Signal processing in migrating T24 human bladder carcinoma cells: role of the autocrine interleukin-8 loop

T24 human bladder carcinoma cells reveal a high locomotor activity (70% locomoting cells) within a 3-dimensional collagen matrix. This high migratory activity is induced by an autocrine engagement of the interleukin-8 receptor A, as was shown by antibodies neutralizing the secreted interleukin-8. Treatment of the cells with these specific antibodies reduced the locomotor activity by half. The intracellular signal transduction underlying the interleukin-8-induced T24 locomotion involves the activity of protein tyrosine kinases (PTKs), the phospholipase Cgamma (PLCgamma) and the protein kinase C (PKC), as proven by the use of specific enzyme inhibitors. These results suggest the following model for the regulatory signal transduction of interleukin-8-induced human T24 bladder carcinoma cell migration: The engagement of the interleukin-8-receptor, a receptor of the serpentine family, leads to the beta-arrestin-mediated activation of PTKs. These kinases phosphorylate the PLCgamma, which generates the second messengers diacylglycerol (DAG) and inositol-1,4,5-trisphosphate (IP(3)). DAG activates the PKC, whereas IP(3) mediates the release of calcium from the endoplasmatic reticulum. By means of confocal laser microscopy, we observed an oscillation of the cytosolic calcium concentration in migrating T24 cells, which were loaded with the calcium-dye fluo-3/AM. Here, we report on a new autocrine function of secreted interleukin-8 and the intracellular signal transduction leading to the regulation of cytosolic calcium and to a migratory tumor cell phenotype.