Thalidomide Target Identified

Thalidomide prescribed to pregnant women during the 1950s and 1960s induced birth defects, most notably limb and ear malformations. Although thalidomide is still used to treat leprosy and some types of cancer, little is known about its direct molecular targets. Ito et al . report that affinity purification of HeLa cell extracts with thalidomide-coated beads identified a protein called cereblon (CRBN), which is part of an E3 ubiquitin ligase complex that also includes the damaged DNA binding protein 1 (DDB1), Cullin 4A (Cul4A), and regulator of cullins 1 (Roc1). Wild-type CRBN underwent autoubiquitination in untreated 293T cells, but not in 293T cells treated with thalidomide, whereas a mutant version of CRBN that could not bind thalidomide ubiquitinated itself regardless of the presence of thalidomide. The zebrafish homolog of CRBN (zCrbn) was affinity-purified from embryonic extracts as a direct target of thalidomide, and tagged zCrbn produced in 293T cells interacted with endogenous DDB1. Inhibiting zCrbn or zCul4a in fish embryos by morpholino oligonucleotide injection induced pectoral fin and otic vesicle defects similar to those induced by thalidomide treatment. Overexpression of a transgene encoding a thalidomide-insensitive mutant version of zCrbn rescued thalidomide-induced phenotypes in fish embryos. Expression of fibroblast growth factor 8a ( fgf8a ) in the apical ectodermal ridge (AER) in fins of embryos treated with thalidomide was reduced relative to untreated embryos but was rescued by injecting mRNA encoding thalidomide-insensitive zCrbn. Similar effects of thalidomide treatment on fgf8 expression in limb buds were also observed in chicken embryos. These findings suggest that the teratogenic effects of thalidomide are mediated at least in part through the inhibition of a CRBN-containing E3 ubiquitin ligase complex, at least one target of which regulates Fgf8, one of many growth factors known to play a role in limb growth and patterning. T. Ito, H. Ando, T. Suzuki, T. Ogura, K. Hotta, Y. Imamura, Y. Yamaguchi, H. Handa, Identification of a primary target of thalidomide teratogenicity. Science 327 , 1345–1350 (2010). [Abstract][Full Text]