The IL-3, IL-5, and GM-CSF common receptor beta chain mediates oncogenic activity of FLT3-ITD-positive AML

Anne Charlet,Anna L Illert,Max Kappenstein,Cornelius Miething,Michael Reth,Sivahari P Gorantla,Teresa Poggio,Kathrin Kläsener,Cornelia Endres,Jana Sänger,Philip Keye,Christoph Rummelt,Justus Duyster,Stefanie Kreutmair,Nikolas Von Bubnoff

doi:10.1038/s41375-021-01462-4

Abstract

FLT3-ITD is the most predominant mutation in AML being expressed in about one-third of AML patients and is associated with a poor prognosis. Efforts to better understand FLT3-ITD downstream signaling to possibly improve therapy response are needed. We have previously described FLT3-ITD-dependent phosphorylation of CSF2RB, the common receptor beta chain of IL-3, IL-5, and GM-CSF, and therefore examined its significance for FLT3-ITD-dependent oncogenic signaling and transformation. We discovered that FLT3-ITD directly binds to CSF2RB in AML cell lines and blasts isolated from AML patients. A knockdown of CSF2RB in FLT3-ITD positive AML cell lines as well as in a xenograft model decreased STAT5 phosphorylation, attenuated cell proliferation, and sensitized to FLT3 inhibition. Bone marrow from CSF2RB-deficient mice transfected with FLT3-ITD displayed decreased colony formation capacity and delayed disease onset together with increased survival upon transplantation into lethally irradiated mice. FLT3-ITD-dependent CSF2RB phosphorylation required phosphorylation of the FLT3 juxtamembrane domain at tyrosines 589 or 591, whereas the ITD insertion site and sequence were of no relevance. Our results demonstrate that CSF2RB participates in FLT3-ITD-dependent oncogenic signaling and transformation in vitro and in vivo. Thus, CSF2RB constitutes a rational treatment target in FLT3-ITD-positive AML.

Highlights

The internal tandem duplication (ITD) mutation of the class III receptor tyrosine kinase FMS-like Tyrosine Kinase 3 (FLT3) is found in 25% of all AML cases and is associated with a dismal prognosis [1]
CSF2RB interacts with FLT3 and is phosphorylated in an FLT3ITD-dependent manner approved by the institutional review board of the University of Freiburg
CSF2RB activation leads to STAT5 activation [17, 18], the key oncogenic signal of FLT3-ITD [3,4,5], and we were able to show that CSF2RB knockdown attenuated FLT3-ITD dependent STAT5 activation and cell growth

Summary

Introduction

The internal tandem duplication (ITD) mutation of the class III receptor tyrosine kinase FMS-like Tyrosine Kinase 3 (FLT3) is found in 25% of all AML cases and is associated with a dismal prognosis [1]. Despite recent advances with combinations of standard chemotherapy and specific FLT3 tyrosine kinase inhibitors (TKIs), the only cure for patients diagnosed with a high FLT3-ITD allelic ratio AML is allogeneic stem cell transplantation [2]. The ITD mutation is predominantly located within the juxtamembrane domain (JMD) of FLT3 and leads to constitutive activation of the receptor and to downstream signaling events in the absence of ligand [3]. It has been demonstrated that FLT3-ITD shares activation of PI3K-AKT and MAPK (ERK) with ligand-stimulated FLT3, but in addition strongly activates STAT5 [3,4,5]. The mechanism of STAT5 activation by FLT3-ITD is unknown. Direct activation has been proposed [6] as well as activation via signaling intermediates such as SRC, GRB2, BTK, or SYK [7,8,9,10,11]

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