RING finger mutations that abolish c-Cbl-directed polyubiquitination and downregulation of the EGF receptor are insufficient for cell transformation.
The c-Cbl protooncogene can function as a negative regulator of receptor protein tyrosine kinases (RPTKs) by targeting activated receptors for polyubiquitination and downregulation. This function requires its tyrosine kinase binding (TKB) domain for targeting RPTKs and RING finger domain to recruit E2 ubiquitin-conjugating enzymes. It has therefore been proposed that oncogenic Cbl proteins act in a dominant-negative manner to block this c-Cbl activity. In testing this hypothesis, we found that although mutations spanning the RING finger abolish c-Cbl-directed polyubiquitination and downregulation of RPTKs, they do not induce transformation. In contrast, it is mutations within a highly conserved alpha-helical structure linking the SH2 and RING finger domains that render Cbl proteins oncogenic. Thus, Cbl transformation involves effects additional to polyubiquitination of RPTKs that are independent of the RING finger and its ability to recruit E2-conjugating enzymes.
Thien
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CB
Department of Pathology, University of Western Australia, Western Australia 6009, Crawley, Australia.
Walker
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F
Langdon
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WY
D016475:3T3 Cells; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002471:Cell Transformation, Neoplastic; D015536:Down-Regulation; D004705:Endocytosis; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D008025:Ligases / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism; D017433:Protein Structure, Secondary; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D016415:Sequence Alignment; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*; D016335:Zinc Fingers / Q000235:genetics; D018909:src Homology Domains / Q000235:genetics
D011518:Proto-Oncogene Proteins; D014452:Ubiquitins; D044763:Ubiquitin-Conjugating Enzymes; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D066246:ErbB Receptors; D015688:Oncogene Protein pp60(v-src); D008025:Ligases; C067419:CBL protein, human; C493849:Cbl protein, mouse