Intracellular localization of the Ret finger protein depends on a functional nuclear export signal and protein kinase C activation.
The Ret finger protein (RFP) was identified initially as an oncogene product and belongs to a family of proteins that contain a tripartite motif consisting of a RING finger, a B box, and a coiled-coil domain. RFP represses transcription by interacting with Enhancer of Polycomb and is localized to the cytoplasm or nucleus depending on the cell type. Here, we have identified the nuclear export signal (NES) located in the coiled-coil region of RFP. Mutation of this NES or treatment with leptomycin B abrogated the nuclear export of RFP in NIH3T3 cells. In addition, fusion of this NES to other nuclear proteins, such as yeast transcription factor Gal4, resulted in their release into the cytoplasm of NIH3T3 cells. Although the NES function of RFP in HepG2 cells is masked by another domain in RFP or by another protein, 12-O-tetradecanoylphorbol-13-acetate treatment or overexpression of constitutively active protein kinase Calpha (PKCalpha) abrogated masking, leading to the cytoplasmic localization of RFP. Furthermore, treatment of NIH3T3 cells with PKC inhibitors blocked the function of NES, resulting in nuclear localization of RFP. Thus, the nuclear export of RFP is regulated positively by PKC activation. However, RFP was not a direct substrate of PKC, and additional signaling pathways may be involved in the regulation of nuclear export of RFP.
Harbers
M
M
RIKEN Tsukuba Institute and Core Research for Evolutionary Science and Technology (CREST) Project of Japan Science and Technology Corporation, 3-1-1 Koyadai, Tsukuba, Ibaraki.
Nomura
T
T
Ohno
S
S
Ishii
S
S
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D044767:Ubiquitin-Protein Ligases; D000070584:Tripartite Motif Proteins
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011493:Protein Kinase C; D011993:Recombinant Fusion Proteins; D044767:Ubiquitin-Protein Ligases; C064419:TRIM27 protein, human; D000070584:Tripartite Motif Proteins; C489296:Trim27 protein, mouse