Takayuki Ikezoe

Mutations of the CHK2 gene are found in some osteosarcomas, but are rare in breast, lung, and ovarian tumors.

Checkpoint genes, activated in response to DNA damage and other stresses, are frequently targeted for alteration in cancer. Checkpoint kinase 2 (CHK2, CDS1, RAD53) is activated by ataxia telangiectasia mutated (ATM) in response to γ irradiation. Activated CHK2 stabilizes TP53, and acts on other cell cycle and stress regulators. These findings place CHK2 in the middle of a pathway frequently targeted in cancer. Because of this, and the observation that CHK2 mutations are inherited in some Li‐Fraumeni cancer syndrome families, we decided to examine the role of CHK2 mutations in sporadic cancers. Exploiting the genomic sequence of chromosome 22, we looked for mutations in the exons and intron junctions of the CHK2 gene in DNA samples from 170 patients (57 osteosarcomas, 25 other sarcomas, 35 nonsmall‐cell lung, 20 ovarian, and 33 breast cancers). Missense mutations affecting the forkhead and kinase domains were detected in four osteosarcomas and in one ovarian and one lung cancer. These findings of CHK2 gene mutations are consistent with osteosarcoma being a defining tumor of Li‐Fraumeni syndrome. The occurrence of CHK2 mutations in sporadic cancers emphasizes the importance of the stress pathway which includes TP53.

C/EBP-β, C/EBP-δ, PU.1, AML1 genes: mutational analysis in 381 samples of hematopoietic and solid malignancies

Abstract Mutations of transcription factors are associated with the pathogenesis of cancer. Genomic DNA from 381 cancers and cell lines representing leukemias, lymphomas and a variety of solid tumors were examined for mutations of genes coding for the C/EBP-β, C/EBP-α, PU.1, and AML1 transcription factors using single strand conformation polymorphism (SSCP) and direct DNA sequencing. Mutation of C/EBP-β (a chronic myelogenous leukemia cell line, Kcl22) and C/EBP-δ (a Burkitt’s lymphoma cell line, Raji) were found. Interestingly, the sample with a C/EBP-β alterations had two missense (P236L and G252A) and two silent mutations in a highly conserved region of the gene. The C/EBP-δ alteration in Raji was a missense mutation (A177G). These findings suggest that mutations of the C/EBP-β, C/EBP-δ, PU.1, and AML1 rarely contribute to the development of hematopoietic or solid cancers.

Mutation analysis of the DNA-damage checkpoint gene CHK2 in myelodysplastic syndromes and acute myeloid leukemias.

Checkpoint genes code for a family of proteins which sense DNA damage in eukaryotic cells. They play an important role in the control of the cell cycle. The human CHK2 is a homolog of the yeast G(2) checkpoint kinases known as CDS1 and RAD53. The CHK2 may be a tumor suppressor gene because it was found to be mutated in some individuals with the Li-Fraumeni syndrome. These cases had a normal, non-mutated p53 gene. We performed a mutational analysis of the CHK2 gene using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) in 41 bone marrow samples from individuals with myelodysplastic syndrome (MDS) and 41 samples of acute myeloid leukemias (AML). We found a novel G to C transversion resulting in a change from Ala to Gly at codon 507 of CHK2 in one MDS sample, but normal cells from this individual did not have the abnormality. In addition, we demonstrated a previously described polymorphism at codon 84 (A to G at nucleotide 252) of exon 1 of CHK2 in three of 41 MDS and three of 41 AML patients. The presence of a CHK2 mutation in MDS highlights the importance of alterations of cell cycle checkpoint genes in this disease.