Summary Membrane compartments function as segregated signaling platforms for different cellular functions. It is not clear how Src is regulated at different membrane compartments. To visualize local Src activity in live cells, a FRET-based Src biosensor was targeted in or outside of lipid rafts at the plasma membrane, via acylation or prenylation modifications on targeting tags either directly fused to the biosensor or coupled to the biosensor through an inducible heterodimerization system. In response to growth factors and pervanadate, the induction of Src activity in rafts was slower and weaker, dependent on actin and possibly its mediated transportation of Src from perinuclear regions to the plasma membrane. In contrast, the induction of Src activity in non-rafts was faster and stronger, dependent on microtubules. Hence, the Src activity is differentially regulated via cytoskeleton at different membrane compartments.

Both Src kinase and membrane type 1 matrix metalloproteinase (MT1-MMP) play critical roles in cancer invasion and metastasis. It is not clear, however, how the spatiotemporal activation of these two critical enzymes is coordinated in response to an oncogenic epithelial growth factor (EGF) stimulation. Here, we have visualized the activities of Src and MT1-MMP concurrently in a single live cell by combining two fluorescence resonance energy transfer (FRET) pairs with distinct spectra: (a) cyan fluorescent protein (CFP) and yellow FP (YFP), and (b) orange FP (mOrange2) and red FP (mCherry). The new FRET pair, mOrange2 and mCherry, was first characterized in vitro and in cultured mammalian cells. When integrated with the CFP/YFP pair, this new pair allowed the revelation of an immediate, rapid, and relatively dispersed Src activity. In contrast, the MT1-MMP activity displayed a slow increase at the cell periphery, although Src was shown to play a role upstream to MT1-MMP globally. This difference in the activation patterns of MT1-MMP and Src in response to EGF is further confirmed using an optimized MT1-MMP biosensor capable of being rapidly cleaved by MT1-MMP. The results indicate that although Src and MT1-MMP act globally in the same signaling pathway, their activations differ in space and time upon EGF stimulation, possibly mediated by different sets of intermediates at different subcellular locations. Our results also showed the potential of mOrange2/mCherry as a new FRET pair, together with the popular variants of CFP and YFP, for the simultaneous visualization of multiple molecular activities in a single live cell. Cancer Res; 70(6); 2204-12. ©2010 AACR.