The Anoikis Effector Bit1 Inhibits EMT through Attenuation of TLE1-Mediated Repression of E-Cadherin in Lung Cancer Cells

Targeting anoikis resistance as a strategy for cancer therapy

Anoikis, known as matrix detachment-induced apoptosis or detachment-induced cell death, is crucial for tissue development and homeostasis. Cancer cells develop means to evade anoikis, e.g. anoikis resistance, thereby allowing for cells to survive under anchorage-independent conditions. Uncovering the mechanisms of anoikis resistance will provide details about cancer metastasis, and potential strategies against cancer cell dissemination and metastasis. Here, we summarize the principal elements and core molecular mechanisms of anoikis and anoikis resistance. We discuss the latest progress of how anoikis and anoikis resistance are regulated in cancers. Furthermore, we summarize emerging data on selective compounds and nanomedicines, explaining how inhibiting anoikis resistance can serve as a meaningful treatment modality against cancers. Finally, we discuss the key limitations of this therapeutic paradigm and possible strategies to overcome them. In this review, we suggest that pharmacological modulation of anoikis and anoikis resistance by bioactive compounds could surmount anoikis resistance, highlighting a promising therapeutic regimen that could be used to overcome anoikis resistance in cancers.

Roles of transducin-like enhancer of split (TLE) family proteins in tumorigenesis and immune regulation

Mammalian transducin-like enhancer of split family proteins (TLEs) are homologous to Drosophila Groucho (Gro) and are essential transcriptional repressors. Seven TLE family members, TLE1-7, have been identified to date. These proteins do not bind DNA directly; instead, they bind a set of transcription factors and thereby inhibit target gene expression. Loss of TLEs in mice usually leads to defective early development; however, TLE functions in developmentally mature cells are unclear. Recent studies have revealed that TLEs are dysregulated in certain human cancer types and may function as oncogenes or tumor suppressors in different contexts. TLE levels also affect the efficacy of cancer treatments and the development of drug resistance. In addition, TLEs play critical roles in the development and function of immune cells, including macrophages and lymphocytes. In this review, we provide updates on the expression, function, and mechanism of TLEs; discuss the roles played by TLEs in tumorigenesis and the inflammatory response; and elaborate on several TLE-associated signaling pathways, including the Notch, Wnt, and MAPK pathways. Finally, we discuss potential strategies for targeting TLEs in cancer therapy.

Anoikis-Associated Lung Cancer Metastasis: Mechanisms and Therapies

Simple Summary

Anoikis is a programmed cell death process resulting from the loss of interaction between cells and the extracellular matrix. Therefore, it is necessary to overcome anoikis when tumor cells acquire metastatic potential. In lung cancer, the composition of the extracellular matrix, cell adhesion-related membrane proteins, cytoskeletal regulators, and epithelial–mesenchymal transition are involved in the process of anoikis, and the initiation of apoptosis signals is a critical step in anoikis. Inversely, activation of growth signals counteracts anoikis. This review summarizes the regulators of lung cancer-related anoikis and explores potential drug applications targeting anoikis.

Abstract

Tumor metastasis occurs in lung cancer, resulting in tumor progression and therapy failure. Anoikis is a mechanism of apoptosis that combats tumor metastasis; it inhibits the escape of tumor cells from the native extracellular matrix to other organs. Deciphering the regulators and mechanisms of anoikis in cancer metastasis is urgently needed to treat lung cancer. Several natural and synthetic products exhibit the pro-anoikis potential in lung cancer cells and in vivo models. These products include artonin E, imperatorin, oroxylin A, lupalbigenin, sulforaphane, renieramycin M, avicequinone B, and carbenoxolone. This review summarizes the current understanding of the molecular mechanisms of anoikis regulation and relevant regulators involved in lung cancer metastasis and discusses the therapeutic potential of targeting anoikis in the treatment of lung cancer metastasis.

Involvement of Anoikis in Dissociated Optic Nerve Fiber Layer Appearance

Dissociated optic nerve fiber layer (DONFL) appearance is characterized by dimpling of the fundus when observed after vitrectomy with the internal limiting membrane (ILM) peeling in macular diseases. However, the cause of DONFL remains largely unknown. Optical coherence tomography (OCT) findings have indicated that the nerve fiber layer (NFL) and ganglion cells are likely to have been damaged in patients with DONFL appearance. Since DONFL appearance occurs at a certain postoperative period, it is unlikely to be retinal damage directly caused by ILM peeling because apoptosis occurs at a certain period after tissue damage and/or injury. However, it may be due to ILM peeling-induced apoptosis in the retinal tissue. Anoikis is a type of apoptosis that occurs in anchorage-dependent cells upon detachment of those cells from the surrounding extracellular matrix (i.e., the loss of cell anchorage). The anoikis-related proteins βA3/A1 crystallin and E-cadherin are reportedly expressed in retinal ganglion cells. Thus, we theorize that one possible cause of DONFL appearance is ILM peeling-induced anoikis in retinal ganglion cells.

Downregulation of lncRNA FGF12-AS2 suppresses the tumorigenesis of NSCLC via sponging miR-188-3p

Background

Non-small-cell lung carcinoma (NSCLC) seriously threatens the health of human beings. Aberrant expression of lncRNAs has been confirmed to be related with the progression of multiple malignant tumors, including NSCLC. LncRNA FGF12-AS2 has been considered to be upregulated in NSCLC. However, the mechanism by which FGF12-AS2 promotes the tumorigenesis of NSCLC remains elusive.

Methods

Gene and protein expressions in NSCLC cells were measured by q-PCR and western blot, respectively. CCK-8 and immunofluorescence staining were performed to detect the cell proliferation. Cell apoptosis was tested by flow cytometry. Transwell assay was used to detect the cell migration and invasion. Finally, the dual luciferase report assay was used to verify the relation among FGF12-AS2, miR-188-3p, and NCAPG2.

Results

Downregulation of FGF12-AS2 significantly inhibited the proliferation of NSCLC cells via inducing apoptosis. In addition, FGF12-AS2 silencing notably suppressed the migration and invasion of A549 cells. Meanwhile, FGF12-AS2 modulated the progression of NSCLC via regulation of miR-188-3p/NCAPG2 axis. Finally, knockdown of FGF12-AS2 inhibited the tumorigenesis of NSCLC via suppressing the EMT process of NSCLC.

Conclusion

Downregulation of lncRNA FGF12-AS2 suppressed the tumorigenesis of NSCLC via sponging miR-188-3p. Thus, FGF12-AS2 may serve as a potential target for the treatment of NSCLC.

PTRH2: an adhesion regulated molecular switch at the nexus of life, death, and differentiation

Peptidyl-tRNA hydrolase 2 (PTRH2; Bit-1; Bit1) is an underappreciated regulator of adhesion signals and Bcl2 expression. Its key roles in muscle differentiation and integrin-mediated signaling are central to the pathology of a recently identified patient syndrome caused by a cluster of Ptrh2 gene mutations. These loss-of-function mutations were identified in patients presenting with severe deleterious phenotypes of the skeletal muscle, endocrine, and nervous systems resulting in a syndrome called Infantile-onset Multisystem Nervous, Endocrine, and Pancreatic Disease (IMNEPD). In contrast, in cancer PTRH2 is a potential oncogene that promotes malignancy and metastasis. PTRH2 modulates PI3K/AKT and ERK signaling in addition to Bcl2 expression and thereby regulates key cellular processes in response to adhesion including cell survival, growth, and differentiation. In this Review, we discuss the state of the science on this important cell survival, anoikis and differentiation regulator, and opportunities for further investigation and translation. We begin with a brief overview of the structure, regulation, and subcellular localization of PTRH2. We discuss the cluster of gene mutations thus far identified which cause developmental delays and multisystem disease. We then discuss the role of PTRH2 and adhesion in breast, lung, and esophageal cancers focusing on signaling pathways involved in cell survival, cell growth, and cell differentiation.

TLE2 is associated with favorable prognosis and regulates cell growth and gemcitabine sensitivity in pancreatic cancer

Background

The transducin-like enhancer of split (TLE) proteins are a group of transcriptional corepressors. They play a crucial role in cellular homeostasis and are involved in various cancers. Compared with other TLE family members, little is known about the role and the underlying mechanism of TLE2 in human cancers. This study aimed to investigate the role of TLE2 in pancreatic ductal adenocarcinoma (PDAC) using in silico analysis and in vitro experiments.

Methods

Data were obtained from the Cancer Genome Atlas (TCGA) database to evaluate the prognostic value of TLE2 in PDAC. The MiaPaCa-2 cell line was transfected with siRNA to inhibit endogenous TLE2 expression, and a PANC-1 cell line with stable TLE2 overexpression was constructed using lentiviral transfection, which were confirmed by real-time polymerase chain reaction and western blotting. MTT assay, transwell invasion assays, and flow cytometry were carried out to assess cell viability, invasion, and apoptosis, respectively. TLE2 expression in PDAC cells was altered to evaluate their sensitivity to gemcitabine. Gene set enrichment analysis (GSEA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were conducted to predict the biological role of TLE2.

Results

High expression of TLEs was significantly associated with increased overall survival (OS) and disease-free survival (DFS) in patients with PDAC. Among the PDAC cell lines, TLE2 expression was lowest and highest in PANC-1 cells and MiaPaCa-2 cells, respectively. TLE2 overexpression impaired the proliferation ability of PANC-1 cells and downregulation of TLE2 promoted the proliferation of MiaPaCa-2 cells. Upregulation of TLE2 in PANC-1 cells induced S-phase accumulation and sensitivity to gemcitabine. In contrast, the downregulation of TLE2 in MiaPaCa-2 cells promoted resistance to gemcitabine. Moreover, bioinformatics analysis also revealed the potential tumor suppressor role of TLE2 and uncovered a close relationship between TLE2 expression and cell cycle regulation.

Conclusions

Our results suggest that TLE2 expression is correlated with prognosis in patients with PDAC and show that TLE2 plays a central role in the regulation of cell proliferation, the cell cycle, and gemcitabine sensitivity. This study provides new insights and evidence that TLE2 functions as a tumor suppressor gene and prognostic marker in PDAC.

Bit1 Silencing Enhances the Proliferation, Migration, and Invasion of Glioma Cells Through Activation of the IL-6/STAT3 Pathway

Background

Several studies have indicated that the anoikis effector Bcl-2 inhibitor of transcription 1 (Bit1) can promote or inhibit tumor progression depending on the nature of the malignancy. However, its regulatory effects on gliomas are unknown.

Methods

This study aimed at assessing Bit1 expression in glioma tissues and cells, its subsequent effects on glioma cell apoptosis, proliferation, invasion, and migration, and the underlying molecular mechanisms.

Results

The findings showed that lower Bit1 expressions in glioma tissues as well as a negative correlation between Bit1 expression and glioma grade. Additional findings also revealed that Bit1 silencing significantly inhibited anoikis and enhanced glioma cell proliferation, invasion, and migration. Further analysis showed that the decrease in Bit1 expressions led to malignancy proliferation and anoikis resistance through activation of the IL-6/STAT3 signaling pathway.

Conclusion

Our data suggested that Bit1 may play an anti-oncogenic role in glioma cells and that a decrease in its expressions might induce glioma cell proliferation, migration, and invasion through the IL-6/STAT3 signaling pathway.

Downregulation of Bit1 expression promotes growth, anoikis resistance, and transformation of immortalized human bronchial epithelial cells via Erk activation-dependent suppression of E-cadherin

The mitochondrial Bit1 protein exerts tumor-suppressive function in NSCLC through induction of anoikis and inhibition of EMT. Having this dual tumor suppressive effect, its downregulation in the established human lung adenocarcinoma A549 cell line resulted in potentiation of tumorigenicity and metastasis in vivo. However, the exact role of Bit1 in regulating malignant growth and transformation of human lung epithelial cells, which are origin of most forms of human lung cancers, has not been examined. To this end, we have downregulated the endogenous Bit1 expression in the immortalized non-tumorigenic human bronchial epithelial BEAS-2B cells. Knockdown of Bit1 enhanced the growth and anoikis insensitivity of BEAS-2B cells. In line with their acquired anoikis resistance, the Bit1 knockdown BEAS-2B cells exhibited enhanced anchorage-independent growth in vitro but failed to form tumors in vivo. The loss of Bit1-induced transformed phenotypes was in part attributable to the repression of E-cadherin expression since forced exogenous E-cadherin expression attenuated the malignant phenotypes of the Bit1 knockdown cells. Importantly, we show that the loss of Bit1 expression in BEAS-2B cells resulted in increased Erk activation, which functions upstream to promote TLE1-mediated transcriptional repression of E-cadherin. These collective findings indicate that loss of Bit1 expression contributes to the acquisition of malignant phenotype of human lung epithelial cells via Erk activation-induced suppression of E-cadherin expression.

ATF4 regulated by MYC has an important function in anoikis resistance in human osteosarcoma cells

Anoikis resistance is a crucial step in the process of tumor metastasis. This step determines whether the tumor cells will survive when they become detached from the extracellular matrix. However, the specific mechanism of tumor cells to bypass anoikis and become resistant remains to be elucidated. The present study aimed to determine the internal mechanism of bypassing anoikis through comparison of human osteosarcoma cell lines with human normal cell lines. High activating transcription factor 4 (ATF4) and myelocytomatosis oncogene (MYC) expression levels were observed in MG-63 and U-2 OS human osteosarcoma cell lines. It is possible that ATF4 and MYC contribute to tumor progression. Subsequently, the expression levels of ATF4 and MYC in HUVEC and CHON-001 human normal cell lines were upregulated and their adhesion abilities were reduced; whereas their ability to bypass anoikis increased significantly. Simultaneously, after we Following a knock-down of ATF4 and MYC expression levels in MG-63 and U-2 OS human osteosarcoma cell lines, their adhesion ability increased and their ability to bypassing anoikis was significantly reduced. Upregulation of MYC resulted in an upregulation of ATF4, and chromatin immunoprecipitation and luciferase reporter gene technology demonstrated that MYC binds to the promoter of ATF4. These findings suggest that ATF4 regulated by MYC might contribute to resistance to anoikis in human osteosarcoma cells.

TLE1 inhibits anoikis and promotes tumorigenicity in human lung cancer cells through ZEB1-mediated E-cadherin repression

The Transducin-like enhancer of split 1 (TLE1) corepressor protein is overexpressed in human lung tumors and is a putative lung-specific oncogene. However, the molecular mechanism underlying its oncogenic function remains to be delineated. Here, we report an important role of TLE1 in promoting lung tumorigenesis by a mechanism involving induction of anoikis resistance. Using the human lung adenocarcinoma A549 and immortalized bronchial epithelial BEAS-2B cell lines, we observed that TLE1 inhibits anoikis through transcriptional repression of E-cadherin gene. In support of E-cadherin as a downstream target of TLE1 to block anoikis, forced expression of E-cadherin attenuated TLE1-induced anoikis resistance while E-cadherin downregulation decreased the anoikis sensitivity of TLE1 knockdown cells. Furthermore, we determined that E-cadherin expression is transcriptionally induced upon loss of cell attachment and functions as an effector of anoikis. Loss of E-cadherin via the siRNA strategy or exogenous TLE1 expression was sufficient to attenuate anoikis in A549 and BEAS-2B cells. Importantly, we demonstrated that the ZEB1 transcriptional factor is required for TLE1-mediated E-cadherin repression and anoikis resistance. ZEB1 interacted with and recruited the TLE1 to the E-cadherin promoter to impose histone deacetylation and gene silencing. In vivo, TLE1 strongly promoted tumorigenicity of A549 cells in a ZEB1-dependent manner. Underscoring its role in anoikis insensitivity of lung cancer cells, the TLE1-mediated E-cadherin repression was negatively regulated by the tumor suppressor Bcl-2 inhibitor of transcription 1 (Bit1) to effect anoikis. These findings identify the ZEB1/TLE1/E-cadherin transcriptional mechanism as a novel pathway that promotes anoikis resistance and oncogenicity of lung cancer cells.