THE ROLE OF CBL IN RELATION TO RAS-PATHWAY ACTIVATION IN PEDIATRIC AML

Sborník

Background. Leukemogenesis in acute myeloid leukemia(AML) is hypothesized to evolve from mutations disrupting proliferation and differentiation. Several mutations resulting in activation of the RAS-pathway have been described in AML and MLL-rearranged ALL. Recently, mutations in the Casitas B lineage lymphoma(CBL) gene were reported to be involved in RAS-pathway activation in various myeloid malignancies. So far, the role of CBL in pediatric AML is unknown. Aims. We aimed to study the role of CBL mutations and CBL expression in pediatric AML and MLL-rearranged ALL. Methods. We performed mutation analysis in 277 initial and 33 relapse pediatric AML samples, and 18 MLLrearranged infant acute lymphoblastic leukemia(ALL) samples. To further evaluate the functional role of CBL in pediatric AML, and RAS-pathway activation, we studied CBL mRNA and protein expression and performed CBL RNA interference knock-down experiments. Results. We identified only two mutant cases( 0.7%) in newly diagnosed pediatric AML, and none in relapsed cases. One mutant case was MLL-rearranged; the other had a normal karyotype. No CBL mutations were present in infant ALL cases. CBL mRNA expression in mutated cases did not differ from non-mutated AML cases nor between any of the cytogenetic groups. Western blotting of patient samples showed no significant difference in protein expression of the two CBL mutants versus nine non-mutant AML cases(p=0.8)., and protein expression had a poor correlation with mutation status or CBL mRNA expression as determined by gene expression profiling and confirmed by RT-qPCR(Spearman r=0.17). Also, phosphorylated extracellular signal-regulated kinase(pERK) and CBL protein expression did not correlate. Nevertheless, CBL RNA interference knock-down experiments resulted in an upregulation of pERK protein expression in the Kasumi-1 cell line, with a maximum of 3-fold at t=48 hours. Summary and Conclusions. In conclusion, we report a very low CBL mutation frequency(0.7%) in pediatric AML and MLL-rearranged infant ALL and poor correlation with expression of CBL mRNA, CBL protein and pERK protein. However, enforced decreased CBL protein expression led to RAS-pathway activation in a pediatric AML cell line.

Haematologica, 2012; 97(s1):  265