JSPS Postdoctoral Research Fellow The University of Tokyo Bunkyo-ku, Tokyo, Japan
Chiaki Murakami (Chiba University, The University of Tokyo)| Masataka Furuta (Chiba University)| Yuki Numagami (Chiba University)| Fumio Sakane (Chiba University)
Mammalian sphingomyelin (SM) synthase (SMS) consists of two isoform (SMS1, SMS2). SMS produces diacylglycerol (DG) by the transfer of phosphocholine from phosphatidylcholine (PC) to ceramide. SMS-related protein (SMSr) also generates DG via synthesis of ceramide phosphoethanolamine, a SM analog, using phosphatidylethanolamine. Mammalian DG kinase (DGK) consists of ten isozymes (α, β, γ, δ, η, ε, κ, ι, ζ, θ) and governs a wide range of physiological and pathological events such as type 2 diabetes. Among them, SMS1, SMSr, DGKδ and DGKη contain a steraile a motif domain (SAMD), a protein-protein interaction module.
We previously reported that DGKδ interacts with SMSr, but not SMS1, via SAMDs [Murakami et al. J. Biol. Chem. 295, 2932–47, 2020]. Moreover, SMSr provided DG to DGKδ. However, it is still unclear whether other DGK isozymes interact with SMSs. In the present study, we analyzed interaction between DGKs and SMSs by co-immunoprecipitation analysis.
Results and Conclusion
First, we determined whether SAMD-containing DGKs (DGKδ and DGKη) interact with SAMD-containing SMSs (SMS1 and SMSr). Although DGKη-SAMD co-sedimented with DGKη-SAMD itself, SMS1- and SMSr-SAMD failed to interact with DGKη-SAMD. Furthermore, only the combination of full-length DGKδ and full-length SMSr could form a heteromeric complex. These results suggest that the interaction via heteromerization of SAMDs is specific to DGKδ and SMSr.
Next, we analyzed whether other DGKs, which contain no SAMD, interact with SMSs. We found that DGKζ was strongly co-immunoprecipitated with SMSr and SMS1, but not SMS2. These results suggest that DGKζ can interact with SMS1 and SMSr without heteromerization between SAMDs.
Taken together, these results suggest that, in addition to DGKδ, DGKζ is a new candidate that acts downstream of SMSr and SMS1. SMSr produces palmitic acid (16:0)-containing DG molecular species and SMS1 generates PC-derived DG species including 16:0-containing DGs. Moreover, DGKζ preferably phosphorylates 16:0-containing DG species during neuronal cell differentiation. Therefore, it is possible that these enzymes compose a new pathway independent of the phosphatidylinositol turnover, which primary utilizes arachidonic acid (20:4)-containing DG species.
Support or Funding Information
This work was supported in part by grants from MEXT/JSPS KAKENHI (Grant Numbers: JP18J20003 to C.M.); The Chiba Bank (to C.M.); the Chiba University Venture Business Laboratory (to C.M.); Chiba University Open Recruitment for International Exchange Program at the Institute for Global Prominent Research (to C.M.); and the American Society for Biochemistry and Molecular Biology (ASBMB 2019 Graduate/Postdoctoral Travel Award to C.M).