Type I diacylglycerol kinase (DGK) isozymes (alpha, beta, and gamma) contain recoverin homology domains and calcium-binding EF-hand motifs at their N-termini. The gamma-isoform of DGK is abundantly expressed in retinal and Purkinje cells; however, its function in neuronal cells remains unknown. Here, we report that the mRNA and protein levels of DGK gamma, but not DGK alpha or beta, were markedly increased in N1E-115 neuroblastoma cells upon cellular differentiation by serum starvation. Interestingly, overexpression of wild-type DGK gamma, which was partially located at the plasma membrane, considerably induced the formation of slender, filopodia-like cytoplasmic projections from N1E-115 cell bodies. Deletion of the recoverin homology domain and the EF-hand motifs, which potentiated the plasma membrane localization of the isozyme, significantly enhanced the formation of the filopodia-like protrusions. Intriguingly, the catalytic activity of the isozyme is not essential for the protrusion formation. The N-terminal half of the catalytic domain and a short stretch of amino acid residues at the C-terminus are responsible for plasma membrane localization and filopodia-like process formation. Taken together, we have described a potentially novel morphological function of the C-terminal DGK gamma catalytic region that is independent of its enzymatic activity.
