Downregulation of ubiquitin-specific peptidase 39 suppresses the proliferation and induces the apoptosis of human colorectal cancer cells

USP39 attenuates the antitumor activity of cisplatin on colon cancer cells dependent on p53

Cisplatin is the effective chemotherapeutic drug in colon cancer treatment, but its therapeutic efficacy is limited by intrinsic or acquired drug resistance and detrimental side effects. Therefore, improving the effect of cisplatin chemotherapy remains a great challenge. The previous study identified that USP39 was relevant to cisplatin resistance of lung cancer. However, the function and mechanisms of USP39 regulating the chemosensitivity of cisplatin in colorectal cancer remain unclear. In this study, we reveal that USP39 is associated with colon cancer cells sensitivity to cisplatin. Depletion of USP39 enhances the cisplatin-induced apoptosis in HCT116 cells. Conversely, overexpression of USP39 attenuates apoptosis in RKO cells. Furthermore, we demonstrate that USP39 depletion promotes apoptosis induced by cisplatin, which is related with the induction of oxidative stress and DNA damage response. Further studies show that USP39 regulates cisplatin-induced apoptosis dependent on p53. The underlying mechanism is demonstrated by knocking down USP39, that results in p53 upregulation, associated with its prolonged half-life. Collectively, our findings reveal that USP39 might be a negative factor of the p53 mediated cisplatin sensitivity of colon cancer, and suggest USP39 as a potential molecular target for cisplatin chemotherapy of colon cancer.

miR-381 Inhibits Proliferation and Invasion of Non-Small-Cell Cancer Cells by Targeting USP39

It is known that miR-381 plays a therapeutic role in a variety of cancers, but the regulatory mechanism of miR-381 in the treatment of lung cancer remains unclear. This study is aimed at exploring the expression level and mechanism of miR-381 in lung cancer. In this experiment, quantitative real-time PCR (qRT-PCR), western blot, and other methods were used to detect the expression of miR-381 and ubiquitin-specific protease 39 (USP39) in lung cancer tissues. The target genes of miR-381 were predicted by bioinformatics techniques, and the targeting relationship between miR-381 and USP39 was verified by the dual-luciferase reporting method. The expression levels of miR-381 and USP39 were adjusted to verify the effect of miR-381 on the expression of USP39 gene. The effect of miR-381 expression on proliferation of lung cancer cells was verified by cell proliferation and invasion experiments. miR-381 was downregulated in non-small-cell lung cancer tissues and cell lines, while USP39 was upregulated. The dual-luciferase reporter gene assay showed that miR-381 and USP39 had targeted binding sites. After transfection with miR-381 mimics, USP39 expression was significantly decreased, cell proliferation decreased, and apoptosis increased. After transfection with miR-381 inhibitor, USP39 expression was significantly increased, cell proliferation increased, and cell apoptosis decreased. Overexpression of USP39 significantly increased the invasion ability and cell survival curve (p < 0.05). In conclusion, overexpression of miR-381 can regulate the expression of USP39, inhibit the proliferation and invasion of cancer cells, and induce apoptosis of cancer cells. This may provide a new perspective and strategy for targeted therapy of non-small-cell lung cancer.

Ubiquitin-Specific Proteases: Players in Cancer Cellular Processes

Ubiquitination represents a post-translational modification (PTM) essential for the maintenance of cellular homeostasis. Ubiquitination is involved in the regulation of protein function, localization and turnover through the attachment of a ubiquitin molecule(s) to a target protein. Ubiquitination can be reversed through the action of deubiquitinating enzymes (DUBs). The DUB enzymes have the ability to remove the mono- or poly-ubiquitination signals and are involved in the maturation, recycling, editing and rearrangement of ubiquitin(s). Ubiquitin-specific proteases (USPs) are the biggest family of DUBs, responsible for numerous cellular functions through interactions with different cellular targets. Over the past few years, several studies have focused on the role of USPs in carcinogenesis, which has led to an increasing development of therapies based on USP inhibitors. In this review, we intend to describe different cellular functions, such as the cell cycle, DNA damage repair, chromatin remodeling and several signaling pathways, in which USPs are involved in the development or progression of cancer. In addition, we describe existing therapies that target the inhibition of USPs.

Identifying Novel Actionable Targets in Colon Cancer

Colorectal cancer is the fourth cause of death from cancer worldwide, mainly due to the high incidence of drug-resistance toward classic chemotherapeutic and newly targeted drugs. In the last decade or so, the development of novel high-throughput approaches, both genome-wide and chemical, allowed the identification of novel actionable targets and the development of the relative specific inhibitors to be used either to re-sensitize drug-resistant tumors (in combination with chemotherapy) or to be synthetic lethal for tumors with specific oncogenic mutations. Finally, high-throughput screening using FDA-approved libraries of “known” drugs uncovered new therapeutic applications of drugs (used alone or in combination) that have been in the clinic for decades for treating non-cancerous diseases (re-positioning or re-purposing approach). Thus, several novel actionable targets have been identified and some of them are already being tested in clinical trials, indicating that high-throughput approaches, especially those involving drug re-positioning, may lead in a near future to significant improvement of the therapy for colon cancer patients, especially in the context of a personalized approach, i.e., in defined subgroups of patients whose tumors carry certain mutations.

Knocking down USP39 Inhibits the Growth and Metastasis of Non-Small-Cell Lung Cancer Cells through Activating the p53 Pathway

Ubiquitin-specific protease 39 (USP39), a member of the deubiquitinating enzyme family, has been reported to participate in cytokinesis and metastasis. Previous studies determined that USP39 functions as an oncogenic factor in various types of cancer. Here, we reported that USP39 is frequently overexpressed in human lung cancer tissues and non-small-cell lung cancer (NSCLC) cell lines. USP39 knockdown inhibited the proliferation and colony formation of A549 and HCC827 cells and decreased tumorigenic potential in nude mice. Specifically, knocking down USP39 resulted in cell cycle arrest at G2/M and subsequent apoptosis through the activation of the p53 pathway, including upregulation of p21, cleaved-cas3, cleaved-cas9 and downregulation of CDC2 and CycinB1. Moreover, USP39 knockdown significantly inhibited migration and invasion of A549 and HCC827 cells, also via activation of the p53 pathway, and downregulation of MMP2 and MMP9. Importantly, we verified these results in metastasis models in vivo. Collectively, these results not only establish that USP39 functions as an oncogene in lung cancer, but reveal that USP39 has an essential role in regulating cell proliferation and metastasis via activation of the p53 pathway.

RNA splicing factor USP39 promotes glioma progression by inducing TAZ mRNA maturation

Increasing evidence demonstrates that ubiquitin specific protease 39 (USP39) plays an oncogenic role in various human tumors. Here, using expression analysis of the publicly available Oncomine database, clinical glioma patient samples, and glioma cells, we found that USP39 was overexpressed in human gliomas. Knockdown of USP39 in glioma cells demonstrated that the protein promoted cell growth, invasion and migration in vitro and in a tumor model in nude mice. To identify mediators of USP39 growth-promoting properties, we used luciferase reporter constructs under transcriptional control of various promoters specific to seven canonical cancer-associated pathways. Luciferase activity from a synthetic TEAD-dependent YAP/TAZ-responsive reporter, as a direct readout of the Hippo signaling pathway, was decreased by 92% in cells with USP39 knockdown, whereas the luciferase activities from the other six cancer pathways, including MAPK/ERK, MAPK/JNK, NFκB, Notch, TGFβ, and Wnt, remained unchanged. TAZ protein expression however was decreased independent of canonical Hippo signaling. Immunohistochemistry revealed a positive correlation between USP39 and TAZ proteins in orthotopic xenografts derived from modified glioma cells expressing USP39 shRNAs and primary human glioma samples (p < 0.05). Finally, loss of USP39 decreased TAZ pre-mRNA splicing efficiency in glioma cells in vitro, which led to reduced levels of TAZ protein. In summary, USP39 has oncogenic properties that increase TAZ protein levels by inducing maturation of its mRNA. USP39 therefore provides a novel therapeutic target for the treatment of human glioma.

USP39 regulates the cell cycle, survival, and growth of human leukemia cells

Ubiquitin-specific peptidase 39 (USP39) is one member of the cysteine proteases of the USP family, which represents the largest group of DeUbiquitinases with more than 50 members in humans. The roles of USP39 in human cancer have been widely investigated. However, the roles of USP39 in human leukemia and the underlying mechanism remain unknown. Here we reported the function of USP39 in human leukemia. We observed that the expression of USP39 was up-regulated in human leukemia cells and the high expression of USP39 was correlated with poor survival of the patients with leukemia. Lentivirus-mediated knockdown of USP39 repressed the proliferation and colony formation of human leukemia cell lines HL-60 and Jurkat cells. Mechanism study showed that USP39 knockdown induced the arrest of cell cycle and apoptosis of leukemia cells. In addition, our microarray and bioinformatic analysis demonstrated that USP39 regulated diverse cellular signaling pathways that were involved in tumor biology, and several pivotal genes (IRF1, Caspase 8, and SP1) have been validated by quantitative real-time polymerase chain reaction. Knockdown or IRF1 partially restored the proliferation rate of leukemia cells with USP39 knockdown. Taken together, our findings implicate that USP39 promotes the development of human leukemia by regulating cell cycle, survival, and proliferation of the cells.