The truncation that generated the v-cbl oncogene reveals an ability for nuclear transport, DNA binding and acute transformation.

Abstract

The v‐cbl oncogene is the transforming gene of the murine Cas NS‐1 retrovirus which induces pre‐B cell lymphomas and myeloid leukaemias. Sequencing of c‐cbl has revealed that v‐cbl was generated by a large truncation that removed 60% of the C‐terminus of the corresponding protein. In this study we prepared antibodies to cbl and found that c‐cbl encodes a 120 kDa protein which is localized in the cytoplasm with a cytosolic and cytoskeletal distribution. Immunofluorescence studies show a striking pattern of brightly staining vesicles in mitotic cells similar to that observed with cytokeratin antibodies. In contrast to p120c‐cbl, which is exclusively cytoplasmic, the p100gag‐v‐cbl encoded by Cas NS‐1 is localized in both the cytoplasm and the nucleus. This redistribution to the nucleus correlates with the ability of cbl to induce acute transformation. Furthermore the truncated protein encoded by v‐cbl can bind DNA, unlike the full‐length protein. These results suggest that the C‐terminus of cbl is involved in the retention of p120c‐cbl in the cytoplasm and the inhibition of DNA binding. The findings also suggest that a truncated protein encoded by c‐cbl exists in the nucleus of normal cells.

Specific association of phosphatidylinositol 3‐kinase with the protooncogene product Cbl in Fcγ receptor signaling

“…The direct binding of phosphorylated Cbl to PI 3-kinase must lead to phagocytosis as a result of activation of the lipid kinase. A possibility could not be excluded, however, for other signaling roles of Cbl, which is capable of binding to SH3 domains of intracellular proteins via its proline-rich motifs [36,37]. In fact, Grb2/Ash coprecipitated with Cbl from lysates of stimulated or unstimulated THP-1 cells (unpublished observation), in accordance with previous reports on T-cell lines [12,15].…”

Tyrosine kinase activity of the EGF receptor is enhanced by the expression of oncogenic 70Z-Cbl

“…NhEGFR is a stable cell line derived from NIH3T3 ®broblasts and established by infection with helper-free stocks of the pBABE retroviral vector containing the human EGFR cDNA and selected in 2 mg/ml puromycin (Sigma). HA-tagged Cbl constructs were stably expressed in NhEGFR cells using the pJZenNeo retroviral vector and selected in 400 mg/ml geneticin (G418, Gibco BRL0) as previously described (Blake et al, 1993).…”

“…Polyclonal rabbit anti-HA and anti-Cbl (R2) antibodies have been described previously (Bowtell and Langdon, 1995;Blake et al, 1993). Monoclonal anti-HA antibody was isolated from 12CA5 culture supernatants and the monoclonal anti-phosphotyrosine antibody 4G10 was kindly provided by Dr Brian Druker.…”

CSF-1 stimulation induces the formation of a multiprotein complex including CSF-1 receptor, c-Cbl, PI 3-kinase, Crk-II and Grb2

“…v-cbl has been shown to induce preB lymphomas and myelogenous leukemias, while the cellular homologue does not have this capacity, even when it is overexpressed. This is probably due to a truncation of 60% of the C-terminal region of the proto-oncogene product which confers to v-Cbl the ability to migrate to the nucleus and to bind DNA, which is not the case for c-Cbl (Blake et al, 1993). Owing to the transforming activity of v-Cbl, it has been suggested that c-Cbl may play a signi®cant role in the control of proliferation.…”