Protein Kinase A-dependent Transactivation by the E2A-Pbx1 Fusion Protein

Atsushi Ogo,Michael R Waterman,Mark P Kamps,Norio Kagawa

doi:10.1074/jbc.270.43.25340

Atsushi Ogo, Michael R Waterman + Show 2 more

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https://doi.org/10.1074/jbc.270.43.25340

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Abstract

The chimeric gene E2A-PBX1 is formed by the t(1;19) chromosomal translocation exclusively associated with pediatric pre-B cell acute lymphoblastic leukemia (pre-B ALL). The resultant fusion protein from this chimeric gene contains the DNA-binding homeodomain of Pbx1. The first and only functional Pbx1 binding site has been localized in bovine CYP17 to a sequence (CRS1) that participates in cAMP-dependent transcription of this gene encoding the steroid hydroxylase, 17 alpha-hydroxylase cytochrome P450. Because Pbx1 is not expressed in pre-B cells, it may be possible that the E2a-Pbx1 fusion protein expressed in pre-B cells having this translocation will activate, in response to cAMP, transcription of genes not normally expressed in these cells leading to arrest of differentiation at the pre-B cell stage. We have now shown that reporter genes comprising CRS1 are activated transcriptionally by protein kinase A (PKA) in the pre-B cell line 697, which endogenously expresses the fusion protein, and that overexpression of E2A-Pbx1 in additional cell lines enhances transcription of reporter genes in a PKA-dependent fashion. Thus, it seems plausible that arrest in the pre-B stage leading to pre-B ALL includes cAMP-dependent activation of E2A-Pbx1.

Highlights

The chimeric gene E2A-PBX1 is formed by the t(1;19) chromosomal translocation exclusively associated with pediatric pre-B cell acute lymphoblastic leukemia
In this study we have shown that 697 pre-B Acute lymphoblastic leukemia (ALL) cells, which express E2A-Pbx1, have a gel shift pattern clearly distinct from cells which express members of the PBX gene family, yet they enhance transcription mediated by the Pbx binding site in a cAMP-dependent fashion
Does endogenous E2A-Pbx1 have this effect in pre-B ALL cells, but co-expression of E2APbx1 shows this effect in several different cell types

Summary

Introduction

The chimeric gene E2A-PBX1 is formed by the t(1;19) chromosomal translocation exclusively associated with pediatric pre-B cell acute lymphoblastic leukemia (pre-B ALL). In the same way as Pbx, alternative splicing of E2A-Pbx transcripts leads to the production of two different E2A-Pbx fusion proteins, E2A-Pbx1a and E2A-Pbx1b [3, 4] These fusion proteins containing the transactivation domain of E2A and the DNA-binding homeodomain of Pbx have been investigated intensively and shown to be capable of transformation in fibroblast [9], myeloid [10], and T lineage cells [11]. We discovered the Pbx binding site in a cAMPregulatory sequence, designated CRS1, which enhances the expression of 17␣-hydroxylase cytochrome P450 (P450c17) encoded by the CYP17 gene [14, 15] Both Pbx1a and Pbx1b are involved in the cAMP-dependent regulation of CYP17 [15]. E2A-Pbx is reported to enhance reporter gene transcription through PRS [12, 13, 16], its role as a transcription factor in leukemogenesis remains unknown

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