TRAFFICKING AND FUNCTIONAL INTERACTIONS OF THE ONCOFOETAL TROPHOBLAST GLYCOPROTEIN 5T4

  • Georgi Marinov

Student thesis: Phd

Abstract

5T4 is expressed during embryonic development but shows only low levels in adult tissues. 5T4 expression has also been found in many tumours and often correlates with poor clinical outcome. In mouse embryonic cells, 5T4 expression influences the functional availability of the chemokine receptor CXCR4 at the cell surface and the chemotactic response to its ligand CXCL12. This project aimed to provide a better understanding of the mechanisms underlying the chemotaxis promoting function of 5T4 and to give a better insight into the trafficking machinery involved in the expression and turnover of 5T4. The 5T4/CXCR4 functional relationship discovered in mouse embryonic cells was also investigated in human cancers.Here it is shown that WT and 5T4 KO MEFs immortalized with the E6/E7 HPV genes retain their distinct chemotactic properties and reintroduction of 5T4 in the 5T4 KO cells rescues their chemotactic potential. It was also found that 5T4 and CXCR4 employ distinct trafficking pathways for transport to the cell surface, constitutive and ligand induced endocytosis and turnover. The results from a FRET study do not indicate a direct interaction between 5T4 and CXCR4. It seems likely that functional CXCR4 and 5T4 interactions may be achieved via additional molecules, likely including actin binding proteins and may take place in clathrin-coated pits. 5T4 influence of chemotaxis was further analysed in human cancer cells. A B-ALL leukaemia cell line (SupB15), heterogeneous for 5T4 expression was used to study the role of 5T4 in CXCR4 function in cancer. Only cells expressing 5T4 exhibit chemotaxis to CXCL12 and this correlates with delayed internalization of CXCR4. Unlike in the MEFs, expression of 5T4 in the 5T4 negative cells did not rescue their chemotactic ability or CXCR4 internalization profile. A correlation between 5T4 expression and chemotactic potential was also evident in SCLC with a 5T4 positive cell line H1048 showing an increased chemotactic response compared to the 5T4 negative cell line DMS114. Furthermore 5T4 knockdown in H1048 cells led to loss of chemotactic responsiveness.Collectively these results suggest that 5T4 is necessary for a CXCL12 chemotactic response in some embryonic cells and malignant cells and in the later this may facilitate metastasis. It is clear that chemotactic responsiveness to CXCL12 requires more than expression of the CXCR4 receptor and 5T4.
Date of Award1 Aug 2013
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorPeter Stern (Supervisor)

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