Effects of RNAi-mediated TUSC3 silencing on radiation-induced autophagy and radiation sensitivity of human lung adenocarcinoma cell line A549 under hypoxic condition

Molecular Mechanisms Involving the Sonic Hedgehog Pathway in Lung Cancer Therapy: Recent Advances

According to the latest statistics from the International Agency for Research on Cancer (IARC), lung cancer is one of the most lethal malignancies in the world, accounting for approximately 18% of all cancer-associated deaths. Yet, even with aggressive interventions for advanced lung cancer, the five-year survival rate remains low, at around 15%. The hedgehog signaling pathway is highly conserved during embryonic development and is involved in tissue homeostasis as well as organ development. However, studies have documented an increasing prevalence of aberrant activation of HH signaling in lung cancer patients, promoting malignant lung cancer progression with poor prognostic outcomes. Inhibitors targeting the HH pathway have been widely used in tumor therapy, however, they still cannot avoid the occurrence of drug resistance. Interestingly, natural products, either alone or in combination with chemotherapy, have greatly improved overall survival outcomes for lung cancer patients by acting on the HH signaling pathway because of its unique and excellent pharmacological properties. In this review, we elucidate on the underlying molecular mechanisms through which the HH pathway promotes malignant biological behaviors in lung cancer, as well as the potential of inhibitors or natural compounds in targeting HH signaling for clinical applications in lung cancer therapy.

Crosstalk of the Wnt/β-Catenin Signaling Pathway in the Induction of Apoptosis on Cancer Cells

The Wnt/β-catenin signaling pathway plays a major role in cell survival and proliferation, as well as in angiogenesis, migration, invasion, metastasis, and stem cell renewal in various cancer types. However, the modulation (either up- or downregulation) of this pathway can inhibit cell proliferation and apoptosis both through β-catenin-dependent and independent mechanisms, and by crosstalk with other signaling pathways in a wide range of malignant tumors. Existing studies have reported conflicting results, indicating that the Wnt signaling can have both oncogenic and tumor-suppressing roles, depending on the cellular context. This review summarizes the available information on the role of the Wnt/β-catenin pathway and its crosstalk with other signaling pathways in apoptosis induction in cancer cells and presents a modified dual-signal model for the function of β-catenin. Understanding the proapoptotic mechanisms induced by the Wnt/β-catenin pathway could open new therapeutic opportunities.

Downregulation of microRNA-320a inhibits proliferation and induces apoptosis of retinoblastoma cells via targeting TUSC3

MicroRNA (miR)-320a is specific to vertebrates and has been indicated to serve a role in a number of cancer types, such as gastric, colorectal, pancreatic and ovarian cancer. miR-320a has been reported to be expressed at high levels in retinoblastoma tissues; however its role and mechanism of function in retinoblastoma remain to be elucidated. The aim of the present study was to investigate the role of miR-320a in retinoblastoma cells and the underlying mechanisms. The expression of miR-320a in retinoblastoma cell lines Y79 and WERI-Rb-1, and normal human retinal pigment epithelial cell line ARPE-19 was examined via reverse transcription-quantitative PCR (RT-qPCR). TargetScan bioinformatics analysis and dual-luciferase reporter assay were used to predict and reveal the target gene of miR-320a. Target gene expression was detected via RT-qPCR in retinoblastoma cell lines and ARPE-19 cells. Subsequently, gain- or loss-of-function experiments for miR-320a and tumor suppressor candidate 3 (TUSC3) were performed to study the role of miR-320a/TUSC3 in retinoblastoma cells. Cell viability and apoptosis were assessed via MTT and flow cytometry analysis, respectively. Compared with ARPE-19 cells, miR-320a was prominently expressed in retinoblastoma cell lines. TUSC3 was predicted to be a target gene of miR-320a. Compared with ARPE-19 cells, the expression of TUSC3 in retinoblastoma cell lines was reduced. The results of MTT and flow cytometry analysis revealed that overexpression of TUSC3 reduced the viability of retinoblastoma cells and induced apoptosis. Additional analysis indicated that miR-320a inhibitor enhanced the expression of the target gene TUSC3, thereby inhibiting retinoblastoma cell viability and inducing apoptosis. The effects of miR-320a inhibitor on retinoblastoma cells were inhibited by TUSC3-short hairpin RNA. miR-320a regulated the viability and apoptosis of retinoblastoma cells via targeting TUSC3. Therefore, the present study provided a reference for investigating a potential target for the clinical treatment of retinoblastoma.

miR-873-5p inhibits the progression of colon cancer via repression of tumor suppressor candidate 3/AKT signaling

BACKGROUND AND AIM

We previously discovered that tumor suppressor candidate 3 (TUSC3) was overexpressed and predicted worse prognosis in colon cancer patients. However, the mechanisms of upregulation of TUSC3 in colon cancer remained unclear.

METHODS

MiR-873-5p was predicted and identified as the regulator of TUSC3 via online programs and luciferase reporter assays. The roles of miR-873-5p in regulating colon cancer cell proliferation, colony formation, and invasion were evaluated in vitro. Animal studies were performed to investigate the effects of miR-873-5p on proliferation and lung metastasis. Moreover, the miR-873-5p/TUSC3 related signaling pathway and the prognostic value of combining miR-873-5p and TUSC3 for colon cancer patients were also explored.

RESULTS

Here, we identified miR-873-5p as a novel regulator of TUSC3 in colon cancer. Functionally, ectopic expression or silencing of miR-873-5p, respectively, inhibited or promoted colon cancer cells proliferation, colony formation, and invasion, as well as prevented or enhanced the metastasis of colon cancer cells in vitro and in vivo. Molecularly, miR-873-5p functioned as a tumor suppressor by inhibiting the TUSC3/AKT pathway. Overexpression or silencing of TUSC3 could partially reverse the effects of the overexpression or repression of miR-873-5p on colon cancer progression caused by activation of the AKT pathway. Clinically, low miR-873-5p expression predicted poor survival in colon cancer patients, especially combined with high TUSC3 expression.

CONCLUSIONS

We identified miR-873-5p as a tumor suppressor, which acts by directly repressing TUSC3 in colon cancer.

TUSC3 induces autophagy in human non-small cell lung cancer cells through Wnt/β-catenin signaling

We investigated the effects of tumor suppressor candidate 3 (TUSC3) on autophagy in human non-small cell lung cancer (NSCLC) cells. A total of 118 NSCLC patients (88 males and 30 females) who underwent surgery at our institute were enrolled in the study. Immunohistochemical analysis revealed that TUSC3 protein expression was lower in NSCLC specimens than adjacent normal tissue. Correspondingly, there was greater methylation of TUSC3 in NSCLC than adjacent normal tissue. After transient transfection of A549 NSCLC cells with constructs designed to up-regulate or down-regulate TUSC3 expression, we analyzed the effects of inhibiting the Wnt pathway (XAV939) and autophagy (chloroquine, CQ) on the behavior of NSCLC cells. We also performed TOP/FOP-Flash reporter assays, MTT assays, Annexin V-FITC/propidium iodide staining, and acridine orange staining to evaluate Wnt/β-catenin signaling, cell proliferation, apoptosis, and autophagy, respectively. Expression of Wnt/β-catenin pathway components and autophagy-related proteins was analyzed using qRT-PCR and Western blotting. We found that TUSC3 inhibited cell proliferation and promoted both apoptosis and autophagy in A549 cells. In addition, TUSC3 increased expression of autophagy-related proteins. It also increased expression of Wnt/β-catenin signaling pathway components and promoted nuclear transfer of β-catenin, resulting in activation of Wnt/β-catenin signaling. TUSC3 thus induces autophagy in human NSCLC cells through activation of the Wnt/β-catenin signaling pathway.

Oncogenic function of TUSC3 in non-small cell lung cancer is associated with Hedgehog signalling pathway

Non-small cell lung cancer (NSCLC) represents 75-80% of all lung carcinomas, which is the most common cause of death from cancer. Tumour suppressor candidate 3 (TUSC3) is pivotal in many biochemical functions and cytological processes. Dis-regulation of TUSC3 is frequently observed in epithelial cancers. In this study, we observed up-regulated TUSC3 expression at the mRNA and protein levels in clinical NSCLC samples compared with adjacent non-tumorous lung tissues. The expression level of TUSC3 is significantly correlated with tumour metastasis and patient survival. Overexpression of TUSC3 in NSCLC cells led to increased proliferation, migration, and invasion in vitro and accelerated xenograft tumour growth in vivo, while the opposite effects were achieved in TUSC3-silenced cells. Increased GLI1, SMO, PTCH1, and PTCH2 abundance were observed in TUSC3 overexpressed cells using western blotting. Co-immunoprecipitation and immunofluorescence analyses further revealed interaction between TUSC3 and GLI1. In conclusion, our study demonstrated an oncogenic role of TUSC3 in NSCLC and showed that dis-regulation of TUSC3 may affect tumour cell invasion and migration through possible involvement in the Hedgehog (Hh) signalling pathway.