The role of PARP10 in alleviating replication stress and promoting cellular proliferation and tumorigenesis

Project Summary Identification of molecular pathways that are preferentially employed and relied upon by cancer cells compared to normal cells is key to designing novel personalized cancer therapies. PARP10 is a poorly characterized member of the PARP family. We previously showed that PARP10 promotes translesion synthesis (TLS)- mediated bypass of DNA lesions during DNA replication, thereby alleviating replication stress. More recently, we also showed that PARP10 is a novel oncogene. We found that the PARP10 gene is amplified and/or overexpressed in a large number of tumors including breast and ovarian, with very few observed occurrences of downregulation or loss. We found that the PARP10 gene is amplified and/or overexpressed in a large proportion of human tumors including breast and ovarian, with almost no occurrences of downregulation or loss. Moreover, we found that PARP10 overexpression in, non-transformed human epithelial RPE1 cells results in enhanced proliferation, resistance to replication stress, and increased xenograft tumor formation in immunocompromised mice. The opposing phenotypes were found upon knockout of PARP10 in cancer HeLa cells. These findings suggest that PARP10 is a putative oncogene and its expression promotes tumor formation and growth. Mutagenic TLS has been previously proposed to promote transformation by both allowing hyper-proliferation and inducing genomic instability. Thus, we hypothesize that PARP10 expression suppresses replication stress through TLS-mediated bypass of replication arresting structures, thereby allowing hyper-proliferation of cancer cells. We propose here to directly test this, in three specific aims which address the hypothesis at three different levels: Aim 1 will investigate the mechanism employed by PARP10 to modulate PCNA-dependent TLS at the molecular level, using biochemical and cellular localization and interaction assays. Aim 2 will functionally test the impact of this mechanism of cellular processes including genomic stability and DNA replication. Aim 3 will employ a mouse genetic model to unambiguously investigate if Parp10 expression induces tumor formation or promotes tumor growth. Using state-of-the-art cellular, molecular and genomic tools (including: CRISPR/Cas9-mediated genome editing; molecular DNA fiber combing to measure fork stability; next generation sequencing approaches to measure mutagenesis and mutation burden) we will investigate here the molecular mechanisms underlying this novel oncogenic function of PARP10. This may eventually result in validation of a new target for cancer therapy.