G-PKDrep-live, a genetically encoded FRET reporter to measure PKD activity at the trans-Golgi-network.

The serine/threonine protein kinase D (PKD) is recruited to the trans-Golgi-network (TGN) by interaction with diacylglycerol (DAG) and Arf1 and promotes the fission of vesicles containing cargo destined for the plasma membrane. PKD activation is mediated by PKC(-induced phosphorylation. However, signaling pathways that activate PKD specifically at the TGN are only poorly characterized. Recently we created G-PKDrep, a genetically encoded fluorescent reporter for PKD activity at the TGN in fixed cells. To establish a reporter useful for monitoring Golgi-specific PKD activity in living cells we now refined G-PKDrep to generate G-PKDrep-live. Specifically, phosphorylation of G-PKDrep-live expressed in mammalian cells results in changes of fluorescence resonance energy transfer (FRET), and allows for indirect imaging of PKD activity. In a proof-of-principle experiment using phorbolester treatment, we demonstrate the reporter's capability to track rapid activation of PKD at the TGN. Furthermore, activation-induced FRET changes are reversed by treatment with PKD-specific pharmacological inhibitors. Thus, the newly developed reporter G-PKDrep-live is a suitable tool to visualize dynamic changes in PKD activity at the TGN in living cells. See accompanying commentary by Gautam DOI: 10.1002/biot.201100424.