Fluorescence microscopy image showing the distribution of endogenous Amot (green) and YAP (red) proteins in cultured human breast cancer cells
The ‘Hippo’ signaling pathway regulates organ size by controlling cell proliferation and programmed cell death. It does so by chemically modifying the transcription co-factors TAZ and YAP, causing them to be degraded or moved out of the nucleus. In research that could have implications for the future treatment of cancer, Wanjin Hong and co-workers at the A*STAR Institute of Molecular and Cell Biology have found that the activity of TAZ and YAP can be restricted independently of the Hippo pathway via a protein initially identified as a regulator of endothelial cell migration into developing blood vessels.
The researchers treated cultured human breast cancer cells with an antibody that recognizes and binds to TAZ. They found that two proteins, Angiomotin (Amot) and Angiomotin-like 1 (AmotL1), always precipitated with TAZ and its antibody when they were isolated from the cells, except when a mutant form of TAZ lacking a region called the WW domain was used. This suggests that TAZ interacts with Amot and AmotL1, and that the WW domain of TAZ is required for the interaction. YAP contains two WW domains, and similar experiments revealed that these domains are also necessary for the interaction with Amot and AmotL1.
To investigate the significance of the interactions, the researchers examined how Amot and AmotL1 affect the distribution of another form of TAZ containing a mutation that prevents its redistribution to the cytoplasm in response to Hippo pathway activation. When expressed alone in cultured cells, Amot was localized predominantly in the cytoplasm and TAZ and YAP in the nucleus (see image). However, expressing Amot and TAZ together in the same cells caused TAZ to be shifted from the nucleus into the cytoplasm, suggesting that Amot can induce TAZ redistribution independently of the Hippo pathway.
These results were confirmed in a further set of experiments investigating the expression of the CTGF and Cyr61 genes, which are activated by TAZ. Cyr61 expression was enhanced in cells expressing TAZ alone, but was compromised in cells that co-expressed Amot. Furthermore, silencing the expression of endogenous Amot led to increased expression of endogenous CTGF, demonstrating that Amot is actively restricting CTGF expression.
The findings demonstrate that Amot negatively regulates the oncogenic property of TAZ and YAP. “Suppressing Amot protein expression may activate TAZ and YAP to promote cancer development and progression,” says Hong. “Interventions that restore or enhance Amot expression will have a negative impact on cancer cell proliferation.”
The A*STAR-affiliated researchers contributing to this research are from the Institute of Molecular and Cell Biology.
