Mutation of the casein kinase II phosphorylation site abolishes the anti-proliferative activity of p53

The p53 tumour suppressor protein is phosphorylated by several protein kinases, including casein kinase II. In order to understand the functional significance of phosphorylation by casein kinase II, we have introduced mutations at serine 386 in mouse p53, the residue phosphorylated by this kinase, and investigated their effects on the ability of p53 to arrest cell growth. Replacement of serine 386 by alanine led to loss of growth suppressor activity, while aspartic acid at this position partially retained suppressor function. These data suggest that the anti-proliferative activity of p53 is activated by phosphorylation at serine 386, and establish a direct link between the covalent modification of a growth suppressor protein and regulation of its activity in mammalian cells.