Abstract A30: The prevalence of RON isoforms in experimental and clinical tumor samples.

Abstract

Abstract The role of the RON receptor or MST1R in tumor development has been demonstrated in multiple tumor models. As a result of alternative pre-mRNA splicing, protein truncation and alternative transcription, several isoforms of RON (WT, delta-55, delta-110, delta-155, delta-160, delta-165, and delta-170) are known to exist. In contrast to WT RON, which localizes to the cell membrane, some RON variants (delta-155, delta-165) are constitutively active in the cytoplasm. Despite the previously documented role of RON in tumor development, the prevalence of individual RON isoforms in different tumor tissues remains largely unknown. Due to a high level of conservation between the RON isoforms which results largely from in frame exon 5, 6 and/or 11 deletions, protein-based variant characterization is unfeasible. We therefore decided to focus on an mRNA-based detection technique using a PCR-based sizing assay. In total 63 samples, including 28 tumor cell lines, 16 patient-derived tumor models and 19 colorectal tumors were analyzed. Total RNA was isolated and converted to cDNA followed by standard PCR amplification and Bio-Analyzer quantification and analysis for specific isoforms including RON delta-155, delta-160, delta-165, and delta-170/WT. In 35/48 samples tested (73%), the most prevalent isoform was RON delta-165 followed by WT RON. FACS analysis of lung adenocarcinoma A549 cells, which displayed only RON delta-165 mRNA expression, confirmed intracellular localization of RON protein. Analysis of RNA sequencing data in TCGA data sets which include over 5,000 patient tumor samples also demonstrated high prevalence of RON delta-165 expression across different tumor indications. More than 98% of samples, both tumor and normal, showed the RON delta-165 variant. Prevalence, defined as a delta-165: WT ratio > 1, was seen in 28.6% and 24.3% of cases, respectively. Analysis of the lung and colon subsets revealed differentially higher RON delta-165 prevalence in lung (26%) and colon (25%) tumors, compared to respective normal tissue (7% and 0% respectively). Taken together, this data indicates that RON delta-165 is expressed in multiple tumor types and alludes to an altered RON isoform expression pattern in lung and colon cancer. Given a unique biology of this variant (constitutive activation and intracellular localization), isoform-specific targeted therapies should be developed for the inhibition of this pathway. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A30. Citation Format: Michael Amatulli. The prevalence of RON isoforms in experimental and clinical tumor samples. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A30.