RESUMEN
The translocation t(4;11)(q21;q23) is the hallmark genetic abnormality associated with infant pro-B acute lymphoblastic leukemia (B-ALL) and has the highest frequency of rearrangement in Mixed-lineage leukemia (MLL) leukemias. Unlike other MLL translocations, MLL-AF4-induced proB-ALL is exceptionally difficult to model in mice/humans. Previous work has investigated the relevance of the reciprocal translocation fusion protein AF4-MLL for t(4;11) leukemia, finding that AF4-MLL is capable of inducing proB-ALL without requirement for MLL-AF4 when expressed in murine hematopoietic stem/progenitor cells (HSPCs). Therefore, AF4-MLL might represent a key genetic lesion contributing to t(4;11)-driven leukemogenesis. Here, we aimed to establish a humanized mouse model by using AF4-MLL to analyze its transformation potential in human cord blood-derived CD34+ HSPCs. We show that AF4-MLL-expressing human CD34+ HSPCs provide enhanced long-term hematopoietic reconstitution in primary immunodeficient recipients but are not endowed with subsequent self-renewal ability upon serial transplantation. Importantly, expression of AF4-MLL in primary neonatal CD34+ HSPCs failed to render any phenotypic or hematological sign of disease, and was therefore not sufficient to initiate leukemia within a 36-week follow-up. Species-specific (epi)-genetic intrinsic determinants may underlie the different outcome observed when AF4-MLL is expressed in murine or human HSPCs.
RESUMEN
The chromosomal translocation t(4;11)(q21;q23) is the most frequent genetic aberration of the human MLL gene, resulting in high-risk acute lymphoblastic leukemia (ALL). To elucidate the leukemogenic potential of the fusion proteins MLL.AF4 and AF4.MLL, Lin(-)/Sca1(+) purified cells (LSPCs) were retrovirally transduced with either both fusion genes or with MLL.AF4 or AF4.MLL alone. Recipients of AF4.MLL- or double-transduced LSPCs developed pro-B ALL, B/T biphenotypic acute leukemia, or mixed lineage leukemia. Transplantation of MLL.AF4- or mock-transduced LSPCs did not result in disease development during an observation period of 13 months. These findings indicate that the expression of the AF4.MLL fusion protein is capable of inducing acute lymphoblastic leukemia even in the absence of the MLL.AF4 fusion protein. In view of recent findings, these results may imply that t(4;11) leukemia is based on 2 oncoproteins, providing an explanation for the very early onset of disease in humans.
Asunto(s)
Transformación Celular Neoplásica/metabolismo , Proteínas de Unión al ADN/metabolismo , Regulación Leucémica de la Expresión Génica , Proteína de la Leucemia Mieloide-Linfoide/metabolismo , Proteínas Nucleares/metabolismo , Proteínas de Fusión Oncogénica/metabolismo , Leucemia-Linfoma Linfoblástico de Células Precursoras B/metabolismo , Animales , Transformación Celular Neoplásica/genética , Cromosomas de los Mamíferos/genética , Cromosomas de los Mamíferos/metabolismo , Proteínas de Unión al ADN/genética , N-Metiltransferasa de Histona-Lisina , Humanos , Masculino , Ratones , Proteína de la Leucemia Mieloide-Linfoide/genética , Proteínas Nucleares/genética , Proteínas de Fusión Oncogénica/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras B/genética , Transducción Genética , Translocación GenéticaRESUMEN
The human AF4 (ALL-1 fused gene on chromosome 4) gene (4q11) is recurrently involved in reciprocal translocations to the MLL (mixed lineage leukemia) gene (11q23), correlated with high-risk acute lymphoblastic leukemia (ALL) in infants and early childhood. The t(4;11) translocation is one of the most frequent MLL translocations known today. In general, MLL translocations are the result of an illegitimate recombination process leading to reciprocal fusions of unrelated translocation partner (TP) genes with the MLL gene. Owing to the constant presence of the derivative (11) product, it was hypothesised that only MLL.TP fusion genes are responsible for the leukemogenic process. This concept has been successfully tested for some known MLL fusions, while other MLL fusions failed. Here, we demonstrate growth-transforming potential of AF4 wild-type and the AF4.MLL fusion protein. The underlying oncogenic mechanism involves the two E3 ubiquitin ligases SIAH1 and SIAH2, the N-terminal portion of AF4 and the protection of the AF4.MLL fusion protein against proteosomal degradation.
Asunto(s)
Cromosomas Humanos Par 11 , Cromosomas Humanos Par 4 , Proteínas de Unión al ADN/metabolismo , Proteínas Nucleares/metabolismo , Proto-Oncogenes , Proteínas Recombinantes de Fusión/metabolismo , Factores de Transcripción , Translocación Genética , Animales , División Celular , Proteínas de Unión al ADN/genética , N-Metiltransferasa de Histona-Lisina , Humanos , Ratones , Proteína de la Leucemia Mieloide-Linfoide , Proteínas Nucleares/genética , Unión Proteica , Proteínas Recombinantes de Fusión/genética , Recombinación Genética , Factores de Elongación Transcripcional , Técnicas del Sistema de Dos Híbridos , Ubiquitina-Proteína LigasasRESUMEN
The determination of placental fatty acid metabolism using stable isotope-labeled tracers was investigated in the human placental choriocarcinoma (JAR) cell line. Stable isotope incorporation was measured by MDGC-MS. The cultured trophoblast cells incorporated and metabolized the essential fatty acids to long-chain polyunsaturated fatty acids. The described method enables the detection of a low Delta(6)-desaturase activity in this human placental cell line. The developed MDGC-MS method allows the assessment of long-chain polyunsaturated fatty acid biosynthesis in cultured cells with high sensitivity and selectivity. In this respect, tracer studies with MDGC-MS will be a powerful tool to clarify the significance of placental fatty acid metabolism.