Access Type
Open Access Embargo
Date of Award
January 2023
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Cancer Biology
First Advisor
Gen Sheng Wu
Abstract
Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer that lacks targeted therapies. Previous studies have shown that TNBC cells are highly sensitive to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), making it a promising agent for treating TNBC. However, the development of TRAIL resistance limits its further clinical development, and the underlying mechanisms are not fully understood. In this study, we report the role of PD-L1 and inflammation in TRAIL resistance. Specifically, we found that TRAIL treatment increases PD-L1 expression in TRAIL-sensitive cells and that basal PD-L1 expression is increased in acquired TRAIL-resistant cells. Mechanistically, we found that increased PD-L1 expression was accompanied by increased ERK activation. Using both genetic and pharmacological approaches, we showed that knockdown of ERK by siRNA or inhibition of ERK activation by the MEK inhibitor U0126 decreased PD-L1 expression and increased TRAIL-induced cell death. Furthermore, we found that knockout or knockdown of PD-L1 enhances TRAIL-induced apoptosis, suggesting that PD-L1-mediated TRAIL resistance is independent of its ability to evade immune suppression. These findings suggest that the mechanisms of TRAIL resistance extend beyond intrinsic and extrinsic apoptosis pathways. Because TRAIL-resistant cells were not eliminated after PD-L1 knockdown and knockout, we speculate that there are other TRAIL resistance mechanisms in these TNBC cells. To better understand the mechanism of TRAIL resistance, we performed RNA sequencing and gene expression analysis in TRAIL-sensitive and TRAIL-resistant MDA231 and SUM159 cells. This approach led us to identify several differentially expressed genes (DEGs) and pathways in MDA231-R and SUM159-R cells when compared to their TRAIL-sensitive counterparts. We showed that a number of DEGs and pathways were associated with immune response and inflammation in MDA231-R and SUM159-R cells. Among these pathways, we found that cytokine-cytokine receptor interaction and TNF signaling were the most affected. Because TRAIL is a TNF superfamily cytokine, we wanted to know if it played a noncanonical role in inducing inflammation and whether this was caused by pro-inflammatory cytokines IL-6 and IL-1α in TRAIL-resistant cells. Using western blot analysis, we showed that basal levels of IL-6 and IL-1α were increased in MDA231-R and SUM159-R cells. Furthermore, we found that knockdown of IL-6 and IL-1α enhances TRAIL-induced apoptosis, suggesting that inflammation plays a role in TRAIL resistance in TNBC. In summary, this dissertation has identified two new noncanonical mechanisms by which PD-L1, IL-6, and IL-1α promote TRAIL resistance in TNBC cells, which could be targeted for TNBC therapy.
Recommended Citation
Pimentel, Julio Macias, "The Mechanisms Of Trail Resistance In Triple-Negative Breast Cancer" (2023). Wayne State University Dissertations. 3889.
https://digitalcommons.wayne.edu/oa_dissertations/3889