The CFTR Associated Protein CAP70 Interacts with the Apical Cl-/HCO3- Exchanger DRA in Rabbit Small Intestinal Mucosa
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- 作者：Heidi Rossmann ; Petra Jacob ; Susannah Baisch ; Racha Hassoun ; Julia Meier ; Dorgam Natour ; Karim Yahya ; Chris Yun ; Jü ; rg Biber ; Karl J. Lackner ; Walter Fiehn ; Michael Gregor ; Ursula Seidler ; and Geo
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：March 22, 2005
- 年：2005
- 卷：44
- 期：11
- 页码：4477 - 4487
- 全文大小：453K
- 年卷期：v.44,no.11(March 22, 2005)
- ISSN：1520-4995
文摘
DRA (down regulated in adenoma) is an intestinal anion exchanger, acting in parallel withNHE3 to facilitate ileal and colonic NaCl absorption. Furthermore it is involved in small intestinalbicarbonate secretion. Because DRA has a PDZ interaction motif, which may influence its properties, wesearched for DRA-interacting PDZ adapter proteins in the small intestine. Using an overlay assay withthe recombinant DRA C-terminus as a ligand, a 70 kDa protein was labeled, which was restricted to thebrush border membrane in rabbit duodenal and ileal mucosa and was not detected in the colon. Destructionof the C-terminal PDZ interaction motif abolished this band, suggesting a specific protein-proteininteraction. The 70 kDa protein was identified as CAP70 (CFTR associated protein of 70 kDa) by ananti-CAP70 antibody and by two in vitro binding assays after cloning CAP70 from rabbit duodenum andileum. The interaction was recapitulated in HEK cells transfected with DRA and PDZK1, the humanorthologue of CAP70. Corresponding to the overlay assay, no CAP70 mRNA or protein was detected inthe colon. In vitro protein-protein interaction studies revealed specific binding of DRA to the 2nd and3rd PDZ domain, while CFTR is known to interact with PDZ1, PDZ3, and PDZ4. The composition ofmacromolecular complexes assembled by CAP70 in the distal small bowel is unknown. Its restrictedexpression shows that it cannot be involved in NaCl absorption in the proximal colon. We suggest thatCAP70 mediates regulatory functions specific to the small intestine.