High impact information on EPN1

• Structural analysis of the ENTH domain of the endocytic protein epsin has suggested a new mechanism, in which the ENTH domain pushes its way into membranes, thus bending them into shape [1].
• The 1.9 A resolution crystal structure of this domain reveals a single binding site for its ligands, which include amphiphysin, Eps15, and epsin [2].
• Epsin is targeted to areas of endocytosis by binding the membrane lipid phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P(2)) [3].
• Epsin is associated with clathrin coats in situ, can be co-precipitated with AP-2 and Eps15 from brain extracts, but does not co-purify with clathrin coat components in a clathrin-coated vesicle fraction [4].
• Here we investigate the function of Eps15 by characterizing an important binding partner for its region containing EH domains; this protein, epsin, is closely related to the Xenopus mitotic phosphoprotein MP90 and has a ubiquitous tissue distribution [4].

Biological context of EPN1

• Epsin binds to the EH domain of POB1 and regulates receptor-mediated endocytosis [5].
• Epsin is phosphorylated and ubiquitinated, and these post-translational modifications are necessary for the regulation of endocytosis [6].
• Using structure-directed mutagenesis, we demonstrate the ability of the beta 2 appendage alone to bind directly to clathrin and the accessory proteins AP180, epsin and eps15 at the same site [7].
• Regulation of complex formation of POB1/epsin/adaptor protein complex 2 by mitotic phosphorylation [8].
• Leptomycin B, an antifungal antibiotic, which inhibits the Crm1- dependent nuclear export pathway, induces an accumulation of epsin 1 in the nucleus [9].

Anatomical context of EPN1

• The epsin N-terminal homology (ENTH) domain (about 140 amino acid residues) is well conserved in eukaryotes and is considered to be important for actin cytoskeleton organization in endocytosis [10].
• The enrichment of epsin within clathrin-coated vesicles purified from different tissue sources varies and correlates with sorting of multiubiquitinated cargo, and in cultured cells, polyubiquitin, rather than non-conjugable monoubiquitin, promotes rapid internalization [11].
• Epsin 2, like epsin 1, is enriched in brain, is present in a brain-derived clathrin-coated vesicle fraction, is concentrated in the peri-Golgi region and at the cell periphery of transfected cells, and partially colocalizes with clathrin [12].
• Surprisingly, WT epsin showed little colocalization with this chimera, whereas UIM-containing epsin constructs that lack the clathrin and AP2 binding region, strikingly colocalized with this chimera on endocytic vacuoles [13].
• Consistent with a role in microtubule processes, the over-expression of epsin ENTH domain in PC12 cells stimulates neurite outgrowth [14].

Associations of EPN1 with chemical compounds

• Epsin 1 and 2 are most similar in their NH(2)-terminal region, which represents a module (epsin NH(2) terminal homology domain, ENTH domain) found in a variety of other proteins of the data base [12].
• We have also identified and characterized the interaction of epsin 1, via the ENTH domain, with the transcription factor promyelocytic leukemia Zn(2)+ finger protein (PLZF) [9].
• Alanine scanning mutagenesis shows that clathrin binding depends on the sequence (257)LMDLADV located within the epsin 1 DPW domain [15].
• HIP1 and HIP1r stabilize receptor tyrosine kinases and bind 3-phosphoinositides via epsin N-terminal homology domains [16].

Physical interactions of EPN1

• Here, we analyzed these sequences, which we term type II sequences, and show that the (257)LMDLA sequence in rat epsin 1 appears to be a weak clathrin-binding variant of the sequence (417)PWDLW originally found in human amphiphysin II [17].

Other interactions of EPN1

• In addition to a single LLDLD-based, type I clathrin-binding sequence, both amphiphysin and epsin contain a second, distinct sequence that is also capable of binding to clathrin directly [17].
• Solution structure of the epsin N-terminal homology (ENTH) domain of human epsin [10].
• The U-box ligase carboxyl-terminus of Hsc 70-interacting protein ubiquitylates Epsin [18].
• The EH domain of POB1 bound directly to Epsin and Eps15 [19].
• These results suggest that phosphorylation of Epsin in mitotic phase inhibits receptor-mediated endocytosis by disassembly of its complex with POB1 and alpha-adaptin [8].

Analytical, diagnostic and therapeutic context of EPN1

• In this study, we discovered that the U-box ubiquitin ligase carboxyl-terminus of Hsc70 interacting protein (CHIP) ubiquitylated Epsin [18].
• The technique of RNA interference (RNAi) was exploited to generate a cell line constitutively silencing epsin expression in a sequence-specific manner In these Caco-2(eps-) cells, quantitative reverse transcription PCR (RT-PCR) revealed a severe depletion of the epsin messenger RNA (mRNA) level in cells, reaching a factor > 10(6) [20].

References