Differente Expression der Multidrug-Resistenz-Proteine 4/5 in nicht und stark metastasierenden Melanomzellen unter Hypergravitationsbedingungen

摘要

Multidrug resistance proteins (MRPs) are transmembrane proteins with the potential to export a wide range of substances in the extracellular space preventing cells from toxification. MRP4 and 5, on which this investigation is focused, particularly mediate nucleoside-analogue export, i.e. guanosine 3´, 5´-cyclic monophosphate (cGMP) and conjugated nucleosides. cGMP plays an important signaling role in melanocytic physiology, especially in the UV-B induced melanogenesis. Previous studies could show that long-term exposure to mechanical stress in terms of hypergravity leads to an increased cGMP efflux in non-metastatic melanoma cell lines, whereas the highly metastatic phenotype appeared to be insensitive. Biochemical analysis let assume that overexpressed MRP4, 5 and 8 could be responsible for these effects. Based on these results the aim of the present study was to investigate the effects of hypergravity (5xg for 24 h) on mRNA and protein levels of MRP4, 5, and/or 8. The data show that the mRNA as well as the protein levels of MRP4 and MRP5 were about 1.4-fold higher in non-metastatic melanoma cells exposed to hypergravity in comparison to 1xg controls. In contrary, the expressions of MRP4 and 5 in highly metastatic cells remained unaffected. For MRP8 we basically measured low mRNA and protein expression levels in all investigated cell lines independent of gravity alterations. Our studies indicate that the previously found elevated cGMP export in hypergravity could be a consequence of an upregulated expression of MRP4 and MRP5 in non-metastatic melanoma cells, whereas a MRP8-driven export can be excluded. Furthermore, the elevated cGMP efflux and MRP expressions seems to be a part of an adaptation process for non-metastatic melanoma cells to hypergravity conditions. Since enhanced MRP expression is responsible for a decreased drug uptake in cells, a gravity-modified MRP expression on long-term space flights can lead to an altered drug tolerance and efficiency in astronauts.