LEF1 Gene Mutations In Childhood T-Cell Acute Lymphoblastic Leukemia and T Cell Non-Hodgkin's Lymphoma

Abstract 276

LEF1 is a member of the LEF/TCF family of DNA-binding transcription factors, which interact with beta-catenin in the WNT signaling pathway. N-terminal LEF1 mutations that impair beta-catenin binding are commonly found inhuman sebaceous skin tumors, and expression of an N-terminal–deleted Lef1 mutant that lacks the beta-catenin binding domain leads to sebaceous skin tumors. The intracellular domain of NOTCH1 has also been shown to function as a co-activator of LEF1, leading to the up-regulation of target genes distinct from those activated by beta-catenin binding. Recently, inactivating mutations of LEF gene have been reported in T-cell acute lymphoblastic leukemia (T-ALL) cases. In this study, we analyzed the frequencies and clinical significance of LEF1 mutations in pediatric T-ALL and T-cell non-Hodgkin's lymphoma (T-NHL). Mutation analysis was performed on 138 of the primary T-ALL and T-NHL patient samples. The clinical data were available 55 newly diagnosed T-ALL and 14 T-NHL patients. These children, aged under 15 years were enrolled into the Japan Association of Childhood Leukemia Study (JACLS) protocol ALL-97 between 1997–2001 and JACLS trial NHL-T98 between 1998–2002. At the time of diagnosis, bone marrow and/or peripheral blood cells were obtained from T-ALL patients and lymph nodes and/or pleural effusions were obtained from T-NHL patients. A total of 69 patients were included in the present study; 49 were male and 20 female; 55 were children diagnosed with T-ALL (median age of 9.5 years; range: 2.0 – 15.0 years) and 14 with T-NHL (median age of 11.0 years; range: 3.7 – 15.0 years). We performed high-resolution array comparative genomic hybridization (array CGH) and sequencing was performed on the entire coding region of LEF1. High molecular weight genomic DNA was used for microarray analysis using Affymetrix GeneChip 50K XbaI, HindIII or 250K NspI, according to the manufacturer's instructions. Genome-wide detection of allelic imbalances was performed using CNAG/AsCNAR software. We identified mono or biallelic LEF1 deletions in 7.5% (5 of 67) of these primary samples. An additional 11.6% (16 of 138) of the cases harbored sequence alterations of LEF1 gene. Twelve of the single nucleotide alterations were found in exons 1, 2 and 3, and four of the frame-shift mutations were found in exons 3, 7, and 8. Frame-shift mutations were novel LEF1 mutations, and mutations in exons 3 and 8 were positioned outside catalytic domain and DNA binding region. Missense mutations in exon 1 were located highly conservative lesion of beta-catenin binding domain of LEF1. Of the 8 LEF1 alterations detected in 16 cases also had NOTCH1 mutations. Analysis of the available clinical data showed that LEF1 gene alteration was not a significant predictor of event-free survival in children with T-ALL treated in JACLS ALL-97 and NHL-T98 protocol. However, LEF1 inactivation was associated with a younger age at the time of diagnosis, but not with sex, white blood cell count, central nervous system involvement, or the presence of an anterior mediastinal mass at the time of diagnosis. Furthermore, analysis of the T-ALL cell surface immunophenotype obtained at the time of diagnosis showed that all LEF1-alterd cases were characterized by developmental arrest at a cortical stage of T-cell differentiation. The clinical significance of these gene alterations and detailed data is discussed.