RING finger protein 180 (RNF180), an E3 ubiquitin ligase, is thought to be a tumor suppressor gene. However, the detailed mechanism of its effect on ovarian cancer (OV) has not been elucidated. Importin 4 (IPO4) which belongs to transport protein is reported to have cancer-promoting effects on OV. Here, we explored the potential signaling pathways related to RNF180 and IPO4. It was first verified that RNF180 is downregulated and IPO4 is upregulated in OV. By overexpressing or knocking down RNF180 in OV cells, we confirmed that RNF180 inhibited the malignant behaviors of OV cells both in vitro and in vivo . Bioinformatics analysis and proteomics experiments found that RNF180 could interact with IPO4 and promote the degradation of IPO4 through ubiquitination. In addition, overexpression of IPO4 removed the inhibitory effect of RNF180 on OV. We subsequently found that IPO4 could bind to the oncogene Sex determining Region Y-box 2 (SOX2). Knockdown of IPO4 in OV cells decreased SOX2 protein level in nucleus and promoted cyclin-dependent kinase inhibitory protein-1 (p21) expression. Overexpression of RNF180 also inhibited the expression of SOX2 in nucleus. All these results indicated that RNF180 inhibited the nuclear translocation of SOX2 by promoting ubiquitination of IPO4, which ultimately promoted the expression of p21 and then suppressed the progression of OV. This study verified the tumor suppressor effect of RNF180 on OV, elucidated the mechanism of the molecule network related to RNF180 and IPO4 in OV and identified for OV.
Dysregulation of innate immunity during respiratory RNA virus infections drives systemic hyperinflammation and lung injury. Here, we show that importin β4 (IPO4) has a role in inhibiting antiviral innate immunity. Transcriptomics analysis illustrated a downregulation of IPO4 in alveolar macrophages, lung ciliated epithelium, and peripheral blood mononuclear cells from severely ill patients with COVID-19 or influenza. We further identified CCAAT/enhancer-binding protein beta (CEBPB) as the transcription factor for IPO4 reduction during RNA viral infections. Loss-of-function validation demonstrated that IPO4 dampens the innate antiviral and inflammatory responses in vitro and in vivo . Mechanistically, IPO4 sequesters fatty acid synthase (FASN) to block palmitic acid production, thereby inhibiting mitochondrial antiviral signaling protein (MAVS) activation and the downstream innate immune signaling. Moreover, Adeno-associated virus (AAV)-mediated pulmonary restoration of IPO4 significantly alleviated viral pneumonia in mice. These results indicate that the CEBPB-IPO4-FASN-MAVS axis preserves innate immune homeostasis to avoid inflammatory pathology, highlighting IPO4 as a potential therapeutic target for severe viral pneumonia.
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