Abstract 1990: NF-kB and MAPK signaling pathways coordinate in supporting ovarian cancer relapse

Ovarian cancer is the most lethal gynecological malignancy in the US. Most patients initially respond to platinum-based chemotherapy; however, 70% of advanced stage tumors relapse. Recent studies suggest a minority population of primitive cells, termed tumor-initiating cells (TICs), resist chemotherapy and re-create heterogeneous tumors to cause relapse. Identifying the mechanisms that support this elusive population will be critical for preventing relapse. Work from our lab has identified a critical role for classical and alternative NF-kB transcription factors in supporting ovarian cancer progression. We have found that alternative transcription factor, RelB, maintains quiescent ovarian TICs, whereas classical transcription factor, RelA, maintains a proliferative subpopulation that may depend on MAPK/ERK. Presumably, both populations are required for efficient relapse. Here, we investigate activation of RelA in TICs and non-TICs to distinguish its role in maintaining proliferation and whether this process requires co-activation of MAPK/ERK. In RNA-Sequencing pathway analysis, we found that relative to TIC cultures, non-TIC cultures had increased proliferation pathways, which included MAPK genes: ERK2 and MEKK. These genes were significantly downregulated in RelA shRNA knockdown cells, implying RelA regulation. To further investigate RelA and RelB transcriptional regulation in TICs and non-TICs, we recently completed CHIP sequencing experiments and found that RelA exclusively regulated 1/3 of the total genes in non-TIC cultures, whereas RelB exclusively regulated 1/3 of the genes in TIC cultures. This data supported our previous findings implicating RelA in proliferation and RelB in quiescence and further implicate MAPK/ERK. Preliminary western blot data suggests an upregulation of the MAPK/ERK pathway in non-TIC cultures with RelB upregulation in TIC cultures. Additionally, we have established 100% RelA and RelB knockout CRISPR lines and stable RelA-RFP lines in OV90, OVCAR8, and ACI23 ovarian cancer cells and studies are underway to validate the role of these factors in TIC maintenance and in our established relapse model, where relapse occurs on average 21 days post-treatment. We expect that although only quiescent TICs will be remaining following chemotherapy, efficient relapse will also require a proliferative population dependent on RelA and MAPK/ERK. A better understanding of NF-kB signaling in TICs will guide the design for more effective therapies to overcome chemoresistance and relapse, and improve survival of women with ovarian cancer. Citation Format: Jacqueline Lara, Samuel Gilbert, Mikella Robinson, Jennifer Waters, Omar Lujano-Olazaba, Carrie House. NF-kB and MAPK signaling pathways coordinate in supporting ovarian cancer relapse [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1990.