Two Isoforms of the Guanine Nucleotide Exchange Factor, Daple/CCDC88C Cooperate as Tumor Suppressors

Jason Ear,Jorge Barbazán,Lawrence Liu,Ulrich Nitsche,Klaus-Peter Janssen,Magda K Holda,Nicolas Aznar,Ajay Goel,Ying Dunkel,Yash Mittal,Blaze B C Lim,Pradipta Ghosh

doi:10.1038/s41598-019-48420-w

Jason Ear, Jorge Barbazán + Show 10 more

Open Access

https://doi.org/10.1038/s41598-019-48420-w

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Abstract

Previously, Aznar et al., showed that Daple/CCDC88C enables Wnt receptors to transactivate trimeric G-proteins during non-canonical Wnt signaling via a novel G-protein binding and activating (GBA) motif. By doing so, Daple serves two opposing roles; earlier during oncogenesis it suppresses neoplastic transformation and tumor growth, but later it triggers epithelial-to-mesenchymal-transition (EMT). We have identified and characterized two isoforms of the human Daple gene. While both isoforms cooperatively suppress tumor growth via their GBA motif, only the full-length transcript triggers EMT and invasion. Both isoforms are suppressed during colon cancer progression, and their reduced expression carries additive prognostic significance. These findings provide insights into the opposing roles of Daple during cancer progression and define the G-protein regulatory GBA motif as one of the minimal modules essential for Daple’s role as a tumor suppressor.

Highlights

IntroductionCorrespondence and requests for materials should be addressed to www.nature.com/scientificreports/
We noted that Daple-V2 and V3 differs from Daple-fl by a unique 5′ end (Fig. 1A) which adds a sequence comprised of 5 amino acids (MSVLS) on the N-terminus of the isoforms
When we analyzed a panel of colorectal cancers (CRCs) cell lines representing diverse subtypes of CRCs and harboring different mutant driver oncogenes (Supplementary Fig. 6A), we found that the Aspirin-induced changes we observed in DLD1 cells was observed in some other CRC cell lines, but not in all of them (Fig. 4Q)

Summary

Introduction

Correspondence and requests for materials should be addressed to www.nature.com/scientificreports/. We identified a novel Daple isoform (Daple-V2) which corresponds only to the C-terminal region of full length Daple (Daple-fl; RefSeq NM_001080414). We demonstrate that Daple-V2 possesses all the functional domains to bind Dvl, FZD7 and Gαi and represents the smallest autonomous Daple unit able to inhibit the β-catenin/TCF/LEF pathway and suppress tumor cell growth. We demonstrate that both isoforms have different subcellular distribution, and unlike Daple-fl, Daple-V2 does not enhance tumor cell invasiveness and may, serve as a more effective tumor suppressor and a better prognostic marker than Daple-fl

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