Abl protein-tyrosine kinase selects the Crk adapter as a substrate using SH3-binding sites

To understand the normal and oncogenic functions of the protein-tyrosine kinase Abl, the yeast two-hybrid system has been used for identifying proteins that interact with it. One interacting protein is Crk-I, an SH3/SH2-containing adapter protein that was originally identified as the oncogenic element in the avian sarcoma virus CT10. Direct interaction between the Crk-I SH3 and Abl at novel, ~10 amino acid sites just carboxy-terminal to the Abl kinase domain occurs in vitro and in mammalian cells. There is a nearby site specific for binding another adapter, Nck, and these sites also bind Grb-2. When bound to Abl, Crk-I was phosphorylated on tyrosine. Thus, the SH3-binding sites on Abl serve as substrate recognition sites for the relatively nonspecific kinase of Abl. In Crk-I-transformed cells, Crk-I associates with endogenous c-Abl and is phosphorylated on tyrosine. The association of Crk and Abl suggests that Abl could play a role in v-Crk and Crk-I transformation and that normal Abl function may be partly mediated through bound adapter molecules

WT1 Recruits TET2 to Regulate Its Target Gene Expression and Suppress Leukemia Cell Proliferation

The TET2 DNA dioxygenase regulates cell identity and suppresses tumorigenesis by modulating DNA methylation and expression of a large number of genes. How TET2, like most other chromatin modifying enzymes, is recruited to specific genomic sites is unknown. Here we report that WT1, a sequence-specific transcription factor, is mutated in a mutually exclusive manner with TET2, IDH1 and IDH2 in acute myeloid leukemia (AML). WT1 physically interacts with and recruits TET2 to its target genes to activate their expression. The interaction between WT1 and TET2 is disrupted by multiple AML-derived TET2 mutations. TET2 suppresses leukemia cell proliferation and colony formation in a manner dependent on WT1. These results provide a mechanism for targeting TET2 to specific DNA sequence in the genome. Our results also provide an explanation for the mutual exclusivity of WT1 and TET2 mutations in AML and suggest an IDH1/2-TET2-WT1 pathway in suppressing AML

Loss of IRF-4 Exacerbates the CML-Like Phenotype of IRF-8 Knockout Mice

Abstract IRF-4 and IRF-8 are related interferon regulatory factors that are required for the development and function of myeloid and lymphoid cells. Mice deficient in IRF-8 develop a myeloproliferative disorder with many similarities to human chronic myeloid leukemia (CML). Our group has shown that in B-lymphocyte development, IRF-4 and 8 function redundantly to control the pre-B to B transition. Though expression of IRF-4 has been demonstrated in myeloid cells, its role in these lineages has not been defined. We hypothesized that, similar to their role in B-cells, IRF-4 and 8 may to some extent function redundantly in myeloid cells. To test this hypothesis, myelopoiesis was analyzed in IRF-4/8 double knockout (DKO) mice. We found that from seven weeks of age, the DKO animals have a more aggressive leukemic phenotype than the IRF-8 KO mice. The white blood cell (WBC) counts of DKO animals were typically in the range of 40,000 to 80,000 cells per microliter, campared to 15,000 to 20,000 for age-matched IRF-8 KO animals. FACS analysis showed that the increased WBCs in the DKO animals was due to a massive expansion of mature granulcytes. The absolute granulocyte counts of DKO animals were typically 7-fold to 10-fold higher than those of IRF-8 KO animals. In addition, histologic preparations showed that by 15 weeks of age the spleens, lymph nodes, and bone marrow of DKO animals were invaded by large numbers of mature granulocytes and pseudo-Gaucher cells, with complete effacement of the normal micro-architecture. Age-matched IRF-8 KO animals showed invasion to a lesser degree, with preservation of many of the normal architectural features. In conclusion, IRF-4 is an important myeloid tumor suppressor, whose loss augments the myeloproliferative disease manifested in IRF-8 deficient mice. This suggests the two transcription factors, similar to their role in B-cell development, function redundantly to control the normal maturation of myeloid-lineage cells

Modular binding domains in signal transduction proteins

The transduction of a signal is a change in form of the signal as it is passed from one carrier to another. The root "duce" means "to lead" in Latin; thus, a signal is led through a cell by steps of transduction (the same root is in the words seduce and duct as well as II Duce). The earliest transduction steps that were elucidated involved massive release of small molecule "second messengers", originally cAMP, that flooded a cell with information. With the understanding that such proteins as tyrosine kinases and Ras relatives are signal transducers, came the realization that many signaling pathways are more precise, sending controlled and probably weakly amplified signals to specific targets. These intracellular signals are often maintained in macromolecular form rather than being passed to small molecules

Oncogenic NRAS rapidly and efficiently induces CMML- and AML-like diseases in mice

Activating mutations in RAS, predominantly NRAS, are common in myeloid malignancies. Previous studies in animal models have shown that oncogenic NRAS is unable to induce myeloid malignancies effectively, and it was suggested that oncogenic NRAS might only act as a secondary mutation in leukemogenesis. In this study, we examined the leukemogenicity of NRAS using an improved mouse bone marrow transduction and transplantation model. We found that oncogenic NRAS rapidly and efficiently induced chronic myelomonocytic leukemia (CMML)– or acute myeloid leukemia (AML)– like disease in mice, indicating that mutated NRAS can function as an initiating oncogene in the induction of myeloid malignancies. In addition to CMML and AML, we found that NRAS induced mastocytosis in mice. This result indicates that activation of the RAS pathway also plays an important role in the pathogenesis of mastocytosis. The mouse model for NRAS leukemogenesis established here provides a system for further studying the molecular mechanisms in the pathogenesis of myeloid malignancies and for testing relevant therapies