Cloned mammalian neutral sphingomyelinase: Functions in sphingolipid signaling?

Abstract

Sphingomyelin is an abundant constituent of the plasma membranes of mammalian cells. Ceramide, its primary catabolic intermediate, is released by either acid sphingomyelinase or neutral sphingomyelinase (nSMase) and has emerged as a potential lipid signaling molecule. nSMase is regarded as a key enzyme in the regulated activation of the “sphingomyelin cycle” and cell signaling. We report here the cloning, identification, and functional characterization of murine and human nSMase, a ubiquitously expressed integral membrane protein, which displays all established properties of the Mg 2+ -dependent nSMase of the plasma membrane. Stably nSMase-overexpressing U937 and human embryonic kidney cell lines have been generated for the study of the role of nSMase in signal transduction pathways. Their stimulation by tumor necrosis factor α leads only to a moderately elevated ceramide concentration. Activation of Jun kinase and NFκB and poly(ADP-ribose) polymerase cleavage are identical in mock- and nSMase-transfected cells. Tumor necrosis factor α triggers the ERK1 pathway in none of the cell lines. The cloned nSMase will facilitate further controlled experiments aiming at the definition of a possible role of ceramide as signal transduction molecule.

Transient Mechanoactivation of Neutral Sphingomyelinase in Caveolae to Generate Ceramide

“…To date, several N-SMase isoforms have been cloned (41)(42)(43)(44)(45) or purified (34, 46 -50) from various mammalian tissues, and these isoforms may exhibit distinct tissue and intracellular distribution (43,51,52). Ligand-induced sphingomyelin hydrolysis and the generation of ceramide within caveolin-rich fractions prepared by a nondetergent method was reported previously in fibroblasts (23) and PC12 cells (24).…”

Structural Requirements for Catalysis and Membrane Targeting of Mammalian Enzymes with Neutral Sphingomyelinase and Lysophospholipid Phospholipase C Activities

“…The isolation of mammalian proteins with sequence similarity to bacterial NSM (6) opened a possibility that these proteins could be involved in the regulated generation of ceramide known to be important for a number of cellular functions (1-3). However, related bacterial and mammalian lipid-hydrolyzing enzymes (e.g.…”

Upregulation of smpd3 via BMP2 stimulation and Runx2

“…The acid sphingomyelinase, smpd1, is localized in the endolysosomal compartment, while the neutral SMases, smpd2 and smpd3, are localized in the endoplasmic reticulum membrane and the Golgi apparatus, respectively (4). Sphingomyelin phosphodiesterase 3 (smpd3 or neutral sphingomyelinase-2) is a member of a large superfamily of magnesium-dependent phosphohydrolases (4)(5)(6). This enzyme hydrolyzes sphingosylphosphocholine in the plasma membrane to produce ceramide and was originally identified as a brain-specific neutral sphingomyelinase (2).…”