Restriction lift date: 2025-06-24
Regulation of insulin-like growth factor receptor activity and its therapeutic targeting in cancer
University College Cork
Insulin-like Growth Factor-1 Receptor signalling is essential for cell growth, and also promotes migration, survival and cellular transformation, thus, linking it to cancer progression. IGF-1R activity and signalling in cancer cells is regulated by the C terminal tail of the receptor. In particular the Tyr1250/1251, as their mutation to phenylalanine (FF) profoundly impairs IGF-1 signalling and the crosstalk between Integrin and IGF 1R signalling that facilitates a migratory phenotype in cancer cells. This thesis investigated the mechanisms of adhesion-modulated IGF-1R signalling, the function of Tyr1250/1251, and whether these mechanisms might influence the efficacy of IGF-1R-targeted drugs. Following the identification of FER kinase as a mediator of sensitivity to IGF 1R kinase inhibition, we found that ectopic expression of FER enhanced IGF-1R and SHC/MAPK pathway activation in an IGF-1R kinase independent manner. FER also specifically phosphorylated the IGF-1R on Tyr1250/1251. FER activity was cell adhesion-dependent and FER expression correlated with a migratory cancer phenotype. FER inhibition profoundly decreased IGF-1R and SHC signalling and reduced cell migration in breast cancer cells. The mechanisms and consequences of IGF-1R phosphorylation on Tyr1250/1251 phosphorylation were investigated for their contribution to IGF-1R function. It was established that IGF-1R, FER and FAK kinase activity may all contribute to Tyr1250/1251 phosphorylation and that cell adhesion is required for this phosphorylation. The consequence of Tyr1250/1251 phosphorylation was further investigated using a phosphomimetic Y1250E/Y1251E (EE) and the non-phosphorylatable FF IGF-1R mutant. These studies determined that IGF 1R phosphorylation on Tyr1250/1251 IGF-1R enhanced IGF-1R internalisation and proteasomal degradation. Moreover, the WT and EE receptors became rapidly internalised in response to IGF-1 ligation and accumulated in the Golgi apparatus, while the FF mutant remained at the plasma membrane or sites of cell adhesion. Importantly, Golgi associated IGF 1R signalling correlated with a migratory cancer cell phenotype, and disruption of the Golgi apparatus impaired IGF-1-promoted SHC phosphorylation and cell migration. In migratory cells, the formation of new focal adhesion points caused a transient release of the IGF-1R from the Golgi-apparatus to the membrane and lower IGF-1R Tyr1250/1251 phosphorylation. Thus, phosphorylation on Tyr1250/1251 enables IGF-1R signalling from the Golgi apparatus, and Golgi-derived IGF-1R signalling can support an aggressive cancer phenotype. Overall, this study identifies FER kinase and Tyr1250/1251 phosphorylation as adhesion-dependent mechanisms that modulate IGF-1R signalling and localisation in migratory cancer cells. The fact that the IGF-1R may be activated by other kinases and is predominantly located in the Golgi in migratory cells may explain the poor clinical efficacy of monoclonal antibodies and kinase inhibitors that specifically target the surface IGF-1R.
Cancer , Tyrosine phosphorylation , IGF-1R internalisation and trafficking , Adhesion-modulated IGF-1R signalling
Rieger, L. 2020. Regulation of insulin-like growth factor receptor activity and its therapeutic targeting in cancer. PhD Thesis, University College Cork.