1. YAP and TAZ (Yes-Associated Protein and Transcriptional coactivator with PDZ Binding Motif) Multiple Cancers Lucy Laws
My name is Lucy and I am going to be talking to you about the transcription coactivators YAP and TAZ. Unlike other genes we have talked about that cause cancer due to specific mutations, YAP and TAZ instead are the key factors in a handful of the hallmarks of cancer such as sustaining proliferative signaling, activating invasion and metastasis, and resisting cell death that are found in several different types of cancer.
The Hippo pathway effectors TAZ and YAP in development, homeostasis and disease
Xaralabos Varelas
Development 2014 141:  ; doi:  /dev

2. The transcription co-activators YAP and TAZ are the major effectors in the Hippo Pathway and are activated when the Hippo Pathway is off.
YAP and TAZ are found downstream in the Hippo Pathway which is responsible for restricting tissue growth in adults, and modulating cell proliferation, differentiation, and migration in developing organs. The core Hippo Pathway consists of a kinase cascade involving MST1/2 and LATS1/2, the transcription coactivators YAP/TAZ, and DNA binding partners such as the TEAD family. When the Hippo Pathway is turned “on” MST1/2 phosphorylates and activates LATS1/2 which then phosphorylates and inactivates YAP/TAZ. Inactive YAP/TAZ are localized in the cytoplasm and cannot translocate to the nucleus to bind to TEAD. Whereas, when the pathway is turned off, YAP/TAZ translocate into the nucleus, bind to TEAD, and cause cell proliferation.
While the core Hippo Pathway does play an important role in the control of YAP/TAZ activity, it is not the only source of regulation. Intrinsic cell machineries such as cell-cell contact, cell polarity, and actin cytoskeleton and signals such as cellular energy stress, mechanical cues, and hormonal signals that act through GPCR’s all contribute to the regulation of YAP/TAZ.
Types of signals that inactivate YAP/TAZ: (opposite for actvation)
High cell density
Increases adheren and tight junctions
Detachment of cells from ECM
High energy stress
Soft ECM changes in geometry and cytoskeleton tension
GPCR’s by glucagon and epinephirne

3. While Yap and Taz are inactivated when phosphorylated by LATS1/2, Rho-GTPases and actin cytoskeleton play an essential role in the regulation of YAP and TAZ.
 Classic work using transformed mammary cells showed that once these cells are grown as spheres within a soft ECM, tumor cells displayed a remarkable normalization of their behavior (116, 171, 223). Oppositely, when nontransformed cells where grown in three dimensions in an abnormally rigid ECM, they started to change shape, lose polarity, and display malignant characteristics (116). Mechanical YAP/TAZ modulation is at the root of these behaviors (4), Indicating that loss of tissue architecture and/or altered ECM composition convey a wrong set of instructions to individual cells, wreaking havoc spatial control of proliferation.
The Biology of YAP/TAZ: Hippo Signaling and Beyond
Stefano Piccolo, Sirio Dupont, Michelangelo Cordenonsi
Physiological Reviews Oct 2014, 94 (4)  ; DOI: /physrev
Kieran F. Harvey, Xiaomeng Zhang & David M. Thomas
Nature Reviews Cancer 13,   (April 2013)
doi: /nrc3458

4. Overexpression of homologous transcription co-activator Yki in Drosophila, results in enhanced cell proliferation coinciding with results found from overexpression of YAP/TAZ in mice.
A homologous hippo pathway is also found in Drosophila. Overexpression of both Yki in Drosophila and overexpression of YAP/TAP in mice both result in dramatic increase in organ size. In Drosophila, we can see a normal wing imaginal disc compared with one with overexpressed Yki. In mice, we can see a normal liver compared to an enlarged one due to overexpression of YAP/TAZ. So what role do YAP and TAZ play in cancer?
Pan D. The hippo signaling pathway in development and cancer. DevCell. 2010;19:491–505.

5. Overexpression of TAZ plays a critical role in the migration and tumorigenesis in breast cancer cells.
In a study conducted in 2008, researchers tested the significance of TAZ in several breast cancer cell lines to see the effects of TAZ on cell migration, invasion, and tumorigenesis and found that TAZ was significantly overexpressed in about 20% of their sample. To test for cell migration and invasion a wound healing migration assay was used. The right column contains normal cells containing green fluorescent protein and the left column contains cells overexpressed with TAZ. After 14 hours, the wound area was significantly covered in TAZ overexpressed cells and by 24 hours the wound had been completely recovered compared to GFP cells that only partially covered the wound by 24 hours. The reverse experiment was used to confirm that knockdown of TAZ in tumor cells, leads to suppression of migration and invasion.
To test for tumorigenesis, 2 cell lines, 715 which is from invasive breast cancer cells and 652 which is from knockdown TAZ cancer cells. Results confirm that TAZ is essential for anchorage independent growth of MCF7 cells. These two cell lines were then injected in the thigh and fat pad of nude mice and monitored for tumor growth. As we can see from the pictures, the areas injected with 652 did not result in full tumor development.
A Role for TAZ in Migration, Invasion, and Tumorigenesis of Breast Cancer Cells
Siew Wee Chan, Chun Jye Lim, Ke Guo, Chee Peng Ng, Ian Lee, Walter Hunziker, Qi Zeng and Wanjin Hong
Cancer Res April  (68) (8)  ; DOI:  / CAN

6. High levels of TAZ, YAP, and TEAD lead to poor prognosis in Colorectal Cancer and Ovarian Cancer patients.
YAP and TAZ also are significant factors in cancer prognosis. Here we have examples from two different studies. The first looks at correlation between YAP and TAZ expression in patients with Colorectal Cancer patients with colorectal cancer, had samples taken from their normal cells and from their resected tumors that were tested for their expressions of YAP and TAZ both independently and co-expressed. After 5 year, 90 of the patients had died. After comparing YAP/TAZ expression from those who had died, and those who were still alive, it was found that patients with a high expression of YAP/TAZ had a higher risk of death compared to those with those expression.
Additionally, another study looked at the relationship between levels of YAP and transcription factor family TEAD in human Ovarian Cancer. Testing 45 human ovarian cancer samples, researched confirmed a positive correlation between YAP and TEAD1-4. They tested both expression of TEAD and prognosis and TEAD and YAP co-expression and found high expression of both lead to a significantly worse outcome for patient prognosis.
Wang L, Shi S, Guo Z, Zhang X, Han S, et al. (2013) Overexpression of YAP and TAZ Is an Independent Predictor of Prognosis in Colorectal Cancer and Related to the Proliferation and Metastasis of Colon Cancer Cells. PLOS ONE 8(6): e doi: /journal.pone
Xia Y, Chang T, Wang Y, Liu Y, Li W, et al. (2014) YAP Promotes Ovarian Cancer Cell Tumorigenesis and Is Indicative of a Poor Prognosis for Ovarian Cancer Patients. PLOS ONE 9(3): e doi: /journal.pone

7. Verteporfin inhibits the transcriptional activity of YAP by disrupting the bond between YAP and TEAD leading to YAP degradation.
In respect to treatment, numerous studies are being conducted in order to target YAP/TAZ along with other components downstream in the Hippo Pathway. One drug, Vertporfin, which is currently on the market to treat macular degeneration, has been found to disrupt the bind between YAP/TAZ and TEAD which leads to translocation of YAP/TAZ back into the cytoplasm and halt of gene expression, proliferation. This has been tested in ovarian cancer and liver growth in mice.
Another drug Dobutamine, which is currently used to treat patients with congestive heart failure, has been found to expel YAP from the nucleus in stomach cancer cells.
Lastly, researchers have also found that a peptide mimicking VGLL4 can outcompete YAP in TEAD binding.
Nat Rev Cancer Feb; 15(2): 73–79.
Published online 2015 Jan 16. doi:   /nrc3876

8. References