Investigation into the roles of protein kinase D (PKD) in CXCL12/CXCR4 signalling in cancer cells
The chemokine signalling axis, CXCL12/CXCR4, has long been considered as crucial in regulating cancer metastasis. Receptor internalisation is a major aspect in tuning responsiveness to ligands through desensitisation and resensitisation processes, also contributing to intracellular signalling. Yet, the complexity of signalling mechanism is yet to be elucidated. Characterisation of the receptor-effector interactions is the key to fine tune the signalling system for the development of precision medicine in cancer. Here, we investigated distinct roles of protein kinase D (PKD) in CXCL12/CXCR4 signalling in two cancer cell lines, breast cancer MCF-7 cells and leukaemic Jurkat cells.
Cell were pre-treated with CID755673 and CID2011756 (PKD inhibitors), nystatin and filipin (caveolae-specific inhibitors) for 30 minutes and stimulated with CXCL12 (50nM) for another 30 minutes at 37°C. Immunofluorescence staining was performed at 4°C. CXCR4 receptor and caveolin-1 expressions were quantified using FACS. Actin cytoskeleton was visualised by Phalloidin-iFluor 488 stain.
Our data suggest that PKD has no direct effect on CXCR4 internalisation. PKD might alter Cav-1 cell surface expression in CXCR4 trafficking in Jurkat but not in MCF-7 cells, due to the fact that CXCR4 internalisation in Jurkat is caveolin-dependent. In the aspect of cell migration, PKD possess inhibitory effects on cell motility by regulating actin polymerisation in MCF-7.