The Na⁺‐Taurocholate Cotransporting Polypeptide Traffics with the Epidermal Growth Factor Receptor

<jats:p>Na<jats:sup>+</jats:sup>‐taurocholate cotransporting polypeptide (ntcp) mediates uptake of bile acids as well as serving as the receptor for hepatitis B virus in human liver. Previous studies showed that ntcp traffics on microtubules between the cell surface and endocytic vesicles. Specific inhibition of protein kinase C (<jats:styled-content style="fixed-case">PKC</jats:styled-content>)ζ resulted in loss of microtubule‐based motility of these vesicles <jats:italic>in vitro</jats:italic> and in living cells. The aim of this study was to characterize the <jats:styled-content style="fixed-case">PKCζ</jats:styled-content> target. Incubation of ntcp‐containing endocytic vesicles with γ‐<jats:styled-content style="fixed-case"><jats:sup>32</jats:sup>P‐ATP</jats:styled-content> revealed a 180 <jats:styled-content style="fixed-case">kDa</jats:styled-content> phosphoglycoprotein that was identified as the epidermal growth factor (<jats:styled-content style="fixed-case">EGF</jats:styled-content>) receptor (<jats:styled-content style="fixed-case">EGFR</jats:styled-content>). Surface biotinylation of <jats:styled-content style="fixed-case">HuH7</jats:styled-content> cells expressing green fluorescent protein (<jats:styled-content style="fixed-case">GFP</jats:styled-content>)‐ntcp revealed substantially reduced trafficking of ntcp to the cell surface with <jats:styled-content style="fixed-case">EGFR</jats:styled-content> knockdown. Microtubule‐based motility of ntcp‐containing endocytic vesicles was also significantly reduced when they were not associated with <jats:styled-content style="fixed-case">EGFR</jats:styled-content>. ntcp was also found to undergo cellular redistribution upon stimulation of cells with <jats:styled-content style="fixed-case">EGF</jats:styled-content>, consistent with a model in which ntcp and <jats:styled-content style="fixed-case">EGF–EGFR</jats:styled-content> internalize into common endocytic vesicles from which they segregate, trafficking <jats:styled-content style="fixed-case">EGF–EGFR</jats:styled-content> to lysosomes and recycling ntcp to the plasma membrane. <jats:styled-content style="fixed-case">EGF</jats:styled-content> regulation of ntcp trafficking may play a heretofore unanticipated role in subcellular targeting of ntcp ligands such as hepatitis B.</jats:p><jats:p><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tra12354-gra-0001.png" xlink:title="image" /></jats:p>