Differential contribution of TFE3 isoforms to cell motility and invasion

We and other have previously reported that TFE3 migrates as two distinct bands of approximately 72 and 82 kDa in SDS-PAGE. Interestingly, whereas the smaller form of TFE3 is always present in cell lysates, the higher molecular weight form appears only after specific stress conditions, such as prolonged starvation. A recent report suggested that the 82 kDa form does in fact corresponds to TFE3 full length (TFE3-L). It was proposed that the control of TFE3 stability may constitute the main mechanism of TFE3 regulation. There is, however, a critical question that remains to be addressed regarding the role of the 72 kDa TFE3 short isoform (TFE3-S). TFE3-S is expressed at high levels in most cell types and its expression remains constant both under control and stress conditions. Characterizing the nature and regulation of TFE3-S, as well as its potential transcriptional activity and selectivity, is therefore essential to fully understand TFE3 regulation. Overall design: To investigate the transcriptional capability of TFE3-L and TFE3-S, we generated adenovirus (Ad) expressing either recombinant (r)TFE3-L or rTFE3-S. ARPE-19 cells were infected for 30 hours with Ad-rTFE3-L, or Ad-rTFE3-S or Ad-Null as a negative control to compare.