Purpose: We recently reported that the transcription factor NFATC4, in response to chemotherapy, drives cellular quiescence to increase OvCa chemoresistance. The goal of this work was to better understand the mechanisms of NFATC4 driven OvCa chemoresistance. Experimental Design: We used RNA-seq to identify NFATC4 mediated differential gene expression. CRISPR-Cas9 and FST neutralizing antibody were used to assess impact of loss of FST function on cell proliferation and chemoresistance. ELISA was used to quantify FST induction in patient samples and in vitro in response to chemotherapy. Results: We found that NFATC4 upregulates follistatin (FST) mRNA and protein expression predominantly in quiescent cells and FST is further upregulated following chemotherapy treatment. FST acts in at least a paracrine manner to induce a p-ATF2 dependent quiescent phenotype and chemoresistance in non-quiescent cells. Consistent with this, CRISPR KO of FST in OvCa cells or antibody mediated neutralization of FST sensitizes OvCa cells to chemotherapy treatment. Similarly, CRISPR KO of FST in tumors increased chemotherapy-mediated tumor eradication in an otherwise chemotherapy resistant tumor model. Suggesting a role for FST in chemoresistance in patients, FST protein in the abdominal fluid of OvCa patients significantly increases within 24 hours of chemotherapy exposure. FST levels decline to baseline levels in patients no longer receiving chemotherapy with no evidence of disease. Furthermore, elevated FST expression in patient tumors is correlated with poor progression free, post-progression free, and overall survival. Conclusions: FST is a novel therapeutic target to improve OvCa response to chemotherapy and potentially reduce recurrence rates.

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