Panoply™ Human HRH1 Over-expressing Stable Cell Line

Inflammatory bowel disease (IBD) is a well-known risk factor for colorectal cancer. Previous studies have shown that microbial histamine can ameliorate intestinal inflammation in mice. Here, researchers tested the hypothesis that microbial-derived intraluminal histamine could suppress inflammation-associated colon cancer in Apcmin/+ mice. Mice were implanted with humanized Lactobacillus reuteri. Chronic inflammation was induced by repeated cycles of low-dose dextran sulfate sodium (DSS). Despite the complex intestinal microbiota, mice treated with histamine-producing L. reuteri by oral gavage exhibited a reduced incidence of colon tumors. Furthermore, administration of a histamine H1 receptor (H1R) antagonist inhibited tumor formation, whereas administration of a histamine H2 receptor (H2R) antagonist significantly increased tumor number and size. Histamine has dual functions, including pro-tumorigenic effects via H1R and anti-tumorigenic effects via H2R, findings supported by gene expression profiling of tumor samples from colorectal cancer patients. A higher expression ratio of H2R (HRH2) to H1R (HRH1) is associated with improved overall survival in patients with colorectal cancer. Furthermore, H2R activation inhibits the phosphorylation of mitogen-activated protein kinase (MAPK) and suppresses H1R activation-induced chemokine gene expression in colorectal cancer cells.

To test whether H1R and H2R activation alters ERK phosphorylation in colorectal cancer cells, researchers constructed plasmid-borne H1R and H2R constructs in HCT116 cells and expressed them using either Hrh1 or Hrh2 plasmids. Histamine treatment enhanced JNK and ERK MAPK phosphorylation in HCT116 cells overexpressing HRH1 (Figure 1A). Concomitant H2R overexpression inhibited H1R-mediated ERK and JNK activation at 30 and 60 minutes, as measured by immunoblotting (Figures 1A and B). The activity of these constructs was verified by immunoblotting using H1R and H2R antibodies, respectively (Figure 1C). Furthermore, double immunostaining for H1R (green) and p-ERK was performed in HRH1 overexpressing HCT116 cells treated with histamine (10 µM) for 1 hour. After histamine treatment, immunofluorescence analysis of HCT116 cells revealed the presence of phosphorylated ERK in the nucleus only in cells expressing H1R (Figure 1D), while HRH2-overexpressing cells showed only sparse, if any, signals of phosphorylated ERK (Figure 1E).

Figure 1. H2-receptor (H2R) signaling suppresses MAPK signaling pathways induced by H1-receptor (H1R) activation. (Shi Z, et al., 2019)