Regulatory relationships involving c-MYB in MLL-FP–mediated leukemogenesis. (A) MLL-FPs bind and directly activate the HOXA9, c-MYB, and c-MYC regulatory elements. (B) c-MYB binds directly to endogenous MLL1 potentially recruiting the complex to HOXA9 regulatory elements through N- or C-terminal interactions. (C) HOXA9 directly activates c-MYB and FLT3. (D) c-MYB directly activates the IL7R (not shown) and FLT3 genes, and (E) activation of c-MYC results in activation of Lin28b, which then inhibits processing of miR-150, resulting in increased steady state c-MYB and FLT3 expression. See main text for more detailed explanations and references.