DNase II and the Chk2 DNA damage pathway form a genetic barrier blocking replication of horizontally transferred DNA.
We have previously shown that DNA from dying tumor cells may be transferred to living cells via the uptake of apoptotic bodies and may contribute to tumor progression. DNA encoding H-ras(V12) and c-myc oncogenes may be transferred to the nucleus of the phagocyte but will only integrate and propagate in p53- and p21-deficient mouse embryonic fibroblasts, whereas normal cells are resistant to transformation. Here, we show that this protective mechanism (activation of p53 and p21 after uptake of apoptotic bodies) is dependent on DNA fragmentation, where inhibition of the caspase-activated DNase in the apoptotic cells, in conjunction with genetic ablation of lysosomal DNase II in the phagocytes, completely blocks p53 activation and consequently allows DNA replication of transferred DNA. We, therefore, suggest that there is a causal relationship between DNA degradation during apoptosis and p53 activation. In addition, we could further show that Chk2-/- cells were capable of replicating the hyg(R) gene taken up from engulfed apoptotic cells, suggesting involvement of the DNA damage response. These data show that the phagocytosing cell is sensing the degraded DNA within the apoptotic cell, hence preventing these genes from being replicated, probably through activation of the DNA damage response. We, therefore, hypothesize that DNase II together with the Chk2, p53, and p21 pathway form a genetic barrier blocking the replication of potentially harmful DNA introduced via apoptotic bodies, thereby preventing transformation and malignant development.
Cancer Center Karolinska Hospital, Karolinska Institutet, S-171 76 Stockholm, Sweden.
Anna
A
Bergsmedh
Jacob
J
Ehnfors
Kohki
K
Kawane
Noboru
N
Motoyama
Shigekazu
S
Nagata
Lars
L
Holmgren
D000818:Animals; D017209:Apoptosis; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D064447:Checkpoint Kinase 2; D018920:Coculture Techniques; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004249:DNA Damage; D053938:DNA Fragmentation; D004261:DNA Replication; D004273:DNA, Neoplasm / Q000235:genetics*; D003851:Deoxyribonucleases / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D022761:Gene Transfer, Horizontal; D051379:Mice; D010586:Phagocytes / Q000166:cytology; D010587:Phagocytosis; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D050759:Cyclin-Dependent Kinase Inhibitor p21; D004273:DNA, Neoplasm; D016159:Tumor Suppressor Protein p53; D064447:Checkpoint Kinase 2; C578633:Chek2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D003851:Deoxyribonucleases; D004706:Endodeoxyribonucleases; C109663:caspase-activated deoxyribonuclease; C019329:deoxyribonuclease II