Epithelial-mesenchymal transition is a form of cellular plasticity that is critical for embryonic development and tumor metastasis. This study shows that a signaling network involving autocrine TGF-β signaling, ZEB transcription factors, and the miR-200 family regulates interconversion between epithelial and mesenchymal states.

Glutathione transferases are a family of enzymes that are traditionally known to contribute to the phase II class of detoxification reactions. However, a novel property of the Schistosoma japonicum glutathione transferase (Sj.GST26) involves its translocation from the external medium into a variety of different cell types. Here we explore the efficiency and mechanism of cell entry for this class of protein. Using flow cytometry and confocal microscopy, we have examined the internalisation of Sj.GST26 into live cells under a variety of conditions designed to shed light on the mode of cellular uptake. Our results show that Sj.GST26 can effectively enter cells through an energy-dependent event involving endocytosis. More specifically, Sj.GST26 was found to colocalise with transferrin within the cell indicating that the endocytosis process involves clathrin-coated pits. A comprehensive study into the cellular internalisation of proteins from other classes within the GST structural superfamily has also been conducted. These experiments suggest that the 'GST-fold' structural motif influences cellular uptake, which presents a novel glimpse into an unknown aspect of GST function.

It has recently emerged that glutathione transferase enzymes (GSTs) and other structurally related molecules can be translocated from the external medium into many different cell types. In this study we aim to explore in detail, the structural features that govern cell translocation and by dissecting the human GST enzyme GSTM2-2 we quantatively demonstrate that the α-helical C-terminal domain (GST-C) is responsible for this property. Attempts to further examine the constituent helices within GST-C resulted in a reduction in cell translocation efficiency, indicating that the intrinsic GST-C domain structure is necessary for maximal cell translocation capacity. In particular, it was noted that the α-6 helix of GST-C plays a stabilising role in the fold of this domain. By destabilising the conformation of GST-C, an increase in cell translocation efficiency of up to ∼2-fold was observed. The structural stability profiles of these protein constructs have been investigated by circular dichroism and differential scanning fluorimetry measurements and found to impact upon their cell translocation efficiency. These experiments suggest that the globular, helical domain in the ‘GST-fold’ structural motif plays a role in influencing cellular uptake, and that changes that affect the conformational stability of GST-C can significantly influence cell translocation efficiency.

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