MEX3A control of mitochondrial fitness is essential for ovarian clear cell carcinoma tumorigenesis and liver metastasis

Ovarian cancer (OC) is highly metastatic and chemoresistant. Due to heterogeneity among OC subtypes, the mechanisms underlying OC malignancy and metastasis remain largely unknown. Ovarian clear cell carcinoma (OCCC) accounts for 5-25% of OC and its incidence rate is rising. Liver metastasis is particularly high in OCCC patients and leads to significantly reduced median survival. Why OCCC metastasizes to liver at such high frequency remains elusive. We previously identified MEX3A as a key factor that promotes OCCC tumorigenesis in part by circumventing p53-mediated ferroptosis. Here, we report that MEX3A control of mitochondrial fitness, which occurs independently of p53, is essential for OCCC primary tumor growth and liver metastasis. MEX3A depletion resulted in chronic mitochondrial fragmentation and accumulation of non-functional mitochondria. MEX3A-depleted cells had decreased mitochondrial membrane potential, increased superoxide and decreased NAD+/NADH ratio, resulting in inhibition of oxidative phosphorylation (OXPHOS) and decreased ATP levels. In an environment enriched with mitophagy stressors, such as the liver, MEX3A-depleted OCCC cells had greatly reduced survival due to failure to recover from mitophagy. Consistent with these observations, MEX3A knockdown greatly reduced liver metastasis. Together, these data demonstrate that MEX3A-mediated mitochondrial fitness is a major factor underlying its p53-independent promotion of OCCC tumorigenesis and liver metastasis. Thus, targeting MEX3A will be a promising strategy to inhibit OCCC progression. Statement of significanceUnexpected effects of MEX3A on mitochondrial fitness indicate that the need for high MEX3A expression is an OCCC vulnerability that can be exploited to uncover new treatment strategies.