Gastric intrinsic factor and its receptor

Area of Science:

• Biochemistry
• Gastroenterology
• Molecular Biology

Background:

• Vitamin B12 (Cbl) metabolism and assimilation are intricate processes studied for decades.
• Cbl absorption involves sequential binding to Haptocorrin (Hc) and Intrinsic Factor (IF).
• Recent findings highlight the role of pancreatic trypsin in transferring Cbl from Hc to IF.

Purpose of the Study:

• To detail the complex pathways of Cbl assimilation and transport within the organism.
• To elucidate the synthesis, secretion, and physiological regulation of IF.
• To clarify the molecular mechanisms of Cbl transcytosis through enterocytes.

Main Methods:

• Immunocytochemistry and in situ hybridization for IF localization and synthesis.
• Molecular biology techniques for cDNA encoding and structural characterization of Cbl binders.
• Studies on Cbl binders (IF, Hc, TC) across species and investigation of the IF receptor (IFCR).

Main Results:

• IF is synthesized not only in gastric parietal cells but also in other foregut-derived cells.
• Distinction between Cbl binding site on IF and the IF-Cbl binding site on IFCR established.
• Studies on IFCR expression in cancer cells and immunochemical investigations are clarifying Cbl transport pathways.

Conclusions:

• The enterohepatic circulation of Cbl is confirmed, with absorption in the terminal ileum.
• Advanced techniques are revealing detailed insights into IF secretion and Cbl binding proteins.
• Clarification of Cbl transcytosis through enterocytes is ongoing, despite challenges with experimental models and IFCR structure determination.