The interaction between EEN and Abi-1, two MLL fusion partners, and synaptojanin and dynamin: implications for leukaemogenesis

The mixed lineage leukaemia gene, MLL (also called HRX, ALL-1) in acute leu kaemia is fused to at least 16 identified partner genes that display divers e structural and biochemical properties. Using GST pull down and the yeast two hybrid system, we show that two different MLL fusion partners with SH3 domains, EEN and Abi-1, interact with dynamin and synaptojanin, both of whi ch are involved in endocytosis. Synaptojanin, a member of the inositol phos phatase family that has recently been shown to regulate cell proliferation and survival, is also known to bind to Eps15, the mouse homologue of AF1p, another fusion partner of MLL. Expression studies show that synaptojanin is strongly expressed in bone marrow and immature leukaemic cell lines, very weakly in peripheral blood leukocytes and absent in Raji, a mature B cell l ine. We found that the SH3 domains of EEN and Abi-1 interact with different proline-rich domains of synaptojanin while the EH domains of Eps15 interac t with the NPF motifs of synaptojanin. In vitro competitive binding assays demonstrate that EEN displays stronger binding affinity than Abi-l and may compete with it for synaptojanin. These findings suggest a potential link b etween MLL fusion-mediated leukaemogenesis and the inositol-signalling path way.