Restriction lift date: 2028-09-30
Regulation of intracellular trafficking of the insulin-like growth factor I receptor
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Date
2023
Authors
Godsmark, Grant
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
Insulin-like Growth Factor 1 and its receptor (IGF-1R) are required for normal cellular growth, but aberrant expression is linked to the progression and development of many malignancies. Despite IGF-1R being a promising cancer therapeutic target, clinical targeting has not been generally successful. This has also highlighted gaps in our knowledge on IGF-1 signalling and how the IGF-1R and its regulatory regions function.
Two tyrosine residues Tyr1250/1251 located within the 1248SFYYS1252 signalling motif of the IGF-1R are required for receptor internalisation, transformation and Golgi localisation. This thesis aimed to further investigate how this region and the C-terminal tail contribute to IGF-1R trafficking, sub-cellular localisation and regulation by using a range of cell lines and IGF-1R receptor mutants.
Phosphorylation of Tyr1250/1251 was shown to be required for IGF-1R localisation to the Golgi and that a phosphomimetic EE (Y1250E/Y1251E) IGF-1R mutant is less stable, is more ubiquitinated and undergoes more rapid proteasomal degradation than wild type IGF-1R. Three lysine residues (Lys1256, Lys1294, Lys1324) were identified within the IGF-1R C-terminal tail as putative ubiquitin binding sites, but mutation of these to arginine in mutational studies established that all of these sites have a minor function in receptor ubiquitination.
Peptides encompassing the hydrophobic Tyr1250/1251 site in the IGF-1R were recently proposed as a cargo-sorting motif that binds to the protein trafficking ESCPE-1 (SNX5/SNX6) complex, which rescues the IGF-1R from lysosomal degradation. This was tested this using full-length receptors expressed in different cell models and using siRNA-mediated suppression of SNX5/SNX6. However, our data did not replicate the published observations on SNX5/SNX6 knockout causing reduced IGF-1R protein expression. Furthermore, no effect of SNX5/SNX6 suppression on IGF-1R protein levels or location at different sub-cellular compartments including the Golgi was observed. Interestingly, SNX5/SNX6 suppression induced lysosomal accumulation at the leading edge of cells as well as decreased cellular migration. SNX5/SNX6 was observed to interact with the IGF-1R, but the hydrophilic Y1250E/Y1251E mutant exhibited a stronger interaction, than the hydrophobic Y1250F/Y1251F mutant, which suggest that this interaction may be modulated by phosphorylation in the full-length receptor.
In summary, the findings confirm the importance of the IGF-1R C-terminal tail, in particular, Tyr1250/1251, in IGF-1R signalling and regulation. These tyrosines facilitate ubiquitin binding, SNX5/SNX6 interaction and Golgi localisation of the IGF-1R which all contribute to the transformed phenotype. Further research on the associated mechanisms should assist in tailoring future cancer therapy treatments to improve clinical efficacy.
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Keywords
IGF-1R , Cancer , Golgi , Trafficking , Receptor
Citation
Godsmark, G. K. 2023. Regulation of intracellular trafficking of the insulin-like growth factor I receptor. PhD Thesis, University College Cork.