Black Raspberries Suppress Colorectal Cancer by Enhancing Smad4 Expression in Colonic Epithelium and Natural Killer Cells

Abstract

Innate immune cells in the tumor microenvironment have been proposed to control the transition from benign to malignant stages. In many cancers, increased infiltration of natural killer (NK) cells associates with good prognosis. Although the mechanisms that enable NK cells to restrain colorectal cancer (CRC) are unclear, the current study suggests the involvement of Smad4. We found suppressed Smad4 expression in circulating NK cells of untreated metastatic CRC patients. Moreover, NK cell-specific Smad4 deletion promoted colon adenomas in DSS-treated ApcMin/+ mice and adenocarcinomas in AOM/DSS-treated mice. Other studies have shown that Smad4 loss or weak expression in colonic epithelium associates with poor survival in CRC patients. Therefore, targeting Smad4 in both colonic epithelium and NK cells could provide an excellent opportunity to manage CRC. Toward this end, we showed that dietary intervention with black raspberries (BRBs) increased Smad4 expression in colonic epithelium in patients with FAP or CRC and in the two CRC mouse models. Also, benzoate metabolites of BRBs, such as hippurate, upregulated Smad4 and Gzmb expression that might enhance the cytotoxicity of primary human NK cells. Of note, increased levels of hippurate is a metabolomic marker of a healthy gut microbiota in humans, and hippurate also has antitumor effects. In conclusion, our study suggests a new mechanism for the action of benzoate metabolites derived from plant-based foods. This mechanism could be exploited clinically to upregulate Smad4 in colonic epithelium and NK cells, thereby delaying CRC progression.

Can Natural Products be Used to Overcome the Limitations of Colorectal Cancer Immunotherapy?

“…Natural products can also influence T cells, NK cells and Treg cells. Black raspberries can significantly inhibit CRC progression and increase NK cells in tissues infiltrating the APC Min+/- DSS and AOM/DSS models, and the results were validated in human CRC tissue ( 76 , 77 ). In addition, Ecklonia cava fucoidan (ECF) not only stimulates NK cell activation and proliferation but also induces NK cell activation through DCs ( 78 ).…”

Protocatechuic Acid, a Gut Bacterial Metabolite of Black Raspberries, Inhibits Adenoma Development and Alters Gut Microbiome Profiles in ApcMin/+ Mice

“…We further demonstrated that whole BRBs and 500 ppm PCA decreased inflammatory markers such as COX-2 and PGE 2 . In addition, 500 ppm PCA, but not 1,000 ppm PCA, enhanced IFN-γ and SMAD4 expression in primary cultured natural killer cells; both IFN-γ and SMAD4 are involved in crucial anti-inflammatory signaling in suppressing colorectal cancer development [ 18 , 33 , 34 ]. Our results suggest that an enhanced anti-inflammatory gut microbiome by virtue of whole BRBs and 500 ppm PCA could result in an anti-inflammatory tumor microenvironment and thereby suppress tumor development.…”

“…Human NK cells were isolated from fresh peripheral blood from healthy subjects and PBMC from healthy subjects using the NK Cell Isolation Kit (Miltenyi Biotec, Auburn, CA, USA) according to the manufacturer’s protocol but with minor modifications, as described previously [ 18 ]. Freshly isolated NK cells were cultured in RPMI1640+10% FBS+1% P/S (RPMI, Roswell Park Memorial Institute; FBS, Fetal bovine serum; P/S, Penicillin-Streptomycin) and immediately treated with PCA at 500 ppm or 1,000 ppm or dimethylsulfoxide (DMSO) (Millipore Sigma) for 16 hours.…”

Identification of Circular RNA-Based Immunomodulatory Networks in Colorectal Cancer

“…The interaction between the proteins CD44 and MUC5AC conferred colon cancer cell resistance to 5-FU via the downregulation of p53 and p21 (41). Increasing numbers of studies have indicated that NK cells have achieved good efficacy in treating and killing tumours, especially in colon cancer, and have good prospects for transformation (42,43). Ma (44) constructed an immune-related module that consists of SYP and 13 other genes, which may be innovative biomarkers for the prediction of colon cancer prognosis and response to immunological therapy.…”