Abstract 1243: RET and integrin crosstalk provides functional plasticity
Authors: Cockburn Jessica G. , Goel Anirudh , Wagner Simona , Mulligan Lois M. 
Published: August 2012

Abstract
The RET receptor tyrosine kinase is an important mediator of cell growth, proliferation, and differentiation. RET becomes activated upon formation of a complex with the glial cell-line derived neurotrophic factor (GDNF) ligand and GDNF-family receptor (GFRa), which leads to activation of multiple downstream signalling pathways, including PI3K/AKT, MEK/ERK, STAT3, and SRC. Constitutive activation of RET, through translocations or missense mutations, leads to papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC), respectively. Also, RET expression has been detected in pancreatic and breast cancers, and has been linked to increased metastatic potential. In order to clarify the underlying role of RET in tumour progression, we examined the relationship between RET and two integrin subunits, β1 (ITGB1) and β3 (ITGB3). Integrin proteins are important for cell attachment to the extracellular matrix and focal adhesion (FA) formation. Functionally, integrins are important for cell-adhesion and migration as they provide traction and leverage for cell movement. Previously, we have shown that RET is able to increase cell-migration and adhesion, and that both ITGB1 and ITGB3 are important for these processes. Here, we show that RET-mediated cell-migration is persistent over 24 hours, and that patterns of cell-adhesion fluctuate over this time, predictably representing different forces needed to move across the microenvironment. Cell-adhesion is increased upon 1 hour of GDNF treatment, but is lost between 3-12 hours of GDNF treatment. Interestingly, we observed that ITGB1 activation downstream of RET, detected by co-immunoprecipitation with paxillin, is transient, and lasts for 1 hour. Conversely, ITGB3 activation downstream of RET, detected using an active heterodimer-specific antibody, is sustained between 1-12 hours of GDNF treatment. These results demonstrate unique functional roles for ITGB1 and ITGB3 downstream of RET. We also examined the importance of signalling pathways downstream of RET for integrin activation, and found that, in a 2D collagen environment, PI3K/AKT and MEK/ERK are important for RET-mediated FA formation. However, in a 3D collagen environment where cells formed spheroids, PI3K/AKT and STAT3 are important for cell-outgrowth, downstream of RET activation. This likely represents different cellular responses needed to overcome environment-specific obstacles. Finally, we showed evidence for a relationship between RET, ITGB1 and ITGB3 in tumour progression using a cohort of various clinically annotated thyroid cancer samples. Ultimately, we have shown a role for in activation of two integrin subunits, ITGB1 and ITGB3, downstream of RET and how each of these proteins may contribute to metastatic events, particularly those involved in thyroid cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1243. doi:1538-7445.AM2012-1243