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Open Access Publications from the University of California

Scholarly Works (19 results)

  • Thesis
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UC San Diego Electronic Theses and Dissertations (2018)

The Hippo pathway and its downstream effectors, transcriptional coactivators YAP and TAZ, are important for regulating tissue homeostasis and their dysregulation has been implicated in many human diseases and cancer. However, it is not clear how the Hippo pathway becomes dysregulated because few mutations have been identified in Hippo pathway components. Therefore, recent work in the Hippo field has focused on identifying upstream regulators of the Hippo pathway. Nevertheless, it is not always clear which components are most physiologically relevant in regulating YAP/TAZ. To provide an overview of which components are most physiologically relevant in regulating YAP/TAZ, we used CRISPR/Cas9 to create knockout cell lines for many of these components and tested their responses to a variety of physiological signals to determine which components are most critical in regulating YAP/TAZ. By this approach, we demonstrate that NF2 and RHOA are important regulators of YAP/TAZ, and TAOK1/3 are direct kinases for LATS1/2.

Additionally, YAP and TAZ are traditionally viewed as being largely redundant, although there are evolutionary, structural, and physiological differences that suggest there may be differences in how they are regulated and in their downstream functions. To delineate any differences between YAP and TAZ, we compared LATS1/2 KO cells, in which YAP/TAZ are constitutively-active, YAP KO, TAZ KO, and YAP/TAZ KO cells, in which YAP/TAZ are constitutively-inactive. We found that inactivation of YAP had a much greater negative effect on many measures of cell physiology, including cell spreading, cell volume, glucose uptake and metabolism, cell proliferation, and migration, while YAP activation in the LATS1/2 KO cells had the opposite effect. Differences between YAP and TAZ may be explained by differences in protein stability and expression, as YAP protein expression is much higher than that of TAZ. We also identified some differences in the transcriptional profiles induced by YAP and TAZ, suggesting that, although they are largely similar, there may be important distinctions between YAP and TAZ.

    Cover page: Characterization of Hippo pathway regulation and the physiological implications of its downstream effectors YAP and TAZ
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2015)
    The Hippo signaling pathway is important for controlling organ size and tissue homeostasis. Originally identified in Drosophila melanogaster, the core components of the Hippo pathway are highly conserved in mammals. The Hippo pathway can be modulated by a wide range of stimuli, including G protein-coupled receptor (GPCR) signaling, changes in the actin cytoskeleton, cell-cell contact, and cell polarity. When activated, the Hippo pathway functions as a tumor suppressor to limit cell growth. However, dysregulation by genetic inactivation of core pathway components or amplification or gene fusion of its downstream effectors results in increased cell proliferation and decreased apoptosis and differentiation. Unsurprisingly, this can lead to tissue overgrowth, tumorigenesis, and many other diseases.
      Cover page: Disease implications of the Hippo/YAP pathway
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2020)
      The Hippo pathway is a master regulator of tissue homeostasis and organ size. NF2 is a well-established tumor suppressor, and loss of NF2 severely compromises Hippo pathway activity. However, the precise mechanism of how NF2 mediates upstream signals to regulate the Hippo pathway is not clear. Here we report that, in mammalian cells, NF2's lipid-binding ability is critical for its function in activating the Hippo pathway in response to osmotic stress. Mechanistically, osmotic stress induces PI(4,5)P2 plasma membrane enrichment by activating the PIP5K family, allowing for NF2 plasma membrane recruitment and subsequent downstream Hippo pathway activation. An NF2 mutant deficient in lipid binding is unable to activate the Hippo pathway in response to osmotic stress, as measured by LATS and YAP phosphorylation. Our findings identify the PIP5K family as novel regulators upstream of Hippo signaling, and uncover the importance of phosphoinositide dynamics, specifically PI(4,5)P2, in Hippo pathway regulation.
        Cover page: Critical roles of phosphoinositides and NF2 in Hippo pathway regulation
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2015)
        © 2015 Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences YAP and TAZ are transcriptional co-activators and function as the major effectors of the Hippo tumor suppressor pathway, which controls cell growth, tissue homeostasis, and organ size. Here we show that YAP/TAZ play an essential role in amino acid-induced mTORC1 activation, particularly under nutrient-limiting conditions. Mechanistically, YAP/TAZ act via the TEAD transcription factors to induce expression of the high-affinity leucine transporter LAT1, which is a heterodimeric complex of SLC7A5 and SLC3A2. Deletion of YAP/TAZ abolishes expression of LAT1 and reduces leucine uptake. Re-expression of SLC7A5 in YAP/TAZ knockout cells restores leucine uptake and mTORC1 activation. Moreover, SLC7A5 knockout cells phenocopies YAP/TAZ knockout cells which exhibit defective mTORC1 activation in response to amino acids. We further demonstrate that YAP/TAZ act through SLC7A5 to provide cells with a competitive growth advantage. Our study provides molecular insight into the mechanism of YAP/TAZ target genes in cell growth regulation.Cell Research advance online publication 27 November 2015; doi:10.1038/cr.2015.140.
          Cover page: The Hippo pathway effectors YAP and TAZ promote cell growth by modulating amino acid signaling to mTORC1
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2016)
          The Hippo pathway is important for regulating tissue homeostasis, and its dysregulation has been implicated in human cancer. However, it is not well understood how the Hippo pathway becomes dysregulated because few mutations in core Hippo pathway components have been identified. Therefore, much work in the Hippo field has focused on identifying upstream regulators, and a complex Hippo interactome has been identified. Nevertheless, it is not always clear which components are the most physiologically relevant in regulating YAP/TAZ. To provide an overview of important Hippo pathway components, we created knockout cell lines for many of these components and compared their relative contributions to YAP/TAZ regulation in response to a wide range of physiological signals. By this approach, we provide an overview of the functional importance of many Hippo pathway components and demonstrate NF2 and RHOA as important regulators of YAP/TAZ and TAOK1/3 as direct kinases for LATS1/2.
            Cover page: Characterization of Hippo Pathway Components by Gene Inactivation
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2015)
              Cover page: Opposing roles of conventional and novel PKC isoforms in Hippo-YAP pathway regulation
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2015)
              The mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) integrates environmental and intracellular signals to regulate cell growth. Amino acids stimulate mTORC1 activation at the lysosome in a manner thought to be dependent on the Rag small guanosine triphosphatases (GTPases), the Ragulator complex, and the vacuolar H(+)-adenosine triphosphatase (v-ATPase). We report that leucine and glutamine stimulate mTORC1 by Rag GTPase-dependent and -independent mechanisms, respectively. Glutamine promoted mTORC1 translocation to the lysosome in RagA and RagB knockout cells and required the v-ATPase but not the Ragulator. Furthermore, we identified the adenosine diphosphate ribosylation factor-1 GTPase to be required for mTORC1 activation and lysosomal localization by glutamine. Our results uncover a signaling cascade to mTORC1 activation independent of the Rag GTPases and suggest that mTORC1 is differentially regulated by specific amino acids.
                Cover page: Differential regulation of mTORC1 by leucine and glutamine
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2017)
                The Hippo pathway controls organ size and tissue homeostasis, with deregulation leading to cancer. The core Hippo components in mammals are composed of the upstream serine/threonine kinases Mst1/2, MAPK4Ks and Lats1/2. Inactivation of these upstream kinases leads to dephosphorylation, stabilization, nuclear translocation and thus activation of the major functional transducers of the Hippo pathway, YAP and its paralogue TAZ. YAP/TAZ are transcription co-activators that regulate gene expression primarily through interaction with the TEA domain DNA-binding family of transcription factors (TEAD). The current paradigm for regulation of this pathway centres on phosphorylation-dependent nucleocytoplasmic shuttling of YAP/TAZ through a complex network of upstream components. However, unlike other transcription factors, such as SMAD, NF-κB, NFAT and STAT, the regulation of TEAD nucleocytoplasmic shuttling has been largely overlooked. In the present study, we show that environmental stress promotes TEAD cytoplasmic translocation via p38 MAPK in a Hippo-independent manner. Importantly, stress-induced TEAD inhibition predominates YAP-activating signals and selectively suppresses YAP-driven cancer cell growth. Our data reveal a mechanism governing TEAD nucleocytoplasmic shuttling and show that TEAD localization is a critical determinant of Hippo signalling output.
                  Cover page: Regulation of Hippo pathway transcription factor TEAD by p38 MAPK-induced cytoplasmic translocation
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2015)
                  YAP (Yes-associated protein) and TAZ (transcriptional coactivator with PDZ-binding motif) are major downstream effectors of the Hippo pathway that influences tissue homeostasis, organ size, and cancer development. Aberrant hyperactivation of YAP/TAZ causes tissue overgrowth and tumorigenesis, whereas their inactivation impairs tissue development and regeneration. Dynamic and precise control of YAP/TAZ activity is thus important to ensure proper physiological regulation and homeostasis of the cells. Here, we show that YAP/TAZ activation results in activation of their negative regulators, LATS1/2 (large tumor suppressor 1/2) kinases, to constitute a negative feedback loop of the Hippo pathway in both cultured cells and mouse tissues. YAP/TAZ in complex with the transcription factor TEAD (TEA domain family member) directly induce LATS2 expression. Furthermore, YAP/TAZ also stimulate the kinase activity of LATS1/2 through inducing NF2 (neurofibromin 2). This feedback regulation is responsible for the transient activation of YAP upon lysophosphatidic acid (LPA) stimulation and the inhibition of YAP-induced cell migration. Thus, this LATS-mediated feedback loop provides an efficient mechanism to establish the robustness and homeostasis of YAP/TAZ regulation.
                    Cover page: A YAP/TAZ-induced feedback mechanism regulates Hippo pathway homeostasis
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2017)
                    YAP is the major downstream effector of the Hippo pathway, which controls cell growth, tissue homeostasis, and organ size. Aberrant YAP activation, resulting from dysregulation of the Hippo pathway, is frequently observed in human cancers. YAP is a transcription co-activator, and the key mechanism of YAP regulation is its nuclear and cytoplasmic translocation. The Hippo pathway component, LATS, inhibits YAP by phosphorylating YAP at Ser127, leading to 14-3-3 binding and cytoplasmic retention of YAP Here, we report that osmotic stress stimulates transient YAP nuclear localization and increases YAP activity even when YAP Ser127 is phosphorylated. Osmotic stress acts via the NLK kinase to induce YAP Ser128 phosphorylation. Phosphorylation of YAP at Ser128 interferes with its ability to bind to 14-3-3, resulting in YAP nuclear accumulation and induction of downstream target gene expression. This osmotic stress-induced YAP activation enhances cellular stress adaptation. Our findings reveal a critical role for NLK-mediated Ser128 phosphorylation in YAP regulation and a crosstalk between osmotic stress and the Hippo pathway.
                      Cover page: Osmotic stress‐induced phosphorylation by NLK at Ser128 activates YAP
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