An inhibitor of cholesterol absorption displays anti-myeloma activity by targeting the JAK2-STAT3 signaling pathway

Targeting the oncogenic transcription factor c-Maf for the treatment of multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy derived from clonal expansion of plasma cells within the bone marrow and it may progress to the extramedullary region in late stage of the disease course. c-Maf, an oncogenic zipper leucine transcription factor, is overexpressed in more than 50% MM cell lines and primary species in association with chromosomal translocation, aberrant signaling transduction and modulation of stability. By triggering the transcription of critical genes including CCND2, ITGB7, CCR1, ARK5, c-Maf promotes MM progress, proliferation, survival and chemoresistance. Notably, c-Maf is usually expressed at the embryonic stage to promote cell differentiation but less expressed in healthy adult cells. c-Maf has long been proposed as a promising therapeutic target of MM and a panel of small molecule compounds have been identified to downregulate c-Maf and display potent anti-myeloma activities. In the current article, we take a concise summary on the advances in c-Maf biology, pathophysiology, and targeted drug discovery in the potential treatment of MM.

Inhibition of Ubiquitin Specific Protease 1 Sensitizes Colorectal Cancer Cells to DNA-Damaging Chemotherapeutics

Mutations and altered expression of deubiquitinating enzymes (DUBs) have been found associated with many human diseases including cancers. In this study, Ubiquitin specific protease 1 (USP1) expression was found significantly increased in some colorectal cancers (CRC). The elevated USP1 level was associated with short overall survival of patients and with advanced stages of cancers. In cultured CRC cells, knockdown of USP1 induced growth arrest at G₂/M of cell cycle and reduced the expression of anti-apoptotic proteins Bcl-2 and Mcl-1. Its knockdown also led to reduction of DNA-repair related substrates FANCD2 and ID1. Further investigations found that small molecular inhibitor of USP1 ML323 sensitized CRC cells to DNA-targeting chemotherapeutics, including doxorubicin, TOPI/II inhibitors, and PARP inhibitor, but not to 5-Fu. These results indicate that USP1 plays a critical in colorectal cancer cell survival and is a promising target for anti-colorectal cancer chemotherapy. Targeting USP1 may represent an effective strategy to regulate the DNA-repairing system.

Transcriptional profiling of circulating tumor cells in multiple myeloma: a new model to understand disease dissemination

The reason why a few myeloma cells egress from the bone marrow (BM) into peripheral blood (PB) remains unknown. Here, we investigated molecular hallmarks of circulating tumor cells (CTCs) to identify the events leading to myeloma trafficking into the bloodstream. After using next-generation flow to isolate matched CTCs and BM tumor cells from 32 patients, we found high correlation in gene expression at single-cell and bulk levels (r ≥ 0.94, P = 10^-16), with only 55 genes differentially expressed between CTCs and BM tumor cells. CTCs overexpressed genes involved in inflammation, hypoxia, or epithelial-mesenchymal transition, whereas genes related with proliferation were downregulated in CTCs. The cancer stem cell marker CD44 was overexpressed in CTCs, and its knockdown significantly reduced migration of MM cells towards SDF1-α and their adhesion to fibronectin. Approximately half (29/55) of genes differentially expressed in CTCs were prognostic in patients with newly-diagnosed myeloma (n = 553; CoMMpass). In a multivariate analysis including the R-ISS, overexpression of CENPF and LGALS1 was significantly associated with inferior survival. Altogether, these results help understanding the presence of CTCs in PB and suggest that hypoxic BM niches together with a pro-inflammatory microenvironment induce an arrest in proliferation, forcing tumor cells to circulate in PB and seek other BM niches to continue growing.

S1PR1 promotes proliferation and inhibits apoptosis of esophageal squamous cell carcinoma through activating STAT3 pathway

Background

Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers worldwide, which lacks effective biomarkers for prognosis. Therefore, it is urgent to explore new potential molecular markers to discriminate patients with poorer survival in ESCC.

Methods

Bioinformatics analysis, qRT-PCR, and western blot were applied to investigate S1PR1 expression. CCK-8 assay, colony formation assay, flow cytometry dual staining assay, and immunofluorescence were performed to examine cell proliferation ability and apoptosis rate. Mouse xenograft model of TE-13 cells was established to confirm the roles of S1PR1 in vivo. Gene set enrichment analysis (GSEA) was used to investigate the downstream signaling pathways related to S1PR1 functions. Co-IP was performed to verify the direct binding of S1PR1 and STAT3. Western blot was applied to determine the phosphorylation level of STAT3. Immunohistochemistry was conducted to identify protein expression of S1PR1 and p- STAT3 in tumor tissues.

Results

In the present study, we found that S1PR1 expression was higher in ESCC patients and was a potential biomarker for poor prognosis. Silencing S1PR1 expression inhibited proliferation, and increased apoptosis of ESCC cells, while overexpression of S1PR1 had opposite effects. Mechanistically, S1PR1 played the roles of promoting proliferation and attenuating apoptosis through directly activating p-STAT3. Furthermore, in vivo experiments verified this mechanism.

Conclusion

Our findings indicated that S1PR1 enhanced proliferation and inhibited apoptosis of ESCC cells by activating STAT3 signaling pathway. S1PR1 may serve as a prognostic biomarker for clinical applications.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1369-7) contains supplementary material, which is available to authorized users.

The natural flavonoid glycoside vitexin displays preclinical antitumor activity by suppressing NF-κB signaling in nasopharyngeal carcinoma

Background and objectives: Vitexin is a natural flavonoid glycoside mainly extracted from the leaves of vitex, which has a variety of physiological activities. For example, vitexin has antitumor and anti-inflammation activities, and it can also promote blood circulation in the body. However, the function and mechanism of vitexin in nasopharyngeal carcinoma (NPC) are still unclear.

Materials and methods: Cell Counting Kit-8 assay and cell cycle analysis were performed to examine cell survival in response to vitexin. Immunoblotting was used to analyze relative proteins’ expression. NPC xenograft models were established to assess the effect of vitexin in vivo. The luciferase activity of pNFκB-Luc was analyzed by using Dual-Luciferase Reporter Assay System. Quantitative real-time polymerase chain reaction was performed to detect relative genes’ expression. Kinase activity of IKKβ was analyzed in a cell-free system.

Results: In this study, vitexin was found to display significant antitumor activity in NPC in vitro and in vivo. In NPC cells, vitexin inhibited cell cycle progression in NPC cells and induced the cleavages of PARP and inhibited antiapoptotic proteins’ expression, including Bcl-2 and Mcl1. Further studies indicated that vitexin significantly suppressed the luciferase activity of pNF-κB-Luc and inhibited the activation of NF-κB key regulators, including p65, IκBα and IKKs in NPC cells. Moreover, the kinase activity of IKKβ could be suppressed by vitexin in a cell-free system, and overexpression of CA-IKKβ could attenuate the inhibitory effect of vitexin on p65 phosphorylation.

Conclusion: These results indicated that vitexin displayed antitumor activity by suppressing NF-κB signaling in NPC, which suggested that vitexin could be as a potential drug for the treatment of NPC in the future.

Ubiquitin specific peptidase 5 regulates colorectal cancer cell growth by stabilizing Tu translation elongation factor

Ubiquitin specific peptidase 5 (USP5) is a ubiquitous expressed deubiquitinating enzyme (DUB). It has been shown involved in DNA repair, apoptosis, inflammation, and tumor cell growth. However, the function and molecular mechanism of USP5 in colorectal cancer (CRC) are still unclear. In the present study, we asked how it affected the growth of colorectal cancer cells.

Methods: A shRNA-based high-content screening was performed to identify DUBs affecting the growth of CRC cells. CCK-8 assay and xenografts were used to assess CRC cell growth, survival and tumorigenesis. RT-qPCR, immunoblotting and immunohistochemistry were carried out to quantitate USP5 expression in CRC tissues and cell lines. Immunoprecipitation and mass spectrometry analysis were performed to identify USP5-interacting proteins. Cycloheximide chase was performed to assess Tu translation elongation factor (TUFM) stability. Dual luciferase reporter assay was utilized for USP5 promoter analysis.

Results: We found that USP5 was highly expressed in a group of primary CRC tissues, and the increased USP5 was correlated with clinical stages and shorter overall survival. While USP5 knockdown effectively inhibited CRC cell growth, overexpressed USP5 promoted the growth of CRC cells and made them more resistant to doxorubicin (DOX). TUFM was discovered as a substrate of USP5. USP5 deubiquitinated TUFM and increased its level in CRC cells. Enforced expression of TUFM was able to alleviate the growth inhibition induced by USP5 knockdown. Further analyses showed that EBF transcription factor 1 (EBF1) was a major regulator for USP5 transcription, and DOX inhibited EBF1-USP5-TUFM axis in CRC cells.

Conclusions: USP5 was required for CRC cells and promoted their growth and resistance to chemotherapeutics. TUFM was a USP5 deubiquitinating substrate that mediated the cellular effects of USP5. The transcription of USP5 was regulated by EBF1. Thus, targeting EBF1-USP5-TUFM axis is a potential novel strategy for CRC treatment.

Activation of liver X receptor up-regulates the expression of the NKG2D ligands MICA and MICB in multiple myeloma through different molecular mechanisms

NK cells have an important role in immunosurveillance of multiple myeloma (MM) progression, and their activity is enhanced by combination therapies able to regulate the expression of specific activating ligands. Liver X receptors (LXRs) are nuclear receptors and important regulators of intracellular cholesterol and lipid homeostasis. Moreover, they have regulatory roles in both cancer and immune response. Indeed, they can regulate inflammation and innate and acquired immunity. Furthermore, LXR activation directly acts in cancer cells (e.g., prostate, breast, melanoma, colon cancer, hepatocarcinoma, glioblastoma, and MM) that show an accumulation of cholesterol and alteration of LXR-mediated metabolic pathways. Here, we investigated the role of LXR and cholesterol on the expression of the NK cell-activating ligands major histocompatibility complex class I chain-related molecule A and B (MICA and MICB) in MM cells. The results shown in this work indicate that MM cells are responsive to LXR activation, which induces changes in the intracellular cholesterol content. These changes correlate with an enhanced expression of MICA and MICB in human MM cell lines and in primary malignant plasma cells, 2 ligands of the NK group 2D receptor (NKG2D)/CD314 activating receptor expressed in cytotoxic lymphocytes, rendering MM cells more sensitive to recognition, degranulation, and killing by NK cells. Mechanistically, we observed that LXR activation regulates MICA and MICB expression at different levels: MICA at the transcriptional level, enhancing mica promoter activity, and MICB by inhibiting its degradation in lysosomes. The present study provides evidence that activation of LXR, by enhancing NKG2D ligand expression, can promote NK cell-mediated cytotoxicity and suggests a novel immune-mediated mechanism involving modulation of intracellular cholesterol levels in cancer cells.-Bilotta, M. T., Abruzzese, M. P., Molfetta, R., Scarno, G., Fionda, C., Zingoni, A., Soriani, A., Garofalo, T., Petrucci, M. T., Ricciardi, M. R., Paolini, R., Santoni, A., Cippitelli, M. Activation of liver X receptor up-regulates the expression of the NKG2D ligands MICA and MICB in multiple myeloma through different molecular mechanisms.

MicroRNA-26a inhibits multiple myeloma cell growth by suppressing cyclin-dependent kinase 6 expression

MicroRNA-26a (miR-26a) has been reported to be involved in the tumorigenesis of several tumors, but its biological function and molecular mechanism in multiple myeloma (MM) are still unknown. In this study, we found that overexpression of miR-26a obviously inhibited MM cell growth, and delayed tumor growth in xenografts. Further studies showed that overexpression of miR-26a induced cell cycle arrest at G0/G1 phase in MM cells. MiR-26a mimic down-regulated the expression levels of CDK6 and E2F1, but up-regulated p53 and p21 expression. In contrast, overexpression of CDK6 decreased the effect of miR-26a mimic on MM cell survival. Moreover, miR-26a targeted CDK6 mRNA and thus suppressed CDK6 protein expression. Overexpression of miR-26a also enhanced the cytotoxic action of doxorubicin against MM. These results demonstrated that miR-26a was involved in the development of MM through regulating CDK6 signaling pathway, and indicated that miR-26a could be as a novel target for anti-tumor therapy in clinic as a single strategy or in combination with other anti-tumor drugs in MM.

Ubiquitin-specific peptidase 28 enhances STAT3 signaling and promotes cell growth in non-small-cell lung cancer

BACKGROUND AND OBJECTIVES

Ubiquitin-specific peptidase 28 (USP28) has been reported to play significant roles in several tumors, but its roles in non-small-cell lung cancer (NSCLC) is still unknown. In this study, we aimed to investigate the biological function and molecular mechanisms of USP28 in NSCLC.

MATERIALS AND METHODS

Immunoblotting analysis was used to detect relative proteins' expression. Luciferase assay was performed to explore the activation of signal transducer and activator of transcription 3 (STAT3). Immunoprecipitation was performed to assess whether USP28 interacted with STAT3 or deubiquitinated STAT3. Quantitative real-time PCR was performed to evaluate the relative mRNA levels of STAT3 and USP28. Cycloheximide chase assay was carried out to examine whether USP28 affected the half-life of STAT3 protein. Cell Counting Kit-8 assay and xenograft model were used to assess whether USP28 regulated NSCLC cell growth.

RESULTS

In this study, the deubiquitinating enzyme USP28 was found to mediate STAT3 signaling in NSCLC cells. USP28 interacted with STAT3, and increased the stability of STAT3 by inducing its deubiquitination. Further studies showed that USP28 was upregulated in both the primary tissues and cell lines of NSCLC. The Kaplan-Meier plotter also indicated that USP28 predicted a poor prognosis of NSCLC patients. Moreover, knockdown of USP28 inhibited cell growth of NSCLC cells in vitro and delayed NSCLC tumor growth in vivo.

CONCLUSION

These results demonstrated that USP28 was functional in NSCLC cells, and promoted NSCLC cell growth by inducing STAT3 signaling. This suggests that USP28 could be a novel target for NSCLC therapy.

The anthelmintic agent oxfendazole inhibits cell growth in non‑small cell lung cancer by suppressing c‑Src activation

The c‑Src protein family of tyrosine kinases are important in the tumorigenesis of many types of tumors, and may be a potential target for antitumor drug discovery. In the present study, immunoblotting was performed to analyze protein expression, CCK‑8 assay was carried out to assess cell viability and cell cycle was analyzed using a flow cytometer. The anthelmintic agent oxfendazole was observed to be a novel c‑Src inhibitor that blocked the activation of c‑Src. Oxfendazole also suppressed the cell growth of non‑small cell lung cancer (NSCLC) cells, and overexpression of c‑Src decreased the cytotoxicity of oxfendazole against NSCLC cells. In addition, oxfendazole induced cell cycle arrest at the G0/G1 phase, and downregulated the protein levels of Cyclin‑dependent kinase (CDK)‑4, CDK6, retinoblastoma protein and E2 transcription factor 1, and upregulated the expression levels of p53 and p21 in NSCLC cells. Furthermore, oxfendazole enhanced the cytotoxicity of cisplatin against NSCLC cells. These results demonstrated that oxfendazole exerted its antitumor activity by suppressing c‑Src signaling, and it was also indicated that the anthelmintic agent oxfendazole may be effective for anti‑NSCLC therapy in the clinic as a single agent or in combination with other antitumor drugs.

The natural polyphenol curcumin induces apoptosis by suppressing STAT3 signaling in esophageal squamous cell carcinoma

Background

We and others have previously shown that the STAT3 signaling pathway is activated in some esophageal squamous cell carcinoma (ESCC) cells and is required for the survival and growth of these primary ESCC-derived xenografts. It has also been shown that the natural polyphenol curcumin is an effective anti-tumor agent.

Methods

Luciferase assay and immunoblotting were performed to examine whether curcumin suppressed STAT3 signaling. CCK-8 assay and xenografts were utilized for analyzing ESCC cell growth in culture and mice. Soft agar assay was carried out to determine the colony formation ability of ESCC cells in the presence or absence of curcumin. Cell death and cell cycle were assessed by In CELL Analyzer 2000. Immunohistochemistry and TUNEL assay were used for detecting apoptosis in ESCC tisuses. Molecular docking was performed to evaluate the interaction of curcumin with JAK2. JAK2 activity was assessed using an in vitro cell-free system. HE staining was used to evaluate the ESCC tissues.

Results

The natural polyphenol curcumin inhibited STAT3 phosphorylation rapidly and blocked STAT3-mediated signaling in ESCC cells. It also induced growth arrest and apoptosis in cultured ESCC cells, which were attenuated by enforced expression of STAT3. Furthermore, curcumin preferentially blocked the growth of primary ESCC-derived xenografts that harbored activated STAT3.

Conclusions

Curcumin is able to exert anti-tumor action through inhibiting the STAT3 signaling pathway. Giving its wide use in traditional medicines with low toxicity and few adverse reactions, it is conceivable that curcumin might be further explored as a unique STAT3 inhibitor for anti-cancer therapies.

Knockdown of RNF6 inhibits gastric cancer cell growth by suppressing STAT3 signaling

Background and objective

RNF6, an E3 ligase, has been reported to play an important role in the tumorigenesis in several tissues, but its role in gastric cancer is still unknown. In this study, we aimed to investigate the biological function and molecular mechanisms of RNF6 in gastric cancer.

Materials and methods

The expression levels of RNF6 were detected by quantitative real-time PCR (qRT-PCR) and immunoblotting in gastric cancer tissues and cell lines. Cell Counting Kit-8 assay was performed to evaluate cell proliferation. Cell apoptosis was analyzed by flow cytometer and immunoblotting. Luciferase assay, immunoblotting and qRT-PCR were performed to explore the activation of STAT3. Immunoprecipitation was performed to evaluate the ubiquitination of SHP-1.

Results

In this study, RNF6 was found to be upregulated in both primary tissues and cell lines of gastric cancer. Knockdown or overexpression of RNF6 inhibited or promoted cell growth of gastric cancer cells. Knockdown of RNF6 also induced the cleavage of PARP and promoted cell apoptosis in gastric cancer cells. In addition, knockdown of RNF6 also increased the cytotoxicity of doxorubicin against gastric cancer. Moreover, knockdown of RNF6 inhibited STAT3-derived luciferase activity and downregulated the phosphorylation of STAT3, but upregulated the protein level of SHP-1. Knockdown of RNF6 downregulated the expression of MCL1 and XIAP, which are target genes of STAT3. Further studies showed that RNF6 regulated the stability of SHP-1 by inducing its polyubiquitination.

Conclusion

These results demonstrated that RNF6 was highly expressed in gastric cancer and regulated the growth of gastric cancer cells by affecting SHP-1/STAT3 signaling, which suggested that RNF6 could be a novel target for gastric cancer therapy.

RING finger protein 38 induces gastric cancer cell growth by decreasing the stability of the protein tyrosine phosphatase SHP-1

The function of the E3 ligase RNF38 is still unknown in gastric cancer. Here, we found that RNF38 is upregulated in gastric cancer, and it is associated with the overall survival of gastric cancer patients. Further studies showed that RNF38 interacts with the nonreceptor tyrosine phosphatase SH2-containing protein tyrosine phosphatase 1 (SHP-1) and induces the polyubiquitination of SHP-1, which leads to destabilization of SHP-1 and promotion of STAT3 signaling in gastric cancer cells. In addition, overexpression or knockdown of RNF38 induces or suppresses gastric cancer cell growth in vitro, respectively, and silencing RNF38 delays tumor growth in vivo. These findings demonstrate that RNF38 is functional in gastric cancer and promotes STAT3 signaling by destabilizing SHP-1; thus, RNF38 could be a novel target for gastric cancer therapy.

Antimalarial drug mefloquine inhibits nuclear factor kappa B signaling and induces apoptosis in colorectal cancer cells

Nuclear factor kappa B (NF‐κB) signaling pathway is activated in many colorectal cancer (CRC) cells and in the tumor microenvironment, which plays a critical role in cancer initiation, development, and response to therapies. In the present study, we found that the widely used antimalarial drug mefloquine was a NF‐κB inhibitor that blocked the activation of IκBα kinase, leading to reduction of IκBα degradation, decrease of p65 phosphorylation, and suppressed expression of NF‐κB target genes in CRC cells. We also found that mefloquine induced growth arrest and apoptosis of CRC cells harboring phosphorylated p65 in culture and in mice. Furthermore, expression of constitutive active IKKβ kinase significantly attenuated the cytotoxic effect of the compound. These results showed that mefloquine could exert antitumor action through inhibiting the NF‐κB signaling pathway, and indicated that the antimalarial drug might be repurposed for anti‐CRC therapy in the clinic as a single agent or in combination with other anticancer drugs.

Bavachin induces the apoptosis of multiple myeloma cell lines by inhibiting the activation of nuclear factor kappa B and signal transducer and activator of transcription 3

Bavachin is a phytoestrogen purified from natural herbal plants such as Psoralea corylifolia. In this study, we examined the effect of bavachin in multiple myeloma (MM) cell lines. We found that bavachin decreased the viability of MM cell lines, but was not cytotoxic towards normal cells. It inhibited the activation of nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription 3 (STAT3). Furthermore, bavachin increased the expression of p53 and NOXA, and decreased the expression of X-linked inhibitor of apoptosis protein (XIAP), survivin, B cell lymphoma-extra large (Bcl-xL), and Bcl-2. Additionally, bavachin induced apoptosis by the activation of caspase-3 and caspase-9, implicating the involvement of the mitochondrial pathway. Our results suggest that bavachin induces apoptosis through the inhibition of NF-κB and STAT3 activation in MM cell lines. Most importantly, few NF-κB and STAT3 inhibitors with high efficiency, specificity, and safety are currently available for clinical cancer therapy. Hence, bavachin, which targets NF-κB and STAT3, is a potential anticancer agent for the treatment of MM.