Calcium Mediated Regulation of Ceramide Kinase

Ceramide-1-phosphate (C1P) has proven to be a bioactive sphingolipid with diverse functions within the cell. At this time, ceramide kinase (CERK) is the only known enzyme known to generate C1P in mammalian cells, and this bioactive lipid is responsible for the activation and translocation of cytosolic phospholipase A2, the initial rate limiting step in eicosanoid synthesis. These studies investigate the regulation of ceramide kinase by calcium. While CERK activity has been shown to be calcium sensitive, little is known about how CERK is activated within the cell; one possibility is the interaction with calcium sensor proteins such as calmodulin. In this study, we develop two protocols to efficiently examine the interaction of CERK with calcium dependent proteins: V5 co-immunoprecipitation and Ni-NTA affinity purification. The methods utilize either adenoviral infection or Effectene© transfection of cells to ectopically express CERK with both a 6x His and V5 tag on its C terminus. Unlike the report of Igarashi and co-workers, our findings reveal that CERK does not specifically interact with the calcium sensor, calmodulin, in three different cell types. We also show that the calcium dependent membrane organizer, annexin A2, also does not bind to CERK. In light of these findings, we illustrate that while CERK may be sensitive to calcium, it does not, as previously reported by another laboratory, specifically bind to calmodulin. These studies eliminate possible calcium mediator proteins and are suggestive of another method for the calcium sensitive regulation of CERK lending to new avenues of investigation (i.e. CaMKII). This report also firmly established two successful protocols for investigating protein partners of CERK. Ultimately, through providing a clearer picture behind the calcium regulation of CERK, we can elucidate possible novel therapeutic targets within the inflammatory pathway