RPA and ATR link transcriptional stress to p53.

Abstract

Our genome is constantly under attack from both endogenous and exogenous sources of DNA damaging agents. From endogenous sources alone a single cell incurs approximately 20,000 DNA damaging events per day. This DNA damage must be detected and repaired correctly each day in order to prevent mutations and suppress cancer formation. How our cells detect DNA damage is not well understood. RNA polymerase II (RNAPII) transcription has been proposed to function as a DNA damage sensor and dosimeter since it actively scans the DNA, can activate the DNA damage repair pathway transcription-coupled repair, or trigger cell death. This thesis presents further evidence that RNAPII transcription can act as a sensor for DNA damage by showing that inhibition of transcription leads to the phosphorylation of the tumor suppressor p53, indicative of p53 activation. Direct inhibition of RNAPII through microinjection of RNAPII antibodies into cells demonstrates that inhibition of RNAPII in the absence of DNA damage is sufficient to stimulate the phosphorylation of p53 on ser15. Next, inhibition of the single stranded DNA binding protein RPA and the cellular stress kinase ATR show that ser15 phosphorylation on p53 is mediated by RPA and ATR. Together RNAPII, RPA, ATR, and p53 form a novel cellular stress pathway termed the Transcription Stress Response The evidence in this thesis supports the idea that RNAPII transcription acts as a scanning device for DNA damage and activates a stress response that if the damage is overwhelming induces cell death, thus preventing the onset of tumorogenesis. Since RNAPII is linked to both DNA damage sensing and DNA damage repair pathways it may be an attractive target for novel cancer therapies. Many cancer cells rely on the continued expression of survival factors. Inhibition of RNAPII may alter the balance between survival and cell death factors increasing sensitivity of tumors to chemotherapeutic drugs.