Direct interaction of Ikaros and Foxp1 modulates expression of the G protein-coupled receptor G2A in B-lymphocytes and acute lymphoblastic leukemia.

Jonathan Bond,Isabel Ferreiros-Vidal,Matthias Merkenschlager,Vahid Asnafi,Elizabeth Macintyre,Gareth Gerrard,Renae Domaschenz,Pierangela Sabbattini,Mónica Roman-Trufero,Niall Dillon

doi:10.18632/oncotarget.11688

Abstract

Ikaros and Foxp1 are transcription factors that play key roles in normal lymphopoiesis and lymphoid malignancies. We describe a novel physical and functional interaction between the proteins, which requires the central zinc finger domain of Ikaros. The Ikaros-Foxp1 interaction is abolished by deletion of this region, which corresponds to the IK6 isoform that is commonly associated with high-risk acute lymphoblastic leukemia (ALL). We also identify the Gpr132 gene, which encodes the orphan G protein-coupled receptor G2A, as a novel target for Foxp1. Increased expression of Foxp1 enhanced Gpr132 transcription and caused cell cycle changes, including G2 arrest. Co-expression of wild-type Ikaros, but not IK6, displaced Foxp1 binding from the Gpr132 gene, reversed the increase in Gpr132 expression and inhibited G2 arrest. Analysis of primary ALL samples revealed a significant increase in GPR132 expression in IKZF1-deleted BCR-ABL negative patients, suggesting that levels of wild-type Ikaros may influence the regulation of G2A in B-ALL. Our results reveal a novel effect of Ikaros haploinsufficiency on Foxp1 functioning, and identify G2A as a potential modulator of the cell cycle in Ikaros-deleted B-ALL.

Highlights

Progression through B cell differentiation is tightly regulated by a specific transcription factor program in which members of the Ikaros and forkhead families have key roles
The Ikaros-Foxp1 interaction is abolished by deletion of this region, which corresponds to the IK6 isoform that is commonly associated with high-risk acute lymphoblastic leukemia (ALL)
The possibility that Ikaros and Foxp1 interact directly or as part of a multi-protein complex in pre-B cells was tested by co-immunoprecipitation of protein lysates obtained from wild-type murine fetal liver pre-B cells with anti-Ikaros and anti-Foxp1 antibodies

Summary

Introduction

Progression through B cell differentiation is tightly regulated by a specific transcription factor program in which members of the Ikaros and forkhead families have key roles. Ikaros is a Kruppel-like factor [1, 2] whose expression has been shown to be absolutely required for B cell development [3]. Mutations and deletions in the IKZF1 gene, which encodes Ikaros, are associated with Philadelphia positive (Ph+, known as BCRABL positive) B-ALL and are present in 70-80% of these patients. Several studies have shown IKZF1 deletions to be associated with poor outcome in both Ph+ and Ph- B-ALL, suggesting that Ikaros haploinsufficiency is likely to contribute directly to poor treatment response in these patients [13,14,15]

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Results

Conclusion