Abstract 539: Characterization of the functional roles of RET isoforms in breast cancer.
Authors: Yoganathan Piriya , Wang Ami , Lian Eric , Ding Keyue , Tron Victor A. , Mulligan Lois M. 
Published: August 2014

Abstract
REarranged during Transfection (RET) is a receptor tyrosine kinase crucial for normal development of the kidneys, endocrine tissues and nervous system. RET is normally activated though binding of both a ligand from the Glial Cell-line Derived Neurotrophic Factor (GDNF) family, and a co-receptor of the GDNF Family Receptor alpha (GFRα) proteins. Abnormal RET signalling caused by germline activating mutations of RET,or somatic gene rearrangements are known to play an important role in tumorigenesis and disease progression in thyroid cancers. However, expression of wildtype RET and its ligands have also been linked to other tumour types such as pancreatic cancer, where the expression and activation of RET may lead to more aggressive disease. RET is also expressed in 25-30% of invasive breast cancers, with relatively more frequent expression in hormone receptor-positive sub-types. RET has two major distinct protein isoforms, called RET9 and RET51, that share the first 1062 residues but differ in their C-terminal amino acids. RET9 and RET51 are highly conserved across species, and both isoforms are normally co-expressed in the kidneys and in neural crest-derived tissues during development. Previous studies have begun to elucidate certain isoform-specific differences including: differential phosphorylation patterns after activation, unique target gene expression patterns, and distinct trafficking properties. The functional differences between RET9 and RET51 in breast cancer, however, have not yet been explored. As such, our overarching research objective has been to investigate the roles of individual RET isoforms in breast cancer progression. We used quantitative real-time reverse transcription PCR to assess expression of RET9, RET51, pan-RET (all isoforms of RET) and two GFRα co-receptors, GFRα1 and GFRα3, in both estrogen receptor (ER) negative and ER positive breast cancer cell lines. RET9 and RET51 protein expression were verified by Western blotting. Our data suggest that RET9 is more highly expressed than RET51 in breast cancer cells. We are currently conducting proliferation, migration and invasion assays with tumour cell lines expressing single RET isoforms to explore individual roles of RET9 and RET51 in breast cancer. Further, using well-characterized isoform-specific antibodies, we have examined expression of RET9 and RET51 in two large cohort breast cancer TMAs(&gt;150 samples/array). Analyses are currently ongoing to explore the expression of each individual isoform in tumours. This study may shed light to potential functional differences between RET9 and RET51 in breast cancer, furthering our understanding of RET isoform-specific differences.
Citation Format: Piriya Yoganathan, Ami Wang, Eric Lian, Keyue Ding, Victor A. Tron, Lois M. Mulligan. Characterization of the functional roles of RET isoforms in breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 539. doi:10.1158/1538-7445.AM2013-539