A cell-based assay to screen stimulators of the Hippo pathway reveals the inhibitory effect of dobutamine on the YAP-dependent gene transcription

The mammalian Hippo pathway is composed of mammalian Ste20-like (MST) kinases and large tumour suppressor (LATS) kinases. Upon the activation of the pathway, MST kinases phosphorylate and activate LATS kinases, which in turn phosphorylate transcriptional co-activators, yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), recruit them to the cytosol from the nucleus and turn off cell cycle-promoting and anti-apoptotic gene transcriptions. Thus, the pathway restricts cell overgrowth and prevents tumourigenesis. Although a high cell density and stress signallings are known to activate the pathway, no specific stimulators are so far reported. As the dysfunction of the pathway is frequent in human cancers and correlates with poor prognosis, it is important to find out reagents that stimulate the pathway for not only basic research but also clinical medicine. We here developed a cell-based method of screening reagents that induce the recruitment of YAP to the cytosol. Using this method, we found that dobutamine inhibits the YAP-dependent gene transcription. Contrary to our expectations, the effect of dobutamine is independent of the Hippo pathway but our method opens the possibility to discover Hippo pathway stimulators or Hippo-independent YAP inhibitors.