Sub-cellular localisation studies may spuriously detect the Yes-associated protein, YAP, in nucleoli leading to potentially invalid conclusions of its function

Utility of YAP1 and NUT immunohistochemistry in the diagnosis of porocarcinoma

BACKGROUND

Porocarcinoma is the malignant counterpart of poroma, a benign tumor derived from the eccrine or apocrine units. In contrast to poroma, porocarcinoma is rare and its diagnosis may be challenging. Recent work has identified YAP1-associated gene fusions in most poromas, and a subset of porocarcinomas. These included YAP1-MAML2 and YAP1-NUTM1, the latter being enriched in porocarcinomas over poromas.

METHODS

We studied YAP1 C-terminus and NUT immunohistochemistry in a cohort of 12 porocarcinomas, 10 poromas, 10 squamous cell carcinomas, and 6 hidradenocarcinomas.

RESULTS

Seven of 12 (58%) porocarcinomas showed loss of YAP1 C-terminus expression, consistent with a YAP1 fusion. Of these seven, five showed NUT positivity, implying the presence of the YAP1-NUTM1 fusion. One of 12 (8%) cases showed NUT positivity, but retention of YAP1 C-terminus expression, consistent with a non-YAP1 NUT-associated fusion. Eight of 10 (80%) poromas showed loss of YAP1 C-terminus expression and negative NUT staining, consistent with non-NUT YAP1 fusions. All squamous cell carcinomas and hidradenocarcinomas retained YAP1 C-terminus expression and were negative for NUT.

CONCLUSION

YAP1 C-terminus and NUT immunohistochemistry may be helpful in the diagnosis of porocarcinoma, with the combination of YAP1 C-terminus loss and NUT positivity being particularly informative.

Novel nucleolar localization of clusterin and its associated functions in human oral cancers: An in vitro and in silico analysis

Clusterin (CLU), a multifunctional chaperonic glycoprotein associated with diverse cellular functions has been shown to act as an oncogene or tumour suppressor gene in different cancers, implying a dual role in tumorigenesis. Here, we investigated the expression of CLU isoforms, their subcellular localization and functional significance in oral cancer cells. Significant downregulation of secretory CLU (sCLU) transcripts was observed in oral cancer cell lines and tumours versus normal cells while the nuclear CLU (nCLU) transcripts were undetectable. We demonstrated for the first time the nucleolar localization of sCLU, its response to different nucleolar stresses and association with cajal bodies post nucleolar stress. Functionally, knockdown of CLU revealed its negative association with ribosome biogenesis implying a possible tumour suppressor like role in oral cancers. Further, loss of sCLU in these cells also resulted in altered nuclear morphology and shrunken tubulin filaments. In addition, the levels of nucleolar Nucleophosmin 1(NPM1) and Fibrillarin, known to regulate nuclear morphology were downregulated indicating a possible role of sCLU in their stabilization. Further, an in silico docking approach to gain insights into the interaction of sCLU with nucleolar proteins NPM1, Fibrillarin, UBF and Nucleolin, revealed the involvement of a conserved region comprising of amino acid residues 140-155 of sCLU β-chain, specifically via the Phe152 residue in hydrophobic interactions with these client nucleolar proteins indicating a possible stabilizing or regulatory role of sCLU. SIGNIFICANCE OF THE STUDY: This is the first study to demonstrate the nucleolar localization of sCLU and its associated functions in oral cancer cells. Downregulation of sCLU in oral cancer tissues and cell lines, and its negative association with ribogenesis suggest its tumour suppressor like role in oral cancers. The possible role of sCLU in stabilization or regulation of different nucleolar proteins thereby impacting their functions is also implicated.

Loss of ARF/INK4A Promotes Liver Progenitor Cell Transformation Toward Tumorigenicity Supporting Their Role in Hepatocarcinogenesis

Liver progenitor cells (LPCs) contribute to liver regeneration during chronic damage and are implicated as cells of origin for liver cancers including hepatocellular carcinoma (HCC). The CDKN2A locus, which encodes the tumor suppressors alternate reading frame protein (ARF) and INK4A, was identified as one of the most frequently altered genes in HCC. This study demonstrates that inactivation of CDKN2A enhances tumorigenic transformation of LPCs. The level of ARF and INK4A expression was determined in a panel of transformed and nontransformed wild-type LPC lines. Moreover, the transforming potential of LPCs with inactivated CDKN2A was shown to be enhanced in LPCs derived from Arf^-/- and CDKN2A^fl/fl mice and in wild-type LPCs following CRISPR-Cas9 suppression of CDKN2A. ARF and INK4A abundance is consistently reduced or ablated following LPC transformation. Arf^-/- and CDKN2A^-/- LPCs displayed hallmarks of transformation such as anchorage-independent and more rapid growth than control LPC lines with unaltered CDKN2A. Transformation was not immediate, suggesting that the loss of CDKN2A alone is insufficient. Further analysis revealed decreased p21 expression as well as reduced epithelial markers and increased mesenchymal markers, indicative of epithelial-to-mesenchymal transition, following inactivation of the CDKN2A gene were required for tumorigenic transformation. Loss of ARF and INK4A enhances the propensity of LPCs to undergo a tumorigenic transformation. As LPCs represent a cancer stem cell candidate, identifying CDKN2A as a driver of LPC transformation highlights ARF and INK4A as viable prognostic markers and therapeutic targets for HCC.

Regulation of YAP/TAZ Activity by Mechanical Cues: An Experimental Overview

YAP/TAZ activity is regulated by a complex network of signals that include the Hippo pathway, cell polarity complexes, and signaling receptors of the RTK, GPCR, and WNT pathways and by a seamlessly expanding number of intracellular cues including energy and mevalonate metabolism. Among these inputs, we here concentrate on mechanical cues embedded in the extracellular matrix (ECM) microenvironment, which are key regulators of YAP/TAZ activity. We review the techniques that have been used to study mechano-regulation of YAP/TAZ, including conceptual and practical considerations on how these experiments should be designed and controlled. Finally, we briefly review the most appropriate techniques to monitor YAP/TAZ activity in these experiments and their significance to study the mechanisms linking YAP/TAZ to mechanical cues.

Multiple Mechanisms Cooperate to Constitutively Exclude the Transcriptional Co-Activator YAP from the Nucleus During Murine Oogenesis

Reproduction depends on the generation of healthy oocytes. Improving therapeutic strategies to prolong or rescue fertility depends on identifying the inter- and intracellular mechanisms that direct oocyte development under physiological conditions. Growth and proliferation of multiple cell types is regulated by the Hippo signaling pathway, whose chief effectors are the transcriptional co-activator YAP and its paralogue WWTR1. To resolve conflicting results concerning the potential role of Hippo in mammalian oocyte development, we systematically investigated the expression and localization of YAP in mouse oocytes. We report that that YAP is expressed in the germ cells beginning as early as Embryonic Day 15.5 and subsequently throughout pre- and postnatal oocyte development. However, YAP is restricted to the cytoplasm at all stages. YAP is phosphorylated at serine-112 in growing and fully grown oocytes, identifying a likely mechanistic basis for its nuclear exclusion, and becomes dephosphorylated at this site during meiotic maturation. Phosphorylation at serine-112 is regulated by a mechanism dependent on cyclic AMP and protein kinase A, which is known to be active in oocytes prior to maturation. Growing oocytes also contain a subpopulation of YAP, likely dephosphorylated, that is able enter the oocyte nucleus, but it is not retained there, implying that oocytes lack the cofactors required to retain YAP in the nucleus. Thus, although YAP is expressed throughout oocyte development, phosphorylation-dependent and -independent mechanisms cooperate to ensure that it does not accumulate in the nucleus. We conclude that nuclear YAP does not play a significant physiological role during oocyte development in mammals.

Splice variant insertions in the C-terminus impairs YAP's transactivation domain

The yes-associated protein (YAP) is a key effector of the mammalian Hippo signaling pathway. YAP has eight known alternately spliced isoforms and these are widely expressed across multiple tissues. Variable effects have been ascribed to different YAP isoforms by inducing their expression in cells, but whether these differences are due to variability in the transcriptional potency of individual YAP isoforms has not been addressed. Indeed a systematic comparison of the transcriptional potencies of YAP isoforms has not been done. To address this, using overexpression and transcriptional reporter analyses we investigated the transcriptional activities of several human YAP isoforms and determined the effects of the splice variant insertions within the transactivation domain on its transcriptional potency. Utilising full-length coding sequence constructs we determined that the number of WW domains and disruption of the leucine zipper motif within YAP’s transactivation domain both contribute to transcriptional activity. Notably, disruption of YAP’s leucine zipper had a greater effect on transcriptional activity than the absence of the second WW domain. Using GAL4-YAP transcriptional activation domain fusion proteins we found that disruption of the leucine zipper significantly decreased YAP’s transcriptional activity in several cell lines. Our data indicates that expression of different YAP isoforms with varying transcriptional potencies may enable fine control of Hippo pathway signaling. Furthermore the specific isoform being utilised should be taken into consideration when interpreting published data or when designing experiments to ascribe YAP’s function.

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Transcriptional activities of yes-associated protein (YAP) isoforms were compared.

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YAP’s WW domains and leucine zipper motif both contribute to transcriptional activity.

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Absence of YAP’s second WW domain weakens transcriptional potency.

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Disruption of YAP’s leucine zipper weakens the transactivation domain (TAD).

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Potency of the TAD from YAP α, β, γ, δ isoforms is cell-context dependent.

Analysis of Hippo and TGFβ signaling in polarizing epithelial cells and mouse embryos

The Hippo signaling pathway is involved in numerous biological events ranging from early development to organogenesis and when disrupted, impacts various human diseases including cancer. The Hippo pathway also interacts with and controls the activity of other signaling pathways such as the TGFβ/Smad pathway, in which Hippo pathway activity influences the subcellular localization of Smad transcription factors. Here, we describe techniques for examining crosstalk between Hippo and TGFβ signaling in polarizing mammary epithelial cells. In addition, we provide detailed methods for analyzing the subcellular localization of the Hippo pathway effectors, Taz and Yap using both in vitro cultured epithelial cells and in vivo in pregastrulation mouse embryos.

A modified choline-deficient, ethionine-supplemented diet reduces morbidity and retains a liver progenitor cell response in mice

The choline-deficient, ethionine-supplemented (CDE) dietary model induces chronic liver damage, and stimulates liver progenitor cell (LPC)-mediated repair. Long-term CDE administration leads to hepatocellular carcinoma in rodents and lineage-tracing studies show that LPCs differentiate into functional hepatocytes in this model. The CDE diet was first modified for mice by our laboratory by separately administering choline-deficient chow and ethionine in the drinking water (CD+E diet). Although this CD+E diet is widely used, concerns with variability in weight loss, morbidity, mortality and LPC response have been raised by researchers who have adopted this model. We propose that these inconsistencies are due to differential consumption of chow and ethionine in the drinking water, and that incorporating ethionine in the choline-deficient chow, and altering the strength, will achieve better outcomes. Therefore, C57Bl/6 mice, 5 and 6 weeks of age, were fed an all-inclusive CDE diet of various strengths (67% to 100%) for 3 weeks. The LPC response was quantitated and cell lines were derived. We found that animal survival, LPC response and liver damage are correlated with CDE diet strength. The 67% and 75% CDE diet administered to mice older than 5 weeks and greater than 18 g provides a consistent and acceptable level of animal welfare and induces a substantial LPC response, permitting their isolation and establishment of cell lines. This study shows that an all-inclusive CDE diet for mice reproducibly induces an LPC response conducive to in vivo studies and isolation, whilst minimizing morbidity and mortality.

Summary: This modified choline-deficient, ethionine-supplemented model induces liver injury in mice and reproducibly minimizes morbidity and mortality, whilst maintaining a liver-progenitor-cell response sufficient for cell-line establishment.