ABSTRACT
TAL1/SCL/TCL5 is a critical transcription factor for hematopoietic stem cell maintenance and regulation of early hematopoiesis. However, aberrant expression of TAL1 in committed T-cell precursors is also directly implicated in the development of T-cell leukemia. Roughly 25 years ago TAL1 was identified in early hematopoietic cells and involved in leukemia. Here, we review the wealth of knowledge gained since then on its physiological roles and mechanisms by which TAL1 ectopic expression contributes to leukemogenesis. We emphasize recent findings that shed light into the intricacies of TAL1 (epi)genetic regulation and the transcription network orchestrated by this major T-cell oncogene. Importantly, an exciting time is coming when data using the mechanistic knowledge accumulated on TAL1 may be used to develop novel anti-leukemia targeted therapies.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/physiology , Leukemia, T-Cell/etiology , Neoplastic Stem Cells/pathology , Proto-Oncogene Proteins/physiology , Basic Helix-Loop-Helix Transcription Factors/genetics , Carcinogenesis , Humans , Leukemia, T-Cell/genetics , Leukemia, T-Cell/pathology , Proto-Oncogene Proteins/genetics , T-Cell Acute Lymphocytic Leukemia Protein 1ABSTRACT
Mutation of KIT receptor tyrosine kinase at residue D816 results in ligand-independent constitutive kinase activity. This mutation occurs in most patients with mastocytosis, a myeloproliferative neoplasm, and is detected at lower frequencies in acute myeloid leukemia and in germ cell tumors. Other KIT mutations occur in gastrointestinal stromal tumors (GIST) and mucosal melanoma. KIT is considered as a bona fide therapeutic target as c-kit mutations are driving oncogenes in these pathologies. However, several evidences suggest that KIT-D816V mutant is not as aggressive as other KIT mutants. Here, we show that an intracellular docking site in the juxtamembrane region of KIT maintains a negative regulation on KIT-D816V transforming potential. Sixteen signaling proteins were shown to interact with this motif. We further demonstrate that mutation of this site results in signaling modifications, altered gene expression profile and increased transforming activity of KIT-D816V mutant. This result was unexpected as mutations of the homologous sites on wild-type (WT) KIT, or on the related oncogenic FLT3-ITD receptor, impair their function. Our results support the hypothesis that, KIT-D816V mutation is a mild oncogenic event that is sufficient to confer partial transforming properties, but requires additional mutations to acquire its full transforming potential.
