Sequential mutations in Notch1, Fbxw7, and Tp53 in radiation-induced mouse thymic lymphomas

Abstract

T-cell acute lymphoblastic lymphomas commonly demonstrate activating Notch1 mutations as well as mutations or deletions in Fbxw7. However, because Fbxw7 targets Notch1 for degradation, genetic alterations in these genes are expected to be mutually exclusive events in lymphomagenesis. Previously, by using a radiationinduced Tp53-deficient mouse model for T-cell acute lymphoblastic lymphoma, we reported that loss of heterozygosity at the Fbxw7 locus occurs frequently in a Tp53-dependent manner. In the current study, we show that these thymic lymphomas also commonly exhibit activating Notch1 mutations in the proline-glutamic acidserine-threonine (PEST) domain. Moreover, concurrent activating Notch1 PEST domain mutations and single-copy deletions at the Fbxw7 locus occur with high frequency in the same individual tumors, indicating that these changes are not mutually exclusive events. We further demonstrate that although Notch1 PEST domain mutations are independent of Tp53 status, they are completely abolished in mice with germline Fbxw7 haploinsufficiency. Therefore, Notch1 PEST domain mutations only occur when Fbxw7 expression levels are intact. These data suggest a temporal sequence of mutational events involving these important cancer-related genes, with Notch1 PEST domain mutations occurring first, followed by Fbxw7 deletion, and eventually by complete loss of Tp53. (Blood. 2012; 119(3):805-809)

NOTCH1 mutations are associated with favourable long‐term prognosis in paediatric T‐cell acute lymphoblastic leukaemia: a retrospective study of patients treated on BCH‐2003 and CCLG‐2008 protocol in China

“…Inactivating mutations of FBXW7 , reported in about 20% of T‐ALL patients (Mansour et al , ; Kox et al , ; Zuurbier et al , ; Jenkinson et al , ), result in the inability of FBXW7 to bind the NOTCH1 PEST domain to perform proteolytic cleavage function, thereby increasing the half‐life of the ICN. Furthermore, reduction of FBXW7 activity could also play a role in the development of the disease (Jen et al , ). Therefore, many studies have investigated the impact of mutations of both FBXW7 and NOTCH1 on treatment outcome.…”

Genetic Analysis of T Cell Lymphomas in Carbon Ion-Irradiated Mice Reveals Frequent Interstitial Chromosome Deletions: Implications for Second Cancer Induction in Normal Tissues during Carbon Ion Radiotherapy

“…Protein coding regions were amplified by PCR from tumour cDNA using primers to produce a single amplicon from the Pten and Trp53 genes and several overlapping fragments from the Ikzf1 gene. For Notch1 , primers flanking the HD domain and flanking the PEST domain were used to amplify these two regions known to harbour the majority of Notch1 activating mutations [ 28 ]. PCR amplicons were isolated by excising bands after agarose gel electrophoresis, which were then purified and subjected to direct DNA sequencing using the original PCR primers and in some cases, additional internal primers.…”

Impact of NOTCH1/FBXW7 mutations on outcome in pediatric T-cell acute lymphoblastic leukemia patients treated on the MRC UKALL 2003 trial

“…21 Mutations in the NOTCH1 PEST domain and FBXW7 in the same patient are infrequent, and a mouse model of radiation-induced T-cell acute lymphoblastic lymphomas has shown that reduced Fbxw7 activity precludes the requirement for Notch1 PEST domain mutations for tumor development. 22 However, co-incident NOTCH1 HD domain and FBXW7 mutations do occur and, as with NOTCH1 HD and PEST domain mutations, act in synergy. 19,21,23 Several studies investigating the prognostic significance of NOTCH1 and FBXW7 mutations in pediatric T-ALL have been published.…”