Institute of Medicine, Chung Shan Medical University, Taichung 402, Taiwan, China.
World J Gastroenterol. 2012 Aug 14;18(30):4051-8. doi: 10.3748/wjg.v18.i30.4051.
To investigate the association between human papilloma virus (HPV) infection and colorectal cancer.
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.
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.
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.
探讨人乳头瘤病毒（HPV）感染与结直肠癌的关系。
本研究纳入 69 例经病理证实的原发性结直肠癌患者，包括 6 例Ⅰ期、24 例Ⅱ期、21 例Ⅲ期和 18 例Ⅳ期患者，以探讨 HPV16 是否参与结直肠肿瘤的发生。采用巢式聚合酶链反应（nested-PCR）检测结直肠肿瘤组织中的 HPV16 DNA，并通过原位杂交（ISH）进一步证实。此外，采用免疫组织化学分析检测结直肠肿瘤中的 E6 癌蛋白。为了验证 E6 是否能使 p53 转录功能失活，采用实时逆转录（RT）-PCR 评估 p21 和 Mdm2 mRNA 的表达水平。
在 69 例结直肠肿瘤中，巢式 PCR 检测到 11 例（16%）存在 HPV16 DNA，其中 8 例（73%）经 ISH 证实存在 HPV16 DNA。HPV16 DNA 存在于结直肠肿瘤中与患者的临床参数（年龄、性别、吸烟状态、肿瘤部位）无关，但 HPV16 感染在Ⅰ期患者中更为常见，而在晚期患者（Ⅱ、Ⅲ和Ⅳ期）中较少见。我们接下来探讨 HPV16 感染是否与结直肠癌的发生有关。免疫组化数据表明，11 例 HPV16 DNA 阳性肿瘤中有 8 例存在 E6 癌蛋白表达。此外，我们还观察到 E6 阳性肿瘤的相邻正常组织（包括内皮细胞、淋巴细胞、成纤维细胞和腺细胞）中也存在 E6 癌蛋白表达。此外，4 例 E6 阳性肿瘤中有 3 例（75%） p53 野生型肿瘤免疫组化阴性，但 1 例肿瘤 p53 免疫组化染色较弱。我们进一步研究了 E6 阳性和/或 p53 突变肿瘤是否降低 p53 转录活性。实时 RT-PCR 分析表明，E6/p53 野生型肿瘤中 p21 和 mdm2 mRNA 的表达水平明显低于其相邻正常组织；与预期一致，E6 阳性/p53 突变型肿瘤的 p21 和 mdm2 mRNA 表达水平明显低于其相邻正常组织。这些结果清楚地表明，p53 野生型肿瘤中表达的 E6 癌蛋白可能通过 p53 失活降低 p21 和 mdm2 的表达。
这些结果提示 HPV16 感染可能参与了结直肠癌的发生，我们推测 HPV 向结肠和直肠的传播可能通过外周血淋巴细胞进行。
