SummaryThe heritability of B cell chronic lymphocytic leukemia (CLL) is relatively high; however, no predisposing mutation has been convincingly identified. We show that loss or reduced expression of death-associated protein kinase 1 (DAPK1) underlies cases of heritable predisposition to CLL and the majority of sporadic CLL. Epigenetic silencing of DAPK1 by promoter methylation occurs in almost all sporadic CLL cases. Furthermore, we defined a disease haplotype, which segregates with the CLL phenotype in a large family. DAPK1 expression of the CLL allele is downregulated by 75% in germline cells due to increased HOXB7 binding. In the blood cells from affected family members, promoter methylation results in additional loss of DAPK1 expression. Thus, reduced expression of DAPK1 can result from germline predisposition, as well as epigenetic or somatic events causing or contributing to the CLL phenotype.

gastric intrinsic factor ͉ Imerslund-Grä sbeck syndrome ͉ intrinsic factor deficiency ͉ vitamin B 12 malabsorption ͉ megaloblastic anemia

Nuclear factor (NF)-jB is a positive regulator of tumour development and progression, but how it functions in normal cells leading to oncogenesis is not clear. As cellular senescence has proven to be an intrinsic tumour suppressor mechanism that cells must overcome to establish deregulated growth, we used primary fibroblasts to follow NF-jB function in cells transitioning from senescence to subsequent immortalization. Our findings show that RelA/p65 À/À murine fibroblasts immortalize at considerably faster rates than RelA/p65 þ / þ cells. The ability of RelA/p65 À/À fibroblasts to escape senescence earlier is due to their genomic instability, characterized by high frequencies of DNA mutations, gene deletions and gross chromosomal translocations. This increase in genomic instability is closely related to a compromised DNA repair that occurs in both murine RelA/p65 À/À fibroblasts and tissues. Significantly, these results can also be duplicated in human fibroblasts lacking NF-jB. Altogether, our findings present a fresh perspective on the role of NF-jB as a tumour suppressor, which acts in pre-neoplastic cells to maintain cellular senescence by promoting DNA repair and genomic stability.