AFF4, a Component of the ELL/P-TEFb Elongation Complex and a Shared Subunit of MLL Chimeras, Can Link Transcription Elongation to Leukemia

SummaryChromosomal translocations involving the MLL gene are associated with infant acute lymphoblastic and mixed lineage leukemia. There are a large number of translocation partners of MLL that share very little sequence or seemingly functional similarities; however, their translocations into MLL result in the pathogenesis of leukemia. To define the molecular reason why these translocations result in the pathogenesis of leukemia, we purified several of the commonly occurring MLL chimeras. We have identified super elongation complex (SEC) associated with all chimeras purified. SEC includes ELL, P-TEFb, AFF4, and several other factors. AFF4 is required for SEC stability and proper transcription by poised RNA polymerase II in metazoans. Knockdown of AFF4 in leukemic cells shows reduction in MLL chimera target gene expression, suggesting that AFF4/SEC could be a key regulator in the pathogenesis of leukemia through many of the MLL partners.

Graphical AbstractFigure optionsDownload high-quality image (214 K)Download as PowerPoint slideHighlights
► AFF4 is a shared component of MLL chimeras found in leukemia
► AFF4 is a key component of the super elongation complex (SEC) with ELL and P-TEFb
► AFF4 is required for the transcription of MLL chimera targets in leukemic cells