Previously in the lab we found that RNA Pol II persists around TSS region and blocks replication progression throughout S phase, it subsequently leads to under-replication of TSS region. It has been shown that cells complete duplication of this region using G2/M DNA synthesis after RNA Pol II removal. Promoter proximal pausing is a key step to regulate transcription, and it is regulated by DSIF and NELF complexes. By modulating factors (SUPT5H and NELF-A) involved in regulating promoter proximal pausing, we can control the removal of RNA Pol II from TSS region and alter the level of G2/M DNA synthesis. Additionally, PARPi has been shown to increase mitotic DNA synthesis, and NELF is a known target for PARPi. Here we show that PARPi can also increase G2/M DNA synthesis. Our studies in U2OS cells showed that depletion of SUPT5H and NELF-A leads to no difference in PARPi sensitivity comparing to control cells but failed to rescue PARPi hypersensitivity in BRCA1 knockdown cells. Importantly, we discovered functional links between BRCA1 and BRCA2 with PPP factors. Knockdown of SUPT5H, BRCA1 and BRCA2 exhibit similar pattern of transcriptional defects, and co-depletion of either SUPT5H or NELF-A with BRCA1 can induce synthetic lethality. This may have an impact on the survival/relapse of BRCA1/BRCA2 mutated patients, by analysing BRCA1 and BRCA2 mutant ovarian and breast cancer patients’ clinical data, we found some associations between the expression level of DSIF and NELF complex subunits and patients’ overall survival and relapse rate
