Expression and functional analysis of TCF4 isoforms in human glioma cells

Glutamine Promotes Porcine Intestinal Epithelial Cell Proliferation through the Wnt/β-Catenin Pathway

Glutamine (Gln) is a critical nutrient required by neonatal mammals for intestinal growth, especially for newborn piglets. However, the mechanisms underlying the role of Gln in porcine intestinal epithelium development are not fully understood. The objective of the current study was to explore the possible signaling pathway involved in the promotion of porcine intestinal epithelial cell (IPEC-J2) proliferation by Gln. The results showed that 1 mM Gln promoted IPEC-J2 cell proliferation, and tandem mass tag proteomics revealed 973 differentially expressed proteins in Gln-treated IPEC-J2 cells, 824 of which were upregulated and 149 of which were downregulated. Moreover, gene set enrichment analysis indicated that the Wnt signaling pathway is activated by Gln treatment. Western blotting analysis further confirmed that Gln activated the Wnt/β-catenin signaling pathway. In addition, Gln increased not only cytosolic β-catenin but also nuclear β-catenin protein expression. LF3 (a β-catenin/TCF4 interaction inhibitor) assay and β-catenin knockdown demonstrated that Gln-mediated promotion of Wnt/β-catenin signaling and cell proliferation were blocked. Furthermore, the inhibition of TCF4 expression suppressed Gln-induced cell proliferation. These findings further confirmed that Wnt/β-catenin signaling is involved in the promotion of IPEC-J2 cell proliferation by Gln. Collectively, these findings demonstrated that Gln positively regulated IPEC-J2 cell proliferation through the Wnt/β-catenin pathway. These data greatly enhance the current understanding of the mechanism by which Gln regulates intestinal development.

TNIK influence the effects of antipsychotics on Wnt/β-catenin signaling pathway

RationaleTraf2- and Nck-interacting kinase (TNIK), a member of germinal center kinase (GCK) family, has been implicated as a risk factor in schizophrenia and bipolar disorder as well as the action of antipsychotics. TNIK is an essential activator of Wnt/β-catenin signaling pathway which has been identified involved in the mechanism underlying the effects of antipsychotics. Thus, the effects of TNIK on antipsychotics may be achieved by influencing Wnt/β-catenin signaling pathway proteins.Objectives and methodsIn the current study, the effects of up- or downregulated TNIK on β-catenin, T-cell factor 4 (TCF-4), glycogen synthase kinase-3β (GSK3β), and phosphorylated GSK3β (p-GSK3β) were examined in the human glioma U251 cells. Then, we observed the effects of antipsychotics (clozapine and risperidone) on the above proteins and evaluated the role of differentially expressed TNIK on antipsychotic-treated cell groups.ResultsThe result showed that clozapine treatment decreased β-catenin and TCF-4 levels in U251 cells, and risperidone had the similar effects on β-catenin and p-GSK3β. The downregulated TNIK using siRNA impeded the regulation of antipsychotics on Wnt pathway proteins via increasing the expression levels of TCF-4, β-catenin, or p-GSK3β, whereas the upregulated TNIK made no significant change.ConclusionsThe influence of TNIK on the effects of antipsychotics may be partly through Wnt/β-catenin signaling pathway.

Circ_0001721 enhances doxorubicin resistance and promotes tumorigenesis in osteosarcoma through miR-758/TCF4 axis

Background

Osteosarcoma (OS) is a common type of bone malignancy that often occurs in children and adolescents. Chemoresistance is a huge barrier to cancer therapy. This study aimed to investigate the role and potential mechanism of circ_0001721 in doxorubicin (DXR) resistance and OS development.

Methods

The levels of circ_0001721, miR-758 and transcription factor 4 (TCF4) were detected by quantitative real-time polymerase chain reaction or western blot assay. Cell Counting Kit-8 (CCK-8) assay was used to calculate the half inhibition concentration (IC₅₀) of DXR and assess cell viability. Cell migration and invasion were evaluated by transwell assay. Cell apoptosis was monitored by flow cytometry. The levels of multidrug resistance-related and Wnt/β-catenin pathway-related proteins were measured by western blot assay. The interaction among circ_0001721, miR-758 and TCF4 were confirmed by dual-luciferase reporter assay, RNA immunoprecipitation assay or RNA pull-down assay. The xenograft model was established to analyze tumor growth in vivo.

Results

Circ_0001721 and TCF4 were upregulated, whereas miR-758 was down-regulated in DXR-resistant OS tissues and cells. Circ_0001721 silence reduced DXR resistance of KHOS/DXR and MG63/DXR cells. Circ_0001721 regulated DXR resistance via sponging miR-758. Moreover, miR-758 modulated DXR resistance by targeting TCF4. Besides, circ_0001721 knockdown inhibited tumor growth in vivo.

Conclusion

Circ_0001721 potentiated DXR resistance and facilitated the progression of OS by regulating miR-758/TCF4 axis, which provides promising therapeutic targets for OS treatment.

Transcription Factors in Cancer: When Alternative Splicing Determines Opposite Cell Fates

Alternative splicing (AS) is a finely regulated mechanism for transcriptome and proteome diversification in eukaryotic cells. Correct balance between AS isoforms takes part in molecular mechanisms that properly define spatiotemporal and tissue specific transcriptional programs in physiological conditions. However, several diseases are associated to or even caused by AS alterations. In particular, multiple AS changes occur in cancer cells and sustain the oncogenic transcriptional program. Transcription factors (TFs) represent a key class of proteins that control gene expression by direct binding to DNA regulatory elements. AS events can generate cancer-associated TF isoforms with altered activity, leading to sustained proliferative signaling, differentiation block and apoptosis resistance, all well-known hallmarks of cancer. In this review, we focus on how AS can produce TFs isoforms with opposite transcriptional activities or antagonistic functions that severely impact on cancer biology. This summary points the attention to the relevance of the analysis of TFs splice variants in cancer, which can allow patients stratification despite the presence of interindividual genetic heterogeneity. Recurrent TFs variants that give advantage to specific cancer types not only open the opportunity to use AS transcripts as clinical biomarkers but also guide the development of new anti-cancer strategies in personalized medicine.