EHD3: a protein that resides in recycling tubular and vesicular membrane structures and interacts with EHD1.

Here we report the characterization of an eps15 homology (EH) domain containing protein designated EHD3. EHD3 was mapped to human chromosome 2p22-23, while the murine Ehd3 homolog was mapped to chromosome 17p21. Both the human and the mouse genes contain a polymorphic (CA) repeat in their 3'UTR. One 3.6-kb Ehd3 transcript was mainly detected in adult mouse brain and kidney and at day 7 of mouse development. On the other hand, human tissues exhibited two, 4.2- and 3.6-kb, EHD3 RNA species. They were predominantly expressed in heart, brain, placenta, liver, kidney and ovary. EHD3, expressed as a green fluorescent fusion protein was localized to endocytic vesicles and to microtubule-dependent, membrane tubules. There was a clear colocalization of EHD3-positive structures and transferrin-containing recycling vesicles, implying that EHD3 resides within the endocytic recycling compartment. Shuffling the N-terminal domain of EHD1 (previously shown to reside in the transferrin-containing, endocytic recycling compartment) with that of EHD3 resulted in a chimeric EHD protein that was localized mainly to tubules instead of the endocytic vesicles, implicating the N-terminal domain as responsible for the tubular localization of EHD3. Mutant EHD3 forms, missing the N-terminal or the C-terminal domains, lost their tubular localization. Results of two-hybrid analyses indicated that EHD1 and EHD3 interact with each other. In addition, EHD1 and EHD3 could be coimmunoprecipitated from cellular extracts, confirming the interaction implied by two-hybrid analysis. Moreover, coexpression of EHD1 and EHD3 resulted in their colocalization in microtubule-dependent tubules as well as in punctate forms. Based on its specific intracellular localization and its interaction with EHD1, we postulate that EHD3 localizes on endocytic tubular and vesicular structures and regulates their microtubule-dependent movement.