Introduction Metastatic melanoma is a worldwide health problem accounting for 80% of skin cancer deaths. With 132,000 new cases diagnosed annually, it is also one of the few remaining cancers with an increasing incidence rate. The Endoplasmic Reticulum (ER) plays an important role in the synthesis and maturation of cell surface and secretory protein including protein modification and folding. Various stress conditions such as hypoxia, disrupted Ca2+ and redox homeostasis and nutrient deprivation, all commonly observed in cancer, can result in the accumulation of unfolding/misfolded proteins in the ER. These accumulated proteins result in activation of the Unfolded Protein Response (UPR) which counteracts the lethal consequences of high protein turnover present in cancerous cells. Furthermore the UPR is additionally thought to be advantage to cells during metastasis through the recycling of macromolecules via ER-associated degradation and autophagy thereby sustaining the cell and allowing for adaption to the new environment.
Method Melanoma cell lines MEL-RM and WMM1175 were treated with Thapsigargin, an inducer of ER-stress, then fractionated by differential centrifugation into subcellular proteomes. To identify differentially abundant proteins with drug treatment, the nuclear, mitochondrial and cytosolic proteomes were labeled with isobaric tags for relative and absolute quantitation (iTRAQ) and analysed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Differentially abundant proteins were validated by separation using difference gel electrophoresis (DIGE) and identified with LC-MS/MS.
Results Several proteins were identified as differentially abundant in the melanoma cell lines following Thapsigargin treatment. The proteins identified are involved in stress responses, the UPR in particular, metabolism, cellular signalling, cell survival/ apoptosis and transcriptional regulation.
Discussion The full role of the UPR in melanoma is unknown, in particular its role in metastatic disease and increased knowledge of this process will be valuable in developing therapeutic strategies. The proteins identified in this study are potential drug targets directed towards the UPR for the treatment of metastatic melanoma.