The p53 pathway in breast cancer

Abstract

p53 mutation remains the most common genetic change identified in human neoplasia. In breast cancer, p53 mutation is associated with more aggressive disease and worse overall survival. The frequency of mutation in p53 is, however, lower in breast cancer than in other solid tumours. Changes, both genetic and epigenetic, have been identified in regulators of p53 activity and in some downstream transcriptional targets of p53 in breast cancers that express wild-type p53. Molecular pathological analysis of the structure and expression of constituents of the p53 pathway is likely to have value in diagnosis, in prognostic assessment and, ultimately, in treatment of breast cancer.

Figure 1

A simplified model of some of the components of p53 signalling. Under normal conditions, the p53 pathway operates on 'standby' mode. Activation occurs in response to a variety of cellular stresses such as DNA damage and expression of activated oncogenes. See [1] for a more detailed description of the pathways activated by specific stresses. Post-translational modifications (such as phosphorylation at the indicated serine residues) activate the protein for DNA binding and transactivation of downstream 'effector' genes that mediate the tumour suppressor actions of p53. The outcome of activation depends on the nature and magnitude of the stress, its transduction via specific upstream kinases, and the resultant programme of p53-dependent gene expression. Transcriptional coactivators such as apoptosis stimulating protein of p53 and BRCA1 (not shown) may further 'fine tune' the response and, in some cases, preferentially promote specific cellular responses such as apoptosis. Many of the components of this signalling pathway are targets for genetic and/or epigenetic changes in breast cancer as described in the text. Not shown is the induction of MDM2, which acts as a negative feedback regulator of the pathway by promoting the degradation of p53. Because of space limitations, other important constituents of the pathway have had to be omitted.