Resistance to alkyl-lysophospholipid-induced apoptosis due to downregulated sphingomyelin synthase 1 expression with consequent sphingomyelin- and cholesterol-deficiency in lipid rafts

Arnold H. van Der Luit , Marianne Budde , Shuraila Zerp , Wendy Caan , Jeffrey B. Klarenbeek , Marcel Verheij , Wim J. van Blitterswijk (1)

1 Cellular Biochemistry

The alkyl-lysophospholipid (ALP) 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine induces apoptosis in S49 mouse lymphoma cells. To this end, ALP is internalized by lipid raft-dependent endocytosis and inhibits phosphatidylcholine synthesis. A variant cell line, S49 AR}, made resistant to ALP, was previously found incapable of ALP internalization via this lipid raft pathway. The reason for this uptake failure is not understood. Here, we report that S49 AR} cells are unable to synthesize sphingomyelin due to downregulated sphingomyelin synthase (SMS1) expression. In parental S49 cells, resistance to ALP could be mimicked by small interfering RNA-induced SMS1 suppression, resulting in sphingomyelin deficiency and blockade of raft-dependent internalization of ALP and apoptosis induction. Similar results were obtained by treatment of the cells with myriocin/ISP-1, an inhibitor of general sphingolipid synthesis, or with U18666A, a cholesterol homeostasis disturbing agent. U18666A is known to inhibit Niemann-Pick C1 protein-dependent vesicular transport of cholesterol from endosomal compartments to the trans-Golgi network and the plasma membrane. U18666A reduced cholesterol partitioning in detergent-resistant lipid rafts and inhibited sphingomyelin synthesis in S49 cells, causing ALP resistance similar as in S49 AR} cells. The data are explained by the strong physical interaction between (newly synthesized) sphingomyelin and available cholesterol at the Golgi, which facilitates lipid raft formation at the Golgi. We propose that ALP internalization by raft-dependent endocytosis represents the retrograde route of a constitutive SMS1- and raft-dependent membrane vesicular recycling process.

Mots clés: Life Sciences

Arnold H. van Der Luit, Marianne Budde, Shuraila Zerp, Wendy Caan, Jeffrey B. Klarenbeek, et al.. Resistance to alkyl-lysophospholipid-induced apoptosis due to downregulated sphingomyelin synthase 1 expression with consequent sphingomyelin- and cholesterol-deficiency in lipid rafts. Biochemical Journal, 2006, 401 (2), pp.541-549. ⟨10.1042/BJ20061178⟩. ⟨hal-00478643⟩