Active FAK staining increases in the nucleus of HGSOC patient tumors after neoadjuvant chemotherapy. A, IHC staining of paraffin-embedded serial initial tumor biopsy sections (patient 1014109 and patient 3000276) and corresponding tumor resection after neoadjuvant chemotherapy treatment. Samples were stained with H&E and phosphospecific antibodies to the FAK activation loop Y576 (pY576) within the kinase domain. Scale is 100 μm (inset scale is 25 μm). B, Image quantification of percent of tumor cell area exhibiting FAK pY576 staining. Paired tumor samples (n = 8) from initial biopsy (blue circles) and from surgical tumor debulking after neoadjuvant chemotherapy (red circles). Dotted lines connect paired patient tumor samples collected prior to and after neoadjuvant chemotherapy (***, P < 0.001). Chemo, chemotherapy; H&E, hematoxylin and eosin; NeoAdj, neoadjuvant.
ARTICLE ABSTRACT
Tumor chemotherapy resistance arises frequently and limits high-grade serous ovarian cancer (HGSOC) patient survival. Focal adhesion kinase (FAK) is an intracellular protein–tyrosine kinase encoded by PTK2, a gene that is often gained in HGSOC. Canonically, FAK functions at the cell periphery. However, FAK also transits to the nucleus to modulate gene expression. We find that FAK is tyrosine-phosphorylated and nuclear-localized in tumors of patients with HGSOC surviving neoadjuvant platinum–paclitaxel chemotherapy and that FAK nuclear accumulation occurs upon subcytotoxic cisplatin exposure to ovarian tumor cells in vitro. FAK nuclear localization sequence (NLS) mutational inactivation resulted in tumor cell sensitization to cisplatin in vitro and in vivo relative to wild-type FAK-reconstituted ovarian tumor cells. Cisplatin cytotoxicity was associated with elevated ERK MAPK activation in FAK NLS− cells, cisplatin-stimulated ERK activation was also enhanced upon loss of FAK activity or expression, and cisplatin-stimulated cell death was prevented by an inhibitor of ERK signaling. MAPK phosphastase-1 (MKP1) negatively regulates ERK signaling, and cisplatin-induced MKP1 levels were significantly elevated in wild-type FAK compared with FAK NLS− ovarian tumor cells. Notably, small-molecule MKP1 inhibition enhanced both cisplatin-stimulated ERK phosphorylation and ovarian tumor cell death. Together, our results show that FAK expression, activity, and nuclear localization limit cisplatin cytotoxicity in part by regulating MKP1 levels and preventing noncanonical ERK/MAPK activation.
FAK inhibitors are in combinatorial clinical testing with agents that prevent Ras–Raf–MAPK pathway activation in various cancers. This study suggests that nuclear FAK limits ERK/MAPK activation in supporting HGSOC cell survival to cisplatin stress. Overall, it is likely that targets of FAK-mediated survival signaling may be tumor type– and context-dependent.
