DNA damage signaling is activated during cancer progression in human colorectal carcinoma.
OBJECTIVE
Recent studies have shown that the DNA damage response (DDR) is activated in precancerous lesions, suggesting that neoplastic cells may avoid apoptosis by impairing the DDR which acts as a barrier against tumor progression. To define the role of the DDR pathway in human colorectal carcinoma, we investigated the level of phosphorylated proteins of the DDR pathway.


RESULTS
Immunostaining for pATM, gammaH2AX and pChk2 revealed that all were significantly expressed during tumor progression in advanced carcinoma (vs. normal tissue for pATM [p < 0.05]; vs. normal and adenoma for gammaH2AX [p < 0.05]; and vs. normal tissue for pChk2 [p < 0.05]. Western blot analysis of gammaH2AX and pChk2 revealed that their level increased gradually during tumor progression and was maximal in advanced carcinoma (vs. normal tissue; p < 0.05). No apoptotic cells were found in any tissue sample.


METHODS
Colorectal tissue samples were obtained at the time of surgery, from 55 patients at two hospitals. The tissues were classified into four groups according to pathology: normal mucosa, adenoma, early carcinoma and advanced carcinoma. We evaluated phosphorylated ataxia telangiectasia mutated (pATM), phosphorylated H2AX (gammaH2AX) and Chk2 (pChk2) protein levels by immunohistochemistry and western blot analysis. We also evaluated apoptosis by the TUNEL assay.


CONCLUSIONS
The DDR pathway was activated during cancer progression, but no apoptosis was detected, even among the cells with activated DDR. It is likely that activation of DDR was induced by stress signaling as a consequence of oxidative, replication and mechanical stresses occurring during growth and expansion of the colorectal cancer.
Oka
Kazuhito
K
Department of Surgery and Clinical Science, Yamaguchi University Graduate School of Medicine, Yamaguchi, Japan.
Tanaka
Toshiki
T
Enoki
Tadahiko
T
Yoshimura
Koichi
K
Ohshima
Mako
M
Kubo
Masayuki
M
Murakami
Tomoyuki
T
Gondou
Toshikazu
T
Minami
Yoshihide
Y
Takemoto
Yoshihiro
Y
Harada
Eijirou
E
Tsushimi
Takaaki
T
Li
Tao-Sheng
TS
Traganos
Frank
F
Darzynkiewicz
Zbigniew
Z
Hamano
Kimikazu
K
D000236:Adenoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism*; D064447:Checkpoint Kinase 2; D003106:Colon / Q000378:metabolism / Q000473:pathology; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018450:Disease Progression; D005260:Female; D006657:Histones / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D011446:Prospective Studies; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012007:Rectum / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D055815:Young Adult
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D025521:Tumor Suppressor Proteins; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases