Identification of a functional nuclear export sequence in diacyl glycerol kinase-ζ

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Diacylglycerol kinases (DGKs) are key regulators of diacylglycerol-dependent signaling pathways. Among the 10 DGK isoforms, DGK-ζ is the only nuclear form that contains a nuclear localization signal. Here, by site-directed mutagenesis, we showed that DGK-ζ also displays a functional independent nuclear export signal (NES) sequence between the amino acid residues 363-370. Indeed, the NES mutant forms of DGK-ζ accumulated in the nucleus to a much greater extent than wild type DGK-ζ. Moreover, treatment with leptomycin B, an inhibitor of leucine-rich type NES, resulted in accumulation of both endogenous and ectopically expressed DGK-ζ in the nucleus, demonstrating that nuclear export of DGK-ζ is chromosome regional maintenance protein 1 (CRM1) -dependent. Previously, we reported that nuclear DGK-ζ is a negative regulator of cell cycle progression in C2C12 mouse myoblasts. In this paper, we documented that enhancement of DGK-ζ nuclear localization by NES sequence mutation, increases G0/G1 block in C2C12 cells. Overall, our data demonstrate that DGK-ζ export from nucleus to cytoplasm is regulated by a leucine-rich NES through the exportin CRM1 and suggest that the nuclear localization of DGK-ζ could finely tune its function as a regulator of G1/S cell cycle transition.