Abstract
BackgroundPreviously, we have demonstrated that Interleukin 13 receptor alpha 2 (IL-13Rα2) is overexpressed in approximate 78% Glioblastoma multiforme (GBM) samples. We have also demonstrated that IL-13Rα2 can serve as a target for cancer immunotherapy in several pre-clinical and clinical studies. However, the significance of overexpression of IL-13Rα2 in GBM and astrocytoma and signaling through these receptors is not known. IL-13 can signal through IL-13R via JAK/STAT and AP-1 pathways in certain cell lines including some tumor cell lines. Herein, we have investigated a role of IL-13/IL-13Rα2 axis in signaling through AP-1 transcription factors in human glioma samples in situ.MethodsWe examined the activation of AP-1 family of transcription factors (c-Jun, Fra-1, Jun-D, c-Fos, and Jun-B) after treating U251, A172 (IL-13Rα2 +ve) and T98G (IL-13Rα2 −ve) glioma cell lines with IL-13 by RT-qPCR, and immunocytochemistry (ICC). We also performed colorimetric ELISA based assay to determine AP-1 transcription factor activation in glioma cell lines. Furthermore, we examined the expression of AP-1 transcription factors in situ in GBM and astrocytoma specimens by multiplex-immunohistochemistry (IHC). Student t test and ANOVA were used for statistical analysis of the results.ResultsWe have demonstrated up-regulation of two AP-1 transcription factors (c-Jun and Fra-1) at mRNA and protein levels upon treatment with IL-13 in IL-13Rα2 positive but not in IL-13Rα2 negative glioma cell lines. Both transcription factors were also overexpressed in patient derived GBM specimens, however, in contrast to GBM cell lines, c-Fos is also overexpressed in patient derived specimens. Astrocytoma specimens showed lesser extent of immunostaining for IL-13Rα2 and three AP-1 factors compared to GBM specimens. By transcription factor activation assay, we demonstrated that AP-1 transcription factors (C-Jun and Fra-1) were activated upon treatment of IL-13Rα2 + GBM cell lines but not IL-13Rα2 − GBM cell line with IL-13. Our results demonstrate functional activity of AP-1 transcription factor in GBM cell lines in response to IL-13.ConclusionsThese results indicate that IL-13/IL-13Rα2 axis can mediate signal transduction in situ via AP-1 pathway in GBM and astrocytoma and may serve as a new target for GBM immunotherapy.
Highlights
We have demonstrated that Interleukin 13 receptor alpha 2 (IL-13Rα2) is overexpressed in approximate 78% Glioblastoma multiforme (GBM) samples
IL-13Rα2 negative T98G cells did not show upregulation of any of the AP-1 members. These results indicate that IL-13 upregulates varied degree of AP-1 transcription factors (c-Jun, Fra-1 and JunD) through IL-13Rα2
When IL-13Rα2 is present, the STAT-6 activation is inhibited [35]. These results indicate that IL-13 mediates signaling through AP-1 pathway but not STAT-6 pathway in GBM cells that express IL-13Rα2
Summary
We have demonstrated that Interleukin 13 receptor alpha 2 (IL-13Rα2) is overexpressed in approximate 78% Glioblastoma multiforme (GBM) samples. We have demonstrated overexpression of interleukin 4 (IL-4) and IL-13 receptors on adult and pediatric brain tumors and meningiomas [6,7,8,9,10]. We have demonstrated that IL-13 can mediate signaling through IL-13Rα2 in human pancreatic and ovarian cancer cells [23]. In these models, IL-13 mediated cancer invasion and metastasis through IL-13Rα2 and signaling via AP-1/ERK pathway. IL-13 mediated cancer invasion and metastasis through IL-13Rα2 and signaling via AP-1/ERK pathway Despite these studies, it is not known whether IL-13 can signal through IL-13Rα2 in human glioma tumors in situ and whether it utilizes AP-1 pathway
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