RFX1-dependent activation of SHP-1 induces autophagy by a novel obatoclax derivative in hepatocellular carcinoma cells

Roles of protein tyrosine phosphatases in hepatocellular carcinoma progression (Review)

Hepatocellular carcinoma (HCC) represents almost 80% of all liver cancers, is the sixth most common cancer and is the second‑highest cause of cancer‑related deaths worldwide. Protein tyrosine phosphatases (PTPs), which are encoded by the largest family of phosphatase genes, play critical roles in cellular responses and are implicated in various signaling pathways. Moreover, PTPs are dysregulated and involved in various cellular processes in numerous cancers, including HCC. Kinases and phosphatases are coordinators that modulate cell activities and regulate signaling responses. There are multiple interacting signaling networks, and coordination of these signaling networks in response to a stimulus determines the physiological outcome. Numerous issues, such as drug resistance and inflammatory reactions in the tumor microenvironment, are implicated in cancer progression, and the role of PTPs in these processes has not been well elucidated. Therefore, the present review focused on discussing the relationship of PTPs with inflammatory cytokines and chemotherapy/targeted drug resistance, providing detailed information on how PTPs can modulate inflammatory reactions and drug resistance to influence progression in HCC.

The Interaction Between Autophagy and JAK/STAT3 Signaling Pathway in Tumors

Tumor is one of the important factors affecting human life and health in today’s world, and scientists have studied it extensively and deeply, among which autophagy and JAK/STAT3 signaling pathway are two important research directions. The JAK/STAT3 axis is a classical intracellular signaling pathway that assumes a key role in the regulation of cell proliferation, apoptosis, and vascular neogenesis, and its abnormal cell signaling and regulation are closely related to the occurrence and development of tumors. Therefore, the JAK/STAT3 pathway in tumor cells and various stromal cells in their microenvironment is often considered as an effective target for tumor therapy. Autophagy is a process that degrades cytoplasmic proteins and organelles through the lysosomal pathway. It is a fundamental metabolic mechanism for intracellular degradation. The mechanism of action of autophagy is complex and may play different roles at various stages of tumor development. Altered STAT3 expression has been found to be accompanied by the abnormal autophagy activity in many oncological studies, and the two may play a synergistic or antagonistic role in promoting or inhibiting the occurrence and development of tumors. This article reviews the recent advances in autophagy and its interaction with JAK/STAT3 signaling pathway in the pathogenesis, prevention, diagnosis, and treatment of tumors.

RFX1: a promising therapeutic arsenal against cancer

Regulatory factor X1 (RFX1) is an evolutionary conserved transcriptional factor that influences a wide range of cellular processes such as cell cycle, cell proliferation, differentiation, and apoptosis, by regulating a number of target genes that are involved in such processes. On a closer look, these target genes also play a key role in tumorigenesis and associated events. Such observations paved the way for further studies evaluating the role of RFX1 in cancer. These studies were indispensable due to the failure of conventional chemotherapeutic drugs to target key cellular hallmarks such as cancer stemness, cellular plasticity, enhanced drug efflux, de-regulated DNA repair machinery, and altered pathways evading apoptosis. In this review, we compile significant evidence for the tumor-suppressive activities of RFX1 while also analyzing its oncogenic potential in some cancers. RFX1 induction decreased cellular proliferation, modulated the immune system, induced apoptosis, reduced chemoresistance, and sensitized cancer stem cells for chemotherapy. Thus, our review discusses the pleiotropic function of RFX1 in multitudinous gene regulations, decisive protein–protein interactions, and also its role in regulating key cell signaling events in cancer. Elucidation of these regulatory mechanisms can be further utilized for RFX1 targeted therapy.

Protective Effect of Curcumin on Bone Trauma in a Rat Model via Expansion of Myeloid Derived Suppressor Cells

BACKGROUND Bone fracture, a common injury to bones leads to various biophysiological changes and pathological responses in the body. The current study investigated curcumin for treatment of bone fracture in a rat model of bone trauma, and evaluated the related mechanism. MATERIAL AND METHODS The rats were separated randomly into 3 groups; sham, model, and curcumin treatment groups. The fracture rat model was established by transverse osteotomy in the right femur bone at the mid-shaft. The osteoblast count was determined using hematoxylin and eosin staining. Vascular endothelial growth factor (VEGF) and proliferating cell nuclear antigen (PCNA) expression were measured by western blotting. RESULTS The rpS6-phosphorylation was suppressed and light chain 3 (LC3II) expression elevated in the curcumin treated group of the fracture rat model. In the curcumin-treated group, mineralization of fracture calluses was markedly higher on day 14 of fracture. The formation of osteoblasts was observed at a greater rate in the curcumin treated group compared to the model rat group. Treatment of rats with curcumin significantly (P<0.05) promoted expression of PCNA and VEGF. The decrease in CD11b+/Gr-1+ cell expansion in rats with bone trauma was alleviated significantly by curcumin treatment. A marked increase in arginase-1 expression in rats with bone trauma was caused by curcumin treatment. CONCLUSIONS In summary, curcumin activates autophagy and inhibits mTOR activation in bone tissues of rats with trauma. The curcumin promoted myeloid-derived suppressor cell (MDSC) proliferation and increased expansion of MDSCs in a rat model of trauma. Therefore, curcumin may have beneficial effect in patients with bone trauma and should be evaluated further for development of treatment.

BCL2L10/BECN1 modulates hepatoma cells autophagy by regulating PI3K/AKT signaling pathway

The aim of this study was to investigate BCL2L10 and BECN1 expression and their effect on autophagy in hepatocellular carcinoma (HCC). We found that BCL2L10 expression was low in hepatoma tissues and cells. Overexpression of BCL2L10 decreased the activity of hepatoma cells. To analyze autophagic flux, we monitored the formation of autophagic vesicles by fluorescence protein method. Autophagy-related protein LC3B-II was accumulated and P62 was decreased, which indicated that autophagy was induced by BECN1, while BCL2L10 could suppress this trend. Immunofluorescence assay showed that BCL2L10 and Beclin 1 were co-located in hepatoma cells. Immunoprecipitation showed that BCL2L10 could inhibit the autophagy of hepatoma cells by combining with Beclin 1. ELISA and co-immunoprecipitation suggested that the combination between BCL2L10 and Beclin 1 reduced the bond between Beclin 1 and PI3KC3. Based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, the PI3K/AKT signaling pathway was significantly upregulated in HCC. In conclusions, BCL2L10 had a low expression in HCC tissues and cells, which could release BECN1 to induce autophagy of hepatoma cells by downregulating PI3K/AKT signaling pathway.

Chrysin inhibits sphere formation in SMMC-7721 cells via modulation of SHP-1/STAT3 signaling pathway

Background: Chrysin is a natural flavonoid which has been identified as a candidate anti-cancer agent due to its inhibitory effect on a variety of cancer cells, including targeted inhibition of sphere formation in hepatocellular carcinoma (HCC) cell lines. However, the mechanism by which chrysin modulates HCC spheres remains unclear. Materials and methods: In this study, we investigate the effect of chrysin on the regulation of SHP-1 and its downstream signal molecule STAT3 to explain the mechanism by which chrysin inhibits sphere formation of HCC cell lines. Results: Here, we found that SHP-1 protein expression was markedly down-regulated in the spheres from both SMMC-7721 and MHCC97H cells. Chrysin significantly inhibited sphere formation and upregulated the expression of SHP-1 protein in both SMMC-7721 and MHCC97H cells, as well as reduced p-STAT3 and Twist1 expressions in SMMC-7721 cells. Furthermore, knockdown of SHP-1 in SMMC-7721 cells resulted in the induction of p-STAT3 and Twist1 protein expression and antagonizing the inhibitory effect of chrysin on sphere formation in SMMC-7721 cells. Conclusion: Overall, the study findings demonstrated that chrysin acts as a candidate for the treatment of HCC through modulating SHP-1/STAT3 signaling pathway.

Autophagy and liver cancer

Autophagy is a key biological phenomenon conserved from yeast to mammals. Under basal conditions, activation of autophagy leads to the protein degradation as well as damaged organelles for maintaining cellular homeostasis. Deregulation of autophagy has been identified as a key mechanism contributing to the pathogenesis and progression of several liver diseases, including hepatocellular carcinoma (HCC), one of the most common and mortal types of cancer. Currently used treatment strategies in patients with HCC result in variable success rates. Therefore, novel early diagnosis and treatment techniques should be developed. Manipulation of autophagy may improve responses of cancer cell to treatments and provide novel targeted therapy options for HCC. In this review, we summarized how our understanding of autophagy-cell death connection may have an impact on HCC therapy.

Doxorubicin induces an extensive transcriptional and metabolic rewiring in yeast cells

Doxorubicin is one of the most effective chemotherapy drugs used against solid tumors in the treatment of several cancer types. Two different mechanisms, (i) intercalation of doxorubicin into DNA and inhibition of topoisomerase II leading to changes in chromatin structure, (ii) generation of free radicals and oxidative damage to biomolecules, have been proposed to explain the mode of action of this drug in cancer cells. A genome-wide integrative systems biology approach used in the present study to investigate the long-term effect of doxorubicin in Saccharomyces cerevisiae cells indicated the up-regulation of genes involved in response to oxidative stress as well as in Rad53 checkpoint sensing and signaling pathway. Modular analysis of the active sub-network has also revealed the induction of the genes significantly associated with nucleosome assembly/disassembly and DNA repair in response to doxorubicin. Furthermore, an extensive re-wiring of the metabolism was observed. In addition to glycolysis, and sulfate assimilation, several pathways related to ribosome biogenesis/translation, amino acid biosynthesis, nucleotide biosynthesis, de novo IMP biosynthesis and one-carbon metabolism were significantly repressed. Pentose phosphate pathway, MAPK signaling pathway biological processes associated with meiosis and sporulation were found to be induced in response to long-term exposure to doxorubicin in yeast cells.

SHP-1 Acts as a Tumor Suppressor in Hepatocarcinogenesis and HCC Progression

Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1, also known as PTPN6) is a nonreceptor protein tyrosine phosphatase that acts as a negative regulator of inflammation. Emerging evidence indicates that SHP-1 plays a role in inhibiting the progression of hepatocellular carcinoma (HCC). However, the role of SHP-1 in hepatocarcinogenesis remains unknown. Here, we find that levels of SHP-1 are significantly downregulated in human HCC tissues compared with those in noncancerous tissues (P < 0.001) and inversely correlate with tumor diameters (r = -0.4130, P = 0.0002) and serum α-fetoprotein levels (P = 0.047). Reduced SHP-1 expression was associated with shorter overall survival of patients with HCC with HBV infection. Overexpression of SHP-1 suppressed proliferation, migration, invasion, and tumorigenicity of HCC cells, whereas knockdown of SHP-1 enhanced the malignant phenotype. Moreover, knockout of Ptpn6 in hepatocytes (Ptpn6^HKO ) enhanced hepatocarcinogenesis induced by diethylnitrosamine (DEN) as well as metastasis of primary liver cancer in mice. Furthermore, systemic delivery of SHP-1 by an adenovirus expression vector exerted a therapeutic effect in an orthotopic model of HCC in NOD/SCID mice and DEN-induced primary liver cancers in Ptpn6^HKO mice. In addition, SHP-1 inhibited the activation of JAK/STAT, NF-κB, and AKT signaling pathways, but not the MAPK pathway in primary hepatocytes from DEN-treated mice and human HCC cells. Together, our data implicate SHP-1 as a tumor suppressor of hepatocarcinogenesis and HCC progression and propose it as a novel prognostic biomarker and therapeutic target of HCC.Significance: The nonreceptor protein tyrosine phosphatase SHP-1 acts as a tumor suppressor in hepatocellular carcinoma. Cancer Res; 78(16); 4680-91. ©2018 AACR.

Downregulation of RFX1 predicts poor prognosis of patients with small hepatocellular carcinoma

OBJECTIVE

Regulatory factor X1 (RFX1) deletion has been reported to be correlated with poor prognosis of some types of cancer. The present study aimed to investigate the prognostic value of RFX1 in HCC, especially in small hepatocellular carcinoma.

METHODS

Immunohistochemical assay was used to investigate RFX1 expression in 221 HCC tissues and another validation cohort of 71 small HCC samples. We also performed in vitro experiments to investigate if RFX1 regulated invasive capacity of HCC cells and expression of epithelial-mesenchymal transition (EMT) markers.

RESULTS

We found that RFX1 expression was significantly lower in HCC tissues compared to the corresponding non-tumor tissues. Further survival analysis suggested that the downregulation of RFX1 correlated with poor prognosis and a high recurrence risk in HCC patients, particularly in small HCC patients. Furthermore, another validation cohort of small HCC samples confirmed that downregulation of RFX1 in HCC tissues predicted high recurrence risk and poor prognosis for early stage HCC patients. In vitro studies suggested that knocking down RFX1 facilitated HCC cell invasion, while overexpression of RFX1 reduced the invasion of HCC cells. Western blot assays also indicated that RFX1 regulated expression of some EMT markers. Knocking down RFX1 decreased E-cadherin and increased vimentin expression, while RFX1 overexpression enhanced E-cadherin and decreased vimentin expression.

CONCLUSIONS

Our study demonstrated that RFX1 downregulation is a new predictive marker of high recurrence risk and poor prognosis of HCC; It has potential to help guide treatment for postoperative HCC patients, especially for small HCC patients.

Systematic analyses and comprehensive field synopsis of genetic association studies in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancy in the world. In order to comprehensively examine the association between genetic variants and risk of HCC, a systematic literature search and meta-analyses of the evidences have been performed. With the data from 301 articles, we conducted meta-analyses for 69 polymorphisms involving 46 distinct genes. The result showed that 31 polymorphisms in 25 genes are significantly associated with HCC risk. Cumulative epidemiological evidence for a significant association with HCC risk was graded strong for one polymorphism (NQO1 rs1800566). Furthermore, we provided a database to integrate and analyze the association of genetic variants and HCC risk. To the best of our knowledge, this is the first comprehensive field synopsis and systematic meta-analysis of genetic association with HCC risk. We have provided a useful resource and platform for investigators to explore the association of sequence polymorphisms and HCC risk.

The tyrosine kinase inhibitor nintedanib activates SHP-1 and induces apoptosis in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) remains difficult to treat and urgently needs new therapeutic options. Nintedanib, a multikinase inhibitor, has exhibited efficacy in early clinical trials for HER2-negative breast cancer. In this study, we examined a new molecular mechanism of nintedanib in TNBC. The results demonstrated that nintedanib enhanced TNBC cell apoptosis, which was accompanied by a reduction of p-STAT3 and its downstream proteins. STAT3 overexpression suppressed nintedanib-mediated apoptosis and further increased the activity of purified SHP-1 protein. Moreover, treatment with either a specific inhibitor of SHP-1 or SHP-1-targeted siRNA reduced the apoptotic effects of nintedanib, which validates the role of SHP-1 in nintedanib-mediated apoptosis. Furthermore, nintedanib-induced apoptosis was attenuated in TNBC cells expressing SHP-1 mutants with constantly open conformations, suggesting that the autoinhibitory mechanism of SHP-1 attenuated the effects of nintedanib. Importantly, nintedanib significantly inhibited tumor growth via the SHP-1/p-STAT3 pathway. Clinically, SHP-1 levels were downregulated, whereas p-STAT3 was upregulated in tumor tissues, and SHP-1 transcripts were associated with improved disease-free survival in TNBC patients. Our findings revealed that nintedanib induces TNBC apoptosis by acting as a SHP-1 agonist, suggesting that targeting STAT3 by enhancing SHP-1 expression could be a viable therapeutic strategy against TNBC.

Targeting SHP-1-STAT3 signaling: A promising therapeutic approach for the treatment of cholangiocarcinoma

Sorafenib is a multiple kinase inhibitor which targets Raf kinases, VEGFR, and PDGFR and is approved for the treatment of hepatocellular carcinoma (HCC). Previously, we found that p-STAT3 is a major target of SC-43, a sorafenib derivative. In this study, we report that SC-43-induced apoptosis in cholangiocarcinoma (CCA) via a novel mechanism. Three CCA cell lines (HuCCT-1, KKU-100 and CGCCA) were treated with SC-43 to determine their sensitivity to SC-43-induced cell death and apoptosis. We found that SC-43 activated SH2 domain-containing phosphatase 1 (SHP-1) activity, leading to p-STAT3 and downstream cyclin B1 and Cdc2 downregulation, which induced G2-M arrest and apoptotic cell death. Importantly, SC-43 augmented SHP-1 activity by direct binding to N-SH2 and relief of its autoinhibition. Deletion of the N-SH2 domain (dN1) or point mutation (D61A) of SHP-1 counteracted the effect of SC-43-induced SHP-1 phosphatase activation and antiproliferation ability in CCA cells. In vivo assay revealed that SC-43 exhibited xenograft tumor growth inhibition, p-STAT3 reduction and SHP-1 activity elevation. In conclusion, SC-43 induced apoptosis in CCA cells through the SHP-1/STAT3 signaling pathway.

Expression of regulatory factor X1 can predict the prognosis of breast cancer

Breast cancer (BC) is the most common malignancy among women. Identifying novel biomarkers to predict prognosis accurately is important in managing this disease. The regulatory factor X1 (RFX1) gene is a member of the regulatory factor X gene family. Its protein reportedly downregulates the proto-oncogene c-myc, but its role in BC has been unclear. In this study, expression and methylation status of RFX1 were determined in BC cell lines. We then evaluated RFX1 mRNA expression levels with regard to clinicopathological factors including postoperative prognosis in 167 patients with BC. Expression of RFX1 was heterogeneous among cell lines, and we found no DNA methylation at the RFX1 promoter region. Patients were categorized into groups with high or low RFX1 expression, based on ratio of RFX1 mRNA expression in BC and adjacent non-cancerous tissues. The high RFX1 group was significantly associated with low T factor (P=0.028), earlier disease stage (P=0.015), positive expression of estrogen receptor (P=0.005) and progesterone receptor (P=0.011), negative expression of human epidermal growth factor receptor 2 (P=0.001). The high RFX1 group experienced more favorable disease-free survival (P=0.007) and overall survival (P=0.013). In multivariate analysis, RFX1 expression was an independent prognostic factor for disease-free survival. Our findings indicate that RFX1 may serve as a prognostic marker for BC.

Sorafenib analogue SC-60 induces apoptosis through the SHP-1/STAT3 pathway and enhances docetaxel cytotoxicity in triple-negative breast cancer cells

Recurrent triple-negative breast cancer (TNBC) needs new therapeutic targets. Src homology region 2 domain-containing phosphatase-1 (SHP-1) can act as a tumor suppressor by dephosphorylating oncogenic kinases. One major target of SHP-1 is STAT3, which is highly activated in TNBC. In this study, we tested a sorafenib analogue SC-60, which lacks angiokinase inhibition activity, but acts as a SHP-1 agonist, in TNBC cells. SC-60 inhibited proliferation and induced apoptosis by dephosphorylating STAT3 in both a dose- and time-dependent manner in TNBC cells (MDA-MB-231, MDA-MB-468, and HCC1937). By contrast, ectopic expression of STAT3 rescued the anticancer effect induced by SC-60. SC-60 also increased the SHP-1 activity, but this effect was inhibited when the N-SH2 domain (DN1) was deleted or with SHP-1 point mutation (D61A), implying that SHP-1 is the major target of SC-60 in TNBC. The use of SC-60 in combination with docetaxel synergized the anticancer effect induced by SC-60 through the SHP-1/STAT3 pathway in TNBC cells. Importantly, SC-60 also displayed a significant antitumor effect in an MDA-MB-468 xenograft model by modulating the SHP-1/STAT3 axis, indicating the anticancer potential of SC-60 in TNBC treatment. Targeting SHP-1/p-STAT3 and the potential combination of SHP-1 agonist with chemotherapeutic docetaxel is a feasible therapeutic strategy for TNBC.

Transcription factor RFX1 is ubiquitinated by E3 ligase STUB1 in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease caused by complex interactions between genes and the environment. The expression level of transcription factor regulatory factor X 1 (RFX1) is reduced in T cells from SLE patients. RFX1 can regulate epigenetic modifications of CD70 and CD11a and plays an important role in the development of SLE. However, the mechanisms that mediate reduction of RFX1 in SLE are unclear. Here, we demonstrate that RFX1 protein expression can be tightly regulated by polyubiquitination-mediated proteosomal degradation via STIP1 homology and U-box containing protein 1 (STUB1). The E3 ligase STUB1 is upregulated in CD4(+)T cells of SLE patients compared to healthy subjects. Overexpression of STUB1 in CD4(+)T cells leads to upregulation of levels of CD70 and CD11a in T cells. The modulation of STUB1 activity may provide a novel therapeutic approach for SLE.

The BH3 mimetic drug ABT-737 induces apoptosis and acts synergistically with chemotherapeutic drugs in thyroid carcinoma cells

BACKGROUND

Patients with dedifferentiated and anaplastic thyroid carcinomas that do not take up radioiodine are resistant to chemotherapeutic treatment and external irradiation and thus are difficult to treat. Direct induction of apoptosis is a promising approach in these apoptosis-resistant tumor cells. The BH3 mimetic ABT-737 belongs to a new class of drugs that target anti-apoptotic proteins of the BCL-2 family and facilitate cell death. The purpose of this study was to investigate the effect of ABT-737 alone or in combination with chemotherapeutic drugs on thyroid carcinoma cell lines.

METHODS

A total of 16 cell lines derived from follicular, papillary, and anaplastic thyroid carcinomas were treated with ABT-737. Cell viability was measured with MTT assay. Cell death was determined by cell cycle phase distribution and subG1 peak analyses, determination of caspase 3/7 activity and caspase cleavage products, lactate dehydrogenase (LDH) liberation assays and LC3 analysis by western blot.

RESULTS

The number of viable cells was decreased in all cell lines examined after ABT-737 treatment, with IC50 values ranging from 0.73 to 15.6 μM. Biochemical markers of apoptosis like caspase activities, caspase cleavage products and DNA fragmentation determined as SubG1 peak were elevated after ABT-737 treatment, but no LC3 cleavage was induced by ABT-737 indicating no autophagic processes. In combination with doxorubicin and gemcitabine, ABT-737 showed synergistic effects on cell viability.

CONCLUSIONS

With these experiments we demonstrated the efficacy of the BH3 mimetic drug ABT-737 against dedifferentiated thyroid carcinoma cells of various histological origins and showed synergistic effects with chemotherapeutic drugs. ABT-737-treated cells underwent an apoptotic cell death. ABT-737 and related BH3 mimetic drugs, alone or in combination, may thus be of value as a new therapeutic option for dedifferentiated thyroid carcinomas.

The role of STAT3 in autophagy

Autophagy is an evolutionarily conserved process in eukaryotes that eliminates harmful components and maintains cellular homeostasis in response to a series of extracellular insults. However, these insults may trigger the downstream signaling of another prominent stress responsive pathway, the STAT3 signaling pathway, which has been implicated in multiple aspects of the autophagic process. Recent reports further indicate that different subcellular localization patterns of STAT3 affect autophagy in various ways. For example, nuclear STAT3 fine-tunes autophagy via the transcriptional regulation of several autophagy-related genes such as BCL2 family members, BECN1, PIK3C3, CTSB, CTSL, PIK3R1, HIF1A, BNIP3, and microRNAs with targets of autophagy modulators. Cytoplasmic STAT3 constitutively inhibits autophagy by sequestering EIF2AK2 as well as by interacting with other autophagy-related signaling molecules such as FOXO1 and FOXO3. Additionally, the mitochondrial translocation of STAT3 suppresses autophagy induced by oxidative stress and may effectively preserve mitochondria from being degraded by mitophagy. Understanding the role of STAT3 signaling in the regulation of autophagy may provide insight into the classic autophagy model and also into cancer therapy, especially for the emerging targeted therapy, because a series of targeted agents execute antitumor activities via blocking STAT3 signaling, which inevitably affects the autophagy pathway. Here, we review several of the representative studies and the current understanding in this particular field.

Induction of atypical cell death in thyroid carcinoma cells by the indirubin derivative 7-bromoindirubin-3'-oxime (7BIO)

BACKGROUND

The indirubin derivative 7-bromoindirubin-3'-oxime (7BIO) has already shown anticancer properties by causing cell death in some tumour cell lines and may be a new therapeutic option for treatment-resistant tumour cells. Since dedifferentiated and anaplastic thyroid carcinomas do not take up radioiodine and are insensitive to chemotherapeutic treatment and external radiation, direct cell death induction in these tumour cells may be a promising approach. We thus investigated the effect of 7BIO on thyroid carcinoma cell lines of different histological origins and characterized the type of cell death induction by 7BIO.

METHODS

Cell viability was measured with MTT assay. Cell death was analysed by caspase 3/7 activity, lactate dehydrogenase liberation, caspase cleavage products, DNA fragmentation, cell cycle phase distribution and LC3B analysis.

RESULTS

After 7BIO treatment, cell viability was reduced in all 14 thyroid carcinoma cell lines investigated. Treated cells showed DNA fragmentation, cell cycle arrest and lactate dehydrogenase liberation but no LC3B cleavage. Caspase activation following 7BIO treatment was found in five of six cell lines investigated. Interestingly, inhibition of caspases had no effect on viability of the cells after 7BIO incubation.

CONCLUSIONS

Our results indicate that 7BIO efficiently killed dedifferentiated thyroid carcinoma cells. It induced a non-classical kind of cell death that was caspase-independent and includes DNA fragmentation. 7BIO and related indirubin components thus may have value as a new therapeutic option for dedifferentiated thyroid cancer irrespective of the exact target molecules and the kind of cell death they induce.

miR-146a is directly regulated by STAT3 in human hepatocellular carcinoma cells and involved in anti-tumor immune suppression

MicroRNAs (miRNAs) play an important role in tumorigenesis, but their role in tumor-induced immune suppression is largely unknown. STAT3 signaling, a key pathway mediating immune suppression in the tumor microenvironment, is responsible for the transcription of several important miRNAs. In this study, we observed that miR-146a, a known important regulator of immune responses, was downregulated by blocking activated STAT3 in hepatocellular carcinoma (HCC) cells. Furthermore, miR-146a inhibition in HCC cells not only altered the STAT3 activation-associated cytokine profile but also reversed HCC-induced NK cell dysfunction in vitro and improved the anti-tumor effect of lymphocytes in vivo. Importantly, ChIP and luciferase reporter assays confirmed that STAT3 directly bound to the miR-146a promoter and induced miR-146a expression. These findings indicated that miR-146a expression was regulated by aberrantly activated STAT3 in HCC cells and exerted negative effects on anti-tumor immune response, which resulted in the upregulation of cytokines such as TGF-β, IL-17, VEGF and downregulation of type I IFN to create an immunosuppressive microenvironment. This further insight into understanding the mechanism responsible for tumor-induced immune suppression highlights the potential application of miR-146a as a novel immunotherapeutic target for HCC.

Bone fracture in a rat femoral fracture model is associated with the activation of autophagy

Autophagy, which is a mechanism for the turnover of intracellular molecules and organelles, protects cells during stress responses; however, the role of autophagy in the stages of bone fracture remains to be elucidated. The aim of the present study was to investigate the process of autophagy in bone tissue at different time-points after fracture. A femur fracture model was established in male adult Wistar rats via surgery. The protein expression of microtubule-associated protein II light chain 3 (LC3-II) was analyzed in a femur fracture (experimental) group and a sham-surgery group using immunofluorescence. The protein expression of proliferating cell nuclear antigen (PCNA) was used to investigate the cell proliferation in bone tissue following fracture via immunohistochemical analysis. The correlation between cell proliferation and autophagy was analyzed using linear regression. LC3-II protein was constitutively expressed in the sham-surgery group; however, compared with the expression in the sham-surgery group, the LC3-II expression in the experimental group was significantly increased at each time-point (P<0.05). Similarly, immunohistochemistry revealed that the number of PCNA-positive cells in each section was significantly increased following fracture injury (P<0.01). A comparison of the LC3-II- and PCNA-positive rates in the experimental group rats at each time-point revealed a linear correlation (R²=0.43, P<0.01). In conclusion, surgically induced fracture in rats is associated with an increase in LC3-II and PCNA protein expression during the initial stages of fracture injury, and a correlation exists between the expression of the two proteins. These results suggest that potential treatment aimed at improving fracture healing should target the process of autophagy.

Rapamycin-induced autophagy activity promotes bone fracture healing in rats

Autophagy is a crucial mediating process for normal bone cell function and metabolism in physiology or pathology. Rapamycin has been demonstrated to induce the autophagy pathway by inhibiting the mammalian target of rapamycin (mTOR) pathway. However, the contribution of autophagy in orthopedic diseases is rarely reported. The aim of the present study was to evaluate the capacity of pharmacologically induced autophagy to modify disease function in a rat model of bone fracture. A femur fracture model was established via surgery in adult male Sprague-Dawley rats. Rapamycin (n=63 rats) or dimethyl sulfoxide (DMSO) vehicle control (n=63 rats) was administered intraperitoneally for 2, 4 and 6 weeks, and 21 randomly selected rats were sacrificed in each group at each time point. X-ray micro-computed tomography and hematoxylin and eosin staining were used to evaluate the extent of fracture healing in each group. The effects of rapamycin on autophagy, mTOR signaling and the expression levels of vascular endothelial growth factor (VEGF) and proliferating cell nuclear antigen (PCNA) were analyzed using immunohistochemistry, immunofluorescence staining and western blot analysis. Rapamycin affected the mTOR signaling pathway in rats following fracture, as indicated by the inhibition of the phosphorylation of ribosomal protein S6, a target of mTOR, and activation of microtubule-associated protein 2 light chain 3, a key marker of autophagy. Histomorphometry and image examination indicated that the number of osteoblasts in each section was significantly (P<0.01) increased in the rapamycin group compared with the control group, and this was associated with a significant (P<0.05) increase in mineralized callus fraction. Furthermore, rapamycin treatment increased the expression levels of VEGF and PCNA in the rat callus tissue. These results suggest that rapamycin may serve a beneficial function in fracture healing, and that the underlying mechanism may involve the activation of autophagy.