NUAK1 acts as a growth suppressor in epithelial ovarian cancer.

Epithelial ovarian cancer (EOC) cells form multicellular aggregates, or spheroids, and enter a dormant state during intraperitoneal metastasis. Dormant spheroids reduce anabolic metabolism and cell proliferation, which are linked to chemo-resistance. Liver kinase B1 (LKB1), encoded by the STK11 gene, is a critical regulator of stress metabolic signaling; LKB1 phosphorylates the downstream substrates AMP-activated protein kinase (AMPK) and AMPK-related kinases (ARKs) to mediate stress signaling. We have demonstrated that LKB1 expression and activity is required for EOC spheroid cell survival, yet knockdown of AMPKα1/α2 has no effect on viability. In addition, we have preliminary data demonstrating that phosphorylated AMPK is still maintained in EOC spheroids generated from CRISPR-mediated STK11-deleted cells, which completely lack LKB1 expression. Taken together, these results implicate the importance of other AMPK-independent effectors of LKB1 signaling in spheroid cell viability. Therefore, to identify critical downstream targets of LKB1-mediated signaling in EOC spheroids, we employed multiplex inhibitor beads/mass spectrometry (MIB/MS) using OVCAR8 STK11-knockout cells and OVCAR8 control cells grown in adherent and spheroid culture conditions. Using this proteomic approach, we identified NUAK1 as the sole ARK out of 12 different family members that is negatively affected by LKB1 loss. In fact, both phosphorylated and total NUAK1 protein expression are decreased in STK11-knockout cells and spheroids. NUAK1 can negatively control cell growth and proliferation by direct regulation of cell cycle checkpoint proteins in several cell systems; however, it has been relatively understudied in EOC. In analysis of the serous ovarian carcinoma data from TCGA, NUAK1 is infrequently altered ( Citation Format: Parima Saxena, Olga Collins, Yudith Ramos Valdes, Adrian Buensuceso, Kyle Francis, Kevin Brown, Karen Colwill, Anne-Claude Gingras, Robert Rottapel, Gabriel E. DiMattia, Trevor G. Shepherd. NUAK1 acts as a growth suppressor in epithelial ovarian cancer. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A17.