Abstract A25: Tissue transglutaminase interacts with Frizzled 7 in ovarian cancer stem cells

Abstract

Abstract Increasing evidence correlates the metastatic progression and post-chemotherapy recurrence of ovarian cancer (OC) to a small population of cancer stem cells (CSCs), resistant to traditional chemotherapy and responsible for tumor relapse. Tissue transglutaminase (TG2) is a multifunctional protein, with enzymatic and scaffold functions, overexpressed in ovarian carcinomas, where it promotes metastasis. Independently of its enzymatic function, TG2 can be secreted in the extracellular compartment where it increases cell adhesion to the fibronectin (FN) matrix by regulating integrins clustering and matrix reorganization. We hypothesized that by binding to the integrins and FN, TG2 promotes survival of CSCs and supports OC spheroid formation. Our data demonstrate that TG2, β1 integrin, and FN1 expression are markedly increased in OC spheroids compared with monolayers and are enriched in successive sphere generations. Immunofluorescence (IF) staining supports that TG2 forms abundant complexes with β1 integrin and FN in cells grown as spheroids. TG2 expression is strongly correlated with β1 integrin (ITGB1) (R=0.23, P<0.0001) and with FN1 (R=0.39, P<0.0001) in the TCGA ovarian cancer database, which houses gene expression data of 560 clinically annotated HGSOC tumors. Patients with high TG2 and ITGB1 expression levels had an increased estimated risk of death when compared to those with low TG2 and ITGB1 expression levels (P=0.00652). Use of function-inhibiting antibody against the FN-binding domain of TG2 (4G3) dramatically suppressed TG2/FN/β1 integrin complex formation, spheroid proliferation, and tumor growth in a xenograft model. Furthermore, disruption of TG2/FN complex formation altered key oncogenic signaling pathways, and in particular blocked the canonical Wnt/β-catenin signaling pathway essential to sustaining cancer cell stemness. The Wnt receptor Frizzled genes (Fzd1, Fzd7 and Fzd8) showed the greatest difference in gene expression, indicating a direct correlation between TG2/FN complex and Wnt pathway activation. By co-immunoprecipitation and IF staining we demonstrated that TG2 colocalizes and directly binds to Fzd7 receptor. In conclusion, our data support that TG2/FN/β1 integrin complex formation is essential to promoting ovarian CSCs survival by acting as coreceptor complex with Fzd7 in regulating β-catenin signaling and represents a new target to eradicate chemotherapy-resistant tumors. Citation Format: Salvatore Condello, Livia Sima, Cristina Ivan, Horacio Cardenas, Gary Schiltz, Rama K Mishra, Daniela Matei. Tissue transglutaminase interacts with Frizzled 7 in ovarian cancer stem cells. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A25.