Notch1 mutations are important for leukemic transformation in murine models of precursor-T leukemia/lymphoma

Abstract

NOTCH1 is frequently mutated in human precursor T-cell lymphoblastic leukemia/lymphoma (pre-T LBL). In the current study, we found that 13 of 19 cell lines and 29 of 49 primary tumors from SCL/LMO1, OLIG2/LMO1, OLIG2, LMO1, NUP98/HOXD13, and p27(-/-)/SMAD3(+/-) mice had Notch1 mutations in either the heterodimerization (HD) or the glutamic acid/serine/threonine (PEST) domain but not both. Thymocytes from clinically healthy SCL/LMO1 mice aged 5 weeks did not have Notch1 mutations, whereas thymocytes from clinically healthy SCL/LMO1 mice aged 8 to 12 weeks did have Notch1 mutations and formed tumors upon transplantation into nude mice. Remarkably, all of the HD domain mutations that we identified were single-base substitutions, whereas all of the PEST domain mutations were insertions or deletions, half of which mapped to 1 of 2 mutational "hot spots." Taken together, these findings indicate that Notch1 mutations are very frequent events that are acquired relatively early in the process of leukemic transformation and are important for leukemic cell growth.

Figure 1.

Notch1 mutations in preleukemic thymocytes. (A) Tcrb gene rearrangements in thymocytes from mouse 7151/4 and tumor resulting after transplantation into nude mouse (N5/2). Several oligoclonal rearrangements are evident in the thymocytes, whereas only 2 rearranged bands are seen in the tumor sample. Germ line bands are indicated with arrows. (B) An AluI site in the PEST domain was disrupted by the Notch1 mutation in the N5/2 sample. In 7151/4, the majority of the PCR product was wild type (211 bp), but a faint band (241 bp) indicated a small amount of the mutated allele. Sample 3917 is an SCL/LMO1 tumor that is wild type for the PEST domain used as a control. Restriction map for PEST domain PCR product. A indicates AluI sites; A^*, AluI site disrupted by Notch1 mutation. Size of fragments (bp) is indicated below the map.