Gastrointestinal reflux disease and eosinophilic esophagitis are characterized by basal cell hyperplasia. The extracellular calcium-sensing receptor (CaSR), a G protein-coupled receptor, which may be activated by divalent agonists, is expressed throughout the gastrointestinal system. The CaSR may regulate proliferation or differentiation, depending on cell type and tissue. The current experiments demonstrate the expression of the CaSR on a human esophageal epithelial cell line (HET-1A) and the location and expression of the CaSR in the human esophagus. CaSR immunoreactivity was seen in the basal layer of normal human esophagus. CaSR expression was confirmed in HET-1A cells by RT-PCR, immunocytochemistry, and Western blot analysis. CaSR stimulation by extracellular calcium or agonists, such as spermine or Mg(2+), caused ERK1 and 2 activation, intracellular calcium concentration ([Ca(2+)](i)) mobilization (as assessed by microspecfluorometry using Fluo-4), and secretion of the multifunctional cytokine IL-8 (CX-CL8). HET-1A cells transiently transfected with small interfering (si)RNA duplex against the CaSR manifested attenuated responses to Ca(2+) stimulation of phospho- (p)ERK1 and 2, [Ca(2+)](i) mobilization, and IL-8 secretion, whereas responses to acetylcholine (ACh) remained sustained. An inhibitor of phosphatidylinositol-specific phospholipase C (PI-PLC) (U73122) blocked CaSR-stimulated [Ca(2+)](i) release. We conclude that the CaSR is present on basal cells of the human esophagus and is present in a functional manner on the esophageal epithelial cell line, HET-1A.
Activation of the formylpeptide receptor (FPR), a G-protein-coupled receptor, by its chemotactic peptide ligand N-formylmethionyl-leucyl-phenylalanine (fMLF) promotes the directional migration and survival of human glioblastoma cells. fMLF also stimulates glioblastoma cells to produce biologically active VEGF, an important angiogenic factor involved in tumor progression. In this study, we examined the capacity of FPR to regulate the production of another angiogenic factor, the chemokine IL-8 (CXCL8), in addition to its demonstrated ability to induce VEGF secretion by malignant glioma cells. We showed that the human glioblastoma cell line U87 secreted considerable levels of IL-8 (CXCL8) upon stimulation by the FPR agonist peptide fMLF. Tumor cells transfected with small interference (si)RNA targeting FPR failed to produce IL-8 as well as VEGF in response to fMLF. Glioblastoma cells bearing FPR siRNA exhibited reduced rate of tumorigenicity in nude mice and tumors formed by such tumor cells showed less active angiogenesis and lower level expression of both IL-8 and VEGF. These results suggest that FPR plays an important role in the angiogenesis of human malignant gliomas through increasing the production of angiogenic factors by FPR positive tumor cells.
