Regulation of copper homeostasis by members of the COMMD protein family

Copper is an essential transition metal for all eukaryotes. In mammals, intestinal copper absorption is mediated by the ATP7A copper transporter, whereas copper excretion occurs predominatly through the biliary route and is mediated by the paralog ATP7B. Both transporters have been shown to be actively recycled between the endosomal network and the plasma membrane by a molecular machinery known as the COMMD/CCDC22/CCDC93 or CCC complex. In fact, mutations in COMMD1 can lead to impaired biliary copper excretion and liver pathology in dogs and mice with liver-specific Commd1 deficiency recapitulating aspects of this phenotype as well. Nonetheless, the role of the CCC complex in intestinal copper absorption in vivo has not been studied, and the potential redundancy of various COMMD family members has not been tested. In this study, we examined copper homeostasis in enterocyte-specific and hepatocyte-specific Commd-deficient mice. We find that in contrast to effects in cell lines in culture, COMMD protein deficiency induces minimal changes in ATP7A in enterocytes and does not lead to altered copper levels under low or high copper diets, suggesting that regulation of ATP7A in enterocytes is not of physiologic consequence. In contrast, deficiency of any of 3 Commd genes (Commd1, 6, and 9) all result in hepatic copper accumulation under high copper diets. We find that each of these deficiencies cause destabilization of the entire CCC complex, and suggest that this might explain their shared phenotype. Overall, we conclude that the CCC complex plays an important role in ATP7B endosomal recycling and function

CD73 (ecto‐5′‐nucleotidase) hepatocyte levels differ across mouse strains and contribute to mallory‐denk body formation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100334/1/hep26525.pd

Energy determinants GAPDH and NDPK act as genetic modifiers for hepatocyte inclusion formation

Differential expression and activity of the cellular energy regulators GAPDH and NDPK underlie reactive oxygen species–induced damage in the mouse liver and may contribute to human liver disease progression

Retriever is a multiprotein complex for retromer-independent endosomal cargo recycling

Following endocytosis into the endosomal network, integral membrane proteins undergo sorting for lysosomal degradation or are retrieved and recycled back to the cell surface. Here we describe the discovery of an ancient and conserved multiprotein complex that orchestrates cargo retrieval and recycling and, importantly, is biochemically and functionally distinct from the established retromer pathway. We have called this complex 'retriever'; it is a heterotrimer composed of DSCR3, C16orf62 and VPS29, and bears striking similarity to retromer. We establish that retriever associates with the cargo adaptor sorting nexin 17 (SNX17) and couples to CCC (CCDC93, CCDC22, COMMD) and WASH complexes to prevent lysosomal degradation and promote cell surface recycling of α5β1 integrin. Through quantitative proteomic analysis, we identify over 120 cell surface proteins, including numerous integrins, signalling receptors and solute transporters, that require SNX17-retriever to maintain their surface levels. Our\ua0identification of retriever establishes a major endosomal retrieval and recycling pathway

Mechanisms underlying upregulation of intestinal apical chloride/hydroxyl radical exchange activity by LPA.

Mechanisms underlying upregulation of intestinal apical chloride/hydroxyl radical exchange activity by LPA

Mechanisms of lysophosphatidic acid (LPA) mediated stimulation of intestinal apical Cl−/OH− exchange

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, is a natural component of food products like soy and egg yolk. LPA modulates a number of epithelial functions and has been shown to inhibit cholera toxin-induced diarrhea. Antidiarrheal effects of LPA are known to be mediated by inhibiting chloride secretion. However, the effects of LPA on chloride absorption in the mammalian intestine are not known. The present studies examined the effects of LPA on apical Cl−/OH− exchangers known to be involved in chloride absorption in intestinal epithelial cells. Caco-2 cells were treated with LPA, and Cl−/OH− exchange activity was measured as DIDS-sensitive 36Cl− uptake. Cell surface biotinylation studies were performed to evaluate the effect of LPA on cell surface levels of apical Cl−/OH− exchangers, downregulated in adenoma (DRA) (SLC26A3), and putative anion transporter-1 (SLC26A6). Treatment of Caco-2 cells with LPA (100 μM) significantly stimulated Cl−/OH− exchange activity. Specific agonist for LPA2 receptor mimicked the effects of LPA. LPA-mediated stimulation of Cl−/OH− exchange activity was dependent on activation of phosphatidylinositol 3-kinase/Akt signaling pathway. Consistent with the functional activity, LPA treatment resulted in increased levels of DRA on the apical membrane. Our results demonstrate that LPA stimulates apical Cl−/OH− exchange activity and surface levels of DRA in intestinal epithelial cells. This increase in Cl−/OH− exchange may contribute to the antidiarrheal effects of LPA