Previously, we have demonstrated that IL-13 receptor alpha2 (IL-13Rα2), a high affinity receptor for Th2 cytokine IL-13, is overexpressed in most glioblastoma multiforme (GBM) cell lines and approximately 78% of the patient-derived samples. We have also demonstrated that IL-13Rα2 can be targeted by a number of immunotherapeutic agents including chimeric antigen receptor modified T (CAR-T) cells, targeted lentivirus and adenovirus vectors, and a chimeric fusion immunotoxin consisting of IL-13 and truncated Pseudomonas exotoxin (IL-13-PE). However, the signal transduction initiated by IL-13 in GBM tumor is not known to occur through the IL13Rα2, which has a high affinity for IL-13. We have recently observed that IL-13 can signal through IL-13Rα2 by activating AP-1 transcription factors in human brain tumor cell lines. In this study, we have examined IL-13Rα2 expression in human brain tumor and normal brain specimens, and the subsequent signaling through the AP-1 pathway in situ. Using six human glioblastoma and three astrocytoma specimens, we evaluated the expression of AP-1 transcription factors by immunohistochemistry (IHC) and compared the extent of immunostaining and percent positive fields with three normal brain specimens. Six GBM specimens examined showed high degree of immunostaining for c-Fos, c-Jun, Jun D and Fra-1 (AP-1 family of transcription factors) and a high percentage of positive fields. These specimens also showed strong immunostaining for IL-13Rα2 (4+) in >70% fields (P<0.001 compared to normal brain). Three astrocytoma specimens showed staining for IL-13Rα2 (>2+ and 32% fields, P<0.01 compared to normal brain), but the extent of staining was lower compared to GBM. Similar to IL-13Rα2 expression, the extent of staining and percentage of positive fields for AP-1 transcription factors were highly statistically significant between tumors and normal brain (P<0.001 for GBM compared to normal brain and P<0.01 for astrocytoma compared to normal brain). The extent of immunostaining in GBM was highest for c-Fos (4+, 78% fields) followed by c-Jun (3+, 57% fields), Fra-1 (2+, 70% fields) and Jun-D (2+, 28% fields). Jun-B expression was the lowest among the AP-1 transcription factors (<1+, 7% fields) in GBM specimens. Astrocytoma specimens showed lesser extent of immunostaining for AP-1 members compared to GBM; c-Fos showed 2+ staining and 42% positive fields followed by c-Jun (2+, 12% fields), Fra-1 (2+, 48% fields) and Jun-D (<1+, 18% fields). Jun-B staining intensity was <1+ in only 6% fields. Normal brain specimens showed no immunostaining for AP-1 family members. Our results generally corroborate with data obtained from GBM cell lines and confirm that IL-13 can signal in IL-13Rα2 positive GBM tumors in-situ through the AP-1 pathway, thus indicating that this pathway may be an important target for therapeutic intervention of GBM in addition to targeting IL-13Rα2.
Citation Format: Rukmini Bhardwaj, Akiko Suzuki, Pamela Leland, Bharat H. Joshi, Raj K. Puri. Analysis of IL-13 signaling through IL-13Rα2 in human brain tumor specimens in situ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2438. doi:10.1158/1538-7445.AM2017-2438