Nuclear localization of orphan receptor protein kinase (Ror1) is mediated through the juxtamembrane domain.
BACKGROUND
Several receptor tyrosine kinases (RTKs) such as EGFR, FGFR, TRK, and VEGFR are capable of localizing in the cell nucleus in addition to their usual plasma membrane localization. Recent reports also demonstrate that nuclear-localized RTKs have important cellular functions such as transcriptional activation. On the basis of preliminary bioinformatic analysis, additional RTKs, including receptor tyrosine kinase-like orphan receptor 1 (Ror1) were predicted to have the potential for nuclear subcellular localization. Ror1 is a receptor protein tyrosine kinase that modulates neurite growth in the central nervous system. Because the nuclear localization capability of the Ror1 cytoplasmic domain has not been reported, we examined the cellular expression distribution of this region.


RESULTS
The Ror1 cytoplasmic region was amplified and cloned into reporter constructs with fluorescent tags. Following transfection, the nuclear distribution patterns of transiently expressed fusion proteins were observed. Serial deletion constructs were then used to map the juxtamembrane domain of Ror1 (aa_471-513) for this nuclear translocation activity. Further site-directed mutagenesis suggested that a KxxK-16 aa-KxxK sequence at residues 486-509 is responsible for the nuclear translocation interaction. Subsequent immunofluorescence analysis by cotransfection of Ran and Ror1 implied that the nuclear translocation event of Ror1 might be mediated through the Ran pathway.


CONCLUSIONS
We have predicted several RTKs that contain the nuclear localization signals. This is the first report to suggest that the juxtamembrane domain of the Ror1 cytoplasmic region mediates the translocation event. Ran GTPase is also implicated in this event. Our study might be beneficial in future research to understand the Ror1 biological signaling pathway.
Tseng
Hsiao-Chun
HC
Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 300, Taiwan.
Lyu
Ping-Chiang
PC
Lin
Wen-Chang
WC
D021581:Active Transport, Cell Nucleus; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D019295:Computational Biology; D006801:Humans; D016297:Mutagenesis, Site-Directed; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D057050:Receptor Tyrosine Kinase-like Orphan Receptors / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics; D015533:Transcriptional Activation; D020931:ran GTP-Binding Protein / Q000378:metabolism*
D019913:Nuclear Localization Signals; C120587:RAN protein, human; C078716:ROR1 protein, human; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; D020931:ran GTP-Binding Protein