title: The Nck SH2/SH3 adaptor protein is present in the nucleus and associates with the nuclear protein SAM68.
abstract: SH2/SH3 adaptor proteins are essential components of the signal transduction pathways initiated by tyrosine kinases. Nck is a ubiquitously expressed adaptor protein whose function has been enigmatic. We performed confocal microscopy to localize Nck in NIH3T3 and A431 cells. Surprisingly, Nck was identified in the nucleus as well as the cytoplasm with no visible change in localization due to PDGF or EGF stimulation. Western blot analysis of nuclear and cytosolic fractions confirmed that there was no translocation in response to growth factor and that tyrosine phosphorylation was specific to only cytosolic Nck. Far Western blot analysis with either Nck, the SH2 domain, or the SH3 domains revealed differential binding in nuclear and cytosolic lysates, indicating specific binding partners for each subcellular location. The major target of c-Src during mitosis is SAM68, a RNA-binding protein ordinarily localized to the nucleus. SAM68 was identified as a nuclear specific binding partner of Nck in both nonmitotic and mitotic cells. Several tyrosine kinases can be found in the nucleus but their signal transduction remains undefined. The discovery of an adaptor protein in the nucleus suggests there are signal transduction mechanisms within the nucleus that recapitulate those found in the cytoplasm.
authors.affiliation: Department of Microbiology and Immunology, The Kimmel Cancer Institute, Philadelphia, Pennsylvania 19107, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Lawe
authors.forename: C
authors.initials: C
authors.lastname: Hahn
authors.forename: A J
authors.initials: AJ
authors.lastname: Wong
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015153:Blotting, Western; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018922:HL-60 Cells / Q000737:chemistry; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D015513:Oncogene Proteins / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015398:Signal Transduction; D018909:src Homology Domains
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C489561:Dok1 protein, mouse; C074561:GAP-associated protein p62; C489559:KHDRBS1 protein, human; C513253:Khdrbs1 protein, mouse; C078332:Nck protein; D015513:Oncogene Proteins; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; D016601:RNA-Binding Proteins; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases