCs).
- Understanding the mechanisms of tumor-induced DC apoptosis is crucial for developing cancer immunotherapies.
Purpose of the Study:
- To elucidate the molecular mechanisms by which tumor cells induce apoptosis in dendritic cells.
- To investigate the role of ceramide and the phosphoinositide 3-kinase (PI3K) pathway in this process.
Main Methods:
- Analysis of ceramide levels in DCs using electrospray mass spectrometry.
- Induction of apoptosis in bone marrow-derived DCs using tumor cell supernatants (SN).
- Pharmacological manipulation of ceramide synthesis and PI3K pathway activity.
Main Results:
- Tumor SN increased ceramide levels (C16 and C24) and induced DC apoptosis.
- Inhibitors of ceramide metabolism (N-oleoylethanolamine, PDMP) enhanced DC apoptosis and ceramide levels.
- Inhibitors of ceramide synthesis (L-cycloserine) and a PI3K activator (12-O-tetradecanoylphorbol-13-acetate) protected DCs from apoptosis.
- Tumor SN, N-oleoylethanolamine, and PDMP suppressed Akt, NF-kappaB, and bcl-x(L), indicating PI3K pathway inhibition.
Conclusions:
- Ceramide accumulation mediates tumor-induced DC apoptosis by down-regulating the PI3K pathway.
- Targeting ceramide metabolism or the PI3K pathway may offer strategies to enhance anti-tumor immunity.