antagonist ͉ cancer ͉ Gli ͉ medulloblastoma

Small-molecule inhibition of extracellular proteins that activate membrane receptors has proved to be extremely challenging. Diversity-oriented synthesis and small-molecule microarrays enabled the discovery of robotnikinin, a small molecule that binds the extracellular Sonic Hedgehog (Shh) protein and blocks Shh-signaling in cell lines, human primary keratinocytes and a synthetic model of human skin. Shh pathway activity is rescued by small-molecule agonists of Smoothened, which functions immediately downstream of the Shh receptor Patched.

Epsin (Eps15 interactor) is a cytosolic protein involved in clathrin-mediated endocytosis via its direct interactions with clathrin, the clathrin adaptor AP-2, and Eps15. The NH2-terminal portion of epsin contains a phylogenetically conserved module of unknown function, known as the ENTH domain (epsin NH2-terminal homology domain). We have now solved the crystal structure of rat epsin 1 ENTH domain to 1.8 Å resolution. This domain is structurally similar to armadillo and Heat repeats of β-catenin and karyopherin-β, respectively. We have also identified and characterized the interaction of epsin 1, via the ENTH domain, with the transcription factor promyelocytic leukemia Zn2+ finger protein (PLZF). Leptomycin B, an antifungal antibiotic, which inhibits the Crm1- dependent nuclear export pathway, induces an accumulation of epsin 1 in the nucleus. These findings suggest that epsin 1 may function in a signaling pathway connecting the endocytic machinery to the regulation of nuclear function.

The epsin NH2-terminal homology (ENTH) domain is a membrane interacting module composed by a superhelix of alpha-helices. It is present at the NH2-terminus of proteins that often contain consensus sequences for binding to clathrin coat components and their accessory factors, and therefore function as endocytic adaptors. ENTH domain containing proteins have additional roles in signaling and actin regulation and may have yet other actions in the nucleus. The ENTH domain is structurally similar to the VHS domain. These domains define two families of adaptor proteins which function in membrane traffic and whose interaction with membranes is regulated, in part, by phosphoinositides.