The association of Sam68 with Vav1 contributes to tumorigenesis.
Vav1 functions in the hematopoietic system as a specific GDP/GTP nucleotide exchange factor regulated by tyrosine phosphorylation. An intact C-terminal SH3 domain of Vav1 (Vav1SH3C) was shown to be necessary for Vav1-induced transformation, yet the associating protein(s) necessary for this activity have not yet been identified. Using a proteomics approach, we identified Sam68 as a Vav1SH3C-associating protein. Sam68 (Src-associated in mitosis of 68 kD) belongs to the heteronuclear ribonucleoprotein particle K (hnRNP-K) homology (KH) domain family of RNA-binding proteins. The Vav1/Sam68 interaction was observed in vitro and in vivo. Mutants of Vav1SH3C previously shown to lose their transforming potential did not associate with Sam68. Co-expression of Vav1 and Sam68 in Jurkat T cells led to increased localization of Vav1 in the nucleus and changes in cell morphology. We then tested the contribution of Sam68 to known functions of Vav1, such as focus-forming in NIH3T3 fibroblasts and NFAT stimulation in T cells. Co-expression of oncogenic Vav1 with Sam68 in NIH3T3 fibroblasts resulted in a dose-dependent increase in foci, yet no further enhancement of NFAT activity was observed in Jurkat T cells, as compared to cells overexpressing only Vav1 or Sam68. Our results strongly suggest that Sam68 contributes to transformation by oncogenic Vav1.
Lazer
Galit
G
The Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
Pe'er
Liron
L
Schapira
Vered
V
Richard
Stéphane
S
Katzav
Shulamit
S
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D048430:Cell Shape; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D009154:Mutation; D050778:NFATC Transcription Factors / Q000378:metabolism; D041681:NIH 3T3 Cells; D011485:Protein Binding; D021381:Protein Transport; D040901:Proteomics; D051567:Proto-Oncogene Proteins c-vav / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C489559:KHDRBS1 protein, human; C513253:Khdrbs1 protein, mouse; D050778:NFATC Transcription Factors; D051567:Proto-Oncogene Proteins c-vav; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins