Transforming Properties of the Huntingtin Interacting Protein 1/ Platelet-derived Growth Factor β Receptor Fusion Protein

Theodora S Ross,D Gary Gilliland

doi:10.1074/jbc.274.32.22328

Abstract

We have previously reported that the Huntingtin interacting protein 1 (HIP1) gene is fused to the platelet-derived growth factor beta receptor (PDGFbetaR) gene in a patient with chronic myelomonocytic leukemia. We now show that HIP1/PDGFbetaR oligomerizes, is constitutively tyrosine-phosphorylated, and transforms the murine hematopoietic cell line, Ba/F3, to interleukin-3-independent growth. A kinase-inactive mutant is neither tyrosine-phosphorylated nor able to transform Ba/F3 cells. Oligomerization and kinase activation required the 55-amino acid carboxyl-terminal TALIN homology region but not the leucine zipper domain. Tyrosine phosphorylation of a 130-kDa protein and STAT5 correlates with transformation in cells expressing HIP1/PDGFbetaR and related mutants. A deletion mutant fusion protein that contains only the TALIN homology region of HIP1 fused to PDGFbetaR is incapable of transforming Ba/F3 cells and does not tyrosine-phosphorylate p130 or STAT5, although it is itself constitutively tyrosine-phosphorylated. We have also analyzed cells expressing Tyr --> Phe mutants of HIP1/PDGFbetaR in the known PDGFbetaR SH2 docking sites and report that none of these sites are necessary for STAT5 activation, p130 phosphorylation, or Ba/F3 transformation. The correlation of factor-independent growth of hematopoietic cells with p130 and STAT5 phosphorylation/activation in both the HIP1/PDGFbetaR Tyr --> Phe and deletion mutational variants suggests that both STAT5 and p130 are important for transformation mediated by HIP1/PDGFbetaR.

Highlights

We have previously reported that the Huntingtin interacting protein 1 (HIP1) gene is fused to the plateletderived growth factor ␤ receptor (PDGF␤R) gene in a patient with chronic myelomonocytic leukemia
The correlation of factor-independent growth of hematopoietic cells with p130 and STAT5 phosphorylation/activation in both the HIP1/ PDGF␤R Tyr 3 Phe and deletion mutational variants suggests that both STAT5 and p130 are important for transformation mediated by HIP1/PDGF␤R
These three properties require HIP1 amino acids 690 –752 but do not require any of the known SH2 signal transducing molecule docking sites in the PDGF␤R portion of the fusion. This suggests that in addition to tyrosine kinase activation, HIP1 sequences that function in ways other than self-association may be relevant for transformation of Ba/F3 cells to IL-3-independent growth and that both p130 and the STAT5 are important targets of HIP1/PDGF␤R in mediating transformation

Summary

Introduction

We have previously reported that the Huntingtin interacting protein 1 (HIP1) gene is fused to the plateletderived growth factor ␤ receptor (PDGF␤R) gene in a patient with chronic myelomonocytic leukemia. We show that HIP1/PDGF␤R oligomerizes, is constitutively tyrosine-phosphorylated, and transforms the murine hematopoietic cell line, Ba/F3, to interleukin-3-independent growth. Tyrosine phosphorylation of a 130-kDa protein and STAT5 correlates with transformation in cells expressing HIP1/PDGF␤R and related mutants.

Results

Conclusion