Phase Separation Of TAZ Compartmentalizes Transcription Machinery To Promote Downstream Target Gene Expression

TAZ is an important downstream effector of Hippo signaling.TAZ promotes cell proliferation,tissue regeneration,development and tumorigenesis by regulating downstream target gene transcription.However,how TAZ orchestrates the transcriptional responses remains poorly defined.Here we demonstrate a novel mechanism that TAZ promotes transcription activation.TAZ undergoes liquid-liquid phase separation(LLPS)forming nuclear puncta which compartmentlizes transcription machinery into the nuclear puncta to promote downstream target gene expression.TAZ undergoes LLPS both in vivo and in vitro.Increasing protein concentration,salt concentration or temperature promotes TAZ phase separation.We generated different truncations of TAZ and found that the WW domain and coiled-coil domain was required for TAZ phase separation.YAP,a paralog of TAZ,fails to undergo LLPS under the same condition.Swapping YAP's coiled-coil domain into TAZ inhibits TAZ phase separation,while swapping TAZ's coiled-coil domain into YAP promotes YAP phase separation.Thus,different coiled-coil domains between TAZ and YAP determine their different performance in phase separation.Phase separation of TAZ is negatively regulated by Hippo signaling.Serum starvation and high cell density induce Hippo signaling which represses TAZ phase separation.Phosphorylation by LATS2 also inhibits TAZ phase separation.Functionally,TAZ undergoes LLPS and forms nuclear puncta to recruit transcription factor TEAD4 and other transcription machinery including BRD4?MED1 and CDK9 into the nuclear puncta leading to efficient transcription of downstream target genes in response to different signals.Therefore,our study identifies a novel mechanism for the transcriptional activation by TAZ and demonstrates for the first time that pathway-specific transcription factors also engage the phase separation mechanism for efficient transcription activation.