Microtubule Plus-End-Tracking Proteins Target Gap Junctions Directly from the Cell Interior to Adherens Junctions

Gap junctions are intercellular channels that connect the cytoplasms of adjacent cells. For gap junctions to properly control organ formation and electrical synchronization in the heart and the brain, connexin-based hemichannels must be correctly targeted to cell-cell borders. While it is generally accepted that gap junctions form via lateral diffusion of hemichannels following microtubule-mediated delivery to the plasma membrane, we provide evidence for direct targeting of hemichannels to cell-cell junctions through a pathway that is dependent on microtubules; through the adherens-junction proteins N-cadherin and beta-catenin; through the microtubule plus-end-tracking protein (+TIP) EB1; and through its interacting protein p150(Glued). Based on live cell microscopy that includes fluorescence recovery after photobleaching (FRAP), total internal reflection fluorescence (TIRF), deconvolution, and siRNA knockdown, we propose that preferential tethering of microtubule plus ends at the adherens junction promotes delivery of connexin hemichannels directly to the cell-cell border. These findings support an unanticipated mechanism for protein delivery to points of cell-cell contact.