Chemotherapy has been reported to upregulate sphingomylinases and increase cellular ceramide, often linked to the induction to cell death. In this work, we show that sublethal doses of doxorubicin and vorinostat still increased cellular ceramide, which was located predominantly at the plasma membrane. To interrogate possible functions of this specific pool of ceramide, we used recombinant enzymes to mimic physiological levels of ceramide at the plasma membrane upon chemotherapy treatment. Using mass spectrometry and network analysis, followed by experimental confirmation, the results revealed that this pool of ceramide acutely regulates cell adhesion and cell migration pathways with weak connections to commonly established ceramide functions (eg, cell death). Neutral sphingomyelinase 2 (nSMase2) was identified as responsible for the generation of plasma membrane ceramide upon chemotherapy treatment, and both ceramide at the plasma membrane and nSMase2 were necessary and sufficient to mediate these “side” effects of chemotherapy on cell adhesion and migration. This is the first time a specific pool of ceramide is interrogated for acute signaling functions, and the results define plasma membrane ceramide as an acute signaling effector necessary and sufficient for regulation of cell adhesion and cell migration under chemotherapeutical stress.

This article is available online at http://www.jlr.org differentiation, and intracellular traffi cking ( 1 ). It has been demonstrated that cells adjust SL production in response to metabolic needs ( 2 ). SM is biochemically synthesized through the activity of serine-palmitoyl-CoA transferase, 3-ketosphinganine reductase, ceramide (Cer) synthase, dihydroceramide desaturase, and sphingomyelin synthase (SMS). SMS, which uses Cer and phosphatidylcholine as substrates, is the last enzyme in SM biosynthesis ( 3 ). Two isoforms, SMS1 and SMS2, have been cloned in mammals ( 4 ). SMS1 localizes in the Golgi apparatus, whereas SMS2 can be localized in the PM ( 5 ) but also in the Golgi apparatus. Although SM is principally synthesized by SMS1 activity, it has been reported that both SMS1 and SMS2 are required for SM homeostasis and growth in human HeLa cells ( 6 ). SM synthesis is directly related to correct intracellular protein traffi cking ( 7 ). It has been recently shown that the downregulation of SMSs significantly retards the traffi cking of the reporter protein vesicular stomatitis virus G protein tagged with GFP from the trans-Golgi network to the PM. Moreover, the correct endosomal recycling network is directly related to Golgi SM synthesis ( 8 ).SM is the main SL in mammalian cells. Because of the high affi nity of interaction with cholesterol, SM drives the formation of PM rafts or detergent-resistant microdomains (DRMs) ( 9, 10 ), thus providing a framework for PM organization. Early studies have demonstrated

Ceramides (Cers) and complex sphingolipids with defined acyl chain lengths play important roles in numerous cell processes. Six Cer synthase (CerS) isoenzymes (CerS1-6) are the key enzymes responsible for the production of the diversity of molecular species. In this study, we investigated the changes in sphingolipid metabolism during the differentiation of Madin-Darby canine kidney (MDCK) cells. By MALDI TOF TOF MS, we analyzed the molecular species of Cer, glucosylceramide (GlcCer), lactosylceramide (LacCer), and SM in nondifferentiated and differentiated cells (cultured under hypertonicity). The molecular species detected were the same, but cells subjected to hypertonicity presented higher levels of C24:1 Cer, C24:1 GlcCer, C24:1 SM, and C16:0 LacCer. Consistently with the molecular species, MDCK cells expressed CerS2, CerS4, and CerS6, but with no differences during cell differentiation. We next evaluated the different synthesis pathways with sphingolipid inhibitors and found that cells subjected to hypertonicity in the presence of amitriptyline, an inhibitor of acid sphingomyelinase, showed decreased radiolabeled incorporation in LacCer and cells did not develop a mature apical membrane. These results suggest that hypertonicity induces the endolysosomal degradation of SM, generating the Cer used as substrate for the synthesis of specific molecular species of glycosphingolipids that are essential for MDCK cell differentiation.