**8. Conclusion**

408 Biochemistry

inflammation, it is now well accepted that ceramides are key elements in the inflammatory response (Lamour & Chalfant, 2005; Wijesinghe et al., 2008; Gomez-Munoz et al., 2010). For instance, it was reported that activation of A-SMase and the subsequent formation of ceramides play an important role in pulmonary infections as it facilitates internalization of bacteria into lung epithelial cells (Gulbins & Kolesnick, 2003). In this context, inhibition of

Inflammatory mediators include chemokines, cytokines, vasoactive amines, products of proteolytic cascades, phospholipases, or lipids such as eicosanoids and sphingolipids. A major mediator of inflammation is PLA2 activity. In particular, group IV cytosolic cPLA2 ( or cPLA2-alpha) has been involved in receptor-dependent and independent production of eicosanoids, which are major components of inflammatory responses. Sphingolipids, including ceramides, have also been described as key mediators of inflammation (Hayakawa et al., 1996; Serhan et al., 1996; Manna & Aggarwal, 1998; Newton et al., 2000). More recently a role for ceramide in the development of allergic asthmatic responses and airway inflammation was established (Masini et al., 2008), and exogenous addition of C2 ceramide to cultured astrocytes induced 12-lipoxigenase leading to generation of reactive oxygen species (ROS) and inflammation (Prasad et al., 2008). Also, A-SMase-derived ceramide was involved in platelet activating factor (PAF)-mediated pulmonary edema (Goggel et al., 2004). Subsequently, it was proposed that at least some of the proinflammatory effects of ceramides might in fact be mediated by its further metabolite C1P. The first report on the regulation of arachidonic acid (AA) release and the production of prostaglandins by C1P was from the laboratory of Charles Chalfant (Pettus et al., 2003b). This group demonstrated that C1P was able to stimulate AA release and prostanoid synthesis in A549 lung adenocarcinoma cells. In a follow up report, the same group showed that the mechanism whereby C1P stimulates AA release occurs through direct activation of cPLA2 (Pettus et al., 2004). Subsequently, it was found that C1P is a positive allosteric activator of cPLA2-alpha, and that it enhances the interaction of the enzyme with PC (Subramanian et al., 2005). In further work, the same group demonstrated that activation of cPLA2-alpha by C1P is chain length-specific; in particular, C1P bearing acyl chains equal or higher than six carbons were able to efficiently activate cPLA2-alpha in vitro, whereas shorter acyl chains (in particular C2-C1P) were unable to activate the enzyme. It was concluded that the biological activity of C2-C1P does not occur via eicosanoid synthesis (Wijesinghe et al., 2008). Also, C1P was shown to act in coordination with S1P to ensure maximal production of prostaglandins. Specifically, S1P was shown to induce cyclooxigenase-2 (COX-2) activity, which then uses cPLA2-derived AA as substrate to synthesize prostaglandins (Pettus et al., 2005). Further details on the role of C1P in inflammatory response can be found in different reviews (Chalfant & Spiegel, 2005; Lamour et al., 2007; Wijesinghe et al., 2007), Wijesinghe et al., and recent work by Murayama and co-

A-SMase by C1P could be important to reduce or prevent infection in the lung.

workers (Nakamura et al., 2011).

**6. Ceramide 1-phosphate and the control of cell migration** 

Macrophage populations in tissues are determined by the rates of recruitment of monocytes from the bloodstream into the tissue, the rates of macrophage proliferation and apoptosis, and the rate of macrophage migration or efflux. Recently, our group demonstrated that exogenous addition of C1P to cultured Raw 264.7 macrophages stimulated cell migration The implication of simple sphingolipids in the regulation of cell activation and metabolism has acquired special relevance in the last two decades. Most attention was first paid to the effects elicited by ceramide because this sphingolipid turned out to be essential in the regulation of cell death, differentiation, senescence, and various metabolic disorders and diseases. However, its phosphorylated form, C1P, was thought not to be so important. However, C1P has emerged as a crucial bioactive sphingolipid, and this chapter highlights the relevance of C1P in cell biology. Specifically, C1P has now been established as key regulator of cell growth and survival, and its relevance in the regulation of cell migration is beginning to emerge. Also importantly, the discovery that C1P can act both intracellularly or as receptor ligand opens a broad avenue to investigate its implication in controlling cell metabolism. In addition to this, C1P has been postulated to be a potent proinflammatory agent, acting directly on cPLA2 to trigger eicosanoid production. Therefore, C1P and CerK, the major enzyme responsible for its biosynthesis, may be key targets for developing new pharmacological strategies for treatment of illnesses associated to cell growth and death, and cell migration , such as chronic inflammation, cardiovascular diseases, neurodegeneration, or cancer.
