Dll1-Mediated Notch Signaling Drives Tumor Cell Cross-talk with Cancer-Associated Fibroblasts to Promote Radioresistance in Breast Cancer

Abstract

Resistance to radiotherapy is a major obstacle for effective cancer treatment. Both cancer-associated fibroblasts (CAF) within the tumor microenvironment (TME) and Notch signaling are implicated in radioresistance, but their potential interrelationship is unclear. Here, we report that irradiated samples obtained from luminal breast cancer patient tumors express higher levels of the Notch ligand Dll1 and have a greater number of αSMA- and FAP-expressing activated CAFs. Single cell transcriptomic profiles further revealed enrichment of an αSMA+ myofibroblastic subpopulation of CAF in Dll1+ tumors. In murine and human PDX models, Dll1+ tumor cells were more radioresistant than Dll1- tumor cells, and genetic and pharmacological blocking of Dll1-mediated Notch signaling decreased the number of Dll1+ cancer stem cells (CSC) and CAFs and increased Dll1+ tumor cell radiosensitivity. Dll1+ cells recruited CAFs in an IL-6-dependent fashion and promoted Wnt ligand secretion by Notch2/3-expressing CAFs, thereby driving Wnt/β-catenin-dependent increases in Dll1+ CSC function to promote metastasis. Treatment with the porcupine inhibitor LGK-974 that inhibits Wnt ligand secretion or pharmacological blockade of IL-6 or Dll1 suppressed CAF-dependent enhancement of Dll1+ CSC function and metastasis in radioresistant tumors. Together, these findings reveal an essential crosstalk between Dll1+ cancer cells and CAFs that promotes metastasis and radioresistance, which could be therapeutically exploited to improve the outcome of breast cancer patients.

Signaling pathways in cancer‐associated fibroblasts: recent advances and future perspectives

“…In breast cancer, exosomal miR‐221 secreted by CAFs decreased ER expression and upregulated Notch3 expression in recipient cancer cells, which induced the production of CD133‐overexpressing CSCs and ultimately promoted hormone therapy resistance [ 211 ]. Additionally, DLL1 + breast cancer cells recruited CAFs and promoted Wnt ligand secretion by Notch2/3‐expressing CAFs, resulting in increased Wnt/β‐catenin‐dependent DLL1 + CSC functions to promote metastasis and radioresistance [ 212 ].…”

The stromal-tumor amplifying STC1-Notch1 feedforward signal promotes the stemness of hepatocellular carcinoma

“…The Notch signaling pathway is a highly evolutionarily conserved stemness-related pathway. In breast cancer, Notch signaling drives crosstalk between tumor cells and CAFs to promote the radio-resistance of tumor cells [ 40 ]. Here, our data indicated that CAF-derived STC1 could activate the Notch1 signaling pathway in HCC.…”

Cancer-associated fibroblasts: The chief architect in the tumor microenvironment

“…Production of TGFβ by radio-treated CAFs can also promote cancer cell aggressive and invasive properties, acting as a radiotherapy therapeutic escape and resistance ( Papadopoulou and Kletsas, 2011 ; Zhang et al, 2017 ). Notch signaling in CAFs plays a role in radioresistance, as demonstrated by a recent study that identified single-cell transcriptomic profiles in CAF subpopulations in delta-like canonical Notch ligand 1 , Dll1⁺ tumors ( Nandi et al, 2022 ). The connection between Notch signaling and CAF-associated metastasis and radioresistance could be exploited to improve breast cancer patient outcomes by minimizing radioresistance and stemness ( Nandi et al, 2022 ).…”

“…Notch signaling in CAFs plays a role in radioresistance, as demonstrated by a recent study that identified single-cell transcriptomic profiles in CAF subpopulations in delta-like canonical Notch ligand 1 , Dll1⁺ tumors ( Nandi et al, 2022 ). The connection between Notch signaling and CAF-associated metastasis and radioresistance could be exploited to improve breast cancer patient outcomes by minimizing radioresistance and stemness ( Nandi et al, 2022 ). The increased expression of CXCL12, TGFβ, MMPs, and HGF in CAFs induced by radiation increases the activation of EMT pathways in cancer cells ( Ansems and Span, 2020 ).…”