Human papilloma virus 16 E6 oncoprotein associated with p53 inactivation in colorectal cancer.
OBJECTIVE
To investigate the association between human papilloma virus (HPV) infection and colorectal cancer.


METHODS
Sixty-nine patients with pathologically confirmed primary colorectal cancer including 6 stage I, 24 stage II, 21 stage III, and 18 stage IV patients were enrolled in this study to investigate whether HPV 16 could be involved in colorectal tumorigenesis. Nested-polymerase chain reaction (nested-PCR) was used to detect HPV16 DNA in colorectal tumor tissues and further confirmed by in situ hybridization (ISH). In addition, immunohistochemistry analysis was performed to examine the E6 oncoprotein in colorectal tumors. To verify whether E6 could inactivate the p53 transcriptional function, the levels of p21 and Mdm2 mRNA expression were evaluated by real-time reverse transcription (RT)-PCR.


RESULTS
Of the 69 colorectal tumors, HPV16 DNA was detected in 11 (16%) by nested-PCR, and HPV16 DNA was present in 8 of the 11 (73%) tumors which was confirmed by ISH. The presence of HPV16 DNA in colorectal tumors was not associated with patients' clinical parameters including age, gender, smoking status, tumor site; however, HPV16 infection was more common in stage I patients than in late-stages patients (II, III and IV). We next asked whether HPV16 infection could be linked with colorectal cancer development. Immunohistochemical data indicated that 8 of the 11 HPV16 DNA-positive tumors had E6 oncoprotein expression. Moreover, we also observed that the adjacent normal tissues including endothelial cells, lymphocytes, fibroblasts, and gland cells in E6-positive tumors had E6 oncoprotein expression. In addition, 3 of the 4 (75%) E6-positive tumors carrying p53 wild-type had negative immunostaining, but one tumor had less p53 immunostaining. We further examined whether E6-positive and/or p53 mutated tumors reduce p53 transcriptional activity. Real-time RT-PCR analysis indicated that p21 and mdm2 mRNA expression levels in E6/p53-wildtype tumors were significantly lower than in their adjacent normal tissues; as expected, E6-positive/p53-mutated tumors had lower p21 and mdm2 mRNA expression levels compared with their adjacent normal tissues. These results clearly indicate that the E6 oncoprotein expressed in p53 wildtype tumors may reduce p21 and mdm2 expression via p53 inactivation.


CONCLUSIONS
These results suggest that HPV16 infection may be involved in a subset of colorectal cancer, and we suggest that the transmission of HPV to the colon and rectum might occur through peripheral blood lymphocytes.
Institute of Medicine, Chung Shan Medical University, Taichung 402, Taiwan, China.
Tan-Hsia
TH
Chen
Chi-Chou
CC
Huang
Kun-Tu
KT
Yeh
Shu-Hau
SH
Chang
Shih-Wen
SW
Chang
Wen-Wei
WW
Sung
Ya-Wen
YW
Cheng
Huei
H
Lee
D000368:Aged; D000369:Aged, 80 and over; D003106:Colon / Q000821:virology; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D004279:DNA, Viral / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D052162:Human papillomavirus 16; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D030361:Papillomavirus Infections / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012007:Rectum / Q000821:virology; D012097:Repressor Proteins / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
D004279:DNA, Viral; C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D012333:RNA, Messenger; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2