Schiewer MJ, Mandigo AC, Gordon N, Huang N, Gaur S, de Leeuw R, Zhao SG, Evans J, Han S, Parsons T, Birbe R, McCue P, McNair C, Chand SN, Cendon-Florez, Gallagher P, McCann JJ, Neupane NP, Shafi AA, Dylgjieri A, Brand LJ, Visakorpi T, Raj GV, Lallas CD, Trabulsi EJ, Gomella LG, Dicker AP, Kelly WK, Leiby BE, Knudsen B, Feng FY, and Knudsen KE (2018) PARP1 regulates DNA repair factor availability. EMBO Mol Med, 2018 Dec;10(12). pii: e8816. doi: 10.15252/emmm.201708816.
PARP-1 holds major functions on chromatin, DNA damage repair and transcriptional regulation, both of which are relevant in the context of cancer. Here, unbiased transcriptional profiling revealed the downstream transcriptional profile of PARP-1 enzymatic activity. Further investigation of the PARP-1-regulated transcriptome and secondary strategies for assessing PARP-1 activity in patient tissues revealed that PARP-1 activity was unexpectedly enriched as a function of disease progression and was associated with poor outcome independent of DNA double-strand breaks, suggesting that enhanced PARP-1 activity may promote aggressive phenotypes. Mechanistic investigation revealed that active PARP-1 served to enhance E2F1 transcription factor activity, and specifically promoted E2F1-mediated induction of DNA repair factors involved in homologous recombination (HR). Conversely, PARP-1 inhibition reduced HR factor availability and thus acted to induce or enhance "BRCA-ness". These observations bring new understanding of PARP-1 function in cancer and have significant ramifications on predicting PARP-1 inhibitor function in the clinical setting.
McNair C, Xu K, Mandigo A, Benelli M, Leiby B, Rodrigues D, Lindberg J, Gronberg H, Crespo M, De Laere B, Dirix L, Visakorpi T, Li F, Feng F, De Bono J, Demichelis F, Rubin MA, Brown MA, and Knudsen KE (2017) Differential impact of RB status on E2F1 reprogramming in human cancer. J Clin Invest, Jan 2;128(1):341-358. doi: 10.1172/JCI93566. Epub 2017 Dec 4.
The tumor suppressor protein retinoblastoma (RB) is mechanistically linked to suppression of transcription factor E2F1-mediated cell cycle regulation. For multiple tumor types, loss of RB function is associated with poor clinical outcome. RB action is abrogated either by direct depletion or through inactivation of RB function; however, the basis for this selectivity is unknown. Here, analysis of tumor samples and cell-free DNA from patients with advanced prostate cancer showed that direct RB loss was the preferred pathway of disruption in human disease. While RB loss was associated with lethal disease, RB-deficient tumors had no proliferative advantage and exhibited downstream effects distinct from cell cycle control. Mechanistically, RB loss led to E2F1 cistrome expansion and different binding specificity, alterations distinct from those observed after functional RB inactivation. Additionally, identification of protumorigenic transcriptional networks specific to RB loss that were validated in clinical samples demonstrated the ability of RB loss to differentially reprogram E2F1 in human cancers. Together, these findings not only identify tumor-suppressive functions of RB that are distinct from cell cycle control, but also demonstrate that the molecular consequence of RB loss is distinct from RB inactivation. Thus, these studies provide insight into
Dylgjeri E, McNair C, Goodwin JF, Raymon HK, McCue PA, Shafi AA, Leiby BE, de Leeuw R, Kothari V, McCann JJ, Mandigo AC, Chand SN, Schiewer MJ, Brand LJ, Vasilevskaya IA, Gordon N, Laufer TS, Gomella LG, Lallas CD, Trabulsi EJ, Feng FY Filvaroff EH, Hege K, Rathkopf, D, and Knudsen KE(2019) Pleiotropic impact of DNA-PK in cancer and implications for therapeutic strategies. Clinical Cancer Research, Sep 15;25(18):5623-5637. doi: 10.1158/1078-0432.CCR-18-2207.
DNA-dependent protein kinase catalytic subunit (DNA-PK) is a pleiotropic kinase involved in DNA repair and transcriptional regulation. DNA-PK is deregulated in selected cancer types and is strongly associated with poor outcome. The underlying mechanisms by which DNA-PK promotes aggressive tumor phenotypes are not well understood. Here, unbiased molecular investigation in clinically relevant tumor models reveals novel functions of DNA-PK in cancer. DNA-PK function was modulated using both genetic and pharmacologic methods in a series of in vitro models, in vivo xenografts, and patient-derived explants (PDE), and the impact on the downstream signaling and cellular cancer phenotypes was discerned. Data obtained were used to develop novel strategies for combinatorial targeting of DNA-PK and hormone signaling pathways.
Key findings reveal that:
A. DNA-PK regulates tumor cell proliferation
B. pharmacologic targeting of DNA-PK suppresses tumor growth both in vitro, in vivo, and ex vivo
C. DNA-PK transcriptionally regulates the known DNA-PK-mediated functions as well as novel cancer-related pathways that promote tumor growth
D. Dual targeting of DNA-PK/TOR kinase (TORK) transcriptionally upregulates androgen signaling, which can be mitigated using the androgen receptor (AR) antagonist enzalutamide
E. Cotargeting AR and DNA-PK/TORK leads to the expansion of antitumor effects, uncovering the modulation of novel, highly relevant protumorigenic cancer pathways
F. Cotargeting DNA-PK/TORK and AR has cooperative growth inhibitory effects in vitro and in vivo
These findings uncovered novel DNA-PK transcriptional regulatory functions and led to the development of a combinatorial therapeutic strategy for patients with advanced prostate cancer, currently being tested in the clinical setting.