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CtIP is a DNA end resection factor widely implicated in alternative end-joining (A-EJ)-mediated translocations in cell-based reporter systems. To address the physiological role of CtIP, an essential gene, in translocation-mediated lymphomagenesis, we introduced the T855A mutation at murine CtIP to nonhomologous end-joining and Tp53 double-deficient mice that routinely succumbed to lymphomas carrying A-EJ-mediated IgH-Myc translocations. T855 of CtIP is phosphorylated by ATM or ATR kinases upon DNA damage to promote end resection. Here, we reported that the T855A mutation of CtIP compromised the neonatal development of Xrcc4 -/- mice. Mechanistically, the T855A mutation limits DNA end resection length without affecting hairpin opening, translocation frequency, or fork stability. Meanwhile, after radiation, CtIP-T855A mutant cells showed a consistent decreased Chk1 phosphorylation and defects in the G2/M cell cycle checkpoint. Consistent with the role of T855A mutation in lymphomagenesis beyond translocation, the CtIP-T855A mutation also delays splenomegaly in λ-Myc mice. Collectively, our study revealed a role of CtIP-T855 phosphorylation in lymphomagenesis beyond A-EJ-mediated chromosomal translocation.Tp53 -/- mice and the IgH-Myc translocation-driven lymphomagenesis in DNA-PKcs -/- Tp53 -/- mice. Mechanistically, the T855A mutation limits DNA end resection length without affecting hairpin opening, translocation frequency, or fork stability. Meanwhile, after radiation, CtIP-T855A mutant cells showed a consistent decreased Chk1 phosphorylation and defects in the G2/M cell cycle checkpoint. Consistent with the role of T855A mutation in lymphomagenesis beyond translocation, the CtIP-T855A mutation also delays splenomegaly in λ-Myc mice. Collectively, our study revealed a role of CtIP-T855 phosphorylation in lymphomagenesis beyond A-EJ-mediated chromosomal translocation., Competing Interests: The authors declare no competing interest.

Richter syndrome (RS) represents the transformation of chronic lymphocytic leukemia to aggressive lymphoma. We explored intraclonal diversification (ID) of immunoglobulin genes in order to (i) follow the evolutionary history of the RS clone (ii) compare the role of ID in clonally related RS vs. clonally unrelated cases. Most (10/11, 90.9%) clonally related RS stem from the predominant clone observed at CLL diagnosis. One single RS had a transformation pattern compatible with sequential evolution from a secondary CLL subclone. Once RS transformation had occurred, all secondary CLL subclones disappeared and were substituted by the dominant RS clone with its own descendants. These observations suggest that genetic lesions associated with RS transformation are acquired by a cell belonging to the original CLL clone, rather than being progressively accumulated by later CLL subclones. Accordingly, most (9/11, 81.1%) clonally related RS harbored a genetic lesion disrupting TP53 that was already present, though at subclonal levels, in 5/11 (45.5%) samples of the paired CLL phase. A fraction of clonally related RS switched off ID (4/11, 36.4%) or reduced the levels of ID (5/11, 45.4%) at transformation. Conversely, all clonally unrelated RS harbored ID and were characterized by a significantly higher mutation frequency compared to clonally related RS (median: 1.18 × 10(-3) vs. 0.13 × 10(-3); p =0.002). These data indicate that (i) clonally related RS stems from a cell that is already present within the initial CLL clone and (ii) clonally unrelated and clonally related RS are biologically distinct disorders also in terms of antigen affinity maturation., (Copyright © 2011 UICC.)

Richter syndrome (RS) represents the transformation of chronic lymphocytic leukaemia (CLL) to aggressive lymphoma. Risk factors of CLL transformation to RS are only partly known. We explored the role of the host genetic background as a risk factor for RS occurrence. Forty-five single nucleotide polimorphisms (SNPs) known to be relevant for CLL prognosis were genotyped in a consecutive cohort of 331 CLL, of which 21 had transformed to RS. After correcting for multiple testing and adjusting for previously reported RS risk factors, the LRP4 rs2306029 TT variant genotype was the sole SNP independently associated with a higher risk of RS transformation (Hazard Ratio: 4·17; P = 0·001; q = 0·047). The enrichment of LRP4 TT genotype in RS was confirmed in an independent series (n = 44) used for validation purposes. The LRP4 protein was expressed in CLL (n =66). Bioinformatic analysis scored LRP4 rs2306029 as a variant with possible deleterious and damaging variant of LRP4. LRP4 genotyping may help the recognition of patients with increased risk of RS at the time of CLL diagnosis., (© 2010 Blackwell Publishing Ltd.)