The role of Wnt/[beta]-catenin in cancer stemness and chemoresistance in three-dimensional cultures

Abstract

Three-dimensional (3D) culture is increasingly being recognized due to its superior capacity to simulate tissue-like structures compared with two-dimensional (2D) monolayers. Although much is known about the various characteristics of 2D and 3D cultures in certain cancer types, the knowledge on other tumor types is limited. In nasopharyngeal carcinoma (NPC), although Epstein-Barr virus (EBV) is consistently present in undifferentiated NPCs, most studies have focused on EBV-negative NPC cells. In Chapter 2, 3D spheroid models of EBV-positive NPC cells were developed and characterized, and they were compared with conventional 2D cultures, which showed different features of tumor phenotypes and treatment responses. In addition, RNA sequencing analysis indicated substantial transcriptomic differences between 3D spheroids and 2D monolayers. Specifically, Wnt/β-catenin and Eph/ephrin cell signaling pathways were discovered and recognized as activated signals in NPC spheroids as compared to 2D monolayers. United States Food and Drug Administration approved drugs targeting these signaling pathways involved in 3D spheroids can eliminate NPC cell growth/survival. These findings indicate the differential signaling in 3D NPC spheroids of potential therapeutic implications.

Cisplatin and paclitaxel are the main chemotherapeutic agents used for the treatment of ovarian cancer. However, their effectiveness is limited due to inherent and acquired chemoresistance. Cancer stem cells (CSCs) are shown to be chemoresistant. In Chapter 3, a subpopulation of c-Kit (CD117)-positive CSCs was enriched under 3D stem cell-selective conditions to elucidate the critical transcriptional activators of CSCs. The CBP/β-catenin interaction plays a role in the maintenance of cancer stemness. Using coimmunoprecipitation on nuclear β-catenin followed by mass spectrometry analysis, SP100 and HRP2 were identified as novel transcription co-activators that bound β-catenin. SP100- and HRP2-β-catenin interactions were essential for the expansion and drug resistance of CSCs and correlated with poor clinical outcomes. These findings reveal novel interacting partners of β-catenin in cancer stemness and chemoresistance in ovarian cancer.

Together, these findings provide a better understanding of 3D spheroids in NPC and ovarian cancer and demonstrate an essential role of Wnt/β-catenin signaling in these 3D cultures. (328 words)