Figure 4.

Galectin-9 secretion induced by T cells in MCF-7 human breast cancer cells can occur through two mechanisms. (A) Possible biochemical mechanisms underlying T cell-induced galectin-9 secretion in human solid cancer cells. Two potential mechanisms were investigated. First, Ca²⁺/PKC-dependent translocation of galectin-9 onto the cell surface followed by proteolytic shedding by matrix metalloproteinases (MMPs), which can also be activated by PKC. Another mechanism could possibly be associated with galectin-9 in complex with a carrier protein joining autophagosomes, which merge with lysosomes, where galectin-9 is shed and secreted via lysosomal exocytosis. (B) MCF-7 cells (adherent) were cocultured with Jurkat T cells (suspension) for 16 hours at a ratio of 1:1. Jurkat T cells were then removed and washed away from MCF-7 cells. After replacing the culture medium, MCF-7 cells were incubated for 4 hour and galectin-9 release was measured after 2, 3 and 4 hour. To investigate the mechanisms, replacement medium contained respective pharmacological inhibitors (PIC—protease inhibitor cocktail)—U73122—30 µM, Gö6983–70 nM, AZD2014—10 µM, EDTA—200 µM. Data are the mean values±SEM of 5 independent experiments.