Comparative analysis of Nuclear and Cytoplasmic p21 Expression with p53 and cdk2 Expression in Canine Tumours

The present study was undertaken to evaluate the comparative expression of cell cycle regulators- p53, p21 and cdk2 in spontaneous canine tumours. Out of 46 cases diagnosed as tumour by histopathology, 19 were benign and 27 were malignant. Expression of p53, p21 and cdk2 was analyzed by employing immunohistochemical staining technique and their expression was detected in 84.62%, 69.23% and 69.23% cases, respectively. The percent expressions of p53, p21 and cdk2 showed variation among different histopathological types of tumours. Visceral/mucosal tumours exhibited higher expression of p53 when compared to
cutaneous tumours. Expression of p21 was found to be 62.5% and 80% whereas cdk2 was 68.75% and 70% in skin and visceral/mucosal tumours, respectively. Analysis of individual cases for the expression and localization of these three biomarkers revealed seven different patterns. Out of 15 tumours which showed both p53 and p21 overexpression, 11 tumours showed cytoplasmic expression of p21 along with overexpression of cdk2, which indicated that cytoplasmic p21 was not able to perform its normal function of blocking the expression of cdk2. Overexpression of p53 along with cdk2 was observed in 5 cases where p21 expression was totally absent indicating overexpression of abnormal or mutated p53 which was not able to induce the expression of p21 leading to overexpression of cdk2. From present study it can be concluded that cytoplasmic or abnormal p21 expression is induced by either the abnormal/mutated p53 or any other pathway independent of p53.