LAUSR

The WNT/PCP pathway is an evolutionarily conserved developmental process which is essential in embryogenesis and development of polarized structures in metazoans. Its importance in human diseases is best demonstrated in neural tube closure defects and cancer. WNT/PCP signaling involves a set of evolutionarily conserved WNT/PCP genes encoding WNT ligands, transmembrane (vangl2, frizzled, fat, dachsous) and cytoplasmic (scribble, prickle, dishevelled, diego) molecules triggering a genetically well-defined non-canonical WNT-JNK pathway. Recent work has linked defects of this pathway to breast cancer aggressiveness. We have shown that the non-canonical WNT/PCP transmembrane receptor VANGL2 is overexpressed in poor prognosis basal breast cancers and implicated in tumor growth. We also found that VANGL2 binds through its C-terminal sequence to Scribble and p62/SQSTM1 which are involved in cancer cell migration and growth. A recent in silico study has suggested the existence of an N-terminally extended VANGL2 isoform (VANGL2-Long), owing to the occurrence of an alternative non-AUG translation initiation site, upstream of the conventional start site. Translation initiation from this alternative site is expected to add an N-terminal extension of 48 amino acids. Accordingly, by analyzing VANGL2 immunoprecipitates by mass spectrometry, we identified a peptide mapping upstream of the first methionine supporting the existence of a longer isoform of VANGL2. While missing in Drosophila, this N-terminal extension is found in all vertebrate VANGL2 sequences that have been examined, suggesting a function for VANGL2-Long. We provide further experimental evidence in favor of the VANGL2-Long isoform, using polyclonal antibodies that have been raised against the predicted VANGL2 N-terminal extension. Using these tools, we characterized VANGL2-Long and showed that it dimerizes with VANGL2 and VANGL1, a close homologue, at the endogenous level in living cells. Our data depict a complex organization of VANGL1/VANGL2 molecules at the plasma membrane and improve the mechanistic understanding of VANGL2 in normal and cancer cells. Citation Format: Jean-Paul Borg, Alexandra Walton, Eric Bailly, Sylvie Marchetto, Stephane Audebert. Identification of a novel isoform of WNT/planar cell polarity VANGL2 in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 339. doi:10.1158/1538-7445.AM2017-339