Pre-TCR expression cooperates with TEL-JAK2 to transform immature thymocytes and induce T-cell leukemia

Abstract

The TEL-JAK2 gene fusion, which has been identified in human leukemia, encodes a chimeric protein endowed with constitutive tyrosine kinase activity. TEL-JAK2 transgenic expression in the mouse lymphoid lineage results in fatal and rapid T-cell leukemia/lymphoma. In the present report we show that T-cell leukemic cells from ESR␣-TEL-JAK2 transgenic mice present an aberrant CD8 ؉ differentiation phenotype, as determined by the expression of stage-specific cell surface markers and lineage-specific genes. TEL-JAK2 transforms immature CD4 ؊ CD8 ؊ double-negative thymocytes, as demonstrated by the development of T-cell leukemia with full penetrance in a Rag2-deficient genetic background. This disease is similar to the bona fide TEL-JAK2 disease as assessed by phenotypic and gene profiling analyses. Pre-TCR signaling synergizes with TEL-JAK2 to transform immature thymocytes and initiate leukemogenesis as shown by (1) the delayed leukemia onset in Rag2-, CD3⑀-and pT␣-deficient mice, (2) the occurrence of recurrent chromosomal alterations in pre-TCR-deficient leukemia, and (3) the correction of delayed leukemia onset in Rag2-deficient TEL-JAK2 mice by an H-Y TCR␣␤ transgene that mimics pre-TCR signaling. Although not affecting leukemia incidence and mouse survival, TCR␣␤ expression was shown to facilitate leukemic cell expansion in secondary lymphoid organs. IntroductionIn the thymus, T cells develop from a common CD4 Ϫ CD8 Ϫ double-negative (DN) progenitor into 2 main lineages, ␣␤ and ␥␦, which are defined by the selection of productive rearrangements in the respective T-cell receptor (TCR) loci (for a review, see Aifantis et al 1 ). In mice, DN thymocytes are divided in 4 categories according to CD25 and CD44 expression: DN1 (CD25 Ϫ CD44 ϩ ), DN2 (CD25 ϩ CD44 ϩ ), DN3 (CD25 ϩ CD44 Ϫ ), and DN4 (CD25 Ϫ CD44 Ϫ ). Rag-mediated rearrangement of the TCR␤ locus at the DN3 stage leads to cell surface expression of a functional TCR␤ chain, which assembles with the surrogate pT␣ chain and CD3-signaling proteins to form the pre-TCR complex. Constitutive survival, proliferation, and differentiation signals emanating from the pre-TCR allow T cells to pass through the ␤-selection checkpoint and mature to the DN4, CD4 Ϫ CD8 ϩ immature single-positive (ISP) and CD4 ϩ CD8 ϩ double-positive (DP) stages. The ␤-selected cells rearrange their TCR␣ locus, and only the minority of cells expressing a functional TCR␣␤ complex at the cell surface will either undergo negative selection and die or undergo positive selection and become mature CD4 or CD8 single-positive (SP) thymocytes.Chromosomal rearrangements or point mutations in oncogenes or tumor suppressor genes occur in hematopoietic stem cells (HSCs), uncommitted and committed lymphoid progenitors, or developing thymocytes, thus leading to T-cell leukemia. Chromosomal translocations involving the juxtaposition of protooncogenes to the promoter and enhancer sequences of TCR loci result in deregulated oncogene expression. Chromosomal translocations can also create fusion genes encoding fu...

The calcineurin/NFAT signaling pathway: A NOVEL therapeutic target in leukemia and solid tumors

“…13 In the TEL-JAK2 and ICN1-induced mouse models we have used, 17 the rapid emergence of leukemia is critically dependent upon pre-TCR signaling and these clonal leukemias express a functional TCR. 47,48 Since the pre-TCR and the TCR are well characterized receptors coupled to calcium/calcineurin/NFAT activation, 9,49 we considered the possibility that sustained calcium/calcineurin signaling in leukemic cells could reflect acquired hypersensitivity of these cells to pre-TCR/TCR-dependent signals. This is not the case since both TEL-JAK2-and ICN1-induced leukemias generated in Rag2-deficient mice-which cannot rearrange the genes encoding TCRα and β and thus cannot express neither the pre-TCR nor a TCR-present persistent activation of the calcineurin/NFAT signaling module in a similar fashion as leukemias obtained in RAG2-proficient mice (ref.…”

Modeling T-cell acute lymphoblastic leukemia induced by the SCL and LMO1 oncogenes

“…In leukemogenesis, the contribution of the pre-TCR appears variable, as it is dispensable in some mouse models (Liao et al 1998;Engel and Murre 2002) but important in others (Bellavia et al 2002;dos Santos et al 2007). In the latter, the precise contribution of the pre-TCR to the leukemogenic process remains unknown.…”

Thymic expression of a T-cell receptor targeting a tumor-associated antigen coexpressed in the thymus induces T-ALL

“…[19][20][21] TCR signaling during early thymopoiesis appears sufficient to induce T-ALL in some animal models, and in others the aberrant TCR signal plays a cooperating role as part of an oncogenic cascade. [22][23][24][25] Interestingly, T-ALL induced in patients receiving IL2Rgc-expressing hematopoietic progenitors was associated with other oncogenic mutations, in particular those involving the NOTCH1 oncogene. 26 Thus, although insertional mutagenesis poses a risk for gene therapy involving hematopoietic progenitors, expression of signaling receptors themselves during early thymopoiesis may also be oncogenic, especially when combined with cooperating mutations in partner oncogenes.…”

“…To generate Sur-TCR-Tg mice, C57BL/6 mice were vaccinated twice 1 week apart with 100 mL of a Db-binding peptide derived from mouse survivin [20][21][22][23][24][25][26][27][28] extracted, and TCR a-and b-chains were cloned using 59-rapid amplification of cDNA ends (Life Technologies). TCR a-and b-transcripts were found to be Va8/Ja24/Ca and Vb13/Db2/Jb2/Cb2.…”

“…Sequence-validated purified PCR products were cloned into a human CD2 minigene-based vector as previously described 30 (kindly provided by Al Singer, NCI, National Institutes of Health [NIH]), and coinjected into fertilized C57BL/6 embryos yielding 11 transgenic founder lines. Three founder lines with a high frequency of Sur [20][21][22][23][24][25][26][27][28] tetramer-binding CD8 1 T cells were bred, housed at the NIH, and underwent further analysis.…”