S100A6 binds p53 and affects its activity.

S100A6 (calcyclin) is a calcium-binding protein implicated in many cellular processes and often up-regulated in cancer. Its various biological effects possibly originate from the fact that it may bind to other proteins and modulate their function by inducing conformational changes or interfering with posttranslational modifications. Thus, to elucidate the biological role of S100A6 it is important to identify its targets. Here, we report, based on affinity chromatography and co-immunoprecipitation results that S100A6 interacts with p53 in the presence of calcium ions. We investigated functional implications of the S100A6-p53 interaction by comparing various aspects of p53 activity in HEp-2 cells with either unaltered or diminished S100A6 content due to stable expression of siRNA. We found that the presence of S100A6 results in higher p53 transcriptional activity which is also reflected by higher cell susceptibility to apoptosis evoked by hydrogen peroxide. As revealed by electrophoretic mobility shift assay (EMSA) S100A6 does not affect p53 binding to DNA. On the other hand, we observed that the presence of S100A6 coincides with more efficient nuclear accumulation of p53 under stress conditions. Collectively, our results indicate that S100A6 interacts with p53 and affects its biological activity.