Basolateral sorting and transcytosis define the Cu+-regulated translocation of ATP7B to the bile canaliculus

Abstract

The Cu + pump ATP7B plays an irreplaceable role in the elimination of excess Cu + by the hepatocyte into the bile. The trafficking and site of action of ATP7B are subjects of controversy. One current proposal is that an increase in intracellular Cu + results in the translocation of ATP7B to the lysosomes and excretion of excess Cu + through lysosomal-mediated exocytosis at the bile canaliculus. Here, we show that ATP7B is transported from the trans-Golgi network (TGN) to the bile canaliculus by basolateral sorting and endocytosis, and microtubule-mediated transcytosis through the subapical compartment. Trafficking ATP7B is not incorporated into lysosomes, and addition of Cu + does not cause relocalization of lysosomes and the appearance of lysosome markers in the bile canaliculus. Our data reveal the pathway of the Cu + -mediated transport of ATP7B from the TGN to the bile canaliculus and indicates that the bile canaliculus is the primary site of ATP7B action in the elimination of excess Cu + .

Pluripotent stem cell-derived bile canaliculi-forming hepatocytes to study genetic liver diseases involving hepatocyte polarity

“…Copper-treatment resulted in reduced ATP7B colocalization with Golgin-97 ( Figure 4B) and its appearance at the ZO-1-bordered canaliculi ( Figure 4C-D). ATP7B in copper-treated hiHeps also appeared at LAMP1positive compartments ( Figure 4E), which have been implicated in the trafficking of ATP7B to the bile canaliculi [12,23] although debated [34]. Fluorescence intensity boxplots covering the intracellular ATP7B compartments and the canalicular domain illustrated ATP7B translocation by the appearance of overlapping ABCC2 and ATP7B peaks in the copper-treated conditions ( Figure 4F).…”

From and to the Golgi – defining the Wilson disease protein road map

“…Recent studies in hepatic HepG2 cells, in human hepatocytes and in mouse liver tissue indicate that ATP7B vesicles belong to the late endosomal (LE)/lysosomal compartments [21,33,34]. In contrast, other reports suggest that ATP7B moves from the Golgi to early endosomes in Can10 and WIF-B hepatic cells [35,36].…”

“…A different and quite surprising mechanism of ATP7B delivery to the apical domain of hepatocytes has been recently proposed by Lalioti et al . , who provided evidence showing transcytosis of ATP7B from the basolateral to the apical surface of polarized Can10 cells. However, these findings appear to be in conflict with the rest of the existing data on ATP7B trafficking.…”

Transcytosis maintains CFTR apical polarity in the face of constitutive and mutation-induced basolateral missorting

“…ii) The results of CFTR mutagenesis and siRNA screens showed that transcytosis of CFTR in CFBE is independent of N-glycans, AP-1B, Rab3b, Rab17, Rab25 or the exocyst complex that are essential for the apical transcytosis of pIgR, TfR and FcRn (Hunziker and Peters, 1998;Nelms et al, 2017;Perez Bay et al, 2014;Tzaban et al, 2009;van et al, 2002). iii) Finally, transcytotic CFTR seems to avoid the CRE and ARE compartments that are commonly used by other transcytotic cargoes (Jerdeva et al, 2010;Lalioti et al, 2016). Interestingly, constitutive TfR apical transcytosis in AP-1B-expressing MDCK or CFBE (Figures S3C-E and S4H) also avoids the Rab11 + ARE, similar to that of FcRn (Tzaban et al, 2009).…”