Phospholipase C delta 1 contains a functional nuclear export signal sequence

We have previously observed, using a green fluorescent protein (GFP) fusion system, that PLC-delta 1 is localized mainly at the plasma membrane and in the cytosol, whereas little is present in the nucleus in Madin-Darby canin e kidney cells (Fujii, M., Ohtsubo, M., Ogawa, T., Kamata, H., Hirata, H., and Yagisawa, H. (1999) Biochem. Biophys. Res. Commun. 254, 284-291). Herei n, we demonstrate that PLC-delta 1 has a functional nuclear export signal ( NES) sequence in amino acid residues 164-177 of the EF-hand domain. The flu orescence of NES-disrupted GFP/PLC-delta 1 expressed in Madin-Darby canine kidney cells was present not only at the plasma membrane and in the cytosol but also in the nucleus. Moreover, treatment with leptomycin B, a specific inhibitor of NES-dependent nuclear export, resulted in the accumulation of GFP/PLC-delta 1 in the nucleus. A site directed mutant containing a plecks trin homology domain, which does not bind inositol 1,4,5-trisphosphate and cannot hydrolyze phosphatidylinositol 4,5-bisphosphate in vitro, accumulate d in the nucleus to a much greater extent than wildtype GFP/PLC-delta 1 aft er treatment with leptomycin B. These results suggest that PLC-delta 1 is s huttled between the cytoplasm and the nucleus; its nuclear export is depend ent on the leucine-rich NES sequence and its active nuclear import is regul ated by an unidentified signal(s).