61P - Tumor cell-released autophagosomes (TRAPs) remodel the breast tumor microenvironment by inducing the formation of inflammatory cancer-associated fibroblasts (CAFs)

Background

Cancer-associated fibroblasts (CAFs) are the most prominent stromal cells in the tumor microenvironment, playing a significant role in tumor progress. However, the specific mechanisms underlying CAF formation and their role in remodeling the tumor microenvironment remain unclear. Previous studies have demonstrated that tumor cell-released autophagosomes (TRAPs) can arrival to lung tissue and regulate the function of lung fibroblasts to form premetastatic niche.

Methods

Primary breast adipose fibroblasts (NFs) were obtained from fourth mammary fat pads of mice, and co-cultured with TRAPs for 48 hours. The chemokines in collected supernatant were measured by ELISA. The expression of PD-L1 on the surface of fibroblasts and the ability to inhibit T cells were measured by flow cytometry (FCM). DAMPs on the TRAP surface blocked by antibodies, and fibroblasts pretreated with inhibitors were used to detect the ligand receptors between TRAP and NFs. Mouse experiments were performed as follows: 1)Tumor-bearing mice were constructed using TRAP low-expression cell lines (Beclin1KD/Raba8a KD); 2) NFs and 4T1 cells, with or without TRAP stimulation, were mixed and implanted in mice to detect the proportion and function of various cells in the tumor microenvironment by FCM.

Results

In vitro experiments revealed that the proteins (HSP27/70) on the surface of TRAP bind to TLR4 on NFs, exerting their functions via the HSP27/70-TLR4-MyD88- NF-κB signal cascade, ultimately expressing higher levels of PD-L1. Compared to the normal control (NC) group, the proportion of neutrophils and monocytes in the tumor microenvironment decreased, opposite T cells increased. Furthermore, the ability of T cells to secrete IFN-γ partially recovered. The level of PD-L1 on the surface of fibroblasts decreased, and their ability to inhibit T cells weakened.

Conclusions

TRAPs induce the formation of inflammatory and immune-suppressive fibroblasts by secreting CXCL1/2 and CCL5 to attract neutrophils and monocytes to the tumor microenvironment. Additionally, TRAPs directly inhibit T cells, ultimately contributing to the formation of the tumor microenvironment.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

X. Zhou, X. Wang, F. Zhu.

Funding

National Natural Science Foundation, China.

Disclosure

The author has declared no conflicts of interest.