The chromosomal translocation t(12;21) - generating the ETV6/RUNX1 fusion -, is detectable in approximately 20% of childhood acute lymphoblastic leukemia (ALL) cases and represents the most common chromosomal rearrangement in this age group. Despite a high cure rate with contemporary treatment protocols, a small proportion of cases suffer from a relapse and approximately half of the patients experience side and late effects, which predominantly result from treatment related toxicity. While the importance of ETV6/RUNX1 for leukemia initiation and maintenance is widely studied, the contribution of secondary alterations to the leukemia phenotype remains largely unexplored.
ALL cells harboring the ETV6/RUNX1 fusion gene often display a deletion of the non-rearranged ETV6 allele. As knowledge concerning the role of wtETV6 in ETV6/RUNX1-expressing leukemia is scarce, a lentiviral shRNA-mediated knockdown (KD) of ETV6 was performed in a genetically modified ALL cell line (Nalm6) that conditionally expresses ETV6/RUNX1 (Nalm6#2C).
ETV6 KD effects in the Nalm6 system were examined at the transcriptional and functional level. One week after transducing Nalm6 cells with a shRNA containing lentivirus, a substantial reduction of ETV6 transcripts was found, thereby confirming a successful KD. Functional read outs in ETV6/RUNX1-expressing Nalm6 cells revealed cell cycle (G0/G1) arrest but no increase in apoptosis suggesting reduction in proliferation. These findings are currently confirmed and extended.