Discovery of a fusion kinase in EOL-1 cells and idiopathic hypereosinophilic syndrome

Abstract

Idiopathic hypereosinophilic syndrome (HES) is a myeloproliferative disease of unknown etiology. Recently, it has been reported that imatinib mesylate (Gleevec), an inhibitor of Bcr-Abl kinase useful in the treatment of chronic myeloid leukemia, is also effective in treating HES; however, the molecular target of imatinib in HES is unknown. This report identifies a genetic rearrangement in the eosinophilic cell line EOL-1 that results in the expression of a fusion protein comprising an N-terminal region encoded by a gene of unknown function with the GenBank accession number NM 030917 and a C-terminal region derived from the intracellular domain of the platelet-derived growth factor receptor ␣ (PDGFR␣). The fusion gene was also detected in blood cells from two patients with HES. We propose naming NM 030917 Rhe for Rearranged in hypereosinophilia. Rhe-PDGFR␣ fusions result from an apparent interstitial deletion that links Rhe to exon 12 of PDGFR␣ on chromosome 4q12. The fusion kinase Rhe-PDGFR␣ is constitutively phosphorylated and supports IL-3-independent growth when expressed in BaF3 cells. Proliferation and viability of EOL-1 and BaF3 cells expressing Rhe-PDGFR␣ are ablated by the PDGFR␣ inhibitors imatinib, vatalanib, and THRX-165724.

How I treat hypereosinophilic syndromes

“…10 The majority of these imatinib-responders with HES were ultimately found to have an interstitial deletion in chromosome 4q12 causing the constitutively active fusion tyrosine kinase, FIP1L1-PDGFRA, which can be detected by FISH or reverse transcriptase-polymerase chain reaction (RT-PCR) in peripheral blood or bone marrow. 7,18 Many other imatinib-sensitive PDGFR fusions, including KIF5B-PDGFRA and ETV6-PDGFRB, 19-21 and point mutations in PDGFRA 22 have been described in patients presenting with clinical features of HES, but are uncommon.…”

Five years since the discovery of FIP1L1–PDGFRA: what we have learned about the fusion and other molecularly defined eosinophilias

“…In the case of PDGFRA fusions, both the BCR-PDGFRA 16,17 and FIP1L1-PDGFRA 8,18 fusions were identified in 2002-2003 as recurrent rearrangements, with the FIP1L1-PDGFRA fusion being the most common fusion. A few other variant PDGFRA fusion genes have now also been described (Table 3).…”

“…The essential role of FIP1L1-PDGFRA is clear from in vitro studies with the EOL-1 cell line, from mouse models of FIP1L1-PDGFRA induced disease, and from the remarkable responses of FIP1L1-PDFGRA-positive CEL patients to imatinib treatment. 8,18,65,66 The mouse model, however, has also suggested that expression of the FIP1L1-PDGFRA fusion is most likely not sufficient to cause eosinophilia, as mice expressing FIP1L1-PDGFRA in their bone marrow cells develop a general myeloproliferative disease without eosinophilia. 65 Expression of FIP1L1-PDGFRA together with overexpression of IL-5, however, mimics the disease much better in the mouse, with typical features of HES such as tissue infiltration of eosinophils.…”

“…8,18 Five years since the discovery of FIP1L1-PDGFRA J Gotlib and J Cools tyrosine kinase as the therapeutic target of imatinib, which was ultimately identified as FIP1L1-PDGFRa. 8,18 Of the 16 HES/CEL patients enrolled in the study of Cools et al, 8 11 were treated with imatinib. Hematologic responses were observed in 10 of 11 HES patients treated with imatinib doses of 100-400 mg daily.…”

Gastrointestinal Eosinophilia

“…Further investigation of the ability of imatinib mesylate to treat HES patients revealed the existence of an 800 kilobase deletion in chromosome 4 bringing together an upstream DNA sequence homologous to a yeast protein, referred to as FIP1, and designated as like FIP1, or FIP1-L1 and the gene for the cytoplasmic domain of the platelet derived growth factor alpha (PDGFRA) receptor. [65,70] This fusion gene is transcribed and translated yielding a novel kinase referred to as FIP-L1-PDGFRA; FIP-L1-PDGFRA is exquisitely sensitive to imatinib in vitro, thus explaining the remarkable sensitivity of HES patients to this drug. The FIP-L1-PDGFRA fusion gene cooperates with IL-5 overexpression in a murine model of HES, suggesting that both pathogenic events cooperate in disease etiology.…”