Palazzo J P, Kafka N J, Grasso L, Chakrani F, Hanau C, Cuesta K H, Mercer W E
Department of Pathology, Kimmel Cancer Center, Jefferson Medical College, Philadelphia, PA 19107, USA.
Hum Pathol. 1997 Oct;28(10):1189-95. doi: 10.1016/s0046-8177(97)90257-4.
Genetic alterations in the p53 tumor suppressor gene are common in human colorectal cancers, occurring in approximately 70% of tumors. In vitro studies have shown that wild-type p53 is involved in controlling cell cycle checkpoint functions and apoptosis involved in the cytotoxic response induced by ionizing radiation and several anticancer chemotherapeutic agents. Wild-type p53 protein can transcriptionally activate the WAF gene, which encodes a cyclin-dependent kinase inhibitory protein, p21WAF1/C1PI protein, and transcriptionally repress the bcl-2 gene, which encodes an inhibitor of apoptosis. To learn more about the in vivo relationship between p53 protein and the expression of p21WAF1/C1PI and bcl-2 proteins in human colorectal cancers treated with radiation therapy, we examined the expression of these proteins by immunohistochemistry in pre-irradiated biopsy specimens and surgical specimens with residual tumor of 27 patients with colorectal carcinoma. Cell proliferation was measured using Ki-67 expression in the tumor cells. The p53 protein was not detected in normal colorectal mucosa, but it was expressed in 21 of 27 (78%) of pre-irradiated tumor samples and in 19 of 27 (70%) of post-irradiated tumors. Expression of the bcl-2 protein in normal colorectal mucosa was confined to the basal epithelial cells of the crypts. Diffuse bcl-2 staining was detected in tumor cells in 13 of 27 (48%) of pre-irradiated samples and in 14 of 27 (52%) of post-irradiated samples. p21WAF1/C1PI expression was detected in 14 of 27 (52%) of pre-irradiated samples but only in 7 of 27 (26%) of post-irradiated samples. No inverse relationship between expression of p53 protein and abnormal bcl-2 expression was apparent. p21WAF1/C1PI was expressed in most nonproliferating Ki-67-negative epithelial cells at the apical tips of the crypts in normal colorectal mucosa, but not in proliferating Ki-67-positive cells of adjacent adenomatous mucosa. An inverse relationship between Ki-67 and p21WAF1/C1PI expression was observed in normal colorectal mucosa and adjacent adenomatous mucosa. After radiation therapy, p53 protein accumulation did not change among residual tumors in 18 cases (three of which were initially negative and remained negative); in four cases there was a significant increase, and five cases had a substantial decrease of p53 expression. Aberrant bcl-2 expression is not correlated with expression of p53 and does not increase significantly in post-irradiated tumor cells. p21WAF1/C1PI expression is markedly reduced in tumor cells that survive radiation therapy.
p53肿瘤抑制基因的遗传改变在人类结直肠癌中很常见，约70%的肿瘤中会出现。体外研究表明，野生型p53参与控制细胞周期检查点功能以及电离辐射和几种抗癌化疗药物诱导的细胞毒性反应中的细胞凋亡。野生型p53蛋白可转录激活WAF基因，该基因编码一种细胞周期蛋白依赖性激酶抑制蛋白p21WAF1/C1PI蛋白，并转录抑制bcl-2基因，该基因编码一种凋亡抑制剂。为了更深入了解p53蛋白与接受放射治疗的人类结直肠癌中p21WAF1/C1PI和bcl-2蛋白表达之间的体内关系，我们通过免疫组织化学检测了27例结直肠癌患者放疗前活检标本和有残留肿瘤的手术标本中这些蛋白的表达。使用肿瘤细胞中的Ki-67表达来测量细胞增殖。在正常结直肠黏膜中未检测到p53蛋白，但在27例放疗前肿瘤样本中的21例（78%）和放疗后肿瘤中的19例（70%）中表达。正常结直肠黏膜中bcl-2蛋白的表达局限于隐窝的基底上皮细胞。在27例放疗前样本中的13例（48%）和放疗后样本中的14例（52%）的肿瘤细胞中检测到弥漫性bcl-2染色。在27例放疗前样本中的14例（52%）检测到p21WAF1/C1PI表达，但在放疗后样本中仅27例中的7例（26%）检测到。p53蛋白表达与异常bcl-2表达之间没有明显的负相关关系。p21WAF1/C1PI在正常结直肠黏膜隐窝顶端大多数不增殖的Ki-67阴性上皮细胞中表达，但在相邻腺瘤性黏膜增殖的Ki-67阳性细胞中不表达。在正常结直肠黏膜和相邻腺瘤性黏膜中观察到Ki-67与p21WAF1/C1PI表达呈负相关。放射治疗后，18例残留肿瘤中p53蛋白积累没有变化（其中3例最初为阴性且仍为阴性）；4例有显著增加，5例p53表达大幅下降。异常bcl-2表达与p53表达无关，且在放疗后肿瘤细胞中没有显著增加。放疗后存活的肿瘤细胞中p21WAF1/C1PI表达明显降低。
