TSSC3 represses self-renewal of osteosarcoma stem cells and Nanog expression by inhibiting the Src/Akt pathway

FOSL1 promotes stem cell‑like characteristics and anoikis resistance to facilitate tumorigenesis and metastasis in osteosarcoma by targeting SOX2

Metastasis is the leading cause of cancer‑related death in osteosarcoma (OS). OS stem cells (OSCs) and anoikis resistance are considered to be essential for tumor metastasis formation. However, the underlying mechanisms involved in the maintenance of a stem‑cell phenotype and anoikis resistance in OS are mostly unknown. Fos‑like antigen 1 (FOSL1) is important in maintaining a stem‑like phenotype in various cancers; however, its role in OSCs and anoikis resistance remains unclear. In the present study, the dynamic expression patterns of FOSL1 were investigated during the acquisition of cancer stem‑like properties using RNA sequencing, PCR, western blotting and immunofluorescence. Flow cytometry, tumor‑sphere formation, clone formation assays, anoikis assays, western blotting and in vivo xenograft and metastasis models were used to further investigate the responses of the stem‑cell phenotype and anoikis resistance to FOSL1 overexpression or silencing in OS cell lines. The underlying molecular mechanisms were evaluated, focusing on whether SOX2 is crucially involved in FOSL1‑mediated stemness and anoikis in OS. FOSL1 expression was observed to be upregulated in OSCs and promoted tumor‑sphere formation, clone formation and tumorigenesis in OS cells. FOSL1 expression correlated positively with the expression of stemness‑related factors (SOX2, NANOG, CD117 and Stro1). Moreover, FOSL1 facilitated OS cell anoikis resistance and promoted metastases by regulating the expression of apoptosis related proteins BCL2 and BAX. Mechanistically, FOSL1 upregulated SOX2 expression by interacting with the SOX2 promoter and activating its transcription. The results also showed that SOX2 is critical for FOSL1‑mediated stem‑like properties and anoikis resistance. The current findings indicated that FOSL1 is an important regulator that promotes a stem cell‑like phenotype and anoikis resistance to facilitate tumorigenesis and metastasis in OS by regulating the transcription of SOX2. Thus, FOSL1 might represent an attractive target for therapeutic interventions in OS.

PHLDA2 reshapes the immune microenvironment and induces drug resistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a malignancy known for its unfavorable prognosis. The dysregulation of the tumor microenvironment (TME) can affect the sensitivity to immunotherapy or chemotherapy, leading to treatment failure. The elucidation of PHLDA2's involvement in HCC is imperative, and the clinical value of PHLDA2 is also underestimated. Here, bioinformatics analysis was performed in multiple cohorts to explore the phenotype and mechanism through which PHLDA2 may affect the progression of HCC. Then, the expression and function of PHLDA2 were examined via the qRT-PCR, Western Blot, and MTT assays. Our findings indicate a substantial upregulation of PHLDA2 in HCC, correlated with a poorer prognosis. The methylation levels of PHLDA2 were found to be lower in HCC tissues compared to normal liver tissues. Besides, noteworthy associations were observed between PHLDA2 expression and immune infiltration in HCC. In addition, PHLDA2 upregulation is closely associated with stemness features and immunotherapy or chemotherapy resistance in HCC. In vitro experiments showed that sorafenib or cisplatin significantly up-regulated PHLDA2 mRNA levels, and PHLDA2 knockdown markedly decreased the sensitivity of HCC cells to chemotherapy drugs. Meanwhile, we found that TGF-β induced the expression of PHLDA2 in vitro. The GSEA and in vitro experiment indicated that PHLDA2 may promote the HCC progression via activating the AKT signaling pathway. Our study revealed the novel role of PHLDA2 as an independent prognostic factor, which plays an essential role in TME remodeling and treatment resistance in HCC.

The Prognostic Model Established by the Differential Expression Genes Based on CD8+ T Cells to Evaluate the Prognosis and the Response to Immunotherapy in Osteosarcoma

Osteosarcoma (OS) is a malignant tumor with an extremely poor prognosis, especially in progressive patients. Immunotherapy based on immune checkpoint inhibitors (ICIs) is considered to be a promising treatment option for OS. Due to tumor heterogeneity, only a minority of patients benefit from immunotherapy. Therefore, it is urgent to explore a model that can accurately assess the response of OS to immunotherapy. In this study, we obtained the single-cell RNA sequencing datasets of OS patients from public databases and defined 34 cell clusters by dimensional reduction and clustering analysis. PTPRC was applied to identify immune cell clusters and nonimmune cell clusters. Next, we performed clustering analysis on the immune cell clusters and obtained 25 immune cell subclusters. Immune cells were labeled with CD8A and CD8B to obtain CD8⁺ T cell clusters. Meanwhile, we extracted the differentially expressed genes (DEGs) of CD8⁺ T cell clusters and other immune cell clusters. Furthermore, we constructed a prognostic model (CD8-DEG model) based on the obtained DEGs of CD8⁺ T cells, and verified the excellent predictive ability of this model for the prognosis of OS. Moreover, we further investigated the value of the CD8-DEG model. The results indicated that the risk score of the CD8-DEG model was an independent risk factor for OS patients. Finally, we revealed that the risk score of the CD8-DEG model correlates with the immune profile of OS and can be used to evaluate the response of OS to immunotherapy. In conclusion, our study revealed the critical role of CD8 cells in OS. The risk score model based on CD8-DEGs can provide guidance for prognosis and immunotherapy of OS.

Methods for assessing the effect of microRNA on stemness genes

According to the latest concepts, for micrometastasis to develop into macrometastasis, differentiated cancer cells must revert to a dedifferentiated state. Activation of stemness genes plays a key role in this transition. Suppression of stemness gene expression using microRNAs can become the basis for the development of effective anti-metastatic drugs. This article provides an overview of the existing methods for assessing the effect of microRNAs on stemness genes and cancer cell dedifferentiation.

Tumor-Suppressing STF cDNA 3 Overexpression Suppresses Renal Fibrosis by Alleviating Anoikis Resistance and Inhibiting the PI3K/Akt Pathway

BACKGROUND

Myofibroblast (MF) activation is the key event of irreversible renal interstitial fibrosis. Anoikis resistance is the hallmark of active MFs, which is conferred by continuous activation of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (Akt) pathway. Our previous study found that tumor-suppressing STF cDNA 3 (TSSC3) enhances the sensitivity of cells to anoikis via the PI3K/Akt pathway. Therefore, we hypothesized that TSSC3 might suppress renal interstitial fibrosis by inducing anoikis via the PI3K/Akt pathway.

METHODS

Cell anoikis was induced by the exogenous addition of RGD-containing peptides or by culturing cells in suspension. MFs were established by stimulating HK-2 renal tubular epithelial cells with transforming growth factor beta 1 (TGF-β1). Lentivirus vectors were to construct a TSSC3 overexpression cell model. The effects of TSSC3 on the anoikis, growth, migration, invasion, and contraction of MFs were determined using annexin V-fluorescein isothiocyanate assays, cell counting kit-8 assays, wound healing migration assays, matrigel invasion assays, and collagen-based contraction assays.

RESULTS

The results demonstrated that TGF-β1, simultaneous with the induction of MF differentiation, confers significant protection against anoikis-induced cell death, which could be partly reversed by treatment with the PI3K/Akt pathway inhibitor, LY294002. Moreover, overexpression of TSSC3 obviously impaired cell growth, cell migration, cell invasion, contraction, and anoikis resistance of MFs, and decreased the activity of the PI3K/Akt pathway and the production of extracellular matrix molecules, all of which could be attenuated by treatment with the PI3K/Akt pathway activator, 740Y-P. Taken together, this study suggested that TSSC3 attenuates the anoikis resistance and profibrogenic ability of TGF-β1-induced MF by regulating the PI3K-Akt pathway.

CONCLUSION

These findings provide a biological basis for further exploration of the therapeutic significance of targeting MF via TSSC3 in renal interstitial fibrosis.

Gamabufotalin suppressed osteosarcoma stem cells through the TGF-β/periostin/PI3K/AKT pathway

AIMS

To investigate the effect of gamabufotalin (GBT) on metastasis and modulation of stemness features in osteosarcoma, and the molecular mechanisms underlying such effects.

METHODS

Human osteosarcoma U2OS/MG-63 cell lines were used in this study. Cell proliferation, migration, and invasion were determined by MTT assay, wound healing assay, and cell invasion assay, respectively. The inhibitive effect of GBT on stemness was assessed by flow cytometry and mammosphere formation. The protein levels of related proteins were detected by western blotting analysis. The effect of GBT on tumorigenicity and metastasis was determined by immunofluorescence staining and immunohistochemistry in vivo experiments.

RESULTS

We found that GBT suppressed the viability of U2OS/MG-63 cells in a time- and dose-dependent manner. Notably, GBT had no effect on the viability of human fetal osteoblastic (hFOB) 1.19 cells. Moreover, GBT increased the width of wounds, reduced the number of invasive osteosarcoma cells and reversed the epithelial-mesenchymal transition phenotype. Notably, we found that, compared with hFOB1.19 cells, the levels of transforming growth factor-β (TGF-β), periostin, phosphorylated-AKT (p-AKT), and phosphorylated-PI3K (p-PI3K) were higher in spheroids group than in parent cells. In addition, GBT reduced the ratio of CD133+ cells, the size of spheroids and Nanog, as well as the protein levels of SRY-box transcription factor 2 (SOX2), and octamer-binding protein 3/4 (OCT3/4). Our in vivo experiments showed that GBT consistently reduced lung metastasis lesions, the expression levels of matrix metalloproteinase 2 (MMP2), TGF-β, periostin, p-AKT, and p-PI3K (immunohistochemistry staining), as well as that of CD133 in tumor tissues (immunofluorescence analysis). From a mechanistic point of view, exogenous TGF-β/periostin/PI3K/AKT overexpression neutralized the reduction of GBT-decreased invasion/migration and the suppression of stemness properties.

CONCLUSION

Collectively, our data demonstrated that GBT inhibited the viability and tumorigenesis capability of osteosarcoma cells by blocking the TGF-β/periostin/PI3K/AKT signaling pathway. Therefore, GBT may represent a promising therapeutic agent for the management of osteosarcoma.

The Heterogeneity of Osteosarcoma: The Role Played by Cancer Stem Cells

Osteosarcoma is the most common bone sarcoma and is one of the cancer entities characterized by the highest level of heterogeneity in humans. This heterogeneity takes place not only at the macroscopic and microscopic levels, with heterogeneous micro-environmental components, but also at the genomic, transcriptomic and epigenetic levels. Recent investigations have revealed the existence in osteosarcoma of cancer cells with stemness properties. Cancer stem cells are characterized by their specific phenotype and low cycling capacity, and are linked to drug resistance, tumour growth and the metastatic process. In addition, cancer stem cells contribute to the enrichment of tumour heterogeneity. The present manuscript will describe the main characteristic features of cancer stem cells in osteosarcoma and will discuss their impact on maintaining tumour heterogeneity. Their clinical implications will also be briefly addressed.

High expression of ID1 facilitates metastasis in human osteosarcoma by regulating the sensitivity of anoikis via PI3K/AKT depended suppression of the intrinsic apoptotic signaling pathway

A lack of understanding of the molecular basis underlying the regulation of metastatic disease and its effective therapy are the primary causes of high mortality in osteosarcoma. Thus, new insights into metastases and novel effective targets for metastatic osteosarcoma are urgently required. Anoikis resistance is considered a hallmark of cancer cells with metastatic ability. However, the molecular mechanism of anoikis is poorly understood in osteosarcoma. We applied immunohistochemistry to investigate the correlation between inhibitor of differentiation or DNA binding 1 (ID1) and clinicopathological features, and investigated the correlation between ID1 and the metastatic behavior of osteosarcoma cells, in vitro and in vivo. The results revealed that ID1 is overexpressed in human osteosarcoma tissues, is positively associated with lung metastases, and is a potential biomarker of poor prognosis. Overexpression of ID1 could increase anoikis insensitivity of osteosarcoma cells to facilitate metastasis through the PI3K/AKT-dependent mitochondrial apoptosis pathway. Knockdown of ID1 partly reversed the high potential of metastasis in anoikis-resistant osteosarcoma cells. Our findings revealed, that ID1 is a candidate molecular target for metastatic potential osteosarcoma by highlighting the role of anoikis resistance. In addition ID1 might be a potential predictor of poor prognosis in patients with osteosarcoma.

Overexpression of FER1L4 promotes the apoptosis and suppresses epithelial-mesenchymal transition and stemness markers via activating PI3K/AKT signaling pathway in osteosarcoma cells

Novel long non-coding RNA Fer-1-like protein 4 (FER1L4) has been identified as a tumor suppressor in endometrial carcinoma, ovarian cancer, hepatocellular carcinoma, esophageal squamous cell carcinoma. However, the function of FER1L4 in osteosarcoma has not been clear. The aim of the research was to explore the effects of FER1L4 in osteosarcoma. Results showed that FER1L4 was observed to be lowly expressed in osteosarcoma cell lines (US-O2, MG-63 and SaOS-2 cells), especially MG63 cells. Besides, overexpression of FER1L4 remarkably repressed the proliferation, migration and invasion of MG63 cells. FER1L4-induced apoptotic cell death leaded to the activation of caspase-3 and Bax/Bcl2. Moreover, epithelial-mesenchymal transition (EMT) was tremendously suppressed by increased FER1L4, evidences were the increased E-cadherin and reduced vimentin and fibronectin. Blocking FER1L4 expression by sh-FER1L4 treatment increased the expression of SOX9, CD44, ALDH1, Nanog and Oct4, indicating that FER1L4 could effectively decrease cell stemness in osteosarcoma. Furthermore, the protein levels of p-AKT and p-PI3K were remarkably suppressed when FER1L4 was knocked down. In conclusion, the study indicated that FER1L4 acted as a tumor suppressor in osteosarcoma via activating PI3K/AKT pathway may be a new prognostic biomarker and potential therapeutic target for osteosarcoma intervention.

Anoikis‑resistant human osteosarcoma cells display significant angiogenesis by activating the Src kinase‑mediated MAPK pathway

Tumor cells must resist anoikis to metastasize. There is a key role of angiogenesis in the growth and metastasis of tumors. However, the relationship between anoikis resistance and angiogenesis has not been well explored in human osteosarcoma. In the present study, we reported the higher expression of vascular endothelial growth factor-A (VEGF-A) in osteosarcoma cells that were resistant to anoikis than in parental osteosarcoma cells, promoting the proliferation, tube formation, and migration of human umbilical vein endothelial cells (HUVECs). Src, JNK (Jun amino-terminal kinase) and ERK (extracellular signal-regulated kinase) signaling pathway phosphorylation was activated in anoikis-resistant cells; Src inhibitor reduced the expression of VEGF-A and angiogenesis and inhibited JNK and ERK pathway activity. Overexpression of phosphorylated (p)-Src and VEGF-A was positively correlated to the metastatic potential in human osteosarcoma tissues, as quantified by immunohistochemistry. In addition, p-Src expression was directly correlated with VEGF-A expression and microvessel density in vivo. Our findings revealed that anoikis resistance in osteosarcoma cells increased the expression of VEGF-A and angiogenesis through the Src/JNK/ERK signaling pathways. Thus, Src may be a potential therapeutic alternative in osteosarcoma angiogenesis and metastasis.

Novel molecular insights and new therapeutic strategies in osteosarcoma

Osteosarcoma (OS) is one of the most prevalent malignant cancers with lower survival and poor overall prognosis mainly in children and adolescents. Identifying the molecular mechanisms and OS stem cells (OSCs) as new concepts involved in disease pathogenesis and progression may potentially lead to new therapeutic targets. Therefore, therapeutic targeting of OSCs can be one of the most important and effective strategies for the treatment of OS. This review describes the new molecular targets of OS as well as novel therapeutic approaches in the design of future investigations and treatment.

TSSC3 promotes autophagy via inactivating the Src-mediated PI3K/Akt/mTOR pathway to suppress tumorigenesis and metastasis in osteosarcoma, and predicts a favorable prognosis

BACKGROUND

Over the last two or three decades, the pace of development of treatments for osteosarcoma tends has been slow. Novel effective therapies for osteosarcoma are still lacking. Previously, we reported that tumor-suppressing STF cDNA 3 (TSSC3) functions as an imprinted tumor suppressor gene in osteosarcoma; however, the underlying mechanism by which TSSC3 suppresses the tumorigenesis and metastasis remain unclear.

METHODS

We investigated the dynamic expression patterns of TSSC3 and autophagy-related proteins (autophagy related 5 (ATG5) and P62) in 33 human benign bone tumors and 58 osteosarcoma tissues using immunohistochemistry. We further investigated the correlations between TSSC3 and autophagy in osteosarcoma using western blotting and transmission electronic microscopy. CCK-8, Edu, and clone formation assays; wound healing and Transwell assays; PCR; immunohistochemistry; immunofluorescence; and western blotting were used to investigated the responses in TSSC3-overexpressing osteosarcoma cell lines, and in xenografts and metastasis in vivo models, with or without autophagy deficiency caused by chloroquine or ATG5 silencing.

RESULTS

We found that ATG5 expression correlated positively with TSSC3 expression in human osteosarcoma tissues. We demonstrated that TSSC3 was an independent prognostic marker for overall survival in osteosarcoma, and positive ATG5 expression associated with positive TSSC3 expression suggested a favorable prognosis for patients. Then, we showed that TSSC3 overexpression enhanced autophagy via inactivating the Src-mediated PI3K/Akt/mTOR pathway in osteosarcoma. Further results suggested autophagy contributed to TSSC3-induced suppression of tumorigenesis and metastasis in osteosarcoma in vitro and in vivo models.

CONCLUSIONS

Our findings highlighted, for the first time, the importance of autophagy as an underlying mechanism in TSSC3-induced antitumor effects in osteosarcoma. We also revealed that TSSC3-associated positive ATG5 expression might be a potential predictor of favorable prognosis in patients with osteosarcoma.