Studies of Latrophilin Signalling in Cancer Cells

Cancer is one of the major causes of death worldwide. Acute myeloid leukaemia (AML), blood and bone marrow cancer, is usually characterised by rapid growth of malignant leukocytes that have developed several molecular mechanisms to escape immune system attack. Further studies suggest that the same immune escaping mechanism could be employed by solid cancers. However, the signalling mechanisms in cancer cells are poorly understood, and a better comprehension of these processes is vital for the development of biomarkers and potential anti-cancer treatments. Therefore, our aim was to study receptor expression and release of immune protective proteins in two types of cancer cells, AML and breast cancer cells. Here, I report that an aGPCR, LPHN1, is expressed in AML cells and can be used as their biomarker. Our findings demonstrate that stimulation of LPHN1 expressed in AML cells by soluble FLRT3, an endogenous ligand of LPHN1/LPHN2/LPHN3, releases Tim-3 and Gal-9 complex, which helps AML cells to escape immune attack. By contrast, breast cancer cells, which express LPHN2, react to FLRT3 stimulation by trafficking Tim3 and Gal-9 complex to the cell surface rather than releasing it. I also developed a fluorescence-based versatile system for detecting cytosolic Ca2+ changes in adherent or suspension cells, which I used to investigate the LPHNs-mediated signalling in the AML and breast cancer cells. I have found that all cells expressing LPHN1 can be activated by α-LTX, an exogenous ligand of LPHN1, which induces Ca2+ signalling, while FLRT3 causes its signalling without increasing cytosolic Ca2+. Taken together, our work led to the identification of LPHN1 as an absolute biomarker of AML cells and important new insights into intracellular signalling in cancer cells.