Chemotropic Receptor Deleted In Colorectal Cancer (DCC) Prevents Translation Initiation By Directly Inhibiting Ribosome Function

Abstract

Axonal outgrowth and guidance is dictated by a variety of chemotropic signals. Netrin receptors at the growth cones of developing neurons function to attract or repel outgrowth during commissure formation. The dependence receptor Deleted in Colorectal Cancer (DCC) is activated by netrin‐1, and dimerization initiates a variety of responses, including activation of Src tyrosine kinases and focal adhesion kinase. Prior to netrin‐1 activation, the monomeric C‐terminal tail of DCC binds to 80S ribosomes and prevents polysome formation. DCC activation and dimerization releases 80S ribosomes for translation initiation, presumably to promote axonal outgrowth. The C‐terminal tail of DCC is a 35 kDa protein that is composed of three domains (P1‐3) and is predicted 91% unstructured. Dimerization is facilitated by the P3 domain, while the P1 domain binds to the 60S subunit protein, ribosomal protein L5 (rpL5). Yet, the exact mechanism of how the DCC C‐terminal tail inhibits translation is unknown. Titrating the full‐length C‐terminal tail into translation‐competent lysates, we found that the tail specifically inhibits eukaryotic translation, and inhibits protein synthesis of messages that use both cap‐dependent and internal ribosome entry site translation initiation. Hence, we propose that the DCC C‐terminal tail functions primarily through binding the ribosome, not eukaryotic initiation factors. In fact, we have evidence from co‐sedimentation and gel filtration chromatography studies to show that the full‐length tail binds to the small and large subunits, as well as the 80S ribosome in the absence of mRNA. We propose a mechanism by which the C‐terminal tail blocks the decoding groove of the 80S ribosome to stall the apo‐80S complex. Our hypothesis is supported by data showing the P1 domain (and its interaction with rpL5) is not solely responsible for the decrease in translation, and thus the P2‐3 domains are also important for function. Collectively, our results support the idea that the DCC C‐terminal tail inhibits translation by effectively preventing ribosomes from binding to messages, until receptor dimerization and release of 80S ribosomes. Thus chemoattraction via netrin‐induced DCC receptor dimerization might lead to a global (not message‐specific) increase in localized protein synthesis at axonal growth cones.Support or Funding InformationHoward Hughes Medical Institute, Janelia Farm Visiting Scientists Program & Metropolitan State University of Denver Provost GrantThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.