Ralhan R, Agarwal S, Mathur M, Wasylyk B, Srivastava A
Department of Biochemistry, All India Institute of Medical Sciences, Ansari Nagar, New Delhi.
Clin Cancer Res. 2000 Jun;6(6):2440-7.
The cyclin-dependent kinase inhibitor gene p21(Waf1/Cip1) plays a central role in inducing cellular growth arrest, terminal differentiation, and apoptosis. Alterations in this gene may adversely affect regulation of these processes and increase susceptibility for cancer. We have recently reported a novel polymorphism in the p21(Waf1/Cip1) gene in the Indian population and its association with esophageal cancer. An A-->G transition at codon 149 resulted in amino acid substitution from aspartate to glycine in the proliferating cell nuclear antigen binding COOH-terminal domain of p21(Waf1/Cip1) that may affect PCNA-p21(Waf1/Cip1) interactions, thereby affecting regulation of cellular proliferation, and may increase susceptibility for development of cancer. In a parallel study in our laboratory, we searched for putative p21(Waf1/Cip1) mutations in oral premalignant and malignant lesions. No somatic mutation was detected in exon 2 of p21(Waf1/Cip1). Interestingly, a codon 149 polymorphism variant (A-->G) was identified in 11 of 30 (37%) premalignant lesions (7 of 19 hyperplastic lesions and 4 of 11 dysplastic lesions) and 11 of 30 (37%) squamous cell carcinomas (SCCs). This codon 149 variant was also identified in paired lymphocytes of all of the patients with premalignant lesions and SCCs harboring the variant allele, suggesting the occurrence of a polymorphism. Lymphocyte DNA isolated from 50 unrelated age- and gender-matched healthy subjects was screened for this polymorphism. Seven of 50 (14%) normal controls harbored the A-->G codon 149 variant allele. Immunohistochemical analysis of p21(Waf1/Cip1) protein expression showed immunoreactivity in 19 of these 30 (63%) oral premalignant lesions and 16 of 30 (53%) SCCs. The most intriguing features of the study were: (a) the significant increase in frequency of this polymorphism not only in patients with oral SCCs (P = 0.038), but also in patients with premalignant lesions (P = 0.038), compared with normal controls; and (b) the significantly higher frequency of p21(Waf1/Cip1) variants (codon 149) in oral premalignant lesions (10 of 11 cases) and SCCs (11 of 11 cases) with wild-type p53 (P = 0.045) than in lesions with p53 mutations, suggesting that this polymorphism affects the p53 pathway and may play a vital role in oral tumorigenesis. Furthermore, overexpression of p21 protein in oral lesions harboring missense mutations in the p53 gene suggest a p53-independent role for p21 in the pathogenesis of oral cancer.
细胞周期蛋白依赖性激酶抑制剂基因p21（Waf1/Cip1）在诱导细胞生长停滞、终末分化和凋亡过程中发挥核心作用。该基因的改变可能会对这些过程的调节产生不利影响，并增加患癌易感性。我们最近报道了印度人群中p21（Waf1/Cip1）基因的一种新型多态性及其与食管癌的关联。密码子149处的A→G转换导致p21（Waf1/Cip1）增殖细胞核抗原结合COOH末端结构域中的天冬氨酸被甘氨酸取代，这可能会影响PCNA-p21（Waf1/Cip1）相互作用，从而影响细胞增殖的调节，并可能增加患癌易感性。在我们实验室的一项平行研究中，我们在口腔癌前病变和恶性病变中寻找p21（Waf1/Cip1）的推定突变。在p21（Waf1/Cip1）的外显子2中未检测到体细胞突变。有趣的是，在30例癌前病变中的11例（37%）（19例增生性病变中的7例和11例发育异常病变中的4例）和30例鳞状细胞癌（SCC）中的11例（37%）中鉴定出密码子149多态性变体（A→G）。在所有携带变体等位基因的癌前病变和SCC患者的配对淋巴细胞中也鉴定出了这种密码子149变体，提示存在多态性。对从50名年龄和性别匹配的无关健康受试者中分离的淋巴细胞DNA进行该多态性筛查。50名正常对照中有7名（14%）携带A→G密码子149变体等位基因。p21（Waf1/Cip1）蛋白表达的免疫组织化学分析显示，这30例口腔癌前病变中有19例（63%）和30例SCC中有16例（53%）呈免疫反应性。该研究最引人关注的特点是：（a）与正常对照相比，这种多态性的频率不仅在口腔SCC患者中显著增加（P = 0.038），在癌前病变患者中也显著增加（P = 0.038）；（b）野生型p53的口腔癌前病变（11例中的10例）和SCC（11例中的11例）中p21（Waf1/Cip1）变体（密码子149）的频率显著高于p53突变的病变（P = 0.045），提示这种多态性影响p53途径，可能在口腔肿瘤发生中起重要作用。此外，p53基因存在错义突变的口腔病变中p21蛋白的过表达提示p21在口腔癌发病机制中具有p53非依赖性作用。
