TEL/platelet-derived growth factor receptor β activates phosphatidylinositol 3 (PI3) kinase and requires PI3 kinase to regulate the cell cycle

Abstract

IntroductionTyrosine kinase fusion proteins are the products of a growing family of oncogenes associated with both solid tumors and hematologic malignancies. 1 The best known tyrosine kinase fusion protein is the BCR/ABL tyrosine kinase that results from a t(9;22) translocation in patients with chronic myeloid leukemia. 2 Previous work has demonstrated that BCR/ABL activates multiple signal transduction pathways, including the phosphatidylinositol-3 (PI3) kinase pathway and that transformation by BCR/ABL requires activation of PI3 kinase. [3][4][5][6] To determine if tyrosine kinase fusion proteins share common mechanisms of transformation or if each functions in unique ways, we have chosen to study the TEL/plateletderived growth factor receptor ␤ (PDGF␤R) fusion protein that results from the t(5;12) translocation in patients with chronic myelomonocytic leukemia. 7 TEL/PDGF␤R contains the amino-terminal 154 amino acids of TEL fused to the transmembrane and cytoplasmic domains of the PDGF␤R. TEL is a member of the ETS family of transcription factors and has been described as a common site of rearrangement in multiple forms of leukemia. [8][9][10] Structurally, wild-type TEL contains a 5Ј oligomerization domain, designated the PNT domain; this domain is retained in the fusion protein and is essential for the transforming activity of TEL/PDGF␤R as demonstrated by us and others. 11,12 Evidence suggests that the PNT domain may cause multimerization of the fusion protein, not simple dimerization. 13 TEL has been reported to induce G1 arrest in vitro 14 and to be required for yolk sac angiogenesis according to murine knockout experiments. 15 PDGF␤R is a well-characterized plasma membrane receptor with endogenous tyrosine kinase activity that is autophosphorylated in response to binding of dimeric PDGF ligand. 16 In the fusion protein there is retention of the transmembrane domain and the complete tyrosine kinase domain of PDGF␤R. An intact kinase activity is necessary for transforming activity. 17 The protein retains multiple tyrosine sites that act as binding sites for SH2-containing signaling molecules in the wild type PDGF␤R. Furthermore, immunolocalization of TEL/PDGF␤R has demonstrated that the protein is located primarily in the cytosol, retaining neither the nuclear localization of TEL or the plasma membrane localization of PDGF␤R. 12 Thus, initial models of transformation by TEL/ PDGF␤R have suggested that the protein is constitutively oligomerized through the TEL PNT domain, leading to constitutive activation of the kinase activity of the 3Ј PDGF␤R kinase domain and activation of critical signaling pathways. However, the signaling pathways that are necessary for transformation remain undefined.Several signaling pathways have been identified as being activated by TEL/PDGF␤R. In transformed cell lines, TEL/ PDGF␤R is known to associate with or cause phosphorylation of phospholipase C (PLC␥1), SHP2, and JNK. 11,18,19 In addition, we have recently shown that TEL/PDGF␤R activates STAT1 and STAT5 but have been unabl...

Fusion tyrosine kinase mediated signalling pathways in the transformation of haematopoietic cells

“…98 Using Ba/F3 and 32D cell lines as model systems, it has been shown that Tel-PDGFbR, NPM-ALK and Bcr-Abl expression results in inhibition of p27 kip1 as a result of PI 3-kinase activation. 94,99,100 These effects are most likely mediated by Forkhead transcription factors that are activated by Akt downstream of PI 3-kinase, thereby inhibiting the transcription of p27 kip1 . 100,101…”

“…81,[88][89][90][91][92][93][94] The binding sites of PI 3-kinase to the FTKs have been identified and the bridging proteins Cbl, Shc and Gab-2 are involved. 95 Once activated, Akt phosphorylates a plethora of downstream targets altering their activation status.…”

Inhibition of phosphatidylinositol 3-kinase dephosphorylates BAD and promotes apoptosis in myeloid leukemias

“…TEL/platelet-derived growth factor (PDGF) beta R fusion protein resulting from the t(5;12) in CMML activates the kinase activity of PI3K and stimulates phosphorylation of its downstream substrates including AKT. 37 The BCR/ABL fusion protein, a hallmark of CML, also results in the activation of PI3K/AKT signaling. 38 A recent report demonstrated that factors present in plasma promote basal survival of B-CLL cells and resistance to cytotoxic drugs via stimulation of the AKT cytoprotective signaling pathway.…”

ETV6-PDGFRB and FIP1L1-PDGFRA stimulate human hematopoietic progenitor cell proliferation and differentiation into eosinophils: the role of nuclear factor- B

“…(C) FPa + blasts cells from a patient and control leukocytes from a healthy donor were isolated from blood samples. 9 Cells treated with imatinib or LY294002. p65 phosphorylation on ser536 was quantified using a SureFire assay as described in the Design and Methods section.…”

“…8 Several studies showed that TPβ activates multiple signal transduction pathways in these cells, including phosphatidylinositol-3 kinase (PI3K), mitogen-activated protein kinases (MAPK) and the transcription factors STAT1, STAT5 as well as nuclear factor-κB (NF-κB). [9][10][11][12] Mouse transplantation models have demonstrated that TPβ also stimulates hematopoietic cell proliferation in vivo, leading to a myeloproliferative disease, in a process that requires the activation of STAT5. 13 However, this model imperfectly mimics the human disease as mice do not develop eosinophilia in these conditions.…”