title: Interaction of the small GTPase Rac3 with NRBP, a protein with a kinase-homology domain.
abstract: The family of Rac small GTPases including Rac1, Rac2 and Rac3 regulate numerous cellular processes. Since the cellular functions of Rac3 have not been defined, constitutively active V12Rac3 was used to identify targets that transduce its signals. We here identify human NRBP as a Rac family-interacting protein. NRBP formed a complex with activated Rac3. NRBP contains a kinase-homology domain and exhibits an associated kinase activity. NRBP represents a novel family of evolutionarily conserved proteins with homologs in C. elegans, D. melanogaster, mouse and human. Overexpression of NRBP in COS-1 cells failed to activate possible downstream targets of Rac3 including the JNK pathway, the p38 pathway or actin cytoskeletal rearrangements. Also, NRBP failed to co-localize with actin-based stress fibers or microspikes, or with the subcortical actin. However, overexpression of NRBP caused a dramatic redistribution of the Golgi-associated marker p58 to more peripheral locations within the cell, consistent with an impairment of the ER to Golgi transport. Immunocytochemistry showed that NRBP and activated Rac3 co-localized to endomembranes and at the cell periphery in lamellipodia. These results suggest that NRBP functions in subcellular trafficking and may be directed to specific subcellular locations through interaction with small GTPases of the Rho family.
authors.affiliation: Division of Hematology/Oncology, Section of Molecular Carcinogenesis, Childrens Hospital of Los Angeles Research Institute, Los Angeles, CA 90027, USA.
authors.forename: Stijn
authors.initials: S
authors.lastname: De Langhe
authors.forename: Leena
authors.initials: L
authors.lastname: Haataja
authors.forename: Dinithi
authors.initials: D
authors.lastname: Senadheera
authors.forename: John
authors.initials: J
authors.lastname: Groffen
authors.forename: Nora
authors.initials: N
authors.lastname: Heisterkamp
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015415:Biomarkers; D019556:COS Cells; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques; D033921:Vesicular Transport Proteins; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D015415:Biomarkers; C410809:NRBP1 protein, human; C411563:RAC3 protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D033921:Vesicular Transport Proteins; D011494:Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; C498771:Rac3 protein, mouse; D020744:rac GTP-Binding Proteins