Protein phosphatase 4 regulates apoptosis, proliferation and mutation rate of human cells.

The proteins which regulate apoptosis are of great importance both in normal cell biological processes and in the development of pathology in the diverse diseases which involve apoptosis dysfunction. The activity of many of these proteins is controlled by reversible phosphorylation, so that the relevant kinases and phosphatases play crucial roles in apoptosis control. Here we report the analysis of the role of the serine/threonine protein phosphatase, protein phosphatase 4, in controlling the apoptosis of HEK 293 T cells, using the complementary techniques of gene over-expression and down regulation through RNA interference. This analysis has demonstrated that PP4 regulates both apoptosis and proliferation in human cells and has also shown that the level of PP4 has a strong influence on gene mutation rate, which is crucial to oncogenesis. A parallel proteomic analysis has shown that the phosphorylation status of many relevant protein targets is affected by changes in PP4 and has focused attention particularly on the critical apoptosis regulators Bad and PEA-15. The phosphorylation of both of these proteins is increased when PP4 levels are suppressed, and is reduced when PP4 levels are increased, with striking consequences for the fate of the cell.