GPX1 expression promotes stemness and aggressiveness in sarcomas

The sarcomagenic process initiates upon the tumoral transformation of mesenchymal stromal/stem cell (MSCs) or MSC-derived cell types. Experimental evidence also supports that sarcoma evolution is in part driven by the emergence of subpopulations of cancer stem cells (CSCs) after the accumulation of further epigenetic and/or genetic alterations. These CSCs are strongly associated with the evolution of tumors towards more aggressive behaviors. Therefore, the characterization of these subpopulations will contribute to develop more effective therapies against these tumors. With this aim, we used tandem mass spectrometry to the compare the proteome of adherent and CSC-enriched tumorsphere cultures in a tumor progression model of myxoid liposarcoma composed by three cell lines showing increasing aggressiveness after being serially transplanted in mice. In this analysis we found that the expression of the antioxidant enzyme GPX1 increased constantly during the CSC-enrichment process in all the cell lines of the model. Depletion of GPX1 resulted in decreased proliferation, tumorsphere-forming potential and migration capability in vitro and dramatically reduced tumor-formation ability in vivo. Conversely, GPX1 overexpression resulted in increased in vivo tumorigenicity. In agreement with this findings, GPX1 expression in sarcoma patients was associated to advanced tumor stages, more aggressive phenotypes, and a worse prognosis.

To gain insight into the molecular basis behind the anti-tumor effects observed after the inhibition of GPX1 in sarcoma cells, we performed a proteomic LC-MS analysis in a hybrid Q-TOF mass spectrometer using triplicate samples of control and GPX1-depleted cells. ZenoSWATH data-independent acquisition (DIA) was used as the MS method. Comparing sh vs control conditions, we detected 116 differentially expressed proteins, associated with a downregulation of interferon-mediated response, the IL6/JAK/STAT3 axis and the NFκB-mediated signaling in GPX1-silenced cells. Overall, these results suggest that this factor may be a functional marker of aggressive CSCs subpopulations in sarcoma with prognostic and therapeutic implications.