Endometrial carcinoma (ECa) is the most common malignant gynecological cancer, with an increased incidence and fatality rate worldwide, while the pathogenesis is still largely unknown. In this study, we confirmed that FBXO7, a gene coding FBXO7 E3 ubiquitin ligase, is significantly downregulated and mutated (5.87%; 31/528) in ECa specimens, and the abnormal low expression and mutations of FBXO7 are associated with the occurrence of ECa. We also identify the excessive expression of INF2 protein, a key factor that triggers mitochondrial division by recruiting the DRP1 protein, and the elevated INF2 protein is significantly negatively correlated with the low FBXO7 protein in ECa specimens. Mechanistically, FBXO7 restrains ECa through inhibiting INF2-associated mitochondrial division via FBXO7-mediated ubiquitination and degradation of INF2. Moreover, we found that ECa-associated FBXO7 mutants are defective in the ubiquitination and degradation of INF2, promoting ECa cells proliferation, migration and apoptosis inhibition via inducing mitochondrial hyper-division. In addition, we found that it could reverse FBXO7 deletion or ECa-associated FBXO7 mutants-induced proliferation, migration, apoptosis inhibition and mitochondrial hyper-division of ECa cells by INF2 or DNM1L knockdown, or DRP1 inhibitor Mdivi-1. In summary, our study shows that FBXO7 acts as a novel tumor suppressor in ECa by inhibiting INF2-DRP1 axis-associated mitochondrial division through the ubiquitination and degradation of INF2 while the effect is destroyed by ECa-associated FBXO7 and INF2 mutants, highlights the key role of FBXO7-INF2-DRP1 axis in ECa tumorigenesis and provides a new viewpoint to treat ECa patients with FBXO7 deletion or mutations by targeting INF2-DRP1 axis-associated mitochondrial division.

Speckle-type POZ protein (SPOP) is a substrate-binding adaptor of the CULLIN3/RING-box1 E3 ubiquitin ligase complex. SPOP is frequently mutated in prostate cancer (PCa) and endometrial cancer (ECa) while it is overexpressed in renal cell carcinoma (RCC). SPOP can mediate both degradable and non-degradable polyubiquitination of a number of substrates with diverse biological functions such as androgen receptor (AR), SRC-3, TRIM24, BRD4, PD-L1, 53BP1, GLP/G9a, c-Myc, SENP7, among others. Cancer-associated SPOP mutants often impair SPOP binding and polyubiquitination of its substrates to influence various cancer-relevant pathways, which include androgen/AR signaling, DNA repair and methylation, cellular stress surveillance, cancer metabolism and immunity. While SPOP is recognized as a tumor suppressor in PCa and ECa, it acts like a oncoprotein in RCC. This review provides an overview of the recent progress in understanding of the upstream regulators of SPOP and its downstream targets, highlights the significant impact of SPOP mutations and overexpression on cancer pathogenesis, and discusses the potential of targeting SPOP for cancer treatment.

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<div>Abstract<p>Speckle-type POZ protein (SPOP) is a substrate-binding adaptor of the CULLIN3/RING-box1 E3 ubiquitin ligase complex. SPOP is frequently mutated in prostate and endometrial cancers, whereas it is overexpressed in renal cell carcinoma (RCC). SPOP can mediate both degradable and nondegradable polyubiquitination of a number of substrates with diverse biological functions such as androgen receptor (AR), SRC-3, TRIM24, BRD4, PD-L1, 53BP1, GLP/G9a, c-Myc, SENP7, among others. Cancer-associated SPOP mutants often impair SPOP binding and polyubiquitination of its substrates to influence various cancer-relevant pathways, which include androgen/AR signaling, DNA repair and methylation, cellular stress surveillance, cancer metabolism, and immunity. Although SPOP is recognized as a tumor suppressor in prostate and endometrial cancers, it acts like an oncoprotein in RCC. This review provides an overview of the recent progress in understanding of the upstream regulators of SPOP and its downstream targets, highlights the significant impact of SPOP mutations and overexpression on cancer pathogenesis, and discusses the potential of targeting SPOP for cancer treatment.</p></div>