Cten (also known as Tensin4) is the fourth member of the Tensin gene family. It lacks the N terminal actin binding domain while retaining the C terminal SH2 and PTB domains. This helps to bind Cten to the intracytoplasmic tail of β1 integrin and puts it at the heart of focal adhesions. It is reported to be a tumour suppressor in kidney and prostate cancer where normal tissues show high expression. However in a number of tumours, including colorectal cancer, Cten has been labelled as an oncogene. Cten which normally is a cytoplasmic protein gives nuclear staining in colorectal metastatic deposits. It increases motility, invasion and colony formation in colorectal cancer cells. In this study we have tried toexplore the mechanism of functional activity and regulation of Cten. We looked at Cten in the nucleus in vitro and identified new downstream binding targets. In addition we investigated the role of the SH2 domain of Cten concentrating on its downstream signalling molecules and binding partners. Furthermore, we explored regulators of Cten. In this study we have forced nuclear localisation of Cten by tagging it with a nuclear localisation sequence (NLS) and found a significant increase in cell motility. In order to investigate the SH2 domain we used site directed mutagenesis to change potentially important amino acids namely Arginine at 474 to Alanine (R474A), which is important for binding tyrosine phosphorylated proteins. Moreover, we displayed that Cten underwent tyrosine phosphorylation and additionally changed three tyrosine residues i.e. Y449F, Y479F and Y530F via site directed mutagenesis. We found R474 and Y479 to be important in regulating cell motility and that known downstream targets such as ILK and FAK are dependent on an intact SH2 domain. Furthermore we have identified Cten to be physically bound to FAK in the cytoplasm and nucleus and new downstream targets identified such as Src and Paxillin. Regarding possible regulators of Cten, we found that Cten might be a possible substrate for calpain. Another regulator considered was CD24 due to its role in movement of integrins into lipid rafts and we found it was a positive regulator of Cten. In conclusion localisation of Cten into the nucleus causes an augmentation of its motility enhancing functions. Cten regulates cell motility via its SH2 domain. Arginine 474 and Tyrosine 479 are important for its function. Cten regulates levels of ILK, FAK, Src and Paxillin through its SH2 domain and binds to FAK in both cytoplasm and nucleus. Calpain and CD24 were found to possible regulators of Cten in colorectal cancer. Future studies are needed to define its role in signalling at focal adhesions and these studies should be validated in other cancer cell models as well to establish Cten as regulator of cell motility in cancer.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:765396 |
| Date | January 2016 |
| Creators | Akhlaq, Maham |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/32802/ |
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