Therefore, CER up regulation may not be due to the prevalence of an apoptotic response but may be utilized to up regulate autophagy during DENV infection. It has been shown in mammalian cells that autophagy is up regulated and necessary for DENV replication. The prevalence of several intermediates in CER biogenesis, including N-palmitoylsphingosine and diacylglycerol, suggest that the observed CER could result from either de [20] . 2. Inhibition of this process with C75 disrupts the cellular lipid repertoire in mosquito cells to be unfavorable for virus replication. 3. The lipidomic analyses reveal an up regulation of fatty acids such as palmitic (C16) and stearic (C18) acid. These fatty acids are intermediates in the biosynthesis of phospholipids, which is up regulated during DENV infection. Interestingly, in DENV infected cells the prevalent phospholipids primarily consist of C16 and C18 unsaturated acyl chains. Very long chain fatty acids are not significantly up regulated during infection. 4. FAS activity also stimulates de novo sphingolipid biosynthesis. In the lipidomic analyses, the up regulation of intermediates such as N-palmitoylesphingosine suggests sphingolipid biosynthesis is activated during DENV infection. Specifically, SM and CER are enriched in DENV infected cells. Alternately, the up regulation in CER (and DG) during infection could result from the degradation of SM through the activity of sphingomyelinases (Smase). The resulting CER and DG could be redirected into several signaling pathways or be utilized for de novo phospholipid biosynthesis. The glycopshingolipids, GlcCER and GalCER are down regulated during DENV infection, which suggest that they are catabolized to produce CER. 5. Lipidomic analyses also suggest the up regulation of triacylglycerol catabolism (Lipolysis) in DENV infected cells. This pathway results in the generation of MG, DG and palmitic acid. These intermediates are all up regulated in DENV infected cells and could be utilized for downstream signaling or de novo phospholipid biosynthesis. It has also been shown that TG catabolism is necessary for mitochondrial b-oxidation during DENV infection [50] . 6. Elevated levels of LPC in DENV infected cells also suggest activation of PC hydrolysis by PLA 2 . This enzyme is activated during DENV infection. The elevated levels of other phospholipids such as PA, PI, PE, PG as well as PC suggest that the CDG-DG pathway for phospholipid biosynthesis could also be activated. FAS, fatty acid synthase; DENV, dengue virus; C75, inhibitor of FAS; SM, sphingomyelin; CER, ceramide; MG, monoacylglycerol; DG, diacylglycerol; TG, triacylglycerol; LPC, lysophosphatidylcholine; PLA 2 , phospholipase A 2 ; PA, phosphatidic acid; PI, phosphatidylinositol; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PC, phosphatidylcholine. doi:10.1371/journal.ppat.1002584.g008 novo synthesis by serine palmitoyltransferase (SPTLC) in the ER or catabolism of SM by sphingomyelinases (SMases) at the plasma membrane [44] . The lipidomic analyses also indicated a down regulation of GlcCER, which may suggest that a salvage pathway that metabolizes GlcCER to CER may also be active.