Abstract
Collectrin, a homologue of angiotensin converting enzyme 2 (ACE2), is a type I transmembrane protein, and we originally reported its localization to the cytoplasm and apical membrane of collecting duct cells. Recently, two independent studies of targeted disruption of collectrin in mice resulted in severe and general defects in renal amino acid uptake. Collectrin has been reported to be under the transcriptional regulation by HNF-1α, which is exclusively expressed in proximal tubules and localized at the luminal side of brush border membranes. The deficiency of collectrin was associated with reduction of multiple amino acid transporters on luminal membranes. In the current study, we describe that collectrin is a target of HNF-1β and heavily expressed in the primary cilium of renal collecting duct cells. Collectrin is also localized in the vesicles near the peri-basal body region and binds to γ-actin-myosin II-A, SNARE, and polycystin-2-polaris complexes, and all of these are involved in intracellular and ciliary movement of vesicles and membrane proteins. Treatment of mIMCD3 cells with collectrin siRNA resulted in defective cilium formation, increased cell proliferation and apoptosis, and disappearance of polycystin-2 in the primary cilium. Suppression of collectrin mRNA in metanephric culture resulted in the formation of multiple longitudinal cysts in ureteric bud branches. Taken together, the cystic change and formation of defective cilium with the interference in the collectrin functions would suggest that it is necessary for recycling of the primary cilia-specific membrane proteins, the maintenance of the primary cilia and cell polarity of collecting duct cells. The transcriptional hierarchy between HNF-1β and PKD (polycystic kidney disease) genes expressed in the primary cilia of collecting duct cells has been suggested, and collectrin is one of such HNF-1β regulated genes.
Highlights
We identified a member of angiotensin converting enzyme (ACE) gene family, collectrin, by its up-regulation in a mouse model of partial nephrectomy [1], which is a longstanding model for the progressive renal diseases
The binding of HNF-1 to the putative promoter elements in mIMCD3 cells was confirmed by electrophoretic mobility shift assay (EMSA) (Figure 1a)
The collectrin gene promoter was inserted into promoterless pGL3-Basic vector, where the transcription of the luciferase gene was driven by the collectrin promoter
Summary
We identified a member of angiotensin converting enzyme (ACE) gene family, collectrin, by its up-regulation in a mouse model of partial nephrectomy [1], which is a longstanding model for the progressive renal diseases. Collectrin is a type I transmembrane protein and we originally reported its localization to the cytoplasm and apical membrane of collecting duct cells. It is a homologue of ACE2 and identified in immediate proximity of the ace locus. ACE2 may be a chimeric protein emerging from the duplication of two genes, having homology with ACE at the catalytic domain and homology with collectrin in the membrane proximal domain[2]. Two independent studies of targeted disruption of collectrin in mice resulted in a severe and general defects in renal amino acid uptake[3,4]. Collectrin is demonstrated at the luminal side of brush border membranes of proximal tubules and the deficiency of collectrin is associated with reduction of multiple amino acid transporters, such as B0AT1, rBAT, B0,+AT[4], XT3s1/ST1, XT2, XT3 and EAAC1[3], on luminal membranes
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