Adenomatous polyposis coli (<scp>APC</scp>) membrane recruitment 3, a member of the <scp>APC</scp> membrane recruitment family of <scp>APC</scp>‐binding proteins, is a positive regulator of <scp>Wnt</scp>–β‐catenin signalling

Abstract

The adenomatous polyposis coli ( APC ) membrane recruitment ( A mer) family proteins A mer1/ W ilms tumour gene on the X chromosome and A mer2 are binding partners of the APC tumour suppressor protein, and act as negative regulators in the W nt signalling cascade. So far, nothing has been known about the third member of the family, A mer3. Here we show that A mer3 binds to the armadillo repeat domain of APC , similarly to A mer1 and A mer2. A mer3 also binds to the W nt pathway regulator conductin/axin2. Furthermore, we identified A mer1 as binding partner of A mer3. Whereas A mer1 and A mer2 are linked to the plasma membrane by an N ‐terminal membrane localization domain, A mer3 lacks this domain. A mer3 localizes to the cytoplasm and nucleus of epithelial cells, and this is dependent on specific nuclear import and export sequences. Functionally, exogenous A mer3 enhances the expression of a β‐catenin/ T ‐cell factor‐dependent reporter gene, and knockdown of endogenous A mer3 reduces W nt target gene expression in colorectal cancer cells. Thus, A mer3 acts as an activator of W nt signalling, in contrast to A mer1 and A mer2, which are inhibitors, suggesting a nonredundant role of A mer proteins in the regulation of this pathway. Our data, together with those of previous studies, provide a comprehensive picture of similarities and differences within the A mer protein family. Structured digital abstract AMER3 physically interacts with APC by two hybrid ( 1 , 2 ). AMER3 physically interacts with APC by anti tag coimmunoprecipitation ( 1 , 2 , 3 ). APC physically interacts with AMER3 by anti bait coimmunoprecipitation ( View interaction ). AMER3 physically interacts with APC , AMER1 and Conductin by anti bait coimmunoprecipitation ( View interaction ). AMER3 physically interacts with AMER1 by anti tag coimmunoprecipitation ( 1 , 2 ). AMER3 and APC colocalize by fluorescence microscopy ( View interaction ). Conductin physically interacts with AMER3 by anti tag coimmunoprecipitation ( View interaction ). <jats:ext-link xmlns:xlink="http://www.