Casein Binds to the Cell Membrane and Induces Intracellular Calcium Signals in the Enteroendocrine Cell: A Brief Communication

Abstract

Dietary protein but not amino acids stimulates cholecystokinin (CCK) secretion in rat mucosal cells. However, the dietary protein sensory mechanisms and the intracellular signal pathway in the enteroendocrine cells have not yet been clarified. The relationship between dietary protein binding to cell membrane and intracellular calcium responses were examined in the CCK-producing enteroendocrine cell line STC-1. The binding of solubilized STC-1 cell membrane to proteins was analyzed using a surface plasmon resonance sensor. Intracellular calcium concentrations of STC-1 cell suspensions loaded with Fura-2 AM were measured using a spectrafluorophotometer system with continuous stirring. Intracellular calcium concentrations in STC-1 cells were increased by exposure to alpha-casein or casein sodium, but not to bovine serum albumin. Solubilized STC-1 membranes bound to alpha-casein and casein sodium but did not bind to bovine serum albumin. alpha-Casein demonstrated higher membrane binding and intracellular calcium stimulating activities than casein sodium. Thus, protein binding to the STC-1 cell membrane and intracellular calcium responses were correlated. Intracellular calcium responses to alpha-casein were suppressed by an L-type calcium channel blocker. These results suggest that casein, a dietary protein, binds to a putative receptor on the CCK-producing enteroendocrine cell membrane and elicits the subsequent intracellular calcium response via an L-type calcium channel.

Soybean β-Conglycinin Bromelain Hydrolysate Stimulates Cholecystokinin Secretion by Enteroendocrine STC-1 Cells to Suppress the Appetite of Rats under Meal-Feeding Conditions

“…Recent reports have shown that a G-protein coupled receptor (GPCR), GPR93, mediated the peptone-induced CCK secretion in STC-1 cells, 26,27) and we have demonstrated the involvement of the Gq pathway for BconP-induced CCK secretion in these cells. [28][29][30] We have recently found the calcium-sensing receptor, CaR, to function as the receptor for the arginine-rich 51-63 peptide in -conglycinin by inducing intracellular Ca 2þ mobilization for triggering subsequent CCK secretion in EECs. 31) It is therefore possible that these GPCRs can also act as receptors for BconB peptides.…”

Molecular properties of food allergens

“…59 It has been proposed that plasma membrane receptors exist in enteroendocrine cells for casein (in particular a-casein), which are responsible for caseininduced, L-type, calcium channel-mediated increases in intracellular calcium observed in an enteroendocrine cell line, STC-1. 60 Recently, nsLTPs have been demonstrated to bind to ubiquitous plasma membrane receptors in plant cells, and the authors speculated that there might be the possibility of similar interactions taking place with animal membranes that might be relevant to allergenic potential. 61 …”

Casein α s1 Is Expressed by Human Monocytes and Upregulates the Production of GM-CSF via p38 MAPK

“…First, we demonstrated binding of CSN1S1 on monocytic cells; however, this finding does not prove the presence of specific binding sites, because unspecific attachment may occur. Early experiments using bovine casein and human and animal leukocytes and other cell types suggested that casein binding receptors exist (13)(14)(15)47), but this finding cannot easily be transferred to human caseins because sequence homology is weak (31). For instance, the identity between the human CSN1S1 mRNA (accession code NM_001890; http://www.ncbi.nlm.nih.gov/Genbank) and the homologs of cattle (X00564), rat (NM_138874), and mouse (NM_007784) is 57.6, 49.8, and 47.8%, respectively (determined by the Euopean Molecular Biology Open Software Suite Align tool at the European Bioinformatics Institute, http://www.ebi.ac.uk).…”