The elongation domain of ELL is dispensable but its ELL-Associated factor 1 interaction domain is essential for MLL-ELL-induced leukemogenesis

The MLL-ELL chimeric gene is the product of the (11;19)(q23p13.1) transloca tion associated with de novo and therapy-related acute myeloid leukemias (A ML). ELL is an RNA polymerase II elongation factor that interacts with the recently identified EAF1 (ELL associated factor 1) protein. EAF1 contains a limited region of homology with the transcriptional activation domains of three other genes fused to MLL in leukemias, AF4, LAF4, and AF5q31. Using a n in vitro transformation assay of retrovirally transduced myeloid progenit ors, we conducted a structure-function analysis of MLL-ELL. Whereas the elo ngation domain of ELL was dispensable, the EAF1 interaction domain of ELL w as critical to the immortalizing properties of MLL-ELL in vitro. To confirm these results in vivo, we transplanted mice with bone marrow transduced wi th MLL fused to the minimal EAF1 interaction domain of ELL. These mice all developed AML, with a longer latency than mice transplanted with the wild-t ype MLL-ELL fusion. Based on these results, we generated a heterologous MLL -EAF1 fusion gene and analyzed its transforming potential. Strikingly, we f ound that MLL-EAF1 immortalized myeloid progenitors in the same manner as t hat of MLL-ELL. Furthermore, transplantation of bone marrow transduced with MLL-EAF1 induced AML with a shorter latency than mice transplanted with th e MLL-ELL fusion. Taken together, these results indicate that the leukemic activity of MLL-ELL requires the EAF1 interaction domain of ELL, suggesting that the recruitment by MLL of a transactivation domain similar to that in EAF1 or the AF4/LAF4/AF5q31 family may be a critical common feature of mul tiple 11q23 translocations. In addition, these studies support a critical r ole for MLL partner genes and their protein-protein interactions in 11q23 l eukemogenesis.