Abstract
ABSTRACTPRDM14 is an epigenetic regulator known for maintaining embryonic stem cell identity and resetting potency in primordial germ cells. However, hematopoietic expression of Prdm14 at supraphysiological levels results in fully penetrant and rapid-onset T-cell acute lymphoblastic leukemia (T-ALL) in the mouse. Here, we show that PRDM14-induced T-ALLs are driven by NOTCH1, a frequently mutated driver of human T-ALL. Notch1 is activated in this murine model via RAG-dependent promoter deletions and subsequent production of truncated, ligand-independent protein from downstream regions of the Notch1 locus. These T-ALLs also have focal changes in H3K4me3 deposition at the Notch1 locus and global increases in both H3K4me1 and H3K4me3. Using a PRDM14-FLAG mouse model, we show that PRDM14 binds within an intron of Notch1 prior to leukemia development. Our data support the idea that PRDM14 binding promotes a chromatin state that allows access of the RAG recombinase complex to cryptic RAG signal sequences embedded at the Notch1 locus. Indeed, breeding into a RAG recombination-deficient background abrogates T-ALL development and prevents Notch1 deletions, while allowing for transient hematopoietic stem cell (HSC)-like pre-leukemia cell expansion. Together, our data suggest that PRDM14 expands a progenitor cell population while promoting a permissive epigenetic state for the creation of driver mutations (here, in Notch1), enabling cancer development through the misappropriation of endogenous cellular DNA recombination machinery.
Highlights
Factors that control normal growth and differentiation are often the main drivers of neoplasia
PRDM14-induced T-cell acute lymphoblastic leukemia (T-ALL) carry Notch1 5′ deletions that produce NOTCH1 intracellular domain (NICD) We previously showed that induction of R26PR in hematopoietic stem cell (HSC) by Mx1cre or MMTV-cre produced exclusively pre-T-cell ALLs, which express high levels of Notch1 mRNA, NICD protein, and NICD target genes (Carofino et al, 2013)
Because of experimental limitations resulting from the lack of a chromatin immunoprecipitation (ChIP)-grade PRDM14 antibody, we generated another inducible mouse line, ROSA26loxP-STOP-loxP-3XFLAG-PRDM14-P2A-eGFP (R26FLPR), which is similar to R26PR in construction except for the addition of an N-terminal 3×FLAG-tag to PRDM14 and the use of viral peptide 2A (P2A) instead of an internal ribosome entry site (IRES)
Summary
Factors that control normal growth and differentiation are often the main drivers of neoplasia. The PR domain shares 20-30% amino acid sequence identity with the SET domain, the catalytic component of most histone methyltransferases (HMTases) Received 21 February 2016; Accepted 10 April 2016 et al, 2013) Despite this homology, HMTase activity has been reported for only a small number of PRDM family members, suggesting that other PRDMs involved in epigenetic gene regulation may do so via association with catalytically active protein complexes (Fog et al, 2012). In ESCs, PRDM14 supports the maintenance of naïve pluripotency by global DNA hypomethylation and by interacting with polycomb repressive complex 2 (PRC2) to repress differentiation genes (Chan et al, 2013; Ma et al, 2011; Tsuneyoshi et al, 2008)
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