Abstract
SMAD4 is a key transcriptional factor of TGFβ signaling and acts as a tumor suppressor in colorectal cancer. In the present study, we explored the immunologic effect of SMAD4 on the tumor microenvironment. Using 99 clinical specimens and human colorectal cancer cell lines, we investigate the relationship between SMAD4 expression and neutrophil accumulation. We immunohistochemically analyzed expression of SMAD4, CXCL1, CXCL8, CXCR2, and other proteins with clinical specimens. Finally, we determined the serum levels of CXCL1 and CXCL8 in 125 patients with colorectal cancer. SMAD4 knockdown from human colorectal cancer cells upregulated the expression of CXCL1 and CXCL8, which recruited neutrophils to colorectal cancer tumor via CXCR2. In turn, when neutrophils were exposed to the supernatant of SMAD4-negative colorectal cancer cells, they produced a large amount of CXCL1 and CXCL8 by themselves in vitro. In human clinical specimens, we found that neutrophil infiltration into the peritumoral stroma was more marked in SMAD4-negative colorectal cancer compared with that in SMAD4-positive colorectal cancer, and that both CXCL1 and CXCL8 were abundantly expressed in the tumor-infiltrating neutrophils. Neutrophils isolated from primary colorectal cancer expressed significantly higher levels of CXCL1 and CXCL8 than did those isolated from peripheral blood. Furthermore, tumor-infiltrating neutrophils expressed MMP2 and MMP9 in addition to ARG1 and IDO. Serum CXCL8 level was significantly higher in colorectal cancer patients, especially those at stage II/III, and statistical analysis indicated a high CXCL8 level was associated with a shorter overall survival and relapse-free survival. Blockade of the CXCL1/8-CXCR2 axis could be a novel therapeutic approach against SMAD4-negative colorectal cancer.
Highlights
Colorectal cancer is the third most common cause of cancerrelated deaths worldwide
When neutrophils were exposed to the supernatant of SMAD4-negative colorectal cancer cells, they produced a large amount of CXCL1 and CXCL8 by themselves in vitro
We found that neutrophil infiltration into the peritumoral stroma was more marked in SMAD4-negative colorectal cancer compared with that in SMAD4-positive colorectal cancer, and that both CXCL1 and CXCL8 were abundantly expressed in the tumor-infiltrating neutrophils
Summary
Colorectal cancer is the third most common cause of cancerrelated deaths worldwide. Colorectal cancer is thought to result from the accumulation of genetic alterations such as oncogenes and tumor suppressor genes (e.g., APC, Kras, p53, and SMAD4) as well as epigenetic changes of additional genes. SMAD4 is a downstream mediator of the transforming growth factor-b (TGFb) signaling superfamily and acts as a tumor suppressor in colorectal cancer. Loss of the SMAD4 protein is observed in 30% to 40% of colorectal cancer cases and is associated with a poor prognosis [1, 2]. Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/).
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