FIP1L1 presence in FIP1L1-RARA or FIP1L1-PDGFRA differentially contributes to the pathogenesis of distinct types of leukemia.

FIP1-like 1 (FIP1L1) is associated with two leukemogenic fusion genes: FIP1L1-retinoic acid receptor alpha (RARA) and FIP1L1-platelet-derived growth factor receptor alpha (PDGFRA). Analyses of a series of deletion mutants revealed that the FIP1 motif in FIP1L1-RARA plays a pivotal role in its homodimerization and transcriptional repressor activity. However, in FIP1L1-PDGFRA, the C-terminal PDGFRA portion possesses the ability of forming a homodimer by itself, making FIP1L1 dispensable for constitutive activation of this kinase. Both the full-length and the C-terminal PDGFRA portion of FIP1L1-PDGFRA could transform the IL-3-dependent hematopoietic cell line, BAF-B03. Moreover, when either the full-length or the C-terminal PDGFRA portion of FIP1L1-PDGFRA was introduced in these cells, they grew in the absence of IL-3. The cells having the C-terminal PDGFRA portion of FIP1L1-PDGFRA, however, were partially IL-3 dependent, whereas the cells having the full-length FIP1L1-PDGFRA became completely IL-3 independent for their growth. Taken together, these results show that FIP1L1 differentially contributes to the pathogenesis of distinct types of leukemia.