Interference of protein phosphatase PP1 with the DNA-repair capacity

Cells have evolved elaborate sensing and repair mechanisms to deal with various types of DNA damage. We have found that the deletion of NIPP1, a substrate-targeting subunit of protein phosphatase PP1, dramatically increases the DNA-repair capacity. Conversely, the overexpression of PP1-NIPP1 in human cells induces numerous DNA lesions. Here, we propose to study the molecular mechanism(s) by which PP1-NIPP1 reduces the DNA-repair capacity and explore whether the activation of PP1-NIPP1 has therapeutic potential. First, knockout and overexpression models will be used to examine which DNA-repair pathways are regulated by PP1-NIPP1. Next, we will identify the DNA-repair substrates of PP1-NIPP1, using two novel substrate-mapping methods, and investigate how their dephosphorylation affects the expression, targeting and activity of specific DNA-repair factors. We will also engineer cells to allow the inducible activation of endogenous PP1-NIPP1 and examine whether this causes cell death in immortalized cells, before and after their oncogenic transformation. Finally, we will perform a screening for small-molecules that interfere with the interaction between PP1 and a PP1-inhibitory domain of NIPP1 and are predicted to activate PP1-NIPP1. These compounds will be tested for their effects on the viability of a broad panel of cancer cells. This project is expected to yield novel insights into the regulation of the DNA-repair capacity that can be exploited therapeutically.