Cdc48/p97, a ubiquitin-selective chaperone, orchestrates the function of E3 ligases and deubiquitylases (DUBs). Here, we identify a new function of Cdc48 in ubiquitin-dependent regulation of mitochondrial dynamics. The DUBs Ubp12 and Ubp2 exert opposing effects on mitochondrial fusion and cleave different ubiquitin chains on the mitofusin Fzo1. We demonstrate that Cdc48 integrates the activities of these two DUBs, which are themselves ubiquitylated. First, Cdc48 promotes proteolysis of Ubp12, stabilizing profusion ubiquitylation on Fzo1. Second, loss of Ubp12 stabilizes Ubp2 and thereby facilitates removal of ubiquitin chains on Fzo1 inhibiting fusion. Thus, Cdc48 synergistically regulates the ubiquitylation status of Fzo1, allowing to control the balance between activation or repression of mitochondrial fusion. In conclusion, we unravel a new cascade of ubiquitylation events, comprising Cdc48 and two DUBs, fine-tuning the fusogenic activity of Fzo1.

Gastric cancer (GC) is one of the most common malignant tumors and peritoneal metastasis is the primary cause for advanced GC’s mortality. Protein-tyrosine phosphatase 1B (PTP1B) functions as an oncogene and involves in carcinogenesis and cancer dissemination. However, the function and regulation of PTP1B in GC remain poorly understood. In this study, we found that PTP1B was upregulated in GC tissues and overexpression of PTP1B in vitro promoted cell migration and prevented apoptosis. Then, we predicted that PTP1B was a target of miR-338-3p and we revealed an inverse correlation between miR-338-3p levels and PTP1B protein levels in GC tissues. Next, we verified that PTP1B was inhibited by miR-338-3p via direct targeting to its 3′-untranslated regions. Moreover, overexpression of miR-338-3p in vitro attenuated GC cell migration and promoted apoptosis, and these effects could be partially reversed by reintroduction of PTP1B. Finally, we established an orthotopic xenograft model and a peritoneal dissemination model of GC to demonstrate that miR-338-3p restrained tumor growth and dissemination in vivo by targeting PTP1B. Taken together, our results highlight that PTP1B is an oncogene and is negatively regulated by miR-338-3p in GC, which may provide new insights into novel molecular therapeutic targets for GC.

Objectives: The p160 nuclear receptor coactivator, AIB1 (amplified in breast cancer 1), is frequently overexpressed in human breast cancer and has been shown to be associated with tamoxifen resistance. The present study aimed to investigate the role of AIB1 in tamoxifen resistance of breast cancer cells. Methods: We reconstructed the RNA interference expression vector, pGenesil-1-U6, specially targeting AIB1 mRNA, and it was stably transfected into the human breast cancer cell line BT474. Cell proliferation and cell cycle distribution were assessed in the cells transfected with scramble control shRNA (BT474/shControl) and AIB1 shRNA (BT474/shAIB1) to explore the possible functions of AIB1 in breast cancer progression. The expression of AIB1, ERα, HER2 and pS2 was analyzed in the presence of 17β-estradiol or 4-hydroxytamoxifen (Tam) by Western blot analysis. Results: Compared with the parental BT474 and the BT474/shControl cells, the levels of AIB1 mRNA and protein were significantly reduced in BT474/shAIB1 cells. A knockdown of AIB1 levels restored the inhibitory effect of tamoxifen on cell proliferation. Conclusions: Tam behaves like an estrogen agonist in ER-positive breast cancer cells that express high levels of AIB1 and HER2, resulting in de novo resistance. Knockdown of AIB1 can eliminate this cross talk and restore the antitumor effects of tamoxifen.

The protein tyrosine phosphatase PTP1B, which is encoded by PTPN1, is a ubiquitously expressed nonreceptor protein tyrosine phosphatase. PTP1B has long been known to negatively regulate insulin and leptin receptor signalling. Recently, it was reported to be aberrantly expressed in cancer cells and to function as an important oncogene. In this study, we found that PTP1B protein levels are dramatically increased in breast cancer (BC) tissues and that PTP1B promotes the proliferation, and suppresses the apoptosis, of both HER2‐positive and triple‐negative BC cell lines. Bioinformatics analysis identified that the miRNA, miR‐193a‐3p, might potentially target PTP1B. We demonstrate that miR‐193a‐3p regulates PTP1B in BC cells and that it regulates the proliferation and apoptosis of BC cells by targeting PTP1B, both in vitro and in vivo. In conclusion, this study confirms that PTP1B acts as an oncogene in BC and demonstrates that miR‐193a‐3p can serve as a tumour suppressor gene in BC by targeting PTP1B.

p53 is possibly the most important mammalian tumor suppressor and it is mutated or lost in more than half of all human cancers. The stability of p53 is primarily determined by the RING domain E3 ubiquitin ligase Hdm2, which targets p53 for proteasomal degradation, restraining the potent activity of p53 and enabling cell survival and proliferation. UBE4B has been shown to physically interact with p53 and Hdm2 and to negatively regulate p53 stability and function. However, no one has determined whether UBE4B promotes p53 degradation in breast cancer. In this study, UBE4B promoted the degradation and ubiquitination of p53 to inhibit the apoptosis of cancer cells and promote tumorigenesis. Our results indicate that UBE4B regulates p53 in breast cancer and could be a viable target for developing new therapeutic strategies for breast cancer treatment.

Recent studies have suggested that ubiquitin-specific peptidase (USP)18 may act as an oncogene in various types of cancer. Although the role of USP18 in breast cancer cell lines has been elucidated, the underlying mechanisms and clinical role of USP18 in breast cancer are currently not well understood. The bioinformatics analysis and experimental results of the present study demonstrated that aberrant promoter methylation led to increased expression of USP18 in breast cancer. In addition, correlation analysis suggested that a negative correlation between methylation and USP18 mRNA expression was observed in The Cancer Genome Atlas database. USP18 promoted cell proliferation, colony formation and cell cycle progression in vitro. Furthermore, the Gene Set Enrichment Analysis results demonstrated that USP18 may be negatively associated with apoptosis in patients with breast cancer. Bioinformatics analysis results indicated that USP18 was also revealed to be associated with the protein kinase B (AKT) signaling pathway and mammary tumorigenesis in vivo. In addition, the results indicated that USP18 may promote the epidermal growth factor (EGF)-mediated EGF receptor (EGFR)/AKT/S‑phase kinase-associated protein 2 (Skp2) pathway by upregulating EGFR and Skp2 in a AKT/forkhead box O3-dependent manner in breast cancer. The results of bioinformatics analysis revealed that increased USP18 expression was associated with a higher TNM stage and unfavorable prognosis in clinical patients. USP18 was also significantly enhanced in patients with human epidermal growth factor receptor 2-positive breast cancer; furthermore, Kaplan‑Meier curve demonstrated that combining USP18 and Skp2 expression improved prognostic capability in breast cancer. Taken together, these results suggested that USP18 may serve a key role in breast cancer development by upregulating EGFR and subsequently activating the AKT/Skp2 feedback loop pathway. The role of USP18 in breast cancer provides a novel insight into the clinical application of the USP18/AKT/Skp2 pathway.

A number of studies have shown that apoptosis resistance can be observed in multiple human tumors; however the detailed mechanism remains unclear. In the present study, we demonstrated that the abnormal overexpression of the C terminus of Hsc70-interacting protein (CHIP) induced apoptosis resistance by regulating the AKT/FoxO/Bim signaling pathway in the breast cancer cell MCF7 and the human non-tumorigenic cell MCF10A. We found that CHIP overexpression in MCF7 and MCF10A cells activated AKT and inhibited the Forkhead box O (FoxO) transcription factors FoxO1, FoxO3, and FoxO4, thereby inhibiting transcription of the target genes bim and pten. Inhibition of PI3K by a chemical reagent revealed that these events may be critical for CHIP-induced apoptosis resistance. We also determined that inhibition of FoxO3 by CHIP led to the decrease in PTEN and further activated the AKT survival pathway. We corroborated our findings in breast cancer tissues. In general, the CHIP-modulated AKT/FoxO/Bim signaling pathway was shown to induce apoptosis resistance by decreasing the protein level of the tumor suppressor PTEN in both transcriptional and post-translational regulations.

Background: P53 pathway inactivation plays an important role in the process of breast cancer tumorigenesis. Posttranslational protein modification abnormalities have been confirmed to be an important mechanism underlying inactivation of p53. Numerous deubiquitinating enzymes are aberrantly expressed in breast cancer, and a few deubiquitination enzymes can deubiquitinate and stabilize p53. Here, we report that ovarian tumor (OTU) deubiquitinase 3 (OTUD3) is a deubiquitylase of p53 in breast carcinoma (BC). Methods: Correlations between the mRNA expression levels of OTUD3, TP53 and PTEN and the prognosis of BC were assessed with the Kaplan-Meier Plotter tool. OTUD3 protein expression in 80 pairs of specimens in our cohort was examined by immunohistochemistry and western blotting. The relationship among OTUD3, p53, and p21 proteins was analyzed. Half-life analysis and ubiquitylation assay were performed to elucidate the molecular mechanism by which OTUD3 stabilizes p53. The interaction between OTUD3 and p53 in BC cells was verified by a co-immunoprecipitation assay and GST pulldown experiments. MTS assay for proliferation detection, detection of apoptosis induced by cisplatin and colony formation assay were employed to investigate the functional effects of OTUD3 on breast cancer cells. Results: OTUD3 downregulation is correlated with a poor prognosis in BC patients. OTUD3 expression is decreased in breast cancer tissues and not associated with the histological grade. OTUD3 also inhibits cell proliferation and clone formation and increases the sensitivity of BC cells to apoptosis induced by chemotherapy drugs. Reduced OTUD3 expression accompanied by decreased p53 abundance is correlated with human breast cancer progression. Ectopic expression of wild-type OTUD3, but not its catalytically inactive mutant, stabilizes and activates p53. Mechanistically, OTUD3 interacts directly with p53 through the amino-terminal OTU region. Finally, OTUD3 protects p53 from murine double minute 2 (Mdm2)-mediated ubiquitination and degradation, enabling the deubiquitination of p53 in BC cells.