Protein hydrolysate-induced cholecystokinin secretion from enteroendocrine cells is indirectly mediated by the intestinal oligopeptide transporter PepT1

Abstract

Dietary protein is a major stimulant for cholecystokinin (CCK) secretion by the intestinal I cell, however, the mechanism by which protein is detected is unknown. Indirect functional evidence suggests that PepT1 may play a role in CCK-mediated changes in gastric motor function. However, it is unclear whether this oligopeptide transporter directly or indirectly activates the I cell. Using both the CCK-expressing enteroendocrine STC-1 cell and acutely isolated native I cells from CCK-enhanced green fluorescent protein (eGFP) mice, we aimed to determine whether PepT1 directly activates the enteroendocrine cell to elicit CCK secretion in response to oligopeptides. Both STC-1 cells and isolated CCK-eGFP cells expressed PepT1 transcripts. STC-1 cells were activated, as measured by ERK1/2 phosphorylation, by both peptone and the PepT1 substrate Cefaclor; however, the PepT1 inhibitor 4-aminomethyl benzoic acid (AMBA) had no effect on STC-1 cell activity. The PepT1-transportable substrate glycyl-sarcosine dose-dependently decreased gastric motility in anesthetized rats but had no affect on activation of STC-1 cells or on CCK secretion by CCK-eGFP cells. CCK secretion was significantly increased in response to peptone but not to Cefaclor, cephalexin, or Phe-Ala in CCK-eGFP cells. Taken together, the data suggest that PepT1 does not directly mediate CCK secretion in response to PepT1 specific substrates. PepT1, instead, may have an indirect role in protein sensing in the intestine.

Sensing of amino acids by the gut-expressed taste receptor T1R1-T1R3 stimulates CCK secretion

“…We demonstrated that, in response to protein hydrolysates and a tripeptide, STC-1 cells secrete CCK, as has been shown previously (7,21,25,37,48,52,60) (Fig. 1).…”

“…Recent work has shown that the peptide transporter PepT1 is not the I cell luminal membrane receptor involved in mediating peptoneinduced CCK release (37), while the GPCR GPR93 has been proposed as a candidate sensor for peptones in STC-1 cells (8). Further work is required to confirm the peptone-sensing role of this GPCR in the intestine.…”

“…Therefore, we aimed to determine if gut-expressed T1R1-T1R3 is involved in sensing luminal amino acids, activating a pathway leading to CCK release. In light of in vivo and in vitro studies demonstrating that, in response to protein hydrolysates, peptides, and amino acids, intestinal tissue and the murine enteroendocrine cell line STC-1 secrete CCK (7,14,21,25,37,48,52,55,60), we aimed to assess the responsiveness of T1R1-T1R3 to these substrates through the secretion of CCK. We first used the CCK-secreting cell line STC-1, which expresses T1R1, T1R3, and ␣-gustducin (18,63).…”

Gut chemosensing mechanisms

“…Meat hydrolysate has been demonstrated to trigger GLP1 release from vascularly perfused rat small intestine, STC-1 cells (a small intestine enteroendocrine murine cell line) (52), and NCI-H716 cells (derived from human colorectal adenocarcinoma) (53), as well as CCK release from I cells (54). The sensing of these larger protein digestion products has been linked to the activation of MAPKs (52, 53) and the activity of the brush border H + -coupled transporter of dipeptides and tripeptides, peptide transporter 1 (PEPT1) (54,55). Both PEPT1-and CaSR-dependent pathways were recently implicated in the sensing of peptones and dipeptides and tripeptides by primary L cells (56).…”

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“…The small peptides are absorption substrates of the intestinal lumen, which can efficiently accelerate the growth of villi, promote the proactive development of the intestinal tract, and elevate intestinal digestive enzyme activity (Bamba, Fuse, Obata, Sasaki, & Hosoda, 1993). Meanwhile, the rapid absorption of small peptides and free amino acids can trigger intracellular calcium-mediated signaling events, followed by the release of more digestive enzymes (Liou et al, 2011). Nevertheless, the intestinal digestive enzyme activity showed no significant increase with increasing replacement proportions (FMBH48, FMBH64, or FMBH80).…”