Anti-p21 Protein mouse monoclonal, WA-1, supernatant

p21 is a nuclear 21 kD protein, a product of the WAF-1/CIP1 gene. It is a constituent of a large complex of nuclear proteins, including cyclins, cyclin dependent kinases and PCNA. After activation by the wild type tumor suppressor protein p53, WAF-1 acts as an inhibitor of the cell cycle during G1 phase. Normal cells generally display a rather intense nuclear p21 expression. In several malignancies (e.g. breast cancer, bladder cancer, head and neck scc) it has been shown that the presence of mutations in the p53 gene are of prognostic significance. Demonstration of low expression of p21 in a p53 positive tumor will increase the likelihood of the presence of a p53 mutation. p21 immunostaining is therefore most often used in combination with p53 to confirm the presence of a p53 mutation. Overexpression of p53 with normal intensity of p21 argues against a p53 mutation, while p53 overexpression in combination of low or absent p21 expression is consistent with a p53 mutation. Positive control: Tonsil.