CBL mutations in myeloproliferative neoplasms are also found in the gene's proline-rich domain and in patients with the V617FJAK2

Background Despite the discovery of the p.V617F in JAK2 , the molecular pathogenesis of some chronic myeloproliferative neoplasms remains unclear. Although very rare, different studies have identified CBL (Cas-Br-Murine ecotropic retroviral transforming sequence) mutations in V617F JAK2 -negative patients, mainly located in the RING finger domain. In order to determine the frequency of CBL mutations in these diseases, we studied different regions of all CBL family genes ( CBL , CBLB and CBLC ) in a selected group of patients with myeloproliferative neoplasms. We also included V617F JAK2- positive patients to check whether mutations in CBL and JAK2 are mutually exclusive events. Design and Methods Using denaturing high performance liquid chromatography, we screened for mutations in CBL , CBLB and CBLC in a group of 172 V617F JAK2 -negative and 232 V617F JAK2 -positive patients with myeloproliferative neoplasms not selected for loss of heterozygosity. The effect on cell proliferation of the mutations detected was analyzed on a 32D(FLT3) cell model. Results An initial screening of all coding exons of CBL , CBLB and CBLC in 44 V617F JAK2 -negative samples revealed two new CBL mutations (p.C416W in the RING finger domain and p.A678V in the proline-rich domain). Analyses performed on 128 additional V617F JAK2 -negative and 232 V617F JAK2 -positive samples detected three CBL changes (p.T402HfsX29, p.P417R and p.S675C in two cases) in four V617F JAK2 -positive patients. None of these mutations was found in 200 control samples. Cell proliferation assays showed that all of the mutations promoted hypersensitivity to interleukin-3 in 32D(FLT3) cells. Conclusions Although mutations described to date have been found in the RING finger domain and in the linker region of CBL, we found a similar frequency of mutations in the proline-rich domain. In addition, we found CBL mutations in both V617F JAK2 -positive (4/232; 1.7%) and negative (2/172; 1.2%) patients and all of them promoted hypersensitivity to interleukin-3.