Targeting the Hippo Pathway for Breast Cancer Therapy

CYR61 confers chemoresistance by upregulating survivin expression in triple-negative breast cancer

Cysteine-rich angiogenic inducer 61 (CYR61) is a protein from the CCN family of matricellular proteins that play diverse regulatory roles in the extracellular matrix. CYR61 is involved in cell adhesion, migration, proliferation, differentiation, apoptosis, and senescence. Here, we show that CYR61 induces chemoresistance in triple-negative breast cancer (TNBC). We observed that CYR61 is overexpressed in TNBC patients, and CYR61 expression correlates negatively with the survival of patients who receive chemotherapy. CYR61 knockdown reduced cell migration, sphere formation and the cancer stem cell (CSC) population and increased the chemosensitivity of TNBC cells. Mechanistically, CYR61 activated Wnt/β-catenin signaling and increased survivin expression, which are associated with chemoresistance, the epithelial-mesenchymal transition, and CSC-like phenotypes. Altogether, our study demonstrates a novel function of CYR61 in chemotherapy resistance in breast cancer.

STK3 higher expression association with clinical characteristics in intrinsic subtypes of breast cancer invasive ductal carcinoma patients

PURPOSE

STK3 has a central role in maintaining cell homeostasis, proliferation, growth, and apoptosis. Previously, we investigated the functional link between STK3/MST2, and estrogen receptor in MCF-7 breast cancer cells. To expand the investigation, this study evaluated STK3's higher expression and associated genes in breast cancer intrinsic subtypes using publicly available data.

METHODS

The relationship between clinical pathologic features and STK3 high expression was analyzed using descriptive and multivariate analysis.

RESULTS

Increased STK3 expression in breast cancer was significantly associated with higher pathological cancer stages, and a different expression level was observed in the intrinsic subtypes of breast cancer. Kaplan-Meier analysis showed that breast cancer with high STK3 had a lower survival rate in IDC patients than that with low STK3 expression (p < 0.05). The multivariate analysis unveiled a strong correlation between STK3 expression and the survival rate among IDC patients, demonstrating hazard ratios for lower expression. In the TCGA dataset, the hazard ratio was 0.56 (95% CI 0.34-0.94, p = 0.029) for patients deceased with tumor, and 0.62 (95% CI 0.42-0.92, p = 0.017) for all deceased patients. Additionally, in the METABRIC dataset, the hazard ratio was 0.76 (95% CI 0.64-0.91, p = 0.003) for those deceased with tumor. From GSEA outcomes 7 gene sets were selected based on statistical significance (FDR < 0.25 and p < 0.05). Weighted Sum model (WSM) derived top 5% genes also have higher expression in basal and lower in luminal A in association with STK3.

CONCLUSION

By introducing a novel bioinformatics approach that combines GSEA and WSM, the study successfully identified the top 5% of genes associated with higher expression of STK3.

Neurofibromin 2 modulates Mammalian Ste2-like kinases1/2 and large tumor suppressor gene1 expression in A549 lung cancer cell line

AIM

To explore the impact of up- or down-regulation of Neurofibromin 2 (NF2) on the expression of downstream Hippo pathway genes, large tumor suppressor gene1 (LATS1), and phosphorylation of Mammalian Ste2-like kinases1/2 (MST1/2), in lung cancer cells.

METHODS

A549 lung cancer cells were used. The NF2 was down-regulated by si-RNA interference and upregulated by lentiviral vector mediated overexpression. The LATS1 and MST1/2 expressions were evaluated by real-time PCR and western blot.

RESULTS

Down-regulation of NF2 decreased LATS1 and MST1/2 level (P<0.05). Overexpression of NF2 increased LATS1 (P<0.05) and Mammalian Ste2-like kinases1 (MST1) (P<0.05), suggesting LATS1 and MST1 are modulated by NF2 in a lung cancer cell line.

CONCLUSIONS

NF2 mediates the downstream LATS1 and MST1/2 expressions in a lung cancer cell line.

Identification of a new class of activators of the Hippo pathway with antitumor activity in vitro and in vivo

The Hippo pathway is a key regulator of tissue growth, organ size, and tumorigenesis. Activating the Hippo pathway by gene editing or pharmaceutical intervention has been proven to be a new therapeutic strategy for treatment of the Hippo pathway-dependent cancers. To now, a number of compounds that directly target the downstream effector proteins of Hippo pathway, including YAP and TEADs, have been disclosed, but very few Hippo pathway activators are reported. Here, we discovered a new class of Hippo pathway activator, YL-602, which inhibited CTGF expression in cells irrespective of cell density and the presence of serum. Mechanistically, YL-602 activates the Hippo pathway via MST1/2, which is different from known activators of Hippo pathway. In vitro, YL-602 significantly induced tumor cell apoptosis and inhibited colony formation of tumor cells. In vivo, oral administration of YL-602 substantially suppressed the growth of cancer cells by activation of Hippo pathway. Overall, YL-602 could be a promising lead compound, and deserves further investigation for its mechanism of action and therapeutic applications.

Importance of targeting various cell signaling pathways in solid cancers

Most adult human cancers are solid tumors prevailing in vital organs and lead to mortality all over the globe. Genetic and epigenetic alterations in cancer genes or genes of associated signaling pathways impart the most common characteristic of malignancy, that is, uncontrolled proliferation. Unless the mechanism of action of these cells signaling pathways (involved in cell proliferation, apoptosis, metastasis, and the maintenance of the stemness of cancer stem cells and cancer microenvironment) and their physiologic alteration are extensively studied, it is challenging to understand tumorigenesis as well as develop new treatments and precision medicines. Targeted therapy is one of the most promising strategies for treating various cancers. However, cancer is an evolving disease, and most patients develop resistance to these drugs by acquired mutations or mediation of microenvironmental factors or due to tumor heterogeneity. Researchers are striving to develop novel therapeutic options like combinatorial approaches targeting multiple responsible pathways effectively. Thus, in-depth knowledge of cell signaling and its components remains a critical topic of cancer research. This chapter summarized various extensively studied pathways in solid cancer and how they are targeted for therapeutic strategies.

Does YAP influence cell proliferation and apoptosis in benign epithelial odontogenic lesions?

OBJECTIVE

To analyze the immunohistochemical expression of YAP and its correlation with markers involved in cell proliferation and apoptosis in benign epithelial odontogenic lesions.

STUDY DESIGN

The sample consisted of 95 cases of odontogenic lesions (25 dentigerous cysts, 30 non-syndromic odontogenic keratocysts, 30 conventional ameloblastomas, and 10 unicystic ameloblastomas) and 10 dental follicles used as normal odontogenic tissue. The histological sections were submitted to immunohistochemistry with YAP, cyclin D1, Ki-67, and Bcl-2 antibodies. Immunoexpression was analyzed qualitatively and quantitatively using an adapted method. The collected data were analyzed descriptively and statistically (p ≤ 0.05).

RESULTS

The highest YAP expression was observed in odontogenic keratocysts, followed by unicystic ameloblastomas and conventional ameloblastomas, which exhibited moderate immunoreactivity predominantly in peripheral cells. Furthermore, significant differences in YAP immunoexpression were observed between the groups analyzed, with significant positive correlations between YAP and cyclin D1 in dentigerous cysts and unicystic ameloblastomas and between YAP and Ki-67 in unicystic ameloblastomas (p < 0.05). However, there were no statistically significant correlations between YAP and Bcl-2 immunoexpression in the groups studied.

CONCLUSION

YAP may influence epithelial cell proliferation in odontogenic cysts and tumors, suggesting its possible participation in the progression of the odontogenic lesions studied.

Development of Novel Bioluminescent Biosensors Monitoring the Conformation and Activity of the Merlin Tumour Suppressor

Solid tumours can universally evade contact inhibition of proliferation (CIP), a mechanism halting cell proliferation when cell-cell contact occurs. Merlin, an ERM-like protein, crucially regulates CIP and is frequently deactivated in various cancers, indicating its significance as a tumour suppressor in cancer biology. Despite extensive investigations into Merlin's role in cancer, its lack of intrinsic catalytic activity and frequent conformation changes have made it notoriously challenging to study. To address this challenge, we harnessed innovative luciferase technologies to create and validate a NanoBiT split-luciferase biosensor system in which Merlin is cloned between two split components (LgBiT and SmBiT) of NanoLuc luciferase. This system enables precise quantification of Merlin's conformation and activity both in vitro and within living cells. This biosensor significantly enhances the study of Merlin's molecular functions, serving as a potent tool for exploring its contributions to CIP and tumorigenesis.

Therapeutic trial of fluvastatin in a cell line xenograft model of canine mammary gland cancer

The Hippo signalling pathway is involved in breast cancer and canine mammary tumour (CMT). This study sought to evaluate the efficacy of fluvastatin on the Hippo pathway and its main effectors, YAP and TAZ, in vivo in a murine CMT cell line xenograft model. On treatment day 1, mice were divided into four groups: vehicle, fluvastatin, doxorubicin or a combination therapy. Tumour volumes were monitored with callipers and tissues harvested on day 28th of treatment. Histopathological examination of tumour tissues and major organs was performed as well as tumour evaluation of necrosis, apoptosis, cellular proliferation, expression of YAP, TAZ and the mRNA levels of four of their target genes (CTGF, CYR61, ANKRD1 and RHAMM2). Results showed a statistically significant variation in tumour volumes only for the combination therapy and final tumour weight only for the doxorubicin group compared to control. There was no significant difference in tumour necrosis, expression of CC3, ki-67, YAP and TAZ measured by immunohistochemistry and in the mRNA levels of the target genes. Unexpectedly, lung metastases were found in the control group (9) and not in the fluvastatin treated group (7). In addition, mass spectrometry-based quantification of fluvastatin reveals concentrations comparable to levels reported to exert therapeutic effects. This study shows that fluvastatin tumours concentration reached therapeutic levels without having an effect on the hippo pathway or various tumour parameters. Interestingly, only the control group had lung metastases. This study is the first to explore the repurposing of statins for cancer treatment in veterinary medicine.

Expression pattern, prognostic value and potential microRNA silencing of FZD8 in breast cancer

Breast cancer (BC) is one of the most widespread types of cancer affecting females, and therefore, early diagnosis is critical. BC is a complex heterogeneous disease affected by several key pathways. Among these, WNT proteins and their frizzled receptors (FZD) have been demonstrated to be crucial in regulating a number of cellular and molecular events in BC tumorigenesis. The role of the WNT receptor, FZD8, in BC has received minimal attention; for that reason, the present study examined the prognostic value of its protein expression pattern in a BC cohort. FZD8 cytoplasmic expression pattern analysis revealed that ~38% of the primary samples presented with a high expression profile, whereas ~63% of the samples had a low expression profile. Overall, ~46% of the malignant tissues in the lymph node-positive samples exhibited an increased FZD8 cytoplasmic expression, whereas 54% exhibited low expression levels. An increased expression of FZD8 was associated with several clinicopathological characteristics of the patients, including a low survival rate, tumor vascular invasion, tumor size and grade, and molecular subtypes. Affymetrix microarray triple-negative BC datasets were analyzed and compared with healthy breast tissues in order to predict the potential interfering microRNAs (miRNAs) in the WNT/FZD8 signaling pathway. A total of 29 miRNAs with the potential to interact with the WNT/FZD8 signaling pathway were identified, eight of which exhibited a significant prediction score. The target genes for each predicted miRNA were identified. On the whole, the findings of the present study suggest that FZD8 is a potential prognostic marker for BC, shedding some light onto the silencing mechanisms involved in the complex BC signaling.

YAP/STAT3 inhibited CD8+ T cells activity in the breast cancer immune microenvironment by inducing M2 polarization of tumor-associated macrophages

BACKGROUND

Breast cancer (BC) is the leading cause of cancer-related death among women. One of the hallmarks of cancer is sustained angiogenesis. YAP/STAT3 may promote angiogenesis and driving BC progression. This study aimed to investigate how YAP/STAT3 affects the immune microenvironment in BC and understand the underlying mechanism.

METHODS

To establish a tumor-associated macrophages (TAMs) model, macrophages were cultured in the 4T1 cell culture medium. A BC mouse model was created by injecting 4T1 cells. The expression of YAP, STAT3, p-STAT3, VEGF, VEGFR-2, and PD-L1 was analyzed using immunofluorescence, western blotting, and quantitative real-time PCR. Flow cytometry was used to identify M1 and M2 macrophages, CD4+ T, CD8+ T, and Treg cells. Levels of iNOS, IL-12, IL-10, TGF-β, Arg-1, and CCL-22 were measured using enzyme-linked immunosorbent assay. Co-IP was used to verify whether YAP binds to STAT3. Hematoxylin-eosin staining was used to observe tumor morphology. Cell counting kit-8 was selected to detect T-cell proliferation.

RESULTS

YAP, STAT3, P-STAT3, VEGF, VEGFR-2, and PD-L1 were highly expressed in BC tissues. The M2/M1 macrophages ratio increased in the TAMs group compared with the control group. Inhibiting of YAP and STAT3 decreased the M2/M1 macrophages ratio. YAP was found to bind with STAT3. T-cell proliferation was enhanced after YAP inhibition, and overexpression of STAT3 reversed the regulation of YAP on T-cell proliferation. In animal studies, inhibiting YAP inhibited tumor weight and volume development. After YAP inhibition, inflammatory infiltration, M2/M1 macrophage ratio, and Treg cell ratio declined, while CD8+ and CD4+ T-cell ratio increased.

CONCLUSION

In conclusion, this study suggested inhibition of YAP/STAT3 reversed M2 polarization of TAMs and suppressed CD8+ T-cell activity in the BC immune microenvironment. These findings open up new avenues for the development of innovative therapies in the treatment of BC.

NOTCH3 missense mutations as predictor of long-term response to gemcitabine in a patient with epithelioid hemangioendothelioma

PURPOSE

Epithelioid hemangioendothelioma (EHE) as a very rare malignant vascular tumor belongs to the heterogenous group of soft-tissue sarcomas. Depending on the clinical course of the disease, interdisciplinary treatment concepts are required, including surgery, radiotherapy and systemic cancer therapy. However, due to its uncommonness, standard treatment options are lacking so far, especially in advanced disease with distant metastases.

METHODS AND RESULTS

Here we report on an unusual case of a patient with metastasized EHE showing long-term response to second line treatment with gemcitabine over almost 2 decades. Cancer genome sequencing of the patient's tumor tissue detected a NOTCH3 missense mutation which could provide an explanation for these clinical findings. NOTCH3 is known to be a mediator of resistance towards gemcitabine-based cancer treatment, at least in pancreatic cancer and non-small cell lung cancer.

CONCLUSION

The observation that this missense mutation of NOTCH3 is associated with an increased response to treatment with gemcitabine in EHE can be used prospectively to assess NOTCH3 as potential biomarker for predicting therapy response to gemcitabine.

Postoperative effect of sufentanil preemptive analgesia combined with psychological intervention on breast cancer patients

OBJECTIVES

To explore the postoperative effects of sufentanil preemptive analgesia combined with psychological intervention on breast cancer patients undergoing radical surgery.

METHODS

112 female breast cancer patients aged 18-80 years old who underwent radical surgery by the same surgeon were randomly divided into 4 groups, and there were 28 patients in each group. Patients in group A were given 10 µg sufentanil preemptive analgesia combined with perioperative psychological support therapy (PPST), group B had only 10 µg sufentanil preemptive analgesia, group C had only PPST, and group D were under general anesthesia with conventional intubation. Visual analogue scoring (VAS) was used for analgesic evaluation at 2, 12 and 24 h after surgery and compared among the four groups by ANOVA method.

RESULTS

The awakening time of patients in group A or B was significantly shorter than that in group C or D, and the awakening time in group C was significantly shorter than that in group D. Moreover, patients in group A had the shortest extubation time, while the group D had the longest extubation time. The VAS scores at different time points showed significant difference, and the VAS scores at 12 and 24 h were significantly lower than those at 2 h (P < 0.05). The VAS scores and the changing trend of VAS scores were varied among the four groups (P < 0.05). In addition, we also found that patients in group A had the longest time to use the first pain medication after surgery, while patients in group D had the shortest time. But the adverse reactions among the four groups showed no difference.

CONCLUSIONS

Sufentanil preemptive analgesia combined with psychological intervention can effectively relieve the postoperative pain of breast cancer patients.

An indispensable role of TAZ in anoikis resistance promoted by OTUB1 deubiquitinating enzyme in basal-like triple-negative breast cancer cells

Aggressive cancers, such as triple-negative breast cancer (TNBC), are mostly fatal because of their potential to metastasize to distant organs. Cancer cells acquire various abilities to metastasize, including resistance to anoikis, an apoptotic cell death induced by loss of anchorage to the extracellular matrix. Transcriptional coactivator with PDZ binding motif (TAZ) and Yes-associated protein (YAP), the downstream effectors of the Hippo pathway, regulate cell- and tissue-level architectures by responding to mechanical microenvironments of cells, including the cell-extracellular matrix interaction. The Hippo pathway is frequently disrupted in cancer cells, and TAZ and YAP are irrelevantly activated, potentially resulting in anchorage-independent survival/proliferation of cancer cells and metastatic progression. The study aims to investigate the roles of TAZ and YAP in anoikis resistance in basal-like (BL) TNBC cells, which comprise a major subtype (>70%) of TNBC. We found that TAZ and YAP had nonredundant roles in anchorage-independent cancer cell survival or anoikis resistance. Particularly, TAZ was indispensable for anoikis resistance in BL-TNBC cells but not for survival of non-transformed mammary epithelial cells (MECs). In contrast, YAP, a paralog of TAZ, was indispensable for survival of both non-transformed MECs and cancer cells. Therefore, TAZ might be a preferable therapeutic target against dissemination of aggressive cancer cells without killing normal cells. Interestingly, TAZ was abnormally stabilized in BL-TNBC cells under non-adherent conditions, which promoted anoikis resistance. Furthermore, OTUB1, a deubiquitinating enzyme, was responsible for the stabilization of TAZ in detached BL-TNBC cells. Importantly, simultaneous high expression of TAZ and OTUB1 was associated with poor prognosis in BC. Thus, OTUB1 has emerged as a potentially druggable target. Successful inhibition of OTUB1 enzymatic activity is expected to downregulate TAZ and eventually prevents metastasis of aggressive cancers, such as BL-TNBC.

Deciphering Potential Role of Hippo Signaling Pathway in Breast Cancer: A Comprehensive Review

Breast cancer is a heterogeneous disease and a leading malignancy around the world. It is a vital cause of untimely mortality among women. Drug resistance is the major challenge for effective cancer therapeutics. In contrast, cancer stem cells (CSCs) are one of the reasons for drug resistance, tumor progression, and metastasis. The small population of CSCs present in each tumor has the ability of self-renewal, differentiation, and tumorigenicity. CSCs are often identified and enriched using a variety of cell surface markers (CD44, CD24, CD133, ABCG2, CD49f, LGR5, SSEA-3, CD70) that exert their functions by different regulatory networks, i.e., Notch, Wnt/β-catenin, hedgehog (Hh), and Hippo signaling pathways. Particularly the Hippo signaling pathway is the emerging and very less explored cancer stem cell pathway. Here, in this review, the Hippo signaling molecules are elaborated with respect to their ability of stemness as epigenetic modulators and how these molecules can be targeted for better cancer treatment and to overcome drug resistance.

LGR5 promotes invasion and migration by regulating YAP activity in hypopharyngeal squamous cell carcinoma cells under inflammatory condition

High leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) expression caused by an inflammatory condition was reported to promote tumor proliferation and the epithelial-mesenchymal transition (EMT) in various malignant tumors, but those effects have not been studied in hypopharyngeal squamous cell carcinoma (HSCC) and the molecular mechanism remains unclear. This study was aimed to determine whether YAP/TAZ is involved in the regulation of LGR5 expression in the inflammatory condition. Human hypopharyngeal carcinoma FaDu cells were stimulated with inflammatory medium. The cell invasion ability were evaluated through wound healing assay and transwell invasion assay. The expression levels of EMT-related proteins, LGR5, and p-YAP were detected by real time PCR, western blotting, and immunofluorescence. The results showed that LGR5 expression and the EMT process were significantly enhanced under inflammatory condition. The expression of EMT-related proteins was up-regulated, while that of p-YAP was decreased. After inhibiting the high LGR5 expression with short interfering RNA, the expression of EMT-related proteins was also down-regulated, while that of p-YAP was significantly increased. The use of verteporfin (VP), an inhibitor of YAP activity that promotes YAP phosphorylation, did not affect LGR5 expression. In conclusion, we suggest that the inflammatory condition leads to high LGR5 expression, which up-regulating the expression of EMT-related proteins by inhibiting the YAP phosphorylation.

Challenges for Triple Negative Breast Cancer Treatment: Defeating Heterogeneity and Cancer Stemness

The Triple Negative Breast Cancer (TNBC) subtype is known to have a more aggressive clinical course compared to other breast cancer subtypes. Targeted therapies for this type of breast cancer are limited and patients are mostly treated with conventional chemo- and radio-therapies which are not specific and do not target resistant cells. Therefore, one of the major clinical challenges is to find compounds that target the drug-resistant cell populations which are responsible for reforming secondary tumours. The molecular profiling of the different TNBC subtypes holds a promise for better defining these resistant cells specific to each tumour. To this end, a better understanding of TNBC heterogeneity and cancer stemness is required, and extensive genomic analysis can help to understand the disease complexity and distinguish new molecular drivers that can be targeted in the clinics. The use of persister cancer cell-targeting therapies combined with other therapies may provide a big advance to improve TNBC patients' survival.

Functional interplay between long non-coding RNAs and Breast CSCs

Breast cancer (BC) represents aggressive cancer affecting most women’s lives globally. Metastasis and recurrence are the two most common factors in a breast cancer patient's poor prognosis. Cancer stem cells (CSCs) are tumor cells that are able to self-renew and differentiate, which is a significant factor in metastasis and recurrence of cancer. Long non-coding RNAs (lncRNAs) describe a group of RNAs that are longer than 200 nucleotides and do not have the ability to code for proteins. Some of these lncRNAs can be mainly produced in various tissues and tumor forms. In the development and spread of malignancies, lncRNAs have a significant role in influencing multiple signaling pathways positively or negatively, making them promise useful diagnostic and prognostic markers in treating the disease and guiding clinical therapy. However, it is not well known how the interaction of lncRNAs with CSCs will affect cancer development and progression.

Here, in this review, we attempt to summarize recent findings that focus on lncRNAs affect cancer stem cell self-renewal and differentiation in breast cancer development and progression, as well as the strategies and challenges for overcoming lncRNA's therapeutic resistance.

Hippo signaling pathway: A comprehensive gene expression profile analysis in breast cancer

Breast cancer (BC) is the most frequently diagnosed malignancy in women and a major public health concern. The Hippo pathway is an evolutionarily conserved signaling pathway that serves as a key regulator for a wide variety of biological processes. Hippo signaling has been shown to have both oncogenic and tumor-suppressive functions in various cancers. Core components of the Hippo pathway consist of various kinases and downstream effectors such as YAP/TAZ. In the current report, differential expression of Hippo pathway elements as well as the correlation of Hippo pathway mRNAs with various clinicopathologic characteristics, including molecular subtypes, receptor status, and methylation status, has been investigated in BC using METABRIC and TCGA datasets. In this review, we note deregulation of several Hippo signaling elements in BC patients. Moreover, we see examples of negative correlations between methylation of Hippo genes and mRNA expression. The expression of Hippo genes significantly varies between different receptor subgroups. Because of the clear associations between mRNA expression and methylation status, DNA methylation may be one of the mechanisms that regulate the Hippo pathway in BC cells. Differential expression of Hippo genes among various BC molecular subtypes suggests that Hippo signaling may function differently in different subtypes of BC. Our data also highlights an interesting link between Hippo components' transcription and ER negativity in BC. In conclusion, substantial deregulation of Hippo signaling components suggests an important role of these genes in breast cancer.

Paris saponin VII, a Hippo pathway activator, induces autophagy and exhibits therapeutic potential against human breast cancer cells

Dysregulation of the Hippo signaling pathway seen in many types of cancer is usually associated with a poor prognosis. Paris saponin VII (PSVII) is a steroid saponin isolated from traditional Chinese herbs with therapeutic action against various human cancers. In this study we investigated the effects of PSVII on human breast cancer (BC) cells and its anticancer mechanisms. We showed that PSVII concentration-dependently inhibited the proliferation of MDA-MB-231, MDA-MB-436 and MCF-7 BC cell lines with IC₅₀ values of 3.16, 3.45, and 2.86 μM, respectively, and suppressed their colony formation. PSVII (1.2-1.8 μM) induced caspase-dependent apoptosis in the BC cell lines. PSVII treatment also induced autophagy and promoted autophagic flux in the BC cell lines. PSVII treatment decreased the expression and nuclear translocation of Yes-associated protein (YAP), a downstream transcriptional effector in the Hippo signaling pathway; overexpression of YAP markedly attenuated PSVII-induced autophagy. PSVII-induced, YAP-mediated autophagy was associated with increased active form of LATS1, an upstream effector of YAP. The activation of LATS1 was involved the participation of multiple proteins (including MST2, MOB1, and LATS1 itself) in an MST2-dependent sequential activation cascade. We further revealed that PSVII promoted the binding of LATS1 with MST2 and MOB1, and activated LATS1 in the BC cell lines. Molecular docking showed that PSVII directly bound to the MST2-MOB1-LATS1 ternary complex. Microscale thermophoresis analysis and drug affinity responsive targeting stability assay confirmed the high affinity between PSVII and the MST2-MOB1-LATS1 ternary complex. In mice bearing MDA-MB-231 cell xenograft, administration of PSVII (1.5 mg/kg, ip, 4 times/week, for 4 weeks) significantly suppressed the tumor growth with increased pLATS1, LC3-II and Beclin 1 levels and decreased YAP, p62 and Ki67 levels in the tumor tissue. Overall, this study demonstrates that PSVII is a novel and direct Hippo activator that has great potential in the treatment of BC.

Functions of Yes-association protein (YAP) in cancer progression and anticancer therapy resistance

The Hippo pathway, a highly conserved kinase cascade, regulates cell proliferation, apoptosis, organ size, and tissue homeostasis. Dysregulation of this pathway reportedly plays an important role in the progression of various human cancers. Yes-association protein (YAP), the Hippo pathway’s core effector, is considered a marker for cancer therapy and patient prognosis. In addition, studies have indicated that YAP is involved in promoting anticancer drug resistance. This review summarizes current knowledge on YAP’s role in cancer progression, anticancer drug resistance, and advances in the development of YAP-targeting drugs. A thorough understanding of the complex interactions among molecular, cellular, and environmental factors concerning YAP function in cancer progression may provide new insight into the underlying mechanism of anticancer drug resistance. It might lead to improved prognosis through novel combined therapies.

Expression of yes‑associated protein, β‑catenin and smoothened, and their clinical significance in invasive breast cancer

The expression profile and role of yes-associated protein (YAP) in occurrence and development of breast cancer is ambiguous. The present study aimed to explore the relationship among the YAP, β-catenin and smoothened (SMO) signaling pathways to provide a theoretical basis for the clinical diagnosis and treatment of invasive breast cancer. Immunohistochemistry was used to determine the protein expression levels of YAP, β-catenin and SMO in tumor, tumor-adjacent and normal breast tissue. The possible association between the expression levels of these three proteins and the clinicopathological features of patients with breast cancer was then analyzed by the χ² test. The protein expression of YAP was found to be downregulated, whilst β-catenin and SMO expression were found to be upregulated in tumor tissues as compared with that in normal breast tissues. In addition, the expression of YAP in breast cancer tissues was found to be associated with that of human epidermal growth factor receptor 2 (HER2), progesterone and estrogen receptors. By contrast, the protein expression of β-catenin and SMO in breast cancer tissues was only associated with HER2. There was a negative correlation between the expression of YAP and SMO protein in breast cancer tissues. Compared with that in the changes in each of YAP, β-catenin and SMO protein expression levels individually, their combined changes in expression were demonstrated to associate significantly with the tumor histological grade. To conclude, data from the present study suggest that the combined protein expression of YAP, β-catenin and SMO can be used as a prognostic indicator for the treatment of invasive breast cancer.

TEAD4 as an Oncogene and a Mitochondrial Modulator

TEAD4 (TEA Domain Transcription Factor 4) is well recognized as the DNA-anchor protein of YAP transcription complex, which is modulated by Hippo, a highly conserved pathway in Metazoa that controls organ size through regulating cell proliferation and apoptosis. To acquire full transcriptional activity, TEAD4 requires co-activator, YAP (Yes-associated protein) or its homolog TAZ (transcriptional coactivator with PDZ-binding motif) the signaling hub that relays the extracellular stimuli to the transcription of target genes. Growing evidence suggests that TEAD4 also exerts its function in a YAP-independent manner through other signal pathways. Although TEAD4 plays an essential role in determining that differentiation fate of the blastocyst, it also promotes tumorigenesis by enhancing metastasis, cancer stemness, and drug resistance. Upregulation of TEAD4 has been reported in several cancers, including colon cancer, gastric cancer, breast cancer, and prostate cancer and serves as a valuable prognostic marker. Recent studies show that TEAD4, but not other members of the TEAD family, engages in regulating mitochondrial dynamics and cell metabolism by modulating the expression of mitochondrial- and nuclear-encoded electron transport chain genes. TEAD4’s functions including oncogenic activities are tightly controlled by its subcellular localization. As a predominantly nuclear protein, its cytoplasmic translocation is triggered by several signals, such as osmotic stress, cell confluency, and arginine availability. Intriguingly, TEAD4 is also localized in mitochondria, although the translocation mechanism remains unclear. In this report, we describe the current understanding of TEAD4 as an oncogene, epigenetic regulator and mitochondrial modulator. The contributing mechanisms will be discussed.

WISP2/CCN5 Suppresses Vasculogenic Mimicry through Inhibition of YAP/TAZ Signaling in Breast Cancer Cells

Simple Summary

Breast cancer is the most frequent malignancy in women worldwide. Advanced breast cancer with distant organ metastases is considered incurable with currently available therapies. The vasculogenic mimicry (VM) process is associated with an invasive and metastatic cancer phenotype and a poor prognosis for human breast cancer patients. Our aim was to study the effect of WISP2, a matricellular protein, on VM. We found that WISP2 inhibits VM through inhibition of CYR61 protein expression and YAP-TAZ signaling. Our finding may open promising candidates for blocking VM in breast cancer.

Abstract

Vasculogenic mimicry (VM) formed by aggressive tumor cells to create vascular networks connected with the endothelial cells, plays an important role in breast cancer progression. WISP2 has been considered as a tumor suppressor protein; however, the relationship between WISP2 and VM formation remains unclear. We used the in vitro tube formation assay and in vivo immunohistochemical analysis in a mouse model, and human breast tumors were used to evaluate the effect of WISP2 on VM formation. Here we report that WISP2 acts as a potent inhibitor of VM formation in breast cancer. Enforced expression of WISP2 decreased network formation while knockdown of WISP2 increased VM. Mechanistically, WISP2 increased retention of oncogenic activators YAP/TAZ in cytoplasm, leading to decreased expression of the angiogenic factor CYR61. Studies using an in vivo mouse model and human breast tumors confirmed the in vitro cell lines data. In conclusion, our results indicate that WISP2 may play a critical role in VM and highlight the critical role of WISP2 as a tumor suppressor.

The Hippo pathway in cancer: YAP/TAZ and TEAD as therapeutic targets in cancer

Tumorigenesis is a highly complex process, involving many interrelated and cross-acting signalling pathways. One such pathway that has garnered much attention in the field of cancer research over the last decade is the Hippo signalling pathway. Consisting of two antagonistic modules, the pathway plays an integral role in both tumour suppressive and oncogenic processes, generally via regulation of a diverse set of genes involved in a range of biological functions. This review discusses the history of the pathway within the context of cancer and explores some of the most recent discoveries as to how this critical transducer of cellular signalling can influence cancer progression. A special focus is on the various recent efforts to therapeutically target the key effectors of the pathway in both preclinical and clinical settings.

Statins downregulate YAP and TAZ and exert anti-cancer effects in canine mammary tumour cells

Canine mammary tumours (CMTs) are the most common neoplasms in intact bitches, and few chemotherapeutic options are available for highly invasive and metastatic tumours. Recent studies have shown the potential involvement of dysregulated Hippo signalling in CMT development and progression. Statins can activate the Hippo pathway by blocking protein geranylgeranylation (GGylation), resulting in decreased expression and activity of the transcriptional co-activators YAP and TAZ. In this study, we therefore sought to determine if statins could exert anti-cancer effects in CMT cells. Our results demonstrate that Atorvastatin and Fluvastatin are cytotoxic to two CMT cell lines (CMT9 and CMT47), with ED50 values ranging from 0.95 to 23.5 μM. Both statins acted to increase apoptosis and promote cell cycle arrest. Both statins also decreased YAP and TAZ expression and reduced the mRNA levels of key Hippo transcriptional target genes known to be involved in breast cancer progression and chemoresistance (CYR61, CTGF and RHAMM). Moreover, both statins effectively inhibited cell migration and anchorage independent growth, but did not influence matrix invasion. Taken together, our results demonstrate for the first time that statins act upon the Hippo pathway in CMT cells to counteract several molecular and cellular hallmarks of cancer. These findings suggest that targeting the Hippo pathway with statins represents a novel and promising approach for the treatment canine mammary gland cancers.

Identification of cancer-related module in protein-protein interaction network based on gene prioritization

With the rapid development of deep sequencing technologies, a large amount of high-throughput data has been available for studying the carcinogenic mechanism at the molecular level. It has been widely accepted that the development and progression of cancer are regulated by modules/pathways rather than individual genes. The investigation of identifying cancer-related active modules has received an extensive attention. In this paper, we put forward an identification method ModFinder by integrating both biological networks and gene expression profiles. More concretely, a gene scoring function is devised by using the regression model with [Formula: see text]-step random walk kernel, and the genes are ranked according to both of their active scores and degrees in the PPI network. Then a greedy algorithm NSEA is introduced to find an active module with high score and strong connectivity. Experiments were performed on both simulated data and real biological one, i.e. breast cancer and cervical cancer. Compared with the previous methods SigMod, LEAN and RegMod, ModFinder shows competitive performance. It can successfully identify a well-connected module that contains a large proportion of cancer-related genes, including some well-known oncogenes or tumor suppressors enriched in cancer-related pathways.

Drug-Resistant Breast Cancer: Dwelling the Hippo Pathway to Manage the Treatment

Breast cancer can be categorized as a commonly occurring cancer among women with a high mortality rate. Due to the repetitive treatment cycles, it has been noted that the patients develop resistance towards the chemotherapeutic drugs and remain unresponsive towards them. Therefore, many researchers are studying various signaling pathways involved in drug resistance for cancer treatment to overcome the obstacle. Hippo signaling is a widely studied pathway involved in tumor progression and controlling cell proliferation. Hence, understanding the aspects of the gene involved Hippo pathway would provide an insight into the mechanism behind the resistance and result in the development of new treatments. Here, we review the Hippo signaling pathway in humans and how the expression of different components leads to the regulation of resistance against some of the common chemo-drugs used in breast cancer treatment. The article will also discuss the chemotherapeutics that became ineffective due to the resistance and the mechanism following the process.

Lappaol F, an anticancer agent, inhibits YAP via transcriptional and post-translational regulation

CONTEXT

Lappaol F (LAF), a natural lignan from Arctium lappa Linné (Asteraceae), inhibits tumour cell growth by inducing cell cycle arrest. However, its underlying anticancer mechanism remains unclear.

OBJECTIVE

The effects of LAF on the Hippo-Yes-associated protein (YAP) signalling pathway, which plays an important role in cancer progression, were explored in this study.

MATERIALS AND METHODS

Cervical (HeLa), colorectal (SW480), breast (MDA-MB-231) and prostate (PC3) cancer cell lines were treated with LAF at different concentrations and different durations. BALB/c nude mice bearing colon xenografts were intravenously injected with vehicle, LAF (10 or 20 mg/kg) or paclitaxel (10 mg/kg) for 15 days. The expression and nuclear localisation of YAP were analysed using transcriptome sequencing, quantitative PCR, western blotting and immunofluorescence.

RESULTS

LAF suppressed the proliferation of HeLa, MDA-MB-231, SW480 and PC3 cells (IC₅₀ values of 41.5, 26.0, 45.3 and 42.9 μmol/L, respectively, at 72 h), and this was accompanied by significant downregulation in the expression of YAP and its downstream target genes at both the mRNA and protein levels. The expression of 14-3-3σ, a protein that causes YAP cytoplasmic retention and degradation, was remarkably increased, resulting in a decrease in YAP nuclear localisation. Knockdown of 14-3-3σ with small interfering RNA partially blocked LAF-induced YAP inhibition and anti-proliferation effects. In colon xenografts, treatment with LAF led to reduced YAP expression, increased tumour cell apoptosis and tumour growth inhibition.

CONCLUSION

LAF was shown to be an inhibitor of YAP. It exerts anticancer activity by inhibiting YAP at the transcriptional and post-translational levels.

IGF2BP2 promotes the progression of colorectal cancer through a YAP-dependent mechanism

To explore the effect of insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) on colorectal cancer (CRC) by recognizing the m6A modification of YAP mRNA thus activating ErbB2 expression. High expressions of IGF2BP2, YAP, and ErbB2 promoted the proliferation, migration and invasion of CRC cells and reduced their apoptosis. IGF2BP2 recognized the m6A on YAP mRNA and promoted the translation of mRNA. YAP regulated ErbB2 expression by promoting TEAD4 enrichment in ErbB2 promoter region. Therefore, IGF2BP2 promoted the expression of ErbB2 to enhance the proliferation, invasion and migration of CRC cells, to repress cell apoptosis, and to promote solid tumor formation in nude mice. IGF2BP2 activates the expression of ErbB2 by recognizing the m6A of YAP, thus affecting the cell cycle of CRC, inhibiting cell apoptosis, and promoting proliferation.

PMEPA1/TMEPAI Is a Unique Tumorigenic Activator of AKT Promoting Proteasomal Degradation of PHLPP1 in Triple-Negative Breast Cancer Cells

Transmembrane prostate androgen-induced protein (TMEPAI), also known as PMEPA1, is highly expressed in many types of cancer and promotes oncogenic abilities. However, the mechanisms whereby TMEPAI facilitates tumorigenesis are not fully understood. We previously established TMEPAI-knockout (KO) cells from human triple-negative breast cancer (TNBC) cell lines and found that TMEPAI-KO cells showed reduced tumorigenic abilities. Here, we report that TMEPAI-KO cells upregulated the expression of pleckstrin homology (PH) domain and leucine-rich repeat protein phosphatase 1 (PHLPP1) and suppressed AKT Ser473 phosphorylation, which was consistent with TCGA dataset analysis. Additionally, the knockdown (KD) of PHLPP1 in TMEPAI-KO cells partially but significantly rescued AKT Ser473 phosphorylation, as well as in vitro and in vivo tumorigenic activities, thus showing that TMEPAI functions as an oncogenic protein through the regulation of PHLPP1 subsequent to AKT activation. Furthermore, we demonstrated that TMEPAI PPxY (PY) motifs are essential for binding to NEDD4-2, an E3 ubiquitin ligase, and PHLPP1-downregulatory ability. Moreover, TMEPAI enhanced the complex formation of PHLPP1 with NEDD4-2 and PHLPP1 polyubiquitination, which leads to its proteasomal degradation. These findings indicate that the PY motifs of TMEPAI suppress the amount of PHLPP1 and maintain AKT Ser473 phosphorylation at high levels to enhance the tumorigenic potentiality of TNBC.

Lysophosphatidic acid receptor 6 regulated by miR-27a-3p attenuates tumor proliferation in breast cancer

Purpose

Lysophosphatidic acid (LPA) is a bioactive molecule which participates in many physical and pathological processes. Although LPA receptor 6 (LPAR6), the last identified LPA receptor, has been reported to have diverse effects in multiple cancers, including breast cancer, its effects and functioning mechanisms are not fully known.

Methods

Multiple public databases were used to investigate the mRNA expression of LPAR6, its prognostic value, and potential mechanisms in breast cancer. Western blotting was performed to validate the differential expression of LPAR6 in breast cancer tissues and their adjacent tissues. Furthermore, in vitro experiments were used to explore the effects of LPAR6 on breast cancer. Additionally, TargetScan and miRWalk were used to identify potential upstream regulating miRNAs and validated the relationship between miR-27a-3p and LPAR6 via real-time polymerase chain reaction and an in vitro rescue assay.

Results

LPAR6 was significantly downregulated in breast cancer at transcriptional and translational levels. Decreased LPAR6 expression in breast cancer is significantly correlated with poor overall survival, disease-free survival, and distal metastasis-free survival, particularly for hormone receptor-positive patients, regardless of lymph node metastatic status. In vitro gain and loss-of-function assays indicated that LPAR6 attenuated breast cancer cell proliferation. The analyses of TCGA and METABRIC datasets revealed that LPAR6 may regulate the cell cycle signal pathway. Furthermore, the expression of LPAR6 could be positively regulated by miR-27a-3p. The knockdown of miR-27a-3p increased cell proliferation, and ectopic expression of LPAR6 could partly rescue this phenotype.

Conclusion

LPAR6 acts as a tumor suppressor in breast cancer and is positively regulated by miR-27a-3p.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12094-021-02704-8.

Hot Spot Analysis of YAP-TEAD Protein-Protein Interaction Using the Fragment Molecular Orbital Method and Its Application for Inhibitor Discovery

The Hippo pathway is an important signaling pathway modulating growth control and cancer cell proliferation. Dysregulation of the Hippo pathway is a common feature of several types of cancer cells. The modulation of the interaction between yes-associated protein (YAP) and transcriptional enhancer associated domain (TEAD) in the Hippo pathway is considered an attractive target for cancer therapeutic development, although the inhibition of PPI is a challenging task. In order to investigate the hot spots of the YAP and TEAD1 interacting complex, an ab initio Fragment Molecular Orbital (FMO) method was introduced. With the hot spots, pharmacophores for the inhibitor design were constructed, then virtual screening was performed to an in-house library. Next, we performed molecular docking simulations and FMO calculations for screening results to study the binding modes and affinities between PPI inhibitors and TEAD1. As a result of the virtual screening, three compounds were selected as virtual hit compounds. In order to confirm their biological activities, cellular (luciferase activity, proximity ligation assay and wound healing assay in A375 cells, qRT-PCR in HEK 293T cells) and biophysical assays (surface plasmon resonance assays) were performed. Based on the findings of the study, we propose a novel PPI inhibitor BY03 and demonstrate a profitable strategy to analyze YAP-TEAD PPI and discover novel PPI inhibitors.

Chemoresistance and Metastasis in Breast Cancer Molecular Mechanisms and Novel Clinical Strategies

Breast cancer is the most common malignant tumor in females worldwide. Chemotherapy is the standard breast cancer treatment; however, chemoresistance is often seen in patients with metastatic breast cancer. Owing to high heterogeneity, the mechanisms of breast cancer chemoresistance and metastasis have not been fully investigated. The possible molecular mechanisms of chemoresistance in breast cancer include efflux transporters, signaling pathways, non-coding RNAs, and cancer stem cells. However, to overcome this hurdle, the use of novel clinical strategies such as drug carriers, immunotherapy, and autophagy regulation, are being investigated. The goal of this review is to summarize the current data about the molecular mechanisms of breast cancer chemoresistance and the novel clinical strategies; thus, providing a useful clinical tool to explore optimal treatment for breast cancer.

The local anesthetic ropivacaine suppresses progression of breast cancer by regulating miR-27b-3p/YAP axis

Breast cancer is a prevalent malignancy with high mortality and poor prognosis. Ropivacaine is a widely used local anesthetic and presents potential anti-tumor activity. Nevertheless, the function of ropivacaine in breast cancer development remains elusive. Here, we tried to investigate the impact of ropivacaine on breast cancer progression and the underlying mechanism. Significantly, we revealed that ropivacaine was able to reduce the proliferation and induce the apoptosis of breast cancer cells. Ropivacaine could attenuate the invasion and migration in the cells. Mechanically, ropivacaine could enhance the miR-27b-3p expression and miR-27b-3p inhibited breast cancer progression in breast cancer cells. MiR-27b-3p targeted YAP in the breast cancer cells. Ropivacaine decreased the breast cancer progression by modulating miR-27b-3p/YAP axis in vitro. Ropivacaine could inhibit tumor growth in vivo. In conclusion, we discovered that the local anesthetic ropivacaine inhibits the progression of breast cancer via the miR-27b-3p/YAP axis. Our finding presents novel insights into the mechanism of ropivacaine inhibiting the development of breast cancer. Ropivacaine may potentially serve as an anti-tumor candidate in the therapeutic strategy of breast cancer.

Utilizing the Hippo pathway as a therapeutic target for combating endocrine-resistant breast cancer

Drug resistance is always a great obstacle in any endocrine therapy of breast cancer. Although the combination of endocrine therapy and targeted therapy has been shown to significantly improve prognosis, refractory endocrine resistance is still common. Dysregulation of the Hippo pathway is often related to the occurrence and the development of many tumors. Targeted therapies of this pathway have played important roles in the study of triple negative breast cancer (TNBC). Targeting the Hippo pathway in combination with chemotherapy or other targeted therapies has been shown to significantly improve specific antitumor effects and reduce cancer antidrug resistance. Further exploration has shown that the Hippo pathway is closely related to endocrine resistance, and it plays a "co-correlation point" role in numerous pathways involving endocrine resistance, including related pathways in breast cancer stem cells (BCSCs). Agents and miRNAs targeting the components of the Hippo pathway are expected to significantly enhance the sensitivity of breast cancer cells to endocrine therapy. This review initially explains the possible mechanism of the Hippo pathway in combating endocrine resistance, and it concludes by recommending endocrine therapy in combination with therapies targeting the Hippo pathway in the study of endocrine-resistant breast cancers.

Aberrant transcriptional and post-transcriptional regulation of SPAG5, a YAP-TAZ-TEAD downstream effector, fuels breast cancer cell proliferation

Sperm-associated antigen 5 (SPAG5) is an important driver of the cell mitotic spindle required for chromosome segregation and progression into anaphase. SPAG5 has been identified as an important proliferation marker and chemotherapy-sensitivity predictor, especially in estrogen receptor-negative breast cancer subtypes. Here, we report that SPAG5 is a direct target of miR-10b-3p, and its aberrantly high expression associates with poor disease-free survival in two large cohorts of breast cancer patients. SPAG5 depletion strongly impaired cancer cell cycle progression, proliferation, and migration. Interestingly, high expression of SPAG5 pairs with a YAP/TAZ-activated signature in breast cancer patients. Reassuringly, the depletion of YAP, TAZ, and TEAD strongly reduced SPAG5 expression and diminished its oncogenic effects. YAP, TAZ coactivators, and TEAD transcription factors are key components of the Hippo signaling pathway involved in tumor initiation, progression, and metastasis. Furthermore, we report that SPAG5 is a direct transcriptional target of TEAD/YAP/TAZ, and pharmacological targeting of YAP and TAZ severely reduces SPAG5 expression. Collectively, our data uncover an oncogenic feedback loop, comprising miR-10b-3p, SPAG5, and YAP/TAZ/TEAD, which fuels the aberrant proliferation of breast cancer.

Using Biosensors to Study Protein-Protein Interaction in the Hippo Pathway

The Hippo signaling network is dependent on protein–protein interactions (PPIs) as a mechanism of signal transduction to regulate organ size, cellular proliferation and differentiation, tumorigenesis, and other cellular processes. Current efforts aim to resolve the complex regulation of upstream Hippo components or focus on identifying targeted drugs for use in cancer therapy. Despite extensive characterization of the Hippo pathway interactome by affinity purification mass spectrometry (AP-MS) and other methodologies, previous research methods have not been sufficient to achieve these aims. In this review, we describe several recent studies that make use of luciferase-based biosensors as a new approach to study the Hippo Pathway. These biosensors serve as powerful tools with which to study PPIs both in vitro using purified biosensor proteins, and in real time in live cells. Notably, luciferase biosensors have excellent sensitivity and have been used to screen for upstream kinase regulators of the Hippo pathway. Furthermore, the high sensitivity and stability of these biosensors enables their application in high throughput screening for Hippo-targeted chemotherapeutics. Finally, we describe the strengths and weaknesses of this method relative to AP-MS and discuss potential future directions for using biosensors to study Hippo signaling.

New Insights into YES-Associated Protein Signaling Pathways in Hematological Malignancies: Diagnostic and Therapeutic Challenges

Simple Summary

YES-associated protein (YAP) is a co-transcriptional activator that binds to transcriptional factors to increase the rate of transcription of a set of genes, and it can intervene in the onset and progression of different tumors. Most of the data in the literature refer to the effects of the YAP system in solid neoplasms. In this review, we analyze the possibility that YAP can also intervene in hematological neoplasms such as lymphomas, multiple myeloma, and acute and chronic leukemias, modifying the phenomena of cell proliferation and cell death. The possibilities of pharmacological intervention related to the YAP system in an attempt to use its modulation therapeutically are also discussed.

Abstract

The Hippo/YES-associated protein (YAP) signaling pathway is a cell survival and proliferation-control system with its main activity that of regulating cell growth and organ volume. YAP operates as a transcriptional coactivator in regulating the onset, progression, and treatment response in numerous human tumors. Moreover, there is evidence suggesting the involvement of YAP in the control of the hematopoietic system, in physiological conditions rather than in hematological diseases. Nevertheless, several reports have proposed that the effects of YAP in tumor cells are cell-dependent and cell-type-determined, even if YAP usually interrelates with extracellular signaling to stimulate the onset and progression of tumors. In the present review, we report the most recent findings in the literature on the relationship between the YAP system and hematological neoplasms. Moreover, we evaluate the possible therapeutic use of the modulation of the YAP system in the treatment of malignancies. Given the effects of the YAP system in immunosurveillance, tumorigenesis, and chemoresistance, further studies on interactions between the YAP system and hematological malignancies will offer very relevant information for the targeting of these diseases employing YAP modifiers alone or in combination with chemotherapy drugs.

Diagnostic biomarkers from proteomic characterization of cerebrospinal fluid in patients with brain malignancies

Recent technological advances in molecular diagnostics through liquid biopsies hold the promise to repetitively monitor tumor evolution and treatment response of brain malignancies without the need of invasive surgical tissue accrual. Here, we implemented a mass spectrometry-based protein analysis pipeline which identified hundreds of proteins in 251 cerebrospinal fluid (CSF) samples from patients with four types of brain malignancies (glioblastoma, lymphoma, brain metastasis, and leptomeningeal disease [LMD]) and from healthy individuals with a focus on glioblastoma in a retrospective and confirmatory prospective observational study. CSF proteome deregulation via disruption of the blood brain barrier appeared to be largely conserved across brain tumor entities. CSF analysis of glioblastoma patients identified two proteomic clusters that correlated with tumor size and patient survival. By integrating CSF data with proteomic analyses of matching glioblastoma tumor tissue and primary glioblastoma cells, we identified potential CSF biomarkers for glioblastoma, in particular chitinase-3-like protein 1 (CHI3L1) and glial fibrillary acidic protein (GFAP). Key findings were validated in a prospective cohort consisting of 35 glioma patients. Finally, in LMD patients who frequently undergo repeated CSF work-up, we explored our proteomic pipeline as a mean to profile consecutive CSF samples. Therefore, proteomic analysis of CSF in brain malignancies has the potential to reveal biomarkers for diagnosis and therapy monitoring.

Treatment of Luminal Metastatic Breast Cancer beyond CDK4/6 Inhibition: Is There a Standard of Care in Clinical Practice?

BACKGROUND

CDK4/6 inhibitors have become the standard for first-line treatment of metastatic luminal breast cancer based on consistent data from several phase 3 trials demonstrating clinically meaningful improvement of progression-free as well as overall survival. In addition, they are about to become a part of adjuvant treatment for patients with high-risk luminal disease based on positive results from the first randomized phase 3 trial on abemaciclib. Nevertheless, the majority of patients with advanced or metastatic luminal breast cancer and prospectively a relevant proportion of patients treated in the adjuvant setting will eventually develop resistance to this endocrine based combination within 12-36 months, depending on the line of treatment.

CONCLUSION

Potential subsequent therapies include PI3K inhibitors, mTOR inhibitors, endocrine monotherapy, PARP inhibitors, and chemotherapy. However, these therapies have mainly been developed in the pre-CDK4/6 inhibitor era and little is known about potential cross-resistance. The concept of continuing CDK4/6 inhibition beyond progression is supported by some preclinical data, but to date there is very limited clinical evidence to support this strategy. Therefore, treatment of metastatic luminal breast cancer after progression on CDK4/6 inhibitors remains a challenge.

KEY MESSAGES

Here we review current evidence from pro- and retrospective studies and give an outlook on future developments with respect to novel therapeutic agents, including oral SERD and AKT inhibitors, which have the potential to change the therapeutic landscape in the future. Furthermore, clinical treatment algorithms and current research will also be discussed.

The migration of metastatic breast cancer cells is regulated by matrix stiffness via YAP signalling

Matrix stiffness is a driver of breast cancer progression and mechanosensitive transcriptional activator YAP plays an important role in this process. However, the interplay between breast cancer and matrix stiffness, and the significance of this interplay remained largely unknown. Here, we showed an increase in YAP nuclear localization and a higher proliferation rate in both highly metastatic MDA-MB-231 cells and the non-metastatic counterpart MCF-7 cells when they were exposed to the stiff matrix. However, in response to the stiff matrix highly metastatic MDA-MB-231 cells instead of MCF-7 cells exhibited upregulated mobility, which was shown to be YAP-dependent. Consistently, MDA-MB-231 cells exhibited different focal adhesion dynamics from MCF-7 cells in response to matrix stiffness. These results suggested a YAP-dependent mechanism through which matrix stiffness regulates the migratory potential of metastatic breast cancer cells.

Extracts of Perilla frutescens var. Acuta (Odash.) Kudo Leaves Have Antitumor Effects on Breast Cancer Cells by Suppressing YAP Activity

Yes-associated protein (YAP)/WW domain-containing transcription factor (TAZ) is critical for cell proliferation, survival, and self-renewal. It has been shown to play a crucial oncogenic role in many different types of tumors. In this study, we investigated the antitumor effect of the extracts of Perilla frutescens var. acuta (Odash.) Kudo leaves (PLE) on Hippo-YAP/TAZ signaling. PLE induced the phosphorylation of YAP/TAZ, thereby inhibiting their activity. In addition, the treatment suppresses YAP/TAZ transcriptional activity via the dissociation of the YAP/TAZ-TEAD complex. To elucidate the molecular mechanism of PLE in the regulation of YAP activity, we treated WT and cell lines with gene knockout (KO) for Hippo pathway components with PLE. The inhibitory effects of PLE on YAP-TEAD target genes were significantly attenuated in LATS1/2 KO cells. Moreover, we found the antitumor effect of PLE on MDA-MB-231 and BT549, both of which are triple-negative breast cancer (TNBC) cell lines. PLE reduced the viability of TNBC cells in a dose-dependent manner and induced cell apoptosis. Further, PLE inhibited the migration ability in MDA-MB-231 cells. This ability was weakened in YAP and TEAD-activated clones suggesting that the inhibition of migration by PLE is mainly achieved by regulating YAP activity. Taken together, the results of this study indicate that PLE suppressed cell growth and increased the apoptosis of breast cancer (BC) cells via inactivation of YAP activity in a LATS1/2-dependent manner.

The Hippo pathway: Horizons for innovative treatments of peripheral nerve diseases

Initially identified in Drosophila, the Hippo signaling pathway regulates how cells respond to their environment by controlling proliferation, migration and differentiation. Many recent studies have focused on characterizing Hippo pathway function and regulation in mammalian cells. Here, we present a brief overview of the major components of the Hippo pathway, as well as their regulation and function. We comprehensively review the studies that have contributed to our understanding of the Hippo pathway in the function of the peripheral nervous system and in peripheral nerve diseases. Finally, we discuss innovative approaches that aim to modulate Hippo pathway components in diseases of the peripheral nervous system.

NUSAP1 Promotes Gastric Cancer Tumorigenesis and Progression by Stabilizing the YAP1 Protein

The Yes-associated protein (YAP1) is a main effector of the canonical Hippo pathway, which contributes greatly to tumor initiation, progression, and metastasis in multiple cancers, including gastric cancer (GC). Due to limited knowledge of YAP1 upregulation in cancer, it is a great challenge of therapeutic targets toward the Hippo-YAP1 pathway. Here, we identify nucleolar spindle-associated protein 1 (NUSAP1) as a novel binding partner of YAP1. The upregulation of NUSAP1 is associated with unfavorable clinical outcomes in GC patients, and NUSAP1 depletion impairs its oncogenic properties in vitro and in a xenograft model. Mechanistically, we discovered that NUSAP1 functions as a positive regulator of YAP1 protein stability, thereby inducing the transcription of Hippo pathway downstream target genes, such as CTGF and CYR61. More interestingly, we find that the cancer-promoting effects of NUSAP1 on GC cell growth, migration, and invasion are mainly mediated by YAP1. Furthermore, aberrant expression of NUSAP1 and YAP1 is highly correlated in GC cell lines and tissues. We herein clarify the role of the oncogenic NUSAP1-YAP1 axis in GC tumorigenesis and progression and, therefore, provide novel therapeutic targets for GC treatment.

Cell Fitness: More Than Push-Ups

Cell competition (CC) is a feature that allows tumor cells to outcompete and eliminate adjacent cells that are deemed less fit. Studies of CC, first described in Drosophila melanogaster, reveal a diversity of underlying mechanisms. In this review, we will discuss three recent studies that expand our understanding of the molecular features governing CC. In particular, we will focus on a molecular fitness fingerprint, oncogenic pathways, and the importance of cell junction stability. A fitness fingerprint, mediated by flower (hFWE) protein isoforms, dictates that cells expressing the flower-win isoforms will outcompete adjacent flower-loss-expressing cells. The impact of the flower protein isoforms is seen in cancer progression and may have diagnostic potential. The yes-associated protein (YAP) and TAZ transcription factors, central mediators of the oncogenic Hippo pathway, elevate peritumoral fitness thereby protecting against tumor progression and provide a suppressive barrier. Similarly, COL17A1 is a key component in hemidesmosome stability, and its expression in epidermal stem cells contributes to fitness competition and aging characteristics. The contributions of these pathways to disease development and progression will help define how CC is hijacked to favor cancer growth. Understanding these features will also help frame the diagnostic and therapeutic possibilities that may place CC in the crosshairs of cancer therapeutics.

Long Non-Coding RNA A2M-AS1 Promotes Breast Cancer Progression by Sponging microRNA-146b to Upregulate MUC19

Background

Long non-coding RNA (lncRNA) A2M-AS1 has been indicated to be augmented in breast cancer (BC), with its specific function undetermined. Therefore, this study is designed to investigate the mechanism of lncRNA A2M-AS1 in BC.

Methods

The expression of A2M-AS1, microRNA (miR)-146b, and MUC19 in BC tissues and cells was measured. Then, the interaction among A2M-AS1, miR-146b, and MUC19 was detected. After A2M-AS1, miR-146b, and MUC19 expression were altered in BC cells, cell proliferation, invasion, and apoptosis were detected, and the protein levels of Hippo-related proteins (YAP and p-YAP) were evaluated. Tumor growth assay was also performed to validate the effects of A2M-AS1 and miR-146b in vivo.

Results

A2M-AS1 and MUC19 were highly expressed in BC, while miR-146b was poorly expressed. A2M-AS1 acts as a molecular sponge for miR-146b, which targeted and negatively modulated MUC19. A2M-AS1 accelerated BC cell proliferation, invasion, and colony formation and suppressed apoptosis via the miR-146b/MUC19/Hippo axis, which was confirmed in vivo.

Conclusion

Taken above together, an oncogenic role for A2M-AS1 in BC was elicited by acting as a miR-146b sponge to promote MUC19 expression. The findings will present some cues for a further approach to BC.

Weighted dimensionality reduction and robust Gaussian mixture model based cancer patient subtyping from gene expression data

BACKGROUND

The heterogeneous nature of cancer necessitates subtyping of cancer patients into distinct and well separated subgroups. However, computational issues arise because gene expression data is noisy and contains outliers apart from being high dimensional. As such, an attempt to subtype cancer patients from gene expression data leads to highly overlapping Kaplan-Meier (KM) survival plots and thus clear distinction among the discovered subtypes becomes difficult. Here we attempt to achieve a greater separation among the subtypes through a robust clustering pipeline.

METHODS

We propose a robust framework to achieve a better separation among the discovered subtypes. Our framework is based on dimensionality reduction of a weighted gene expression matrix using t-distributed Stochastic Neighbor Embedding (t-SNE) and a robust Gaussian mixture model based clustering approach. Every gene is weighted according to the median absolute deviation (MAD) of the gene before dimensionality reduction. The results are quantified by measuring the minimum pairwise separation among the KM plots and minimum hazard ratio among the subtypes. We also introduce a novel method, called cumulative survival separation, to quantify the separation among the discovered subtypes.

RESULTS

To validate the proposed methodology we obtained five cancer gene expression datasets from The Cancer Genome Atlas (TCGA) and comparisons with Consensus Clustering (CC), Consensus non-negative matrix factorization (CNMF), fast density-aware spectral clustering (Spectrum) and Neighborhood based Multi-Omics clustering (NEMO) methodologies show that the proposed method is able to achieve a greater separation compared to the aforementioned methods in literature. For instance, the minimum pairwise life expectancy difference (in days) between the discovered subtypes for GBM is 61 days for the proposed methodology with MAD scores, whereas it is approximately 33, 19, 49 and 33 days only for CC, Spectrum, Nemo and CNMF respectively. Comparisons are also shown for the proposed framework with and without using the MAD scores and it is observed that MAD score significantly improves the subtype separation. Hazard ratio analysis also shows that the proposed methodology performs better. Furthermore, pathway over-representation analyses were carried to identify relevant genetic pathways which can be possible targets for treatment.

CONCLUSION

The results suggest that the use of median absolute deviation and a robust clustering methodology are helpful in achieving greater separation among the subtypes with better statistical and clinical significance.

The Tumor Microenvironment of Primitive and Metastatic Breast Cancer: Implications for Novel Therapeutic Strategies

Breast cancer evolves thanks to a dense and close interaction with the surrounding tumor microenvironment (TME). Fibroblasts, leukocytes, blood and lymphatic endothelial cells and extracellular matrix are the constituents of this entity, and they synergistically play a pivotal role in all of the stages of breast cancer development, from its onset to its metastatic spread. Moreover, it has been widely demonstrated that variations to the TME can correspond to prognosis variations. Breast cancer not only modulates the transformation of the environment within the mammary gland, but the same process is observed in metastases as well. In this minireview, we describe the features of TME within the primitive breast cancer, throughout its evolution and spread into the main metastatic sites.

The clinical relevance of the Hippo pathway in pancreatic ductal adenocarcinoma

Purpose

The Hippo pathway has broadened in cancer research in the past decade and revealed itself to be an important driver for tumorigenesis and metastatic spread. In this study, we investigated the clinical relevance of the Hippo pathway with regard to metastatic invasion, patients’ outcome and histopathological features.

Methods

Protein expression of components of the Hippo pathway were analyzed by immunohistochemistry (IHC) using paraffin-embedded tissue from 103 patients who had been diagnosed with pancreatic ductal adenocarcinoma and had undergone surgery. Results were correlated with clinicopathological data, disease-free and overall survival.

Results

Immunohistochemistry studies in pancreatic tumour tissues revealed a significant upregulation of MST1, MST2, pLATS, pYAP and 14-3-3, representing the active Hippo pathway, in non-metastasized patients (p < 0.01). In turn, the pathway is more inactive in metastasized patients and relating liver metastases as LATS1, LATS2, YAP, transcriptional factors TEAD2 and TEAD3 were upregulated in these patients (p < 0.01). A higher pYAP expression was associated with a favorable OS and DFS.

Conclusion

The Hippo pathway is inactive in metastasized patients releasing the pro-metastatic and proliferative potential of the pathway. Furthermore, our study underlines the prognostic relevance of the Hippo pathway as a shift in the balance towards the inactive pathway predicts an unfavorable OS and DFS.

Interaction of the Hippo Pathway and Phosphatases in Tumorigenesis

The Hippo pathway is an emerging tumor suppressor signaling pathway involved in a wide range of cellular processes. Dysregulation of different components of the Hippo signaling pathway is associated with a number of diseases including cancer. Therefore, identification of the Hippo pathway regulators and the underlying mechanism of its regulation may be useful to uncover new therapeutics for cancer therapy. The Hippo signaling pathway includes a set of kinases that phosphorylate different proteins in order to phosphorylate and inactivate its main downstream effectors, YAP and TAZ. Thus, modulating phosphorylation and dephosphorylation of the Hippo components by kinases and phosphatases play critical roles in the regulation of the signaling pathway. While information regarding kinase regulation of the Hippo pathway is abundant, the role of phosphatases in regulating this pathway is just beginning to be understood. In this review, we summarize the most recent reports on the interaction of phosphatases and the Hippo pathway in tumorigenesis. We have also introduced challenges in clarifying the role of phosphatases in the Hippo pathway and future direction of crosstalk between phosphatases and the Hippo pathway.