Inhibition of BCL9 Modulates the Cellular Landscape of Tumor-Associated Macrophages in the Tumor Immune Microenvironment of Colorectal Cancer

Zhuang Wei,Jibin Dong,Mengxuan Yang,Rina Rosin-Arbesfeld,Zhongen Wu,Mei Feng,Di Zhu

doi:10.3389/fphar.2021.713331

Abstract

Tumor-associated macrophages (TAMs) are an indispensable part of the tumor microenvironment (TME), and they likely play a negative rather than positive role in cancer treatment. However, the cellular landscape and transcriptional profile regulation of TAMs in the case of tumor gene inactivation or chemical interference remains unclear. The B-cell lymphoma 9/B-cell lymphoma 9-like (BCL9/BCL9L) is a critical transcription co-factor of β-catenin. Suppression of Bcl9 inhibits tumor growth in mouse models of colorectal cancer (CRC). Here, we studied the TAMs of CRC by single-cell sequencing. Bcl9 depletion caused macrophage polarization inhibition from M0 to M2 and changed the CRC TME, which further interferes with the inflammation of M0 and M1. The transcription factor regulating these processes may be related to the Wnt signaling pathway from multiple levels. Furthermore, we also found that the cells delineated from monocyte to NK-like non-functioning cells were significantly different in the BCL9-deprived population. Combining these data, we proposed a TAM-to-NK score to evaluate the dynamic balance in TME of monocyte/TAM cells and NK-like non-functioning cells in The Cancer Genome Atlas (TCGA) clinical samples to verify the clinical significance. We demonstrated that the cell type balance and transcription differences of TAMs regulated by BCL9-driven Wnt signaling affected immune surveillance and inflammation of cancer, ultimately affecting patients’ prognosis. We thereby highlighted the potential of targeting Wnt signaling pathway through cancer immunotherapy.

Highlights

Tumor-associated macrophages (TAMs) are the most significant cluster of immune cells infiltrating colon cancer (Li et al, 2020)
The CT26 tumor cells were implanted s. c. into the right flanks of BALB/c mice; tumor-bearing animals were treated with vehicle control or hsBCL9CT-24 for 17 days hsBCL9CT-24 significantly reduced tumor volume relative to control throughout the study period (Figure 1A) and genetic knockdown of Bcl9 in CT26 significantly reduced tumor growth in compared with non-targeting RNA (NT -shRNA) (Figure 1B)
Through the clustering analysis of all cells, we found that these cells can be divided into eight clusters corresponding to tumor cells, tumor-associated monocytes, TAMs, tumor-associated endothelial cells, fibroblasts, and T cells (Figure 2A), these classifications are based on known markers or bioinformatics research (Wei et al, 2020)

Summary

Introduction

Tumor-associated macrophages (TAMs) are the most significant cluster of immune cells infiltrating colon cancer (Li et al, 2020). The proliferation of CT26 colon carcinoma cells was stimulated when the cells were co-cultured with macrophages derived from the peritoneal cavity (Luput et al, 2017). These conflicting observations may stem from the different origins of macrophages and suggest that the in vitro experiments do not reproduce the exact features of TAMs in CRC. Stratification by TAM infiltration location revealed that a high density of CD68 + TAMs in tumor stroma and tumor islet plus stroma (but not in tumor islet cells) predicted a favorable OS (Li et al, 2020) In resected colorectal liver metastases stained for CD68, a high density of TAMs correlated with longer DFS (Cavnar et al, 2017)

Methods

Results

Conclusion