Gain-of-function of mutated C-CBL tumour suppressor in myeloid neoplasms

Abstract

Acquired uniparental disomy (aUPD) is a common feature of cancer genomes, leading to loss of heterozygosity. aUPD is associated not only with loss-of-function mutations of tumour suppressor genes, but also with gain-of-function mutations of proto-oncogenes. Here we show unique gain-of-function mutations of the C-CBL (also known as CBL) tumour suppressor that are tightly associated with aUPD of the 11q arm in myeloid neoplasms showing myeloproliferative features. The C-CBL proto-oncogene, a cellular homologue of v-Cbl, encodes an E3 ubiquitin ligase and negatively regulates signal transduction of tyrosine kinases. Homozygous C-CBL mutations were found in most 11q-aUPD-positive myeloid malignancies. Although the C-CBL mutations were oncogenic in NIH3T3 cells, c-Cbl was shown to functionally and genetically act as a tumour suppressor. C-CBL mutants did not have E3 ubiquitin ligase activity, but inhibited that of wild-type C-CBL and CBL-B (also known as CBLB), leading to prolonged activation of tyrosine kinases after cytokine stimulation. c-Cbl(-/-) haematopoietic stem/progenitor cells (HSPCs) showed enhanced sensitivity to a variety of cytokines compared to c-Cbl(+/+) HSPCs, and transduction of C-CBL mutants into c-Cbl(-/-) HSPCs further augmented their sensitivities to a broader spectrum of cytokines, including stem-cell factor (SCF, also known as KITLG), thrombopoietin (TPO, also known as THPO), IL3 and FLT3 ligand (FLT3LG), indicating the presence of a gain-of-function that could not be attributed to a simple loss-of-function. The gain-of-function effects of C-CBL mutants on cytokine sensitivity of HSPCs largely disappeared in a c-Cbl(+/+) background or by co-transduction of wild-type C-CBL, which suggests the pathogenic importance of loss of wild-type C-CBL alleles found in most cases of C-CBL-mutated myeloid neoplasms. Our findings provide a new insight into a role of gain-of-function mutations of a tumour suppressor associated with aUPD in the pathogenesis of some myeloid cancer subsets.

EED mutants impair polycomb repressive complex 2 in myelodysplastic syndrome and related neoplasms

“…Detailed clinical information of individual samples was given in our previous report. 10 We identified EED mutations in six cases ( Figure 1a and Supplementary Table 1), which were confirmed by repeated amplification and sequencing. None of these mutations are reported in the 1000 genomes database (a deep catalog of human genetic variation) 11 and the Ensemble gene and the transcript sequences currently available.…”

Uses and Abuses of JAK2 and MPL Mutation Tests in Myeloproliferative Neoplasms

“…22 CBL is an E3-ubiquitin ligase that marks mutant kinases for degradation. 23 CBL mutations are rare TET oncogene family member 2 (TET2) maps to chromosome 4q24. TET2 mutations occur across several of the gene's 12 exons.…”

CBL enhances breast tumor formation by inhibiting tumor suppressive activity of TGF-β signaling

“…A recent report demonstrated that CBL mutants, which have lost E3 ligase activity, acts as an oncogene leading to prolonged tyrosine kinase activation after ligand stimulation. 14 Although the nature of CBLinteracting proteins in distinct cellular compartments is well established, the functional importance of these protein --protein interactions is poorly understood. In this report, we show that the CBL suppresses TGF-b signaling by disrupting the Smad pathway.…”

“…E3 ligase inactive mutations of CBL, such as Q367P and Y371S, which were discovered in myeloid neoplasm, make normal fibroblast cell lines to form tumor in mouse dorsal subcutaneous spaces. 14 Oncogenic mutants of CBL have been investigated on how they induce carcinogenesis. One of the carcinogenic mechanisms of CBL mutants is the inability to ubiquitinate and degrade cell-growthrelated RTKs due to inactivated E3 ligase functions.…”

“…13 --16 CBL mutants (CBL Q367P and CBL Y371S), as well as a mouse lymphoma-derived oncogenic mutant (CBL 70Z) are known to be involved in the pathogenesis of myeloid neoplasms. 14 These transforming mutations all have deletion or mutations within the linker region and RF, and have lost E3 ligase activity. We examined the ability of these mutants to bind Smad3.…”