Effects of tributyltin on cytosolic calcium and actin in human natural killer cells
Natural killer (NK) cells are lymphocytes that non-specifically kill tumor cells, virally infected cells and antibody coated cells. Tributyltin (TBT) is an environmental pollutant widely used for commercial purposes and found in human blood. TBT has been shown to inhibit cytotoxic function of NK cells. Cell damage to T-lymphocytes exposed to TBT has been attributed to changes in cytosolic Ca2+ concentrations ([Ca2+] cyt) and modifications to the cytoskeleton. Studies have also shown a correlation between exposures of NK cells to TBT and decreased cytotoxic function coupled with phosphorylation of mitogen-activated protein kinases (MAPKs). Therefore, it is reasonable that exposure to TBT will cause an increase in [Ca2+]cyt, that this increase will initiate significant rearrangement of actin, contributing to the decrease in cytotoxicity, and that some of this process will be regulated through the activation of MAPKs. These studies investigated fluctuations in [Ca 2+]cyt in NK cells in response to TBT and whether [Ca 2+]cyt changes play a role in reduced cytotoxic function of NK cells due to alteration of the ability of the cytoskeleton to rearrange. Exposures of 500 nM TBT caused increases in [Ca2+]cyt of approximately 100% after 60 min. Exposures to 300 and 200 nM TBT caused increases of about 40% after 60 min and exposure to 100 nM TBT caused an increase of about 20% after 60 min. These increases in [Ca2+] cyt were shown to be primarily from an influx of extracellular calcium. Exposure of NK cells to 500 nM TBT caused a 25% decrease in F-actin after 60 min. Confocal images showed rearrangement of F-actin from the normal polarized configuration to a symmetrical “net-like” appearance. Calcium influx due to a 5 uM calcium ionophore (A23187) was compared to the influx induced by TBT. These studies showed that A23187 produced increases in [Ca 2+]cyt up to 253% while only causing F-actin to depolymerize to a maximum of 32%. Conversely, when exposed to 500 nM TBT, the maximum increase in [Ca2+]cyt was only 82%, whereas maximum F-actin decrease of 38% remained similar to that of A23187. Effects on MAPK activation in NK cells resulting from ionophore-induced changes in [Ca2+] cyt were investigated. Exposure of NK cells to A23187 increased phosphorylation of p44/42 and p38 at 5 min, but not at any other time point. The 500 nM TBT caused no significant increase in phospho-p38, while A23187 caused an approximately 2.6 fold increase at 5 min. ^
Biology, Molecular|Biology, Cell|Chemistry, Biochemistry
Rhonda Lane Coffelt,
"Effects of tributyltin on cytosolic calcium and actin in human natural killer cells"
ETD Collection for Tennessee State University.