casein-kinase-ii and Thymoma

A blockade of CD44 can interfere with haematopoietic and leukemic stem cell homing, the latter being considered as a therapeutic option in haematological malignancies. We here aimed to explore the molecular mechanism underlying the therapeutic efficacy of anti-CD44. We noted that in irradiated mice reconstituted with a bone marrow cell transplant, anti-CD44 exerts a stronger effect on haematopoietic reconstitution than on T lymphoma (EL4) growth. Nonetheless, in the non-reconstituted mouse anti-CD44 suffices for a prolonged survival of EL4-bearing mice, where anti-CD44-prohibited homing actively drives EL4 cells into apoptosis. In vitro, a CD44 occupancy results in a 2-4-fold increase in apoptotic EL4 cells. Death receptor expression (CD95, TRAIL, TNFRI) remains unaltered and CD95 cross-linking-mediated apoptosis is not affected. Instead, CD44 ligation promotes mitochondrial depolarization that is accompanied by caspase-9 cleavage and is inhibited in the presence of a caspase-9 inhibitor. Apoptosis becomes initiated by activation of CD44-associated phosphatase 2A (PP2A) and proceeds via ERK1/2 dephosphorylation without ERK1/2 degradation. Accordingly, CD44-induced apoptosis could be mimicked by ERK1/2 inhibition, that also promotes EL4 cell apoptosis through the mitochondrial pathway. Thus, during haematopoietic stem cell reconstitution care should be taken not to interfere by a blockade of CD44 with haematopoiesis, which could be circumvented by selectively targeting leukemic CD44 isoforms. Beyond homing/settlement in the bone marrow niche, anti-CD44 drives leukemic T cells into apoptosis via the mitochondrial death pathway by CD44 associating with PP2A. Uncovering this new pathway of CD44-induced leukemic cell death provides new options of therapeutic interference.

Topics: Animals; Antibodies, Neoplasm; Apoptosis; Casein Kinase II; Caspase 9; Cell Line, Tumor; Cell Proliferation; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Hematopoiesis; Hyaluronan Receptors; Injections, Intravenous; Injections, Subcutaneous; Lymphoma; Membrane Potential, Mitochondrial; Mice; Mice, Inbred C57BL; Mitochondria; Phosphorylation; Protein Phosphatase 2; T-Lymphocytes; Thymoma; Thymus Neoplasms

Activation of the basic helix-loop-helix (bHLH) gene TAL-1 (or SCL) is the most frequent gain-of-function mutation in pediatric T cell acute lymphoblastic leukemia (T-ALL). Similarly, mis-expression of tal-1 in the thymus of transgenic mice results in the development of clonal T cell lymphoblastic leukemia. To determine the mechanism(s) of tal-1-induced leukemogenesis, we created transgenic mice expressing a DNA binding mutant of tal-1. Surprisingly, these mice develop disease, demonstrating that the DNA binding properties of tal-1 are not required to induce leukemia/lymphoma in mice. However, wild type tal-1 and the DNA binding mutant both form stable complexes with E2A proteins. In addition, tal-1 stimulates differentiation of CD8-single positive thymocytes but inhibits the development of CD4-single positive cells: effects also observed in E2A-deficient mice. Our study suggests that the bHLH protein tal-1 contributes to leukemia by interfering with E2A protein function(s).

Topics: Adaptor Proteins, Signal Transducing; Adenovirus E2 Proteins; Animals; Basic Helix-Loop-Helix Transcription Factors; Casein Kinase II; CD4 Antigens; CD4-Positive T-Lymphocytes; CD8-Positive T-Lymphocytes; Cell Differentiation; Dimerization; Disease Models, Animal; DNA; DNA-Binding Proteins; Helix-Loop-Helix Motifs; Humans; Leukemia-Lymphoma, Adult T-Cell; LIM Domain Proteins; Lymphoma; Metalloproteins; Mice; Mice, Transgenic; Mutagenesis; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; T-Cell Acute Lymphocytic Leukemia Protein 1; TCF Transcription Factors; Thymoma; Thymus Gland; Thymus Neoplasms; Transcription Factor 7-Like 1 Protein; Transcription Factors

Ectopic activation of the TAL-1 gene in T lymphocytes occurs in the majority of cases of human T cell acute lymphoblastic leukemia (T-ALL), yet experiments to date have failed to demonstrate a direct transforming capability for tal-1. The tal-1 gene product is a serine phosphoprotein and basic helix-loop-helix (bHLH) transcription factor known to regulate embryonic hematopoiesis. We have established a transgenic mouse model in which tal-1 mis-expression in the thymus results in the development of clonal T cell lymphoblastic leukemia/lymphoma. Thus, overexpression of tal-1 alone can be transforming, verifying its pathogenic role in human T-ALL. In addition, leukemogenesis is accelerated dramatically by transgenic co-expression of tal-1 and the catalytic subunit of casein kinase IIalpha (CKIIalpha), a serine/threonine protein kinase known to modulate the activity of other bHLH transcription factors. Although tal-1 is a substrate for CKII, the synergy of the tal-1 and CKIIalpha transgenes appears to be indirect, perhaps mediated through the E protein heterodimeric partners of tal-1. These studies prove that dysregulated tal-1 is oncogenic, providing a direct molecular explanation for the malignancies associated with TAL-1 activation in human T-ALL.

Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Casein Kinase II; Disease Models, Animal; DNA-Binding Proteins; Humans; Immunophenotyping; Leukemia-Lymphoma, Adult T-Cell; Mice; Mice, Transgenic; Oncogenes; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; RNA, Messenger; RNA, Neoplasm; T-Cell Acute Lymphocytic Leukemia Protein 1; Thymoma; Thymus Gland; Thymus Neoplasms; Transcription Factors; Transgenes