Downregulated F-Box/LRR-Repeat Protein 7 Facilitates Pancreatic Cancer Metastasis by Regulating Snail1 for Proteasomal Degradation

FBXL8 inhibits post-myocardial infarction cardiac fibrosis by targeting Snail1 for ubiquitin-proteasome degradation

Abnormal cardiac fibrosis is the main pathological change of post-myocardial infarction (MI) heart failure. Although the E3 ubiquitin ligase FBXL8 is a key regulator in the cell cycle, cell proliferation, and inflammation, its role in post-MI ventricular fibrosis and heart failure remains unknown. FBXL8 was primarily expressed in cardiac fibroblasts (CFs) and remarkably decreased in CFs treated by TGFβ and heart subjected to MI. The echocardiography and histology data suggested that adeno-associated viruses (AAV9)-mediated FBXL8 overexpression had improved cardiac function and ameliorated post-MI cardiac fibrosis. In vitro, FBXL8 overexpression prevented TGFβ-induced proliferation, migration, contraction, and collagen secretion in CFs, while knockdown of FBXL8 demonstrated opposite effects. Mechanistically, FBXL8 interacted with Snail1 to promote Snail1 degradation through the ubiquitin-proteasome system and decreased the activation of RhoA. Moreover, the FBXL8ΔC3 binding domain was indispensable for Snail1 interaction and degradation. Ectopic Snail1 expression partly abolished the effects mediated by FBXL8 overexpression in CFs treated by TGFβ. These results characterized the role of FBXL8 in regulating the ubiquitin-mediated degradation of Snail1 and revealed the underlying molecular mechanism of how MI up-regulated the myofibroblasts differentiation-inducer Snail1 and suggested that FBXL8 may be a potential curative target for improving post-MI cardiac function.

Hypoxia-mediated promotion of glucose metabolism in non-small cell lung cancer correlates with activation of the EZH2/FBXL7/PFKFB4 axis

F-box/LRR-repeat protein 7 (FBXL7) was predicted as a differentially expressed E3 ubiquitin ligase in non-small cell lung cancer (NSCLC), which has been suggested to influence cancer growth and metastasis. In this study, we aimed to decipher the function of FBXL7 in NSCLC and delineate the upstream and downstream mechanisms. FBXL7 expression was verified in NSCLC cell lines and GEPIA-based tissue samples, after which the upstream transcription factor of FBXL7 was bioinformatically identified. The substrate PFKFB4 of the FBXL7 was screened out by tandem affinity purification coupled with mass-spectrometry (TAP/MS). FBXL7 was downregulated in NSCLC cell lines and tissue samples. FBXL7 ubiquitinated and degraded PFKFB4, thus suppressing glucose metabolism and malignant phenotypes of NSCLC cells. Hypoxia-induced HIF-1α upregulation elevated EZH2 and inhibited FBXL7 transcription and reduced its expression, thus promoting PFKFB4 protein stability. By this mechanism, glucose metabolism and the malignant phenotype were enhanced. In addition, knockdown of EZH2 impeded tumor growth through the FBXL7/PFKFB4 axis. In conclusion, our work reveals that the EZH2/FBXL7/PFKFB4 axis plays a regulatory role in glucose metabolism and tumor growth of NSCLC, which is expected to be potential biomarkers for NSCLC.

Functional characterization of FBXL7 as a novel player in human cancers

F-box and leucine-rich repeat protein 7 (FBXL7), an F-box protein responsible for substrate recognition by the SKP1-Cullin-1-F-box (SCF) ubiquitin ligases, plays an emerging role in the regulation of tumorigenesis and tumor progression. FBXL7 promotes polyubiquitylation and degradation of diverse substrates and is involved in many biological processes, including apoptosis, cell proliferation, cell migration and invasion, tumor metastasis, DNA damage, glucose metabolism, planar cell polarity, and drug resistance. In this review, we summarize the downstream substrates and upstream regulators of FBXL7. We then discuss its role in tumorigenesis and tumor progression as either an oncoprotein or a tumor suppressor, and further describe its aberrant expression and association with patient survival in human cancers. Finally, we provide future perspectives on validating FBXL7 as a cancer biomarker for diagnosis and prognosis and/or as a potential therapeutic target for anticancer treatment.