Macrophages produce and functionally respond to interleukin-34 in colon cancer

Abstract

In colorectal cancer (CRC), macrophages represent a major component of the tumor mass and exert mostly functions promoting tumor cell survival, proliferation, and dissemination. Interleukin-34 (IL-34) is a cytokine overproduced by colon cancer (CRC) cells and supposed to make a valid contribution to the growth and diffusion of CRC cells. The biological functions of IL-34 are mediated by the macrophage colony-stimulating factor receptor (M-CSFR-1), which controls monocyte/macrophage differentiation, growth, and survival. We here investigated whether, in CRC, tumor-associated macrophages (TAMs) express M-CSFR-1 and functionally respond to IL-34. By flow-cytometry analysis of tumor-infiltrating cells (TICs) and lamina propria mononuclear cells (LPMCs) isolated from normal, adjacent mucosa of CRC patients, we showed that CD68/HLA-DRII-expressing TICs and LPMCs expressed M-CSFR-1. Both these cell types produced IL-34 even though the expression of the cytokine was more pronounced in TICs as compared to normal LPMCs. Moreover, in CRC samples, there was a positive correlation between IL-34-producing cells and CD68-positive cells. Stimulation of LPMCs and TICs with IL-34 resulted in enhanced expression of CD163 and CD206, two markers of type II-polarized macrophages, and this was evident at both RNA and protein level. In the same cell cultures, IL-34 stimulated expression and production of IL-6, a cytokine known to promote CRC cell growth and diffusion. Finally, knockdown of IL-34 in TICs with specific antisense oligonucleotides with: a specific antisesne oligonucleotide decreased IL-6 production and the number of TAMs producing this cytokine. This is the first to show a positive role of IL-34 in the control of TAMs in CRC, further supporting the notion that IL-34 sustains colon tumorigenesis.

Interleukin-34 promotes tumorigenic signals for colon cancer cells

“…Studies in human CRC tissue and experimental models of cancer support the view that locally produced cytokines regulate critical steps of the colon carcinogenesis [ 82 , 83 ]. The findings discussed in this article suggest that IL-34 regulates positively the function of CRC cells as well as other immune cells and non-immune cells in the CRC microenvironment, with the downstream effect of enhancing the growth and invasion of CRC cells [ 59 , 70 , 75 ], (Fig. 3 ).…”

“…3 ). The possibility to use IL-34 inhibitors to block its pro-tumorigenic effects could thus open up a challenging opportunity for a new treatment option in CRC [ 59 , 70 , 75 ]. In this context, however, further work is needed to confirm the in vitro data generated using cells isolated from human CRC samples in pre-clinical models of CRC and ascertain whether IL-34 blockers can enhance the properties of other anti-tumoural drugs, including chemotherapeutics and biologics.…”

“…This hypothesis is also supported by the demonstration that, in CRC, IL-34 expression correlates with the content of CD163, a marker of TAMs [ 60 ]. By flow-cytometry analysis of tumour-infiltrating cells (TICs) and LPMC isolated from normal adjacent mucosa of CRC patients, we have recently shown that CD68/HLA-DRII-expressing TICs and LPMC expressed M-CSF-1-R [ 70 ]. Both these cell types produced IL-34 even though IL-34 expression was more pronounced in TICs as compared to normal LPMC.…”

“…Indeed, stimulation of both TICs and LPMCs with IL-34 enhanced the expression of CD163 and CD206, two markers of type-2-polarized macrophages [ 71 ]. Moreover, stimulation of both TICs and LPMCs with IL-34 enhanced IL-6 synthesis [ 70 ], a cytokine that activates proliferative and survival signals in CRC cells. Consistently, knockdown of IL-34 in TICs with a specific ASO decreased IL-6 production and the number of IL-6-producing TAMs [ 70 ].…”

“…Moreover, stimulation of both TICs and LPMCs with IL-34 enhanced IL-6 synthesis [ 70 ], a cytokine that activates proliferative and survival signals in CRC cells. Consistently, knockdown of IL-34 in TICs with a specific ASO decreased IL-6 production and the number of IL-6-producing TAMs [ 70 ]. These findings are in agreement with the demonstration that expression of IL-34 is associated with increased infiltration and function of type-2-polarized TAMs in other cancer types [ 72 ].…”