ATP8B1 and cellular trafficking

Mutations in the gene ATP8B1 cause progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign intrahepatic cholestasis type 1 (BRIC1). The aim of this thesis was to study the pathogenesis of extrahepatic phenotypes of these diseases, namely diarrhea and pulmonary infection. In chapter 3 we show to what extent several ATP8B1 mutations result in different intracellular localization, interaction with its obligatory beta subunit CDC50A, and stability of the protein, providing an explanation for the difference in presentation of PFIC1 and BRIC1. In chapter 4 the role of ATP8B1 on the expression and function of the intestinal bile salt transporter ASBT in human intestinal Caco-2 cells is analyzed. Moreover, fecal content of several PFIC1 patients is examined in order to determine alterations in intestinal bile salt, nutrient and electrolyte transport. From these data we conclude that diarrhea in PFIC1 patients has a secretory origin to which intestinal bile acid malabsorption can contribute. In chapter 5 we study the effects of ATP8B1 on the function and expression of the CFTR chloride channel in human intestinal Caco-2 and T84 cells, human lung epithelial Calu-3 cells, and ex-vivo mouse intestines. From this study we conclude that ATP8B1 is essential for apical targeting of CFTR. In chapter 6 the localization and activity of the innate immune receptor TLR4 in THP-1 macrophages and primary human and murine macrophages depleted for ATP8B1, ATP11A, or CDC50A is determined. We conclude that CDC50A-interacting P4-ATPases are essential to attenuate endotoxin-induced TLR4-mediated signaling possibly by facilitating the endocytic retrieval of TLR4