The Quiescent Cellular State is Arf/p53-Dependent and Associated with H2AX Downregulation and Genome Stability

Cancer is a disease associated with genomic instability and mutations. Excluding some tumors with specific chromosomal translocations, most cancers that develop at an advanced age are characterized by either chromosomal or microsatellite instability. However, it is still unclear how genomic instability and mutations are generated during the process of cellular transformation and how the development of genomic instability contributes to cellular transformation. Recent studies of cellular regulation and tetraploidy development have provided insights into the factors triggering cellular transformation and the regulatory mechanisms that protect chromosomes from genomic instability

CPP32/Yama/apopain cleaves the catalytic component of DNA-dependent protein kinase in the holoenzyme

AbstractDNA-dependent protein kinase (DNA-PK) is composed of a 460-kDa catalytic component (p460) and a DNA-binding component Ku protein. Immunoblot analysis after treatment of Jurkat cells with anti-Fas antibody demonstrated the cleavage of p460 concomitantly with an increase in CPP32/Yama/apopain activity. Recombinant CPP32/Yama/apopain specifically cleaved p460 in the DNA-PK preparation that had been purified from Raji cells into 230- and 160-kDa polypeptides, the latter of which was detected in anti-Fas-treated Jurkat cells. The regulatory component Ku protein was not significantly affected by CPP32/Yama/apopain. DNA-PK activity was decreased with the disappearance of p460 in the incubation of DNA-PK with CPP32/Yama/apopain. These results suggest that the catalytic component of DNA-PK is one of the target proteins for CPP32/Yama/apopain in Fas-mediated apoptosis

DNA Lesions Induced by Replication Stress Trigger Mitotic Aberration and Tetraploidy Development

During tumorigenesis, cells acquire immortality in association with the development of genomic instability. However, it is still elusive how genomic instability spontaneously generates during the process of tumorigenesis. Here, we show that precancerous DNA lesions induced by oncogene acceleration, which induce situations identical to the initial stages of cancer development, trigger tetraploidy/aneuploidy generation in association with mitotic aberration. Although oncogene acceleration primarily induces DNA replication stress and the resulting lesions in the S phase, these lesions are carried over into the M phase and cause cytokinesis failure and genomic instability. Unlike directly induced DNA double-strand breaks, DNA replication stress-associated lesions are cryptogenic and pass through cell-cycle checkpoints due to limited and ineffective activation of checkpoint factors. Furthermore, since damaged M-phase cells still progress in mitotic steps, these cells result in chromosomal mis-segregation, cytokinesis failure and the resulting tetraploidy generation. Thus, our results reveal a process of genomic instability generation triggered by precancerous DNA replication stress

Involvement of DNA-dependent protein kinase in down-regulation of cell cycle progression.

The catalytic polypeptide of DNA-dependent protein kinase (p470) is encoded by the gene responsible for murine severe combined immunodeficiency (SCID) devoid of DNA double-strand break repair and V(D)J recombination. Here, we have characterized the role of p470 in cell proliferation using SCID mice and the cell lines. In accord with DNA histogram patterns, SCID cell lines (SD/SD-eA and SC3VA2) expressing extremely low level of DNA-PK activity grew faster than a normal mouse cell line (CB/CB-eB) and SC3VA2 complemented with human p470 gene (RD13B2). In regenerating liver after partial hepatectomy, de novo DNA synthesis determined by [(3)H]thymidine incorporation started at 30h in C.B-17/Icr-SCID (SCID) mice and at around 36h in C.B-17/Icr (C.B-17) mice. Compared with normal cells, SCID cells contained slightly higher levels of transcripts of cyclin A, cyclin E, B-Myb and dihydrofolate reductase, which are regulated by E2F-1. E2F-1 playing a key role in G1- to S-phase progression was phosphorylated in vitro by DNA-PK. Importantly, the E2F-1 promoter transcriptional activity in SCID cell lines (SD/SD-eA and SC3VA2) was 4-5-fold higher than that in CB/CB-eB and RD13B2. These results suggest that p470 is involved in down-regulation of cell cycle progression through E2F-1-responsible genes