CREBBP Mutations In Relapsed Acute Lymphoblastic Leukemia

Abstract

413 Relapsed acute lymphoblastic leukemia (ALL) is a leading cause of death due to disease in young people, but the biologic determinants of treatment failure remain poorly understood. To identify novel sequence mutations contributing to relapsed in ALL, we resequenced 300 genes in matched diagnosis and relapse samples from 23 patients with ALL. The cohort included B-progenitor ALL with high hyperdiploidy (N=3), TCF3-PBX1 (N=1), ETV6-RUNX1 (N=3), rearrangement of MLL (N=3), BCR-ABL1 (N=3), and low hyperdiploid, pseudodiploid, or miscellaneous karyotypes (N=10). This identified 52 somatic non-synonymous mutations in 32 genes, many of which were novel, including mutations in the transcriptional coactivators CREBBP and NCOR1, the transcription factors ERG, SPI1, TCF4 and TCF7L2, components of the Ras signalling pathway, histone genes, genes involved in histone modification (CREBBP and CTCF), and genes previously shown to be targets of recurring DNA copy number alteration in ALL. Analysis of an extended cohort of 63 diagnosis-relapse cases and 200 acute leukaemia cases that did not relapse found that 19% of relapse cases had sequence or deletion mutations of CREBBP, which encodes the transcriptional coactivator and histone acetyltransferase (HAT) CREB-binding protein (CBP). The mutations were either present at diagnosis, acquired at relapse, or duplicated to homozygosity at the time of relapse. Moreover, several mutations acquired at relapse were detected in subclones at diagnosis, suggesting that the mutations confer a selective advantage and promote resistance to therapy. The mutations either resulted in truncated alleles or deleterious substitutions in highly conserved residues of the HAT domain. To examine the functional consequences of the mutations, we introduced wild type or mutant Crebbp alleles into Cbp/Ep300flox/flox murine embryonic fibroblasts, (dKO MEFs), and examined histone acetylation, expression of CREBBP target genes, and cellular proliferation. The HAT domain mutations resulted in impaired acetylation of the key Crebbp substrate, H3K18, and resulted in impaired transcriptional regulation of multiple CREBBP targets and pathways, including cAMP, dsRNA and dexamethasone responsive genes. The latter observation suggests that CREBBP mutations may directly result in resistance to corticosteroid therapy, which is a hallmark of high risk ALL. Together, these data these results extend the landscape of genetic alterations in leukemia, and identify mutations targeting transcriptional and epigenetic regulation as a mechanism of resistance in ALL. Disclosures: Pui: EUSA Pharma: Honoraria; Enzon: Honoraria; Sanofi-Aventis: Honoraria.

Inactivating mutations of acetyltransferase genes in B-cell lymphoma

“…Previous extensive surveys in malignancies of epithelial origin have reported inactivating mutations of EP300 and CREBBP in exceedingly rare cases (<2% of primary biopsies) 26 – 28 . Considering their virtual absence in solid tumors, and the finding of recurrent mutations in B-ALL 34 , our results point to a specific role for CREBBP/EP300 inactivation in the pathogenesis of malignancies derived from B-lymphocytes. Overall, CREBBP/EP300 lesions are among the most frequent structural alterations yet detected in FL and DLBCL, thus representing an important feature of the pathogenesis of these common diseases.…”

“…S2 ). This analysis also revealed the existence of several mutational hotspots at specific codons within the HAT domain, including R1446, also mutated in B-cell acute lymphoblastic leukemia (B-ALL) 34 , Y1503 and D1435; in addition, a 3bp in-frame deletion causing the loss of S1680 was observed in 5 cases, suggesting a functional role for this presently uncharacterized serine ( Table S1 ). None of these recurrent changes were detected in paired normal DNA, thus excluding that they represent germline polymorphisms.…”

Resolving fate and transcriptome of hematopoietic stem cell clones

“…S11C). The transcription factor Hoxb2, which is more highly expressed in inactive HSC, has previously been found to be overexpressed in acute myeloid leukemia (28). Therefore, Hoxb2 might be an inhibitor of HSC differentiation.…”

Genetic mutational analysis of pediatric acute lymphoblastic leukemia from a single center in China using exon sequencing

“…Rare germline mutations in the genes PAX5 [9] and ETV6 [10] were found to be linked to familial leukemia, and some chemical agents or radiation exposure could increase the incidence of leukemia [6]. In addition, some molecular alterations, such as CREBBP [11][12][13], NT5C2 [14,15] and PRPS1 mutations [16], are associated with chemo-resistance. Thus, the identification of these abnormalities not only reveals molecular pathology, but also provides important therapeutic targets.…”