The Regulation Of TAZ By PTEN/PI3K Pathway And Its Mechanism

The Hippo tumor suppressor pathway plays a major role in development, organ size control by coordination cell proliferation and apoptosis, and its dysregulation contributes to tumorigenesis. TAZ (transcriptional co-activator with PDZ-binding motif, TAZ or WWTR1) is a transcription co-activator acting downstream of the Hippo pathway and increased TAZ protein levels have been associated with human cancers, such as breast cancer. Previous studies have shown that TAZ is inhibited by LATS dependent phosphorylation, leading to cytoplasmic retention and ubiquitin dependent degradation. The LATS kinase, a core component of the Hippo pathway, phosphorylates the C-terminal phosphodegron in TAZ to promote its degradation. In this study we have found that the N-terminal phosphodegron of TAZ also plays a role in TAZ protein level regulation, particularly in response to different status of cellular PI3K signaling. GSK3, which can be inhibited by high PI3K via AKT dependent inhibitory phosphorylation, phosphorylates the N-terminal phosphodegron in TAZ and the phosphorylated TAZ binds to β-TrCP subunit of the SCFβ-TrCP E3ubiquitin ligase and therefore leading to TAZ ubiquitylation and degradation. We observed that TAZ protein level is elevated in tumor cells with high PI3K signaling, such as in PTEN mutant cancer cells. This study provides a novel mechanism of TAZ regulation and suggests a role of TAZ in modulating tissue growth and tumor development in response to PI3K signaling.