Transcriptional integration of mitogenic and mechanical signals by Myc and YAP

Regulation of TEAD Transcription Factors in Cancer Biology

Transcriptional enhanced associate domain (TEAD) transcription factors play important roles during development, cell proliferation, regeneration, and tissue homeostasis. TEAD integrates with and coordinates various signal transduction pathways including Hippo, Wnt, transforming growth factor beta (TGFβ), and epidermal growth factor receptor (EGFR) pathways. TEAD deregulation affects well-established cancer genes such as KRAS, BRAF, LKB1, NF2, and MYC, and its transcriptional output plays an important role in tumor progression, metastasis, cancer metabolism, immunity, and drug resistance. To date, TEADs have been recognized to be key transcription factors of the Hippo pathway. Therefore, most studies are focused on the Hippo kinases and YAP/TAZ, whereas the Hippo-dependent and Hippo-independent regulators and regulations governing TEAD only emerged recently. Deregulation of the TEAD transcriptional output plays important roles in tumor progression and serves as a prognostic biomarker due to high correlation with clinicopathological parameters in human malignancies. In addition, discovering the molecular mechanisms of TEAD, such as post-translational modifications and nucleocytoplasmic shuttling, represents an important means of modulating TEAD transcriptional activity. Collectively, this review highlights the role of TEAD in multistep-tumorigenesis by interacting with upstream oncogenic signaling pathways and controlling downstream target genes, which provides unprecedented insight and rationale into developing TEAD-targeted anticancer therapeutics.

The Roles of YAP/TAZ and the Hippo Pathway in Healthy and Diseased Skin

Skin is the largest organ of the human body. Its architecture and physiological functions depend on diverse populations of epidermal cells and dermal fibroblasts. Reciprocal communication between the epidermis and dermis plays a key role in skin development, homeostasis and repair. While several stem cell populations have been identified in the epidermis with distinct locations and functions, there is additional heterogeneity within the mesenchymal cells of the dermis. Here, we discuss the current knowledge of how the Hippo pathway and its downstream effectors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) contribute to the maintenance, activation and coordination of the epidermal and dermal cell populations during development, homeostasis, wound healing and cancer.

Mechanotransduction and Cytoskeleton Remodeling Shaping YAP1 in Gastric Tumorigenesis

The essential role of Hippo signaling pathway in cancer development has been elucidated by recent studies. In the gastrointestinal tissues, deregulation of the Hippo pathway is one of the most important driving events for tumorigenesis. It is widely known that Yes-associated protein 1 (YAP1) and WW domain that contain transcription regulator 1 (TAZ), two transcriptional co-activators with a PDZ-binding motif, function as critical effectors negatively regulated by the Hippo pathway. Previous studies indicate the involvement of YAP1/TAZ in mechanotransduction by crosstalking with the extracellular matrix (ECM) and the F-actin cytoskeleton associated signaling network. In gastric cancer (GC), YAP1/TAZ functions as an oncogene and transcriptionally promotes tumor formation by cooperating with TEAD transcription factors. Apart from the classic role of Hippo-YAP1 cascade, in this review, we summarize the current investigations to highlight the prominent role of YAP1/TAZ as a mechanical sensor and responder under mechanical stress and address its potential prognostic and therapeutic value in GC.

Ailanthone inhibits cell growth and migration of cisplatin resistant bladder cancer cells through down-regulation of Nrf2, YAP, and c-Myc expression

BACKGROUND

Ailanthone (Aila) is a natural active compound isolated from the Ailanthus altissima, which has been shown to possess an "in vitro" growth-inhibitory effect against several cancer cell lines. Advanced bladder cancer is a common disease characterized by a frequent onset of resistance to cisplatin-based therapy. The cisplatin (CDDP) resistance is accompanied by an increase in Nrf2 protein expression which contributes to conferring resistance. Recently, we demonstrated a cross-talk between Nrf2 and YAP. YAP has also been demonstrated to play an important role in chemoresistance of bladder cancer.

PURPOSE

We analyzed the antitumor effect of Aila in sensitive and CDDP-resistant bladder cancer cells and the molecular mechanisms involved in Aila activity.

STUDY DESIGN

Sensitive and CDDP-resistant 253J B-V and 253J bladder cancer cells, intrinsically CDDP-resistant T24 bladder cancer cells and HK-2 human renal cortex cells were used. Cells were treated with diverse concentrations of Aila and proliferation, cell cycle, apoptosis and gene expressions were determined.

METHODS

Aila toxicity and proliferation were determined by MTT and colony forming methods, respectively. Cell cycle was determined by cytofluorimetric analysis through PI staining method. Apoptosis was detected using Annexin V and PI double staining followed by quantitative flow cytometry. Expressions of Nrf2, Yap, c-Myc, and house-keeping genes were determined by western blot with specific antibodies. Cell migration was detected by wound healing and Boyden chamber analysis.

RESULTS

Aila inhibited the growth of sensitive and CDDP-resistant bladder cancer cells with the same effectiveness. On the contrary, the growth of HK-2 cells was only slightly reduced by Aila. Cell cycle analysis revealed an accumulation of Aila-treated bladder cancer cells in the G0/G1 phase. Interestingly, Aila strongly reduced Nrf2 expression in these cell lines. Moreover, Aila significantly reduced YAP, and c-Myc protein expression. The random and the oriented migration of bladder cancer cells were strongly inhibited by Aila treatment, in particular in CDDP-resistant cells.

CONCLUSION

Aila inhibited proliferation and invasiveness of bladder cancer cells. Its high effectiveness in CDDP resistant cells could be related to the inhibition of Nrf2, YAP, and c-Myc expressions. Aila could represent a new tool to treating CDDP-resistant bladder cancers.

YAP Partially Reprograms Chromatin Accessibility to Directly Induce Adult Cardiogenesis In Vivo

Specialized adult somatic cells, such as cardiomyocytes (CMs), are highly differentiated with poor renewal capacity, an integral reason underlying organ failure in disease and aging. Among the least renewable cells in the human body, CMs renew approximately 1% annually. Consistent with poor CM turnover, heart failure is the leading cause of death. Here, we show that an active version of the Hippo pathway effector YAP, termed YAP5SA, partially reprograms adult mouse CMs to a more fetal and proliferative state. One week after induction, 19% of CMs that enter S-phase do so twice, CM number increases by 40%, and YAP5SA lineage CMs couple to pre-existing CMs. Genomic studies showed that YAP5SA increases chromatin accessibility and expression of fetal genes, partially reprogramming long-lived somatic cells in vivo to a primitive, fetal-like, and proliferative state.

The Hippo Pathway Prevents YAP/TAZ-Driven Hypertranscription and Controls Neural Progenitor Number

The Hippo pathway controls the activity of YAP/TAZ transcriptional coactivators through a kinase cascade. Despite the critical role of this pathway in tissue growth and tumorigenesis, it remains unclear how YAP/TAZ-mediated transcription drives proliferation. By analyzing the effects of inactivating LATS1/2 kinases, the direct upstream inhibitors of YAP/TAZ, on mouse brain development and applying cell-number-normalized transcriptome analyses, we discovered that YAP/TAZ activation causes a global increase in transcription activity, known as hypertranscription, and upregulates many genes associated with cell growth and proliferation. In contrast, conventional read-depth-normalized RNA-sequencing analysis failed to detect the scope of the transcriptome shift and missed most relevant gene ontologies. Following a transient increase in proliferation, however, hypertranscription in neural progenitors triggers replication stress, DNA damage, and p53 activation, resulting in massive apoptosis. Our findings reveal a significant impact of YAP/TAZ activation on global transcription activity and have important implications for understanding YAP/TAZ function.

Recent advances in searching c-Myc transcriptional cofactors during tumorigenesis

Background

The mechanism by which c-Myc exerts its oncogenic functions is not completely clear and different hypotheses are still under investigation. The knowledge of the capacity of c-Myc to bind exclusively E-box sequences determined the discrepancy between, on the one hand, genomic studies showing the binding of c-Myc to all active promoters and, on the other hand, the evidence that only 60% or less of the binding sites have E-box sequences.

Main body

In this review, we provide support to the hypothesis that the cooperation of c-Myc with transcriptional cofactors mediates c-Myc-induced cellular functions. We produce evidence that recently identified cofactors are involved in c-Myc control of survival mechanisms of cancer cells.

Conclusion

The identification of new c-Myc cofactors could favor the development of therapeutic strategies able to compensate the difficulty of targeting c-Myc.

Interplay between YAP/TAZ and Metabolism

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are two homologous transcriptional coactivators that promote cell proliferation, stem cell maintenance, and tissue homeostasis. Under favorable conditions, YAP and TAZ are active to promote cell growth through a transcriptional program mediated by the TEAD family transcription factors. Given the indispensability of cellular energy and metabolites for survival and growth, YAP and TAZ are inhibited when energy level is low. Indeed, glucose, fatty acids, hormones, and other metabolic factors have been recently revealed to regulate YAP and TAZ. Conversely, YAP and TAZ are also involved in metabolism regulation, such as to promote glycolysis, lipogenesis, and glutaminolysis, suggesting YAP and TAZ as emerging nodes in coordinating nutrient availability with cell growth and tissue homeostasis. In this Review, we summarize recent findings and provide a current overview of YAP and TAZ in metabolism by focusing on the role of YAP and TAZ as integrators for metabolic cues and cell growth.

YAP/TAZ upstream signals and downstream responses

Cell behaviour is strongly influenced by physical, mechanical contacts between cells and their extracellular matrix. We review how the transcriptional regulators YAP and TAZ integrate mechanical cues with the response to soluble signals and metabolic pathways to control multiple aspects of cell behaviour, including proliferation, cell plasticity and stemness essential for tissue regeneration. Corruption of cell-environment interplay leads to aberrant YAP and TAZ activation that is instrumental for multiple diseases, including cancer.

Glutamine-utilizing transaminases are a metabolic vulnerability of TAZ/YAP-activated cancer cells

The transcriptional regulators TAZ and YAP (TAZ/YAP) have emerged as pro-tumorigenic factors that drive many oncogenic traits, including induction of cell growth, resistance to cell death, and activation of processes that promote migration and invasion. Here, we report that TAZ/YAP reprogram cellular energetics to promote the dependence of breast cancer cell growth on exogenous glutamine. Rescue experiments with glutamine-derived metabolites suggest an essential role for glutamate and α-ketoglutarate (AKG) in TAZ/YAP-driven cell growth in the absence of glutamine. Analysis of enzymes that mediate the conversion of glutamate to AKG shows that TAZ/YAP induce glutamic-oxaloacetic transaminase (GOT1) and phosphoserine aminotransferase (PSAT1) expression and that TAZ/YAP activity positively correlates with transaminase expression in breast cancer patients. Notably, we find that the transaminase inhibitor aminooxyacetate (AOA) represses cell growth in a TAZ/YAP-dependent manner, identifying transamination as a potential vulnerable metabolic requirement for TAZ/YAP-driven breast cancer.

dNTP metabolism links mechanical cues and YAP/TAZ to cell growth and oncogene-induced senescence

YAP/TAZ, downstream transducers of the Hippo pathway, are powerful regulators of cancer growth. How these factors control proliferation remains poorly defined. Here, we found that YAP/TAZ directly regulate expression of key enzymes involved in deoxynucleotide biosynthesis and maintain dNTP precursor pools in human cancer cells. Regulation of deoxynucleotide metabolism is required for YAP-induced cell growth and underlies the resistance of YAP-addicted cells to chemotherapeutics targeting dNTP synthesis. During RAS-induced senescence, YAP/TAZ bypass RAS-mediated inhibition of nucleotide metabolism and control senescence. Endogenous YAP/TAZ targets and signatures are inhibited by RAS/MEK1 during senescence, and depletion of YAP/TAZ is sufficient to cause senescence-associated phenotypes, suggesting a role for YAP/TAZ in suppression of senescence. Finally, mechanical cues, such as ECM stiffness and cell geometry, regulate senescence in a YAP-dependent manner. This study indicates that YAP/TAZ couples cell proliferation with a metabolism suited for DNA replication and facilitates escape from oncogene-induced senescence. We speculate that this activity might be relevant during the initial phases of tumour progression or during experimental stem cell reprogramming induced by YAP.