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Insulin-like growth factor-1 receptor (IGF-1R) has been made an attractive anticancer target due to its overexpression in cancers. However, targeting it has often produced the disappointing results as the role played by cross talk with numerous downstream signalings. Here, we report a disobliging IGF-1R signaling which promotes growth of cancer through triggering the E3 ubiquitin ligase MEX3A-mediated degradation of RIG-I. The active β-arrestin-2 scaffolds this disobliging signaling to talk with MEX3A. In response to ligands, IGF-1Rβ activated the basal βarr2 into its active state by phosphorylating the interdomain domain on Tyr64 and Tyr250, opening the middle loop (Leu130‒Cys141) to the RING domain of MEX3A through the conformational changes of βarr2. The models of βarr2/IGF-1Rβ and βarr2/MEX3A could interpret the mechanism of the activated-IGF-1R in triggering degradation of RIG-I. The assay of the mutants βarr2Y64A and βarr2Y250A further confirmed the role of these two Tyr residues of the interlobe in mediating the talk between IGF-1Rβ and the RING domain of MEX3A. The truncated-βarr2 and the peptide ATQAIRIF, which mimicked the RING domain of MEX3A could prevent the formation of βarr2/IGF-1Rβ and βarr2/MEX3A complexes, thus blocking the IGF-1R-triggered RIG-I degradation. Degradation of RIG-I resulted in the suppression of the IFN-I-associated immune cells in the TME due to the blockade of the RIG-I-MAVS-IFN-I pathway. Poly(I:C) could reverse anti-PD-L1 insensitivity by recovery of RIG-I. In summary, we revealed a disobliging IGF-1R signaling by which IGF-1Rβ promoted cancer growth through triggering the MEX3A-mediated degradation of RIG-I.
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Objective To investigate the expression of MEX3A in colorectal cancer (CRC), and to explore the effect and mechanism of MEX3A on the proliferation and migration of colorectal cancer cells. Methods Totally 327 cases of data(41 normal tissues and 286 tumor tissues) were obtained from TCGA database, and 104 cases of clinical samples (77 cases tissues and 27 paracancerous tissues) were collected for immunohistochemistry, then analysed the differences in MEX3A expression between CRC tissues and normal tissues. Western blotting and immunofluorescence staining were used to evaluate the differential expression of MEX3A in CRC cell lines. CL187 cells were selected as the follow-up research vector. Small interfering RNA of MEX3A(siMEX3A) was transfected into CL187 cells to inhibit the expression of MEX3A. The proliferation and migration of CL187 cells were measured by MTT, colony formation assay and Transwell assay. The expression of PI3K, p-PI3K, Akt and p-Akt were detected by Western blotting. Results TCGA database, immunohistochemistry and Western blotting analysis showed that MEX3A was highly expressed in colorectal cancer. The result of immunofluorescence staining showed that MEX3A was concentrated in the cytoplasm and the nucleus. In MTT, colony formation assay and Transwell assay, the proliferation and migration ability of CL187 cells in siMEX3A group decreased significantly than those in control group (P<0.05). Western blotting result showed that the expression of p-PI3K and p-Akt in siMEX3A group down-regulated significantly (P<0.05), and the inhibition of proliferation and migration ability of CL187 cells induced by siMEX3A group could be reversed by 740 Y-P via activating the PI3K/Akt signaling pathway. Conclusion MEX3A is highly expressed in colorectal cancer and promotes the proliferation and migration of CRC cells via PI3K/Akt signaling pathway.
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Objective: To investigate the expression of MEX3A in non-small cell lung cancer (NSCLC) cells and the effects of MEX3A knockout on cell cycle, proliferation, invasion, migration, and apoptosis. Methods: We screened out MEX3A, which was significantly highly expressed, by mRNA microarray and The Cancer Genome Atlas (TCGA) database information analysis. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the expression level of MEX3A in NSCLC cells. A549 and NCI-H292 cells showed high expression of MEX3A. RNA interference (RNAi) method was used to silence MEX3A in A549 and NCI-H292 cells. Cell counting kit-8 (CCK8) and Transwell assays were used to determine the effects of MEX3A knockout on proliferation, invasion, and migration in NSCLC cells. Flow cytometry was used to analyze the effects of MEX3A knockout on cell cycle and apoptosis. Results: A549 and NCI-H292 cells showed high expression of MEX3A. After silencing MEX3A, the proliferation, invasion, and migration of NSCLC cells were significantly decreased, while the cell cycle was blocked at G2/M phase and its apoptotic ability was weakened. Conclusions: MEX3A may play an important role as an oncogene in the growth and proliferation of NSCLC cells.
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Objective To construct an shRNA lentiviral vector targeting the MEX3A gene and establish a bladder cancer cell line with stable MEX3A gene knockdown.Methods Real-time PCR was performed to detect the MEX3A gene expression.The recombinant lentiviral vector targeting the MEX3A gene was constructed using the GV115 plasmid.After identification and sequencing,the vectors were co-transfected with the packaging vector into 293T cells to produce lentiviral particles,which were then transduced into bladder cancer cells after viral titer determination.The cell line stably expressing the siRNA was established by antibiotic selection,and real-time PCR was carried out to detect the efficiency of the knockdown.Results Both bladder cancer cell lines,5637 and T24,expressed the MEX3A gene,and its expression was higher in 5637 than in T24.The identification and sequencing results showed that the MEX3A-shRNA lentiviral vector was successfully constructed,and the virus titer was observed to be higher after packaging.The results of the real-time PCR showed that MEX3A gene expression was stably inhibited in 5637 cells after lentiviral transduction.Conclusion Lentivirus-mediated RNAi technology could successfully establish a cell line with stable MEX3A gene knockdown.