The Hippo kinases LATS1 and 2 control human breast cell fate via crosstalk with ERα

The NFIB-ERO1A axis promotes breast cancer metastatic colonization of disseminated tumour cells

Metastasis is the main cause of deaths related to solid cancers. Active transcriptional programmes are known to regulate the metastatic cascade but the molecular determinants of metastatic colonization remain elusive. Using an inducible piggyBac (PB) transposon mutagenesis screen, we have shown that overexpression of the transcription factor nuclear factor IB (NFIB) alone is sufficient to enhance primary mammary tumour growth and lung metastatic colonization. Mechanistically and functionally, NFIB directly increases expression of the oxidoreductase ERO1A, which enhances HIF1α-VEGFA-mediated angiogenesis and colonization, the last and fatal step of the metastatic cascade. NFIB is thus clinically relevant: it is preferentially expressed in the poor-prognostic group of basal-like breast cancers, and high expression of the NFIB/ERO1A/VEGFA pathway correlates with reduced breast cancer patient survival.

YAP and β-Catenin Cooperate to Drive Oncogenesis in Basal Breast Cancer

Targeting cancer stem cells (CSC) can serve as an effective approach toward limiting resistance to therapies. While basal-like (triple-negative) breast cancers encompass cells with CSC features, rational therapies remain poorly established. We show here that the receptor tyrosine kinase Met promotes YAP activity in basal-like breast cancer and find enhanced YAP activity within the CSC population. Interfering with YAP activity delayed basal-like cancer formation, prevented luminal to basal transdifferentiation, and reduced CSC. YAP knockout mammary glands revealed a decrease in β-catenin target genes, suggesting that YAP is required for nuclear β-catenin activity. Mechanistically, nuclear YAP interacted with β-catenin and TEAD4 at gene regulatory elements. Proteomic patient data revealed an upregulation of the YAP signature in basal-like breast cancers. Our findings demonstrate that in basal-like breast cancers, β-catenin activity is dependent on YAP signaling and controls the CSC program. These findings suggest that targeting the YAP/TEAD4/β-catenin complex offers a potential therapeutic strategy for eradicating CSCs in basal-like breast cancers. SIGNIFICANCE: These findings show that YAP cooperates with β-catenin in basal-like breast cancer to regulate CSCs and that targeting this interaction may be a novel CSC therapy for patients with basal-like breast cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/8/2116/F1.large.jpg.

Elevated MST1 leads to apoptosis via depletion of YAP1 in cardiomyocytes exposed to high glucose

BACKGROUND

Gestational diabetes mellitus is a risk factor for congenital heart defects. The article aimed to investigate the expression and roles of MST1, YAP1, Last1/2 and Survivin in modulating HG-induced cardiomyocyte apoptosis and maternal diabetes-induced heart abnormality.

METHODS

Diabetes mellitus was induced in rats using streptozotocin. The protein expression and phosphorylation analysis in fetal heart tissue was assessed by western blot and immunohistochemical staining. Hoechst 33342 staining assay was performed to explore H9C2 apoptosis. The gene and protein expression in H9C2 cells was assessed by quantitative PCR and western blot. Knockdown of gene expression was assessed by RNA interference.

RESULTS

Our results revealed that increased MST1 protein levels in the heart tissues of the offspring of diabetic rats in vivo and in H9C2 cardiomyocytes under HG treatment in vitro, respectively. Knockdown and overexpression experiments showed that MST1 played a key role in mediating HG-induced apoptosis in cardiomyocytes. Downregulation of YAP1 was associated with HG-induced, MST1-mediated cardiomyocyte apoptosis. Further study showed that MST1 downregulated the protein level of YAP1 through mediation of YAP1 phosphorylation on Ser127 and Ser397; this process also required LATS1/2 participation. MST1 overexpression increased the phosphorylation levels of LATS1/2, which were also shown to be increased in the heart tissues of diabetic offspring. We also found that YAP1 mediated the expression of Survivin during HG-induced apoptosis, and the Survivin-inhibitor YM155 partially inhibited the role of YAP1 in suppressing apoptosis induced by HG in cardiomyocytes.

CONCLUSION

These findings reveal a regulatory mechanism of MST1/YAP1/Survivin signaling in modulating cardiomyocyte apoptosis in vitro and maternal diabetes-induced congenital heart defects in vivo.

Cross-compartment signal propagation in the mitotic exit network

In budding yeast, the mitotic exit network (MEN), a GTPase signaling cascade, integrates spatial and temporal cues to promote exit from mitosis. This signal integration requires transmission of a signal generated on the cytoplasmic face of spindle pole bodies (SPBs; yeast equivalent of centrosomes) to the nucleolus, where the MEN effector protein Cdc14 resides. Here, we show that the MEN activating signal at SPBs is relayed to Cdc14 in the nucleolus through the dynamic localization of its terminal kinase complex Dbf2-Mob1. Cdc15, the protein kinase that activates Dbf2-Mob1 at SPBs, also regulates its nuclear access. Once in the nucleus, priming phosphorylation of Cfi1/Net1, the nucleolar anchor of Cdc14, by the Polo-like kinase Cdc5 targets Dbf2-Mob1 to the nucleolus. Nucleolar Dbf2-Mob1 then phosphorylates Cfi1/Net1 and Cdc14, activating Cdc14. The kinase-primed transmission of the MEN signal from the cytoplasm to the nucleolus exemplifies how signaling cascades can bridge distant inputs and responses.

Activation of the tumor suppressive Hippo pathway by triptonide as a new strategy to potently inhibit aggressive melanoma cell metastasis

Metastatic melanoma has a very high mortality rate despite the availability of chemotherapy, radiotherapy, and immunotherapy; therefore, more effective therapeutics are needed. The Hippo pathway plays an inhibitory role in melanoma progression, but the tumor suppressors Salvador homolog-1 (SAV1) and large tumor suppressor 1 (LATS1) in this pathway are down-regulated in melanoma. As a result, the downstream oncogenic Yes-associated protein (YAP) is active, resulting in uncontrolled melanoma growth and metastasis. Therapeutics for remedying SAV1 and LATS1 deficiency in melanoma have not yet been reported in the literature. Here, we show that the small molecule triptonide (MW 358 Da) robustly suppressed melanoma cell tumorigenicity, migration, and invasion. Furthermore, triptonide markedly reduced tumor growth and melanoma lung metastasis in tumor-bearing mice with low toxicity. Molecular mechanistic studies revealed that triptonide promoted SAV1 and LATS1 expression, strongly activated the tumor-suppressive Hippo pathway, degraded oncogenic YAP via the lysosomal pathway, and reduced levels of tumorigenic microphthalmia-associated transcription factor (MITF) in melanoma cells. Triptonide also strongly inhibited activation of AKT, a SAV1-binding signaling protein. Collectively, our results conceptually demonstrate that induction of SAV1 and LATS1 expression and activation of the tumor-suppressive Hippo pathway by triptonide potently inhibits aggressive melanoma cell growth and metastasis. These findings suggest a new strategy for developing therapeutics to treat metastatic melanoma and highlight a novel drug candidate against aggressive melanoma.

Association of germline variation with the survival of women with BRCA1/2 pathogenic variants and breast cancer

Germline genetic variation has been suggested to influence the survival of breast cancer patients independently of tumor pathology. We have studied survival associations of genetic variants in two etiologically unique groups of breast cancer patients, the carriers of germline pathogenic variants in BRCA1 or BRCA2 genes. We found that rs57025206 was significantly associated with the overall survival, predicting higher mortality of BRCA1 carrier patients with estrogen receptor-negative breast cancer, with a hazard ratio 4.37 (95% confidence interval 3.03-6.30, P = 3.1 × 10-9). Multivariable analysis adjusted for tumor characteristics suggested that rs57025206 was an independent survival marker. In addition, our exploratory analyses suggest that the associations between genetic variants and breast cancer patient survival may depend on tumor biological subgroup and clinical patient characteristics.

New insights into the core Hippo signaling and biological macromolecules interactions in the biology of solid tumors

As an evolutionarily conserved pathway, Hippo signaling pathway impacts different pathology and physiology processes such as wound healing, tissue repair/size and regeneration. When some components of Hippo signaling dysregulated, it affects cancer cells proliferation. Moreover, the relation Hippo pathway with other signaling including Wnt, TGFβ, Notch, and EGFR signaling leaves effect on the proliferation of cancer cells. Utilizing a number of therapeutic approaches, such as siRNAs and long noncoding RNA (lncRNA) to prevent cancer cells through the targeting of Hippo pathways, can provide new insights into cancer target therapy. The purpose of present review, first of all, is to demonstrate the importance of Hippo signaling and its relation with other signaling pathways in cancer. It also tries to demonstrate targeting Hippo signaling progress in cancer therapy.

Cryptotanshinone attenuates the stemness of non-small cell lung cancer cells via promoting TAZ translocation from nuclear to cytoplasm

Background

Cancer stem cells (CSCs) are regarded as the root of tumor progression, thus representing an anti-cancer therapy through targeting this cell sub-population.

Methods

Non-small cell lung cancer (NSCLC) CSCs were enriched by non-adherent spheroid formation analysis. Lentivirus infection was used to stably change gene expression. Cell cycle, EdU incorporation, cell apoptosis, cell viability, ALDH1 activity, spheroid formation and in vivo tumor initiation assays were performed to detect the effects of Cryptotanshinone (CT), a traditional Chinese herb medicine, on the stemness of NSCLC cells. RNA-sequencing combined qRT-PCR and western blot analysis were constructed to explore the underlying mechanism contributing to CT-mediated effects.

Results

CT could attenuate the stemness of NSCLC CSCs, as evident by the reduced spheroid formation ability, stemness marker expression and ALDH1 activity. Additionally, CT provoked NSCLC CSCs entry into the cell cycle. RNA-sequencing analysis showed that Hippo signaling pathway was highly enriched in NSCLC CSCs with CT treatment. Further experiments disclosed that CT decreased TAZ (a regulatory master of Hippo pathway) expression via promoting its nuclear-cytoplasm translocation in NSCLC CSCs. Also, overexpression of TAZ partially saved the attenuation of CT on the stemness of NSCLC CSCs. Notably, CT enhanced the sensitivity of tyrosine kinase inhibitor (TKI) and chemotherapy in NSCLC CSCs.

Conclusions

This work reveals that CT attenuates NSCLC CSC stemness, implying the possibility of CT as an adjuvant therapy for NSCLC.

Regulation and functions of the Hippo pathway in stemness and differentiation

The Hippo pathway plays important roles in organ development, tissue regeneration, and human diseases, such as cancer. In the canonical Hippo pathway, the MST1/2-LATS1/2 kinase cascade phosphorylates and inhibits transcription coactivators Yes-associated protein and transcription coactivator with PDZ-binding motif and thus regulates transcription of genes important for cell proliferation and apoptosis. However, recent studies have depicted a much more complicate picture of the Hippo pathway with many new components and regulatory stimuli involving both chemical and mechanical signals. Furthermore, accumulating evidence indicates that the Hippo pathway also plays important roles in the determination of cell fates, such as self-renewal and differentiation. Here, we review regulations of the Hippo pathway and its functions in stemness and differentiation emphasizing recent discoveries.

The Role of the Hippo Pathway in Breast Cancer Carcinogenesis, Prognosis, and Treatment: A Systematic Review

Background

The Hippo pathway is a developmental pathway recently discovered in Drosophila melanogaster; in mammals it normally controls organ development and wound healing. Hippo signaling is deregulated in breast cancer (BC). MST1/2 and LATS1/2 kinases are the upstream molecular elements of Hippo signaling which phosphorylate and regulate the two effectors of Hippo signaling, YAP1 and TAZ cotranscriptional activators. The two molecular effectors of the Hippo pathway facilitate their activity through TEAD transcription factors. Several molecular pathways with known oncogenic functions cross-talk with the Hippo pathway.

Methods

A systematic review studying the correlation of the Hippo pathway with BC tumorigenesis, prognosis, and treatment was performed.

Results

Recent literature highlights the critical role of Hippo signaling in a wide spectrum of biological mechanisms in BC.

Discussion

The Hippo pathway has a crucial position in BC molecular biology, cellular behavior, and response to treatment. Targeting the Hippo pathway could potentially improve the prognosis and outcome of BC patients.

Targeted Disruption of Lats1 and Lats2 in Mice Impairs Adrenal Cortex Development and Alters Adrenocortical Cell Fate

It has recently been shown that the loss of the Hippo signaling effectors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in adrenocortical steroidogenic cells impairs the postnatal maintenance of the adrenal gland. To further explore the role of Hippo signaling in mouse adrenocortical cells, we conditionally deleted the key Hippo kinases large tumor suppressor homolog kinases 1 and -2 (Lats1 and Lats2, two kinases that antagonize YAP and TAZ transcriptional co-regulatory activity) in steroidogenic cells using an Nr5a1-cre strain (Lats1flox/flox;Lats2flox/flox;Nr5a1-cre). We report here that developing adrenocortical cells adopt characteristics of myofibroblasts in both male and female Lats1flox/flox;Lats2flox/flox;Nr5a1-cre mice, resulting in a loss of steroidogenic gene expression, adrenal failure and death by 2 to 3 weeks of age. A marked accumulation of YAP and TAZ in the nuclei of the myofibroblast-like cell population with an accompanying increase in the expression of their transcriptional target genes in the adrenal glands of Lats1flox/flox;Lats2flox/flox;Nr5a1-cre animals suggested that the myofibroblastic differentiation could be attributed in part to YAP and TAZ. Taken together, our results suggest that Hippo signaling is required to maintain proper adrenocortical cell differentiation and suppresses their differentiation into myofibroblast-like cells.

ARID1A determines luminal identity and therapeutic response in estrogen-receptor-positive breast cancer

Mutations in ARID1A, a subunit of the SWI/SNF chromatin remodeling complex, are the most common alterations of the SWI/SNF complex in estrogen-receptor-positive (ER⁺) breast cancer. We identify that ARID1A inactivating mutations are present at a high frequency in advanced endocrine-resistant ER⁺ breast cancer. An epigenome CRISPR-CAS9 knockout (KO) screen identifies ARID1A as the top candidate whose loss determines resistance to the ER degrader fulvestrant. ARID1A inactivation in cells and in patients leads to resistance to ER degraders by facilitating a switch from ER-dependent luminal cells to ER-independent basal-like cells. Cellular plasticity is mediated by loss of ARID1A-dependent SWI/SNF complex targeting to genomic sites of the luminal lineage-determining transcription factors including ER, forkhead box protein A1 (FOXA1) and GATA-binding factor 3 (GATA3). ARID1A also regulates genome-wide ER-FOXA1 chromatin interactions and ER-dependent transcription. Altogether, we uncover a critical role for ARID1A in maintaining luminal cell identity and endocrine therapeutic response in ER⁺ breast cancer.

SH3BGRL2 inhibits growth and metastasis in clear cell renal cell carcinoma via activating hippo/TEAD1-Twist1 pathway

Background

Clear cell renal cell carcinoma (ccRCC) is one of the most prevalent malignancies in the world, and tumor metastasis is still the main reason for disease progression. Accumulating evidence shows that SH3BGRL2 may play a key role in tumor progression and metastasis. However, the role of SH3BGRL2 in ccRCC has not been systematically investigated and remains elusive.

Methods

The clinical significance of SH3BGRL2 was evaluated by bioinformatic analysis and tissue microarray (TMA) samples. SH3BGRL2 expression was determined by RT-PCR, western blot and immunohistochemistry staining. Tumor suppressive effect of SH3BGRL2 was determined by both in vitro and in vivo studies. Western blot, chromatin immunoprecipitation assay and luciferase report assay were applied for mechanism dissection.

Findings

SH3BGRL2 was crucial for epithelial-mesenchymal transition (EMT) progression and metastasis in ccRCC. Clinically, SH3BGRL2 was identified as an independent prognostic factor for ccRCC patients. Gain- and loss-of-function results suggested that SH3BGRL2 played a critical role in cell proliferation, migration and invasion. Mechanistically, we found that SH3BGRL2 acted as a tumor suppressor through Hippo/TEAD1 signaling, then TEAD1 altered Twist1 expression at the transcriptional level via directly binding to its promoter region.

Interpretation

Our findings established that SH3BGRL2 performed as a tumor suppressor and modulator via Hippo/TEAD1-Twist1 signaling in ccRCC, and the alteration of SH3BGRL2 could serve as a functional response biomarker of tumor progression and metastasis in ccRCC.

Impact of aromatase inhibitor treatment on global gene expression and its association with antiproliferative response in ER+ breast cancer in postmenopausal patients

Background

Endocrine therapy reduces breast cancer mortality by 40%, but resistance remains a major clinical problem. In this study, we sought to investigate the impact of aromatase inhibitor (AI) therapy on gene expression and identify gene modules representing key biological pathways that relate to early AI therapy resistance.

Methods

Global gene expression was measured on pairs of core-cut biopsies taken at baseline and at surgery from 254 patients with ER-positive primary breast cancer randomised to receive 2-week presurgical AI (n = 198) or no presurgical treatment (control n = 56) from the POETIC trial. Data from the AI group was adjusted to eliminate artefactual process-related changes identified in the control group. The response was assessed by changes in the proliferation marker, Ki67.

Results

High baseline ESR1 expression associated with better AI response in HER2+ tumours but not HER2− tumours. In HER2− tumours, baseline expression of 48 genes associated with poor antiproliferative response (p < 0.005) including PERP and YWHAQ, the two most significant, and the transcription co-regulators (SAP130, HDAC4, and NCOA7) which were among the top 16 most significant. Baseline gene signature scores measuring cell proliferation, growth factor signalling (ERBB2-GS, RET/GDNF-GS, and IGF-1-GS), and immune activity (STAT1-GS) were significantly higher in poor AI responders. Two weeks of AI caused downregulation of genes involved in cell proliferation and ER signalling, as expected. Signature scores of E2F activation and TP53 dysfunction after 2-week AI were associated with poor AI response in both HER2− and HER2+ patients.

Conclusions

There is a high degree of heterogeneity in adaptive mechanisms after as little as 2-week AI therapy; however, all appear to converge on cell cycle regulation. Our data support the evaluation of whether an E2F signatures after short-term exposure to AI may identify those patients most likely to benefit from the early addition of CDK4/6 inhibitors.

Trial registration

ISRCTN, ISRCTN63882543, registered on 18 December 2007.

LATS1 but not LATS2 represses autophagy by a kinase-independent scaffold function

Autophagy perturbation represents an emerging therapeutic strategy in cancer. Although LATS1 and LATS2 kinases, core components of the mammalian Hippo pathway, have been shown to exert tumor suppressive activities, here we report a pro-survival role of LATS1 but not LATS2 in hepatocellular carcinoma (HCC) cells. Specifically, LATS1 restricts lethal autophagy in HCC cells induced by sorafenib, the standard of care for advanced HCC patients. Notably, autophagy regulation by LATS1 is independent of its kinase activity. Instead, LATS1 stabilizes the autophagy core-machinery component Beclin-1 by promoting K27-linked ubiquitination at lysine residues K32 and K263 on Beclin-1. Consequently, ubiquitination of Beclin-1 negatively regulates autophagy by promoting inactive dimer formation of Beclin-1. Our study highlights a functional diversity between LATS1 and LATS2, and uncovers a scaffolding role of LATS1 in mediating a cross-talk between the Hippo signaling pathway and autophagy.

STK3/4 Expression Is Regulated in Uterine Endometrial Cells during the Estrous Cycle

The uterus is dynamically regulated in response to various signaling triggered by hormones during the estrous cycle. The Hippo signaling pathway is known as an important signaling for regulating cellular processes during development by balancing between cell growth and apoptosis. Serine/threonine protein kinase 3/4 (STK3/4) is a key component of the Hippo signaling network. However, the regulation of STK3/4-Hippo signaling in the uterus is little known. In this study, we investigated the regulation and expression of STK3/4 in the uterine endometrium during the estrous cycle. STK3/4 expression was dynamically regulated in the uterus during the estrous cycle. STK3/4 protein expression was gradually increased from the diestrus stage and reached the highest in the estrus stage. STK3/4 was exclusively localized in the luminal and glandular epithelial cells of the uterus, and phosphorylated STK3/4 was also increased at the estrus stage. Moreover, the increase of STK3/4 expression in uteri was induced by administration of estradiol, but not by progesterone injection in ovariectomized mice. Pretreatment with an estrogen receptor antagonist ICI 182,780 reduced estrogen-induced STK3/4 expression and its phosphorylation. The estrogen-induced STK3/4 expression was related to the increase in phosphorylation of downstream targets including LATS1/2 and YAP. These findings suggest that STK3/4-Hippo signaling acts a novel signaling pathway in the uterine epithelium and STK3/4-Hippo is one of key molecules for connecting between the estrogen downstream signaling pathway and the Hippo signaling pathway leading to regulate dynamic uterine epithelium during the estrous cycle.

Initiation of human mammary cell tumorigenesis by mutant KRAS requires YAP inactivation

High YAP activity is associated with poor prognosis human breast cancers, but its role during the initial stage of mammary cell transformation is unknown. To address this question, we designed experiments that exploit the ability of KRAS^G12D-transduced subsets of freshly isolated normal human mammary cells to form invasive tumors rapidly and efficiently when transplanted into immunodeficient mice. Initial examination of the newly developing tumors thus generated revealed a consistent marked loss of nuclear YAP, independent of the initial primary human mammary cell type transduced. Conversely, co-transduction of the same subsets of primary human mammary cells with KRAS^G12D plus the constitutively active YAP^S127A prevented tumor formation. These findings contrast with the enhanced display of transformed properties obtained when the immortalized, but non-tumorigenic MCF10A cells are transduced just with YAP^S127A. In addition, we show that YAP^S127A-transduction of the human MDA-MB-231 breast cancer cell line (that carry a similar KRAS mutation) enhances their metastatic activity in vivo. We also discover that the KRAS^G12D-induced early loss of YAP in primary human mammary cells is associated with their induced secretion of amphiregulin. Collectively, these findings suggest that YAP can differentially affect the acquisition of malignant properties by human mammary cells at different stages of their transformation.

A CD146 FACS Protocol Enriches for Luminal Keratin 14/19 Double Positive Human Breast Progenitors

Human breast cancer is believed to arise in luminal progenitors within the normal breast. A subset of these are double positive (DP) for basal and luminal keratins and localizes to a putative stem cell zone within ducts. We here present a new protocol based on a combination of CD146 with CD117 and CD326 which provides an up to thirty fold enrichment of the DP cells. We show by expression profiling, colony formation, and morphogenesis that CD146^high/CD117^high/CD326^high DP cells belong to a luminal progenitor compartment. While these DP cells are located quite uniformly in ducts, with age a variant type of DP (vDP) cells, which is mainly CD146-negative, accumulates in lobules. Intriguingly, in specimens with BRCA1 mutations known to predispose for cancer, higher frequencies of lobular vDP cells are observed. We propose that vDP cells are strong candidates for tracing the cellular origin of breast cancer.

Breast Cancer Stem Cells as Drivers of Tumor Chemoresistance, Dormancy and Relapse: New Challenges and Therapeutic Opportunities

Breast cancer is the most frequent cancer among women worldwide. Therapeutic strategies to prevent or treat metastatic disease are still inadequate although great progress has been made in treating early-stage breast cancer. Cancer stem-like cells (CSCs) that are endowed with high plasticity and self-renewal properties have been shown to play a key role in breast cancer development, progression, and metastasis. A subpopulation of CSCs that combines tumor-initiating capacity and a dormant/quiescent/slow cycling status is present throughout the clinical history of breast cancer patients. Dormant/quiescent/slow cycling CSCs are a key component of tumor heterogeneity and they are responsible for chemoresistance, tumor migration, and metastatic dormancy, defined as the ability of CSCs to survive in target organs and generate metastasis up to two decades after diagnosis. Understanding the strategies that are used by CSCs to resist conventional and targeted therapies, to interact with their niche, to escape immune surveillance, and finally to awaken from dormancy is of key importance to prevent and treat metastatic cancer. This review summarizes the current understanding of mechanisms involved in CSCs chemoresistance, dissemination, and metastasis in breast cancer, with a particular focus on dormant cells. Finally, we discuss how advancements in the detection, molecular understanding, and targeting of dormant CSCs will likely open new therapeutic avenues for breast cancer treatment.

Investigating the regulation mechanism of baicalin on triple negative breast cancer's biological network by a systematic biological strategy

OBJECTIVE

To investigate the regulation mechanism of baicalin on triple negative breast cancer (TNBC)'s biological network by a systematic biological strategy and cytology experiment.

METHODS

A systematic biological methodology is utilized to predict the potential targets of baicalin, collect the genes of TNBC, and analyze the TNBC and baicalin's network. After the systematic biological analysis is performed, the cytology experiment, real-time quantitative PCR (qPCR) is used to validate the key biological processes and signaling pathways.

RESULTS

After systematic biological analysis, two networks were constructed and analyzed: (1) TNBC network; (2) Baicalin-TNBC protein-protein interaction (PPI) network. Several TNBC-related, treatment-related targets, clusters, signaling pathways and biological processes were found. Cytology experiment shows that baicalin can inhibit the proliferation, migration and invasion of breast cancer MDA-MB-231 cells in vitro (P < 0.05). The results of qPCR showed that baicalin increase the expression of E-cadherin mRNA, and decrease the expression of vimentin, β-catenin, c-Myc and MMP-7 mRNA in LPS-induced breast cancer MDA-MB-231 cells (P < 0.05).

CONCLUSION

Baicalin may achieve anti-tumor effects through regulating the targets, biological processes and pathways found in this research.

Stem Cells and the Differentiation Hierarchy in Mammary Gland Development

The mammary gland is a highly dynamic organ that undergoes profound changes within its epithelium during puberty and the reproductive cycle. These changes are fueled by dedicated stem and progenitor cells. Both short- and long-lived lineage-restricted progenitors have been identified in adult tissue as well as a small pool of multipotent mammary stem cells (MaSCs), reflecting intrinsic complexity within the epithelial hierarchy. While unipotent progenitor cells predominantly execute day-to-day homeostasis and postnatal morphogenesis during puberty and pregnancy, multipotent MaSCs have been implicated in coordinating alveologenesis and long-term ductal maintenance. Nonetheless, the multipotency of stem cells in the adult remains controversial. The advent of large-scale single-cell molecular profiling has revealed striking changes in the gene expression landscape through ontogeny and the presence of transient intermediate populations. An increasing number of lineage cell-fate determination factors and potential niche regulators have now been mapped along the hierarchy, with many implicated in breast carcinogenesis. The emerging diversity among stem and progenitor populations of the mammary epithelium is likely to underpin the heterogeneity that characterizes breast cancer.

The Emerging Role of YAP/TAZ in Tumor Immunity

Yes-associated protein (YAP)/WW domain-containing transcription regulator 1 (TAZ) is an important transcriptional regulator and effector of the Hippo signaling pathway that has emerged as a critical determinant of malignancy in many human tumors. YAP/TAZ expression regulates the cross-talk between immune cells and tumor cells in the tumor microenvironment through its influence on T cells, myeloid-derived suppressor cells, and macrophages. However, the mechanisms underlying these effects are poorly understood. An improved understanding of the role of YAP/TAZ in tumor immunity is essential for exploring innovative tumor treatments and making further breakthroughs in antitumor immunotherapy. This review primarily focuses on the role of YAP/TAZ in immune cells, their interactions with tumor cells, and how this impacts on tumorigenesis, progression, and therapy resistance.

CRABP2 regulates invasion and metastasis of breast cancer through hippo pathway dependent on ER status

Background

Triple Negative Breast cancer (TNBC) is incurable cancer with higher rates of relapse and shorter overall survival compared with other subtypes of breast cancer. Cellular retinoic acid binding protein 2 (CRABP2) belongs to fatty acid binding protein (FABP) family which binds with all-trans retinoic acid (RA). Previous studies from the database have reported the patients with high expression of CRABP2 showed different prognosis in ER⁺ and ER⁻ breast cancer. However, its biological role and exact mechanism in breast cancer remain unknown. This aim of this study was to explore how CRABP2 regulated invasion and metastasis based on the estrogen receptor-α (herein called ER) status in breast cancer.

Methods

Immunohistochemical staining method was used to analyze the expression of CRABP2 in human breast cancer tissues. Lentivirus vector-based shRNA technique was used to test the functional relevance of CRABP2 knockdown in breast tumors. Tail vein injection model was used to examine the lung metastasis. Co-immunoprecipitation, Western blotting, immunofluorescence, and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were conducted to investigate the underlying mechanism that influenced the ER to the regulation of CRABP2 to Lats1.

Results

We observed that knockdown of CRABP2 promotes EMT, invasion and metastasis of ER⁺ breast cancer cells in vitro and in vivo, whereas overexpression of CRABP2 yields the reverse results. In ER⁺ mammary cancer cells, the interaction of CRABP2 and Lats1 suppress the ubiquitination of Lats1 to activate Hippo pathway to inhibit the invasion and metastasis of ER⁺ mammary cancer. However, in ER⁻ mammary cancer cells, the interaction of CRABP2 and Lats1 promote the ubiquitination of Lats1 to inactivate Hippo pathway to promote the invasion and metastasis of ER⁻ mammary cancer.

Conclusions

Our findings indicate that CRABP2 can suppress invasion and metastasis of ER⁺ breast cancer and promote invasion and metastasis of ER⁻ breast cancer by regulating the stability of Lats1 in vitro and in vivo, and it provides new ideas for breast cancer therapy.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1345-2) contains supplementary material, which is available to authorized users.

NR1B2 suppress kidney renal clear cell carcinoma (KIRC) progression by regulation of LATS 1/2-YAP signaling

BACKGROUND

Kidney Renal Clear Cell Carcinoma (KIRC) accounts for 75% of all renal cancers. Previous study had conflict evidences regarding NR1B2 role in cancer, and its expression and biological role in KIRC remained unclear. Our aims were to characterize the role of NR1B2 in KIRC.

METHODS

NR1B2 expression in TCGA database were analyzed. Clinical KIRC samples were examined by RT-PCR, western blot and tissue microarray (TMA). The relationship between NR1B2 expression and the clinical characteristics were evaluated. KIRC cell line were stably overexpressed NR1B2 or with an NR1B2 knocked down using lentivirus system. The cells were analyzed by migration and invasion assay, then injected into nude mice to assess tumor growth and metastasis. EMT marker expression and LATS 1/2-YAP pathway demonstration were detected by the TCGA database and western blot.

RESULTS

The expression of NR1B2 in KIRC was significantly down-regulated in the TCGA database and our clinical samples. Moreover, NR1B2 expression negatively correlated with tumor stage and positively correlated with overall and disease-free survival rate. Univariate and multivariate analyses indicated the expression level of NR1B2 could be used as an independent factor for predicting the prognosis of KIRC. Overexpression NR1B2 significantly inhibited and knockdown NR1B2 markedly promoted KIRC cell invasion and metastasis both in vitro and in vivo. Mechanistic investigations revealed that NR1B2 might be a tumor suppressor to inhibit EMT through the LATS1/2-YAP pathway.

CONCLUSIONS

our results defined NR1B2 as a tumor suppressor in KIRC that restricted EMT by the LATS1/2-YAP pathway.

Mammary stem cells and progenitors: targeting the roots of breast cancer for prevention

Breast cancer prevention is daunting, yet not an unsurmountable goal. Mammary stem and progenitors have been proposed as the cells-of-origin in breast cancer. Here, we present the concept of limiting these breast cancer precursors as a risk reduction approach in high-risk women. A wealth of information now exists for phenotypic and functional characterization of mammary stem and progenitor cells in mouse and human. Recent work has also revealed the hormonal regulation of stem/progenitor dynamics as well as intrinsic lineage distinctions between mammary epithelial populations. Leveraging these insights, molecular marker-guided chemoprevention is an achievable reality.

Transcriptional regulation of normal human mammary cell heterogeneity and its perturbation in breast cancer

The mammary gland in adult women consists of biologically distinct cell types that differ in their surface phenotypes. Isolation and molecular characterization of these subpopulations of mammary cells have provided extensive insights into their different transcriptional programs and regulation. This information is now serving as a baseline for interpreting the heterogeneous features of human breast cancers. Examination of breast cancer mutational profiles further indicates that most have undergone a complex evolutionary process even before being detected. The consequent intra-tumoral as well as inter-tumoral heterogeneity of these cancers thus poses major challenges to deriving information from early and hence likely pervasive changes in potential therapeutic interest. Recently described reproducible and efficient methods for generating human breast cancers de novo in immunodeficient mice transplanted with genetically altered primary cells now offer a promising alternative to investigate initial stages of human breast cancer development. In this review, we summarize current knowledge about key transcriptional regulatory processes operative in these partially characterized subpopulations of normal human mammary cells and effects of disrupting these processes in experimentally produced human breast cancers.

A Non-canonical Role of YAP/TEAD Is Required for Activation of Estrogen-Regulated Enhancers in Breast Cancer

YAP/TEAD are nuclear effectors of the Hippo pathway, regulating organ size and tumorigenesis largely through promoter-associated function. However, their function as enhancer regulators remains poorly understood. Through an in vivo proximity-dependent labeling (BioID) technique, we identified YAP1 and TEAD4 protein as co-regulators of ERα on enhancers. The binding of YAP1/TEAD4 to ERα-bound enhancers is augmented upon E₂ stimulation and is required for the induction of E₂/ERα target genes and E₂-induced oncogenic cell growth. Furthermore, their enhancer binding is a prerequisite for enhancer activation marked by eRNA transcription and for the recruitment of the enhancer activation machinery component MED1. The binding of TEAD4 on active ERE-containing enhancers is independent of its DNA-binding behavior, and instead, occurs through protein-tethering trans-binding. Our data reveal a non-canonical function of YAP1 and TEAD4 as ERα cofactors in regulating cancer growth, highlighting the potential of YAP/TEAD as possible actionable drug targets for ERα⁺ breast cancer.

Akt plays indispensable roles during the first cell lineage differentiation of mouse

The first cell lineage differentiation occurs during the development of mouse 8-cell embryo to blastocyst. Akt is a potent kinase whose role during blastocyst formation has not been elucidated. In the present study, immunofluorescence results showed that the Akt protein was specifically localized to the outer cells of the morula. Akt-specific inhibitor MK2206 significantly inhibited mouse blastocyst formation and resulted in decreased expression of the trophectoderm marker Cdx2 and led to granular distribution of ERα in the cytoplasm. Furthermore, knockdown of ERα by siRNA microinjection can also lead to a decrease in the development rate of mouse blastocysts, accompanied by a decrease in the expression level of Yap protein. We conclude that Akt may be indispensable for the first cell lineage differentiation of mouse.

Glucocorticoids promote breast cancer metastasis

Diversity within or between tumours and metastases (known as intra-patient tumour heterogeneity) that develops during disease progression is a serious hurdle for therapy^1-3. Metastasis is the fatal hallmark of cancer and the mechanisms of colonization, the most complex step in the metastatic cascade⁴, remain poorly defined. A clearer understanding of the cellular and molecular processes that underlie both intra-patient tumour heterogeneity and metastasis is crucial for the success of personalized cancer therapy. Here, using transcriptional profiling of tumours and matched metastases in patient-derived xenograft models in mice, we show cancer-site-specific phenotypes and increased glucocorticoid receptor activity in distant metastases. The glucocorticoid receptor mediates the effects of stress hormones, and of synthetic derivatives of these hormones that are used widely in the clinic as anti-inflammatory and immunosuppressive agents. We show that the increase in stress hormones during breast cancer progression results in the activation of the glucocorticoid receptor at distant metastatic sites, increased colonization and reduced survival. Our transcriptomics, proteomics and phospho-proteomics studies implicate the glucocorticoid receptor in the activation of multiple processes in metastasis and in the increased expression of kinase ROR1, both of which correlate with reduced survival. The ablation of ROR1 reduced metastatic outgrowth and prolonged survival in preclinical models. Our results indicate that the activation of the glucocorticoid receptor increases heterogeneity and metastasis, which suggests that caution is needed when using glucocorticoids to treat patients with breast cancer who have developed cancer-related complications.

POPX2 is a novel LATS phosphatase that regulates the Hippo pathway

The Hippo pathway regulates cell proliferation, survival, apoptosis and differentiation. During carcinogenesis, members of the Hippo pathway are mutated to avoid anoikis and promote anchorage independent growth. Although many regulators of the Hippo pathway have been reported, negative regulators of the hippo kinases are not well studied. Through an interactome screen, we found that POPX2 phosphatase interacts with several of the Hippo pathway core kinases, including LATS1 which is the direct kinase regulating the transcription co-activators, YAP and TAZ. Phosphorylated YAP/TAZ are retained in the cytoplasm and prevented from translocation into the nucleus to activate transcription of target genes. We found that POPX2 could dephosphorylate LATS1 on Threonine-1079, leading to inactivation of LATS1 kinase. As a result, YAP/TAZ are not phosphorylated and are able to translocate into the nucleus to activate target genes involved in cell proliferation. Furthermore, POPX2 knock-out using CRISPR in the highly metastatic MDA-MB-231 breast cancer cells results in decreased cell proliferation and impairment of anchorage independent growth. We propose that POPX2 act as a suppressor of the Hippo pathway through LATS1 dephosphorylation and inactivation.

A miRNA-HERC4 pathway promotes breast tumorigenesis by inactivating tumor suppressor LATS1

The E3 ligase HERC4 is overexpressed in human breast cancer and its expression levels correlated with the prognosis of breast cancer patients. However, the roles of HERC4 in mammary tumorigenesis remain unclear. Here we demonstrate that the knockdown of HERC4 in human breast cancer cells dramatically suppressed their proliferation, survival, migration, and tumor growth in vivo, while the overexpression of HERC4 promoted their aggressive tumorigenic activities. HERC4 is a new E3 ligase for the tumor suppressor LATS1 and destabilizes LATS1 by promoting the ubiquitination of LATS1. miRNA-136-5p and miRNA-1285-5p, expression of which is decreased in human breast cancers and is inversely correlated with the prognosis of breast cancer patients, are directly involved in suppressing the expression of HERC4. In summary, we discover a miRNA-HERC4-LATS1 pathway that plays important roles in the pathogenesis of breast cancer and represents new therapeutic targets for human breast cancer.

Hypermethylated LATS2 gene with decreased expression in female breast cancer: A case control study from North India

BACKGROUND

LATS2, a presumed tumor suppressor gene located on chromosome 13q11-12 is involved in cell growth related activity like regulation of cell cycle at G1/S. The reduced expression of LATS2 has been reported in many tumors; including tumors of Breast, which is to the best of our knowledge has not been studied in north Indian female breast cancer population.

OBJECTIVE

Here, we looked upon the expression pattern and methylation status of the LATS2 gene in north Indian female breast cancer cases to further strengthen its role as a tumor suppressor gene and more importantly as a cancer biomarker.

METHODS

mRNA expression level was determined by real time PCR in 140 Breast cancer patients, Protein expression was studied by Immunohistochemistry and Promoter methylation was studied by Methylation specific PCR. All findings were correlated with clinicopathological features.

RESULTS

LATS2 mRNA expression was remarkably downregulated in 67.85% (95/140) cases. The expression of Large Associated Tumor Suppressor 2 at protein level was also absent in 67.85% (95/140) cases. The absence of LATS2 protein strongly correlated with promoter hypermethylation where 91 out of a total of 107 hyper methylated cases showed absence of protein (91/107, 85%). The absence of LATS2 protein was strongly significant with HER2 neu status (0.01), TNM staging (0.009) and Molecular subtype (0.024).

CONCLUSION

The decreased expression in breast cancer seems to be associated with hypermethylation of LATS2 promoter regions. Further LATS2 as a tumor suppressor can be recognized as a promising Biomarker in Breast cancer pathogenesis. Though, further studies, targeting larger sets of breast cancer population are required to establish LATS2 as a promising biomarker.

Targeting the Hippo Pathway for Breast Cancer Therapy

Breast cancer (BC) is one of the most prominent diseases in the world, and the treatments for BC have many limitations, such as resistance and a lack of reliable biomarkers. Currently the Hippo pathway is emerging as a tumor suppressor pathway with its four core components that regulate downstream transcriptional targets. In this review, we introduce the present targeted therapies of BC, and then discuss the roles of the Hippo pathway in BC. Finally, we summarize the evidence of the small molecule inhibitors that target the Hippo pathway, and then discuss the possibilities and future direction of the Hippo-targeted drugs for BC therapy.

LATS1 and LATS2 suppress breast cancer progression by maintaining cell identity and metabolic state

In luminal B tumors LATS2 depletion results in metabolic rewiring whereas LATS1 depletion promotes the expression of basal-like features.

Deregulated activity of LArge Tumor Suppressor (LATS) tumor suppressors has broad implications on cellular and tissue homeostasis. We examined the consequences of down-regulation of either LATS1 or LATS2 in breast cancer. Consistent with their proposed tumor suppressive roles, expression of both paralogs was significantly down-regulated in human breast cancer, and loss of either paralog accelerated mammary tumorigenesis in mice. However, each paralog had a distinct impact on breast cancer. Thus, LATS2 depletion in luminal B tumors resulted in metabolic rewiring, with increased glycolysis and reduced peroxisome proliferator-activated receptor γ (PPARγ) signaling. Furthermore, pharmacological activation of PPARγ elicited LATS2-dependent death in luminal B-derived cells. In contrast, LATS1 depletion augmented cancer cell plasticity, skewing luminal B tumors towards increased expression of basal-like features, in association with increased resistance to hormone therapy. Hence, these two closely related paralogs play distinct roles in protection against breast cancer; tumors with reduced expression of either LATS1 or LATS2 may rewire signaling networks differently and thus respond differently to anticancer treatments.

TAOK3 Regulates Canonical TCR Signaling by Preventing Early SHP-1-Mediated Inactivation of LCK

Activation of LCK is required for canonical TCR signaling leading to T cell responses. LCK activation also initiates a negative feedback loop mediated by the phosphatase SHP-1 that turns off TCR signaling. In this article, we report that the thousand-and-one amino acid kinase 3 (TAOK3) is a key regulator of this feedback. TAOK3 is a serine/threonine kinase expressed in many different cell types including T cells. TAOK3-deficient human T cells had impaired LCK-dependent TCR signaling resulting in a defect in IL-2 response to canonical TCR signaling but not to bacterial superantigens, which use an LCK-independent pathway. This impairment was associated with enhanced interaction of LCK with SHP-1 after TCR engagement and rapid termination of TCR signals, a defect corrected by TAOK3 reconstitution. Thus, TAOK3 is a positive regulator of TCR signaling by preventing premature SHP-1-mediated inactivation of LCK. This mechanism may also regulate signaling by other Src family kinase-dependent receptors.

Genetic variation in the Hippo pathway and breast cancer risk in women of African ancestry

Gene expression changes within the Hippo pathway were found to be associated with large tumor size and metastasis in breast cancer. The combined effect of genetic variants in genes of this pathway may have a causal role in breast cancer development. We examined 7086 SNPs that were not highly correlated (r2  < 0.8) in 35 Hippo pathway genes using data from the genome-wide association study of breast cancer from the Root Consortium, which includes 3686 participants of African ancestry from Nigeria, United States of America, and Barbados: 1657 cases (403 estrogen receptor-positive [ER+], 374 ER-) and 2029 controls. Gene-level analyses were conducted using improved AdaJoint test for large-scale genetic association studies adjusting for age, study site and the first four eigenvectors from the principal component analysis. SNP-level analyses were conducted with logistic regression. The Hippo pathway was significantly associated with risk of ER+ breast cancer (pathway-level P = 0.019), with WWC1 (Padj  = 0.04) being the leading gene. The pathway-level significance was lost without WWC1 (P = 0.12). rs147106204 in the WWC1 gene was the most statistically significant SNP after gene-level adjustment for multiple comparisons (OR = 0.53, 95%CI = 0.41-0.70, Padj  = 0.025). We found evidence of an association between genetic variations in the Hippo pathway and ER+ breast cancer. Moreover, WWC1 was identified as the most important genetic susceptibility locus highlighting the importance of genetic epidemiology studies of breast cancer in understudied populations.

A feed forward loop enforces YAP/TAZ signaling during tumorigenesis

In most solid tumors, the Hippo pathway is inactivated through poorly understood mechanisms that result in the activation of the transcriptional regulators, YAP and TAZ. Here, we identify NUAK2 as a YAP/TAZ activator that directly inhibits LATS-mediated phosphorylation of YAP/TAZ and show that NUAK2 induction by YAP/TAZ and AP-1 is required for robust YAP/TAZ signaling. Pharmacological inhibition or loss of NUAK2 reduces the growth of cultured cancer cells and mammary tumors in mice. Moreover, in human patient samples, we show that NUAK2 expression is elevated in aggressive, high-grade bladder cancer and strongly correlates with a YAP/TAZ gene signature. These findings identify a positive feed forward loop in the Hippo pathway that establishes a key role for NUAK2 in enforcing the tumor-promoting activities of YAP/TAZ. Our results thus introduce a new opportunity for cancer therapeutics by delineating NUAK2 as a potential target for re-engaging the Hippo pathway.

The Hippo pathway is frequently dysregulated in cancer. Here, the authors identify NUAK2 as negative regulator of the Hippo pathway from a siRNA kinome screen and show that NUAK2 promotes YAP/TAZ nuclear localisation while NUAK2 is a transcriptional target of YAP/TAZ, thus providing a feed forward loop to promote tumorigenesis.

GPER/Hippo-YAP signal is involved in Bisphenol S induced migration of triple negative breast cancer (TNBC) cells

Nowadays, risk factors of triple-negative breast cancer (TNBC) metastasis are not well identified. Our present study reveals that an industrial chemical, bisphenol S (BPS), can promote the migration, but not the proliferation, of TNBC cells in vitro. BPS activates YAP, a key effector of Hippo pathway, by inhibiting its phosphorylation, which promotes YAP nuclear accumulation and up-regulates its downstream genes such as CTGF and ANKRD1. Inhibition of YAP blocks the BPS-triggered cell migration and up-regulation of fibronectin (FN) and vimentin (Vim). BPS rapidly decreases the phosphorylation levels of LATS1 (Ser909) in TNBC cells, which regulates the activation and functions of YAP. Silencing LATS1/2 by siRNA increases BPS-induced dephosphorylation of YAP and extended the half-life of YAP protein. Inhibition of G protein-coupled estrogen receptor 1 (GPER) and its downstream PLCβ/PKC signals attenuate the effects of BPS-induced YAP dephosphorylation and CTGF up-regulation. Targeted inhibition of GPER/YAP inhibits BPS-induced migration of TNBC cells. Collectively, we reveal that GPER/Hippo-YAP signal is involved in BPS-induced migration of TNBC cells.

Norcantharidin reverses cisplatin resistance and inhibits the epithelial mesenchymal transition of human non‑small lung cancer cells by regulating the YAP pathway

Non-small cell lung cancer (NSCLC) accounts for >80% of all lung cancer cases, which are the leading cause of cancer-related mortality worldwide. The clinical efficacy of available therapies for NSCLC is often limited due to the development of resistance to anticancer drugs, particularly to cisplatin (DDP). Norcantharidin (NCTD) is a traditional Chinese medicine used in the treatment of many types of cancer, to which patients do not develop resistance. The aim of the present study was to examine the potential synergistic effects of NCTD and DPP on the viability of the the DDP-resistant NSCLC cell line, A549/DDP. We further explored the potential underlying mechanisms by examining the expression of the oncogene, Yes-associated protein 1 (YAP), whose activation was recently found to be associated with drug resistance. We further examined a series of human lung cancer cell lines and tissues from patients with lung cancer, which revealed that YAP activation contributed to lung cancer initiation, progression and metastasis, and was associated with a poor prognosis, and confering resistance against targeted therapies. Moreover, YAP expression was evaluated in the A549/DDP cells treated with NCTD, DDP, or both drugs. The combined treatment significantly sensitized the A549/DDP cells to DDP-induced growth inhibition by reducing YAP promoter activity (based on transcriptional expression) and the expression of its target genes, connective tissue growth factor (CTGF) and cysteine rich angiogenic inducer 61 (CYR61). Furthermore, compared to the individual treatments, combined treatment increased cell apoptosis and senescence, and decreased epithelial-to-mesenchymal transition and the cell migratory and invasive ability. On the whole, our data indicate that the application of NCTD with reverses DDP resistance and thus, this combined treatment may have promising prospects for use in improving the outcome of patients with NSCLC.

AICAR Antiproliferative Properties Involve the AMPK-Independent Activation of the Tumor Suppressors LATS 1 and 2

AICAR (Acadesine) is a pharmacological precursor of purine nucleotide biosynthesis with anti-tumoral properties. Although recognized as an AMP mimetic activator of the protein kinase AMPK, the AICAR monophosphate derivative ZMP was also shown to mediate AMPK-independent effects. In order to unveil these AMPK-independent functions, we performed a transcriptomic analysis in AMPKα1/α2 double knockout murine embryonic cells. Kinetic analysis of the cellular response to AICAR revealed the up-regulation of the large tumor suppressor kinases (Lats) 1 and 2 transcripts, followed by the repression of numerous genes downstream of the transcriptional regulators Yap1 and Taz. This transcriptional signature, together with the observation of increased levels in phosphorylation of Lats1 and Yap1 proteins, suggested that the Hippo signaling pathway was activated by AICAR. This effect was observed in both fibroblasts and epithelial cells. Knockdown of Lats1/2 prevented the cytoplasmic delocalization of Yap1/Taz proteins in response to AICAR and conferred a higher resistance to the drug. These results indicate that activation of the most downstream steps of the Hippo cascade participates to the antiproliferative effects of AICAR.

The role of Hippo signal pathway in breast cancer metastasis

The Hippo pathway is a novel and highly conserved mammalian signaling pathway. Mutations and altered expression of core Hippo pathway components promote the migration, invasion, malignancy, and chemotherapy resistance of breast cancer cells. In cancer metastasis, tumor cells must detach from the primary tumor, invade surrounding tissue, and enter and survive in a foreign microenvironment. The metastatic potential of breast cancer is closely related to individual patient genetic profile. Nevertheless, the exact molecular mechanism that regulates the Hippo pathway in breast cancer metastasis is yet to be fully elucidated. This article discusses the function and regulation of the Hippo pathway, with focus given to its role in the context of breast cancer metastasis.

NEDD4 promotes cell growth and motility in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death worldwide. In China, the situation is even worse as cancer incidence and mortality continue to increase rapidly. Although tremendous progress has been made toward HCC treatments, the benefits for liver cancer patients are still limited. Therefore, it is necessary to identify and develop novel therapeutic methods. Neuronally expressed developmentally downregulated 4 (NEDD4), an E3 ubiquitin ligase, plays a critical role in the development and progression of various types of human cancers. In our study, NEDD4 acts as an oncoprotein in both QGY7703 and SMMC7721 liver cancer cell lines. We found that depletion of NEDD4 by siRNA transfection led to inhibition of cell growth, invasion and migration, and promotion of apoptosis. In contrast, overexpression of NEDD4 via plasmid transfection resulted in facilitated cell proliferation, invasion and migration, and decreased apoptosis. Importantly, we observed that tumor suppressor LATS1, also a core component of Hippo pathway, was negatively regulated by NEDD4 in liver cancer cells. Our findings suggested that NEDD4 may be involved in the HCC progression via regulating LATS1 associated signaling pathway. Therefore, targeting NEDD4-LATS1 signaling could be a potential therapeutic option for HCC treatment.

LATS1 inhibits metastasis and epithelial-mesenchymal transition in head and neck squamous cell carcinoma

LATS1 is a serine/threonine kinase of the Hippo signaling pathway that phosphorylates and inactivates transcriptional co-activators YAP1 and WWTR1. To investigate roles of LATS1 expression in head and neck squamous cell carcinomas (HNSCCs), we transfected LATS1-expressing plasmid into B88 cells and examined the phenotypes and their relevant molecules. LATS1 expression was analyzed using immunohistochemistry on tissue microarray, Oncomine, and TCGA databases. LATS1 overexpression was found to suppress growth, migration and invasion, and induce apoptosis, G2 arrest, and mesenchymal to epithelial transition (MET) (P < 0.05). Both increased expression of P21, Bax, and E-cadherin and decreased expression of Cyclin B1, D1, Bcl-2, and MMPs. Twist and N-cadherin were detected in B88 transfectants, in comparison to mock and control by Western blot. Nuclear LATS1 expression was weaker in primary cancers than in normal squamous tissue and dysplasia (P < 0.05) but versa for cytoplasmic counterpart (P < 0.05). Cytoplasmic LATS1 expression was positively correlated with lymph node metastasis (P < 0.05). Survival analysis showed that differentiation degree was an independent factor of long overall and relapse-free survival of HNSCC patients (P < 0.05). According to bioinformatics analysis, we found upregulated LATS1 mRNA expression in HNSCCs (P < 0.05). Cox proportional hazards model indicated that perineural invasion and distant metastasis were independent prognostic factors for overall survival of HNSCC (P < 0.05). These findings suggest nucleocytoplasmic translocation of LATS1 protein and upregulated expression of LATS1 mRNA during tumorigenesis of HNSCC. LATS1 mRNA overexpression may reverse aggressive phenotypes of HNSCC cells, as a gene therapy target.

Epigenetic restriction of Hippo signaling by MORC2 underlies stemness of hepatocellular carcinoma cells

The evolutionarily conserved Hippo signaling pathway is a key regulator of stem cell self-renewal, differentiation, and organ size. While alterations in Hippo signaling are causally linked to uncontrolled cell growth and a broad range of malignancies, genetic mutations in the Hippo pathway are uncommon and it is unclear how the tumor suppressor function of the Hippo pathway is disrupted in human cancers. Here, we report a novel epigenetic mechanism of Hippo inactivation in the context of hepatocellular carcinoma (HCC). We identify a member of the microrchidia (MORC) protein family, MORC2, as an inhibitor of the Hippo pathway by controlling upstream Hippo regulators, neurofibromatosis 2 (NF2) and kidney and brain protein (KIBRA). Mechanistically, MORC2 forms a complex with DNA methyltransferase 3A (DNMT3A) at the promoters of NF2 and KIBRA, leading to their DNA hyper-methylation and transcriptional repression. As a result, NF2 and KIBRA are crucial targets of MORC2 to regulate confluence-induced activation of Hippo signaling and contact inhibition of cell growth under both physiological and pathological conditions. The MORC2-NF2/KIBRA axis is critical for maintaining self-renewal, sorafenib resistance, and oncogenicity of HCC cells in vitro and in nude mice. Furthermore, MORC2 expression is elevated in HCC tissues, associated with stem-like properties of cancer cells, and disease progression in patients. Collectively, MORC2 promotes cancer stemness and tumorigenesis by facilitating DNA methylation-dependent silencing of Hippo signaling and could be a potential molecular target for cancer therapeutics.