Novel polymorphism in p21waf1/cip1 cyclin dependent kinase inhibitor gene:: association with human esophageal cancer

p21(waf1/cip1), an important regulator of the cell cycle, binds to PCNA and acts as a mediator of the growth suppressing and apoptosis promoting functions of p53. We report a hitherto unobserved polymorphism in the carboxy terminal domain (codon 149) of p21(waf1/cip1) gene, the domain encoding the PCNA binding motif, The codon 149 polymorphism (G (A) under bar T-->G (G) under bar T) was observed in 42 of 50 (84%) esophageal squamous cell carcinomas (ESCCs) and eight of 50 (16%) normal individuals, The resultant amino acid substitution from aspartate to glycine may have vital implication in PCNA mediated cell cycle regulation by p21(waf1/cip1). The second polymorphism at codon 31, involving a C-->A transversion at nucleotide 168 (AG (C) under bar-->AG (A) under bar) changing the amino acid from serine to arginine, was observed in 2/50 (4%) ESCCs at a relatively lower frequency in the Indian population than that reported in the West. No significant association was observed between p21(waf1/cip1) polymorphism at codon 149 and p21(waf1/cip1) protein expression in ESCC in this cohort of patients. Interestingly, the frequency of p21(waf1/cip1) variants (codon 149) in ESCCs (18 of 19 cases) with wild-type p53 was significantly higher than in tumors with p53 mutations, suggesting that this polymorphism affects the p53 pathway and may play an important role in esophageal tumorigenesis, Analysis of p21(waf1/cip1) expression in relation to p53 gene and protein status revealed its induction by p53-dependent as well as independent pathways in esophageal tumorigenesis.