Inactivation of LATS1/2 drives luminal-basal plasticity to initiate basal-like mammary carcinomas

A novel clinically relevant antagonistic interplay between prolactin and oncogenic YAP-CCN2 pathways as a differentiation therapeutic target in breast cancer

Cellular differentiation limits cellular plasticity allowing cells to attain their specialized functional characteristics and phenotypes, whereas loss of differentiation is a hallmark of cancer. Thus, characterizing mechanisms underlying differentiation is key to discover new cancer therapeutics. We report a novel functional antagonistic relationship between the prolactin (PRL)/prolactin receptor (PRLR) differentiation pathway and YAP-CCN2 oncogenic pathway in normal mammary epithelial cells and breast cancer cells that is essential for establishing/maintaining acinar morphogenesis, cell-cell junctions and the intracellular localization of apical-basal polarity protein complexes (Par, Crumb and Scrib). Importantly, using CRISPR knockout of the PRLR in MCF7, HR+ breast cancer cells, further revealed that the negative relationship between PRL/PRLR pathway and YAP-CCN2 pathway is critical in suppressing luminal-to-basal stem-like lineage plasticity. Furthermore, the clinical relevance of this interplay was evaluated using bioinformatics approaches on several human datasets, including samples from normal breast epithelium, breast cancer, and 33 other cancer types. This analysis revealed a positive correlation between PRLR and the YAP suppressor Hippo pathway and a co-expression gene network driving favourable patients' survival outcomes in breast cancer. The therapeutic potential of this interplay was also evaluated in vitro using MDA-MB-231 cells, a preclinical model of human triple-negative breast cancer, where treatment with PRL and Verteporfin, an FDA-approved pharmacological YAP-inhibitor, alone or their combination suppressed the expression of the mesenchymal marker vimentin and the stem cell marker CD44 as well as reduced their Ki67 proliferative marker expression. Collectively, our results emphasize the pro-differentiation role of PRL/PRLR pathway in mammary and breast cancer cells and highlight that promoting PRL/PRLR signaling while inhibiting the YAP-CCN2 oncogenic pathway can be exploited as a differentiation-based combination therapeutic strategy in breast cancer.

LATS1/2 inactivation in the mammary epithelium drives the evolution of a tumor-associated niche

Basal-like breast cancers exhibit distinct cellular heterogeneity that contributes to disease pathology. In this study we used a genetic mouse model of basal-like breast cancer driven by epithelial-specific inactivation of the Hippo pathway-regulating LATS1 and LATS2 kinases to elucidate epithelial-stromal interactions. We demonstrate that basal-like carcinoma initiation in this model is accompanied by the accumulation of distinct cancer-associated fibroblasts and macrophages and dramatic extracellular matrix remodeling, phenocopying the stromal diversity observed in human triple-negative breast tumors. Dysregulated epithelial-stromal signals were observed, including those mediated by TGF-β, PDGF, and CSF. Autonomous activation of the transcriptional effector TAZ was observed in LATS1/2-deleted cells along with non-autonomous activation within the evolving tumor niche. We further show that inhibition of the YAP/TAZ-associated TEAD family of transcription factors blocks the development of the carcinomas and associated microenvironment. These observations demonstrate that carcinomas resulting from Hippo pathway dysregulation in the mammary epithelium are sufficient to drive cellular events that promote a basal-like tumor-associated niche and suggest that targeting dysregulated YAP/TAZ-TEAD activity may offer a therapeutic opportunity for basal-like mammary tumors.

Noncanonical Wnt/Ror2 Signaling Regulates Basal Cell Fidelity and Branching Morphogenesis in the Mammary Gland

The mammary gland epithelium relies on a delicate balance between basal and luminal cell lineages to maintain tissue homeostasis and enable proper development. While the role of canonical Wnt signaling in mammary biology is well-established, the contribution of noncanonical Wnt signaling to lineage identity has remained unclear. Noncanonical Wnt pathways are primarily associated with morphogenesis, cytoskeletal regulation, and cell migration, but whether they are required for maintaining epithelial cell fate remains largely unexplored. Here, we demonstrate that the noncanonical Wnt receptor Ror2 is expressed in both basal and luminal lineages, yet selectively maintained in basal cells throughout development, suggesting a lineage-specific function. Using a p63CreERT2/+ lineage-specific mouse model, we show that Ror2 deletion in basal epithelial cells enhances secondary and tertiary branching while driving a basal-to-luminal fate transition, marked by downregulation of basal markers (K14, K5) and upregulation of luminal markers (K8, K18, ERα). Mechanistically, Ror2 loss disrupts RhoA-ROCK1-YAP1 signaling, leading to cytoskeletal reorganization, chromatin remodeling, and increased accessibility at luminal regulatory loci. Notably, ROCK1 inhibition phenocopies Ror2 loss, reinforcing the critical role of the RhoA-ROCK1 axis in basal cell maintenance. These findings provide direct genetic and mechanistic evidence that noncanonical Wnt signaling is essential for maintaining basal lineage fidelity, offering new insights into the mechanisms regulating epithelial plasticity. Given the fundamental importance of lineage stability in epithelial homeostasis, our results suggest that disruptions in Wnt/Ror2 signaling may contribute to aberrant fate transitions relevant to breast cancer progression.

METTL14 suppresses the expression of YAP1 and the stemness of triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) has pronounced stemness that is associated with relapse. N6-methyladenosine (m6A) plays a crucial role in shaping cellular behavior by modulating transcript expression. However, the role of m6A in TNBC stemness, as well as the mechanisms governing its abundance, has yet to be elucidated.

METHODS

We analyzed proteomic and transcriptomic data derived from breast cancer cohorts, with an emphasis on m6A regulators. To unravel the role of m6A in TNBC, we employed RNA sequencing, methylated RNA immunoprecipitation sequencing, RNA immunoprecipitation, chromatin immunoprecipitation, and luciferase reporter assays with mesenchymal stem-like (MSL) TNBC models. The clinical relevance was validated using human tissue microarrays and publicly accessible databases.

RESULTS

Our findings indicate that the global level of m6A modification in MSL TNBC is downregulated primarily due to the loss of methyltransferase-like 14 (METTL14). The diminished m6A modification is crucial for the maintenance of TNBC stemness, as it increases the expression of yes-associated protein 1 (YAP1) by blocking YTH domain-containing family protein 2 (YTHDF2)-mediated transcript decay, thereby promoting the activation of Hippo-independent YAP1 signaling. YAP1 is essential for sustaining the stemness regulated by METTL14. Furthermore, we demonstrated that the loss of METTL14 expression results from lysine-specific demethylase 1 (LSD1)-mediated removal of histone H3 lysine 4 methylation at the promoter region, which is critical for LSD1-driven stemness in TNBC.

CONCLUSION

These findings present an epi-transcriptional mechanism that maintains Hippo-independent YAP1 signaling and plays a role in preserving the undifferentiated state of TNBC, which indicates the potential for targeting the LSD1-METTL14 axis to address TNBC stemness.

Increased prevalence of hybrid epithelial/mesenchymal state and enhanced phenotypic heterogeneity in basal breast cancer

Intra-tumoral phenotypic heterogeneity promotes tumor relapse and therapeutic resistance and remains an unsolved clinical challenge. Decoding the interconnections among different biological axes of plasticity is crucial to understand the molecular origins of phenotypic heterogeneity. Here, we use multi-modal transcriptomic data-bulk, single-cell, and spatial transcriptomics-from breast cancer cell lines and primary tumor samples, to identify associations between epithelial-mesenchymal transition (EMT) and luminal-basal plasticity-two key processes that enable heterogeneity. We show that luminal breast cancer strongly associates with an epithelial cell state, but basal breast cancer is associated with hybrid epithelial/mesenchymal phenotype(s) and higher phenotypic heterogeneity. Mathematical modeling of core underlying gene regulatory networks representative of the crosstalk between the luminal-basal and epithelial-mesenchymal axes elucidate mechanistic underpinnings of the observed associations from transcriptomic data. Our systems-based approach integrating multi-modal data analysis with mechanism-based modeling offers a predictive framework to characterize intra-tumor heterogeneity and identify interventions to restrict it.

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.

TRPS1 maintains luminal progenitors in the mammary gland by repressing SRF/MRTF activity

The transcription factor TRPS1 is a context-dependent oncogene in breast cancer. In the mammary gland, TRPS1 activity is restricted to the luminal population and is critical during puberty and pregnancy. Its function in the resting state remains however unclear. To evaluate whether it could be a target for cancer therapy, we investigated TRPS1 function in the healthy adult mammary gland using a conditional ubiquitous depletion mouse model where long-term depletion does not affect fitness. Using transcriptomic approaches, flow cytometry and functional assays, we show that TRPS1 activity is essential to maintain a functional luminal progenitor compartment. This requires the repression of both YAP/TAZ and SRF/MRTF activities. TRPS1 represses SRF/MRTF activity indirectly by modulating RhoA activity. Our work uncovers a hitherto undisclosed function of TRPS1 in luminal progenitors intrinsically linked to mechanotransduction in the mammary gland. It may also provide new insights into the oncogenic functions of TRPS1 as luminal progenitors are likely the cells of origin of many breast cancers.

CCDC25 suppresses clear cell renal cell carcinoma progression by LATS1/YAP-mediated regulation of the hippo pathway

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is one of the most prevalent renal cancers, and the molecular mechanisms underlying its progression are still not fully understood. The expression of CCDC25, a notably underexpressed gene in many tumors, has been understudied in ccRCC. This research aims to explore the role of CCDC25 in ccRCC's clinical outcomes and uncover the molecular pathways influenced by it.

METHODS

A multi-tiered approach was adopted involving bioinformatic analysis, tissue sample evaluation, in vitro and in vivo experiments. CCDC25 expression levels in tumor vs. normal tissues were quantified using Western blot and immunofluorescence studies. Cell proliferation and migration were analyzed using CCK8, EDU, Transwell assays, and wound healing assays. RNA sequencing was performed to elucidate the molecular pathways affected, followed by detailed protein-protein interaction studies and mouse xenograft models.

RESULTS

CCDC25 was predominantly underexpressed in ccRCC tumors and associated with advanced clinical stages and poor prognosis. Overexpression of CCDC25 in renal cancer cell lines resulted in reduced proliferation and migration. RNA sequencing revealed significant alterations in the Hippo pathway. Overexpression of CCDC25 inhibited the expression of downstream Hippo pathway proteins ITGA3 and CCND1 and promoted YAP phosphorylation. Mechanistic studies showed that CCDC25 interacts with YAP and influences YAP phosphorylation through LATS1. In vivo, CCDC25 overexpression inhibited tumor growth and promoted apoptosis.

CONCLUSION

CCDC25 acts as a potential tumor suppressor in ccRCC by inhibiting cell proliferation and migration, potentially through regulating the Hippo signaling pathway. These findings highlight the potential of CCDC25 as a therapeutic target in ccRCC treatment.

Knockdown of CCM3 promotes angiogenesis through activation and nuclear translocation of YAP/TAZ

Angiogenesis, a finely regulated process, plays a crucial role in the progression of various diseases. Cerebral cavernous malformation 3 (CCM3), alternatively referred to as programmed cell death 10 (PDCD10), stands as a pivotal functional gene with a broad distribution across the human body. However, the precise role of CCM3 in angiogenesis regulation has remained elusive. YAP/TAZ, as core components of the evolutionarily conserved Hippo pathway, have garnered increasing attention as a novel mechanism in angiogenesis regulation. Nonetheless, whether CCM3 regulates angiogenesis through YAP/TAZ mediation has not been comprehensively explored. In this study, our primary focus centers on investigating the regulation of angiogenesis through CCM3 knockdown mediated by YAP/TAZ. Silencing CCM3 significantly enhances the proliferation, migration, and tubular formation of human umbilical vein endothelial cells (HUVECs), thereby promoting angiogenesis. Furthermore, we observe an upregulation in the expression levels of VEGF and VEGFR2 within HUVECs upon silencing CCM3. Mechanistically, the evidence we provide suggests for the first time that endothelial cell CCM3 knockdown induces the activation and nuclear translocation of YAP/TAZ. Finally, we further demonstrate that the YAP/TAZ inhibitor verteporfin can reverse the pro-angiogenic effects of siCCM3, thereby confirming the role of CCM3 in angiogenesis regulation dependent on YAP/TAZ. In summary, our findings pave the way for potential therapeutic targeting of the CCM3-YAP/TAZ signaling axis as a novel approach to promote angiogenesis.

ID4-dependent secretion of VEGFA enhances the invasion capability of breast cancer cells and activates YAP/TAZ via integrin β3-VEGFR2 interaction

Understanding the mechanisms of breast cancer cell communication underlying cell spreading and metastasis formation is fundamental for developing new therapies. ID4 is a proto-oncogene overexpressed in the basal-like subtype of triple-negative breast cancer (TNBC), where it promotes angiogenesis, cancer stem cells, and BRACA1 misfunction. Here, we show that ID4 expression in BC cells correlates with the activation of motility pathways and promotes the production of VEGFA, which stimulates the interaction of VEGFR2 and integrin β3 in a paracrine fashion. This interaction induces the downstream focal adhesion pathway favoring migration, invasion, and stress fiber formation. Furthermore, ID4/ VEGFA/ VEGFR2/ integrin β3 signaling stimulates the nuclear translocation and activation of the Hippo pathway member's YAP and TAZ, two critical executors for cancer initiation and progression. Our study provides new insights into the oncogenic roles of ID4 in tumor cell migration and YAP/TAZ pathway activation, suggesting VEGFA/ VEGFR2/ integrin β3 axis as a potential target for BC treatment.

Control of stem cell renewal and fate by YAP and TAZ

Complex physiological processes control whether stem cells self-renew, differentiate or remain quiescent. Two decades of research have placed the Hippo pathway, a highly conserved kinase signalling cascade, and its downstream molecular effectors YAP and TAZ at the nexus of this decision. YAP and TAZ translate complex biological cues acting on stem cells - from mechanical forces to cellular metabolism - into genome-wide effects to mediate stem cell functions. While aberrant YAP/TAZ activity drives stem cell dysfunction in ageing, tumorigenesis and disease, therapeutic targeting of Hippo signalling and YAP/TAZ can boost stem cell activity to enhance regeneration. In this Review, we discuss how YAP/TAZ control the self-renewal, fate and plasticity of stem cells in different contexts, how dysregulation of YAP/TAZ in stem cells leads to disease, and how therapeutic modalities targeting YAP/TAZ may benefit regenerative medicine and cancer therapy.

New Insights into YAP/TAZ-TEAD-Mediated Gene Regulation and Biological Processes in Cancer

The Hippo pathway is conserved across species. Key mammalian Hippo pathway kinases, including MST1/2 and LATS1/2, inhibit cellular growth by inactivating the TEAD coactivators, YAP, and TAZ. Extensive research has illuminated the roles of Hippo signaling in cancer, development, and regeneration. Notably, dysregulation of Hippo pathway components not only contributes to tumor growth and metastasis, but also renders tumors resistant to therapies. This review delves into recent research on YAP/TAZ-TEAD-mediated gene regulation and biological processes in cancer. We focus on several key areas: newly identified molecular patterns of YAP/TAZ activation, emerging mechanisms that contribute to metastasis and cancer therapy resistance, unexpected roles in tumor suppression, and advances in therapeutic strategies targeting this pathway. Moreover, we provide an updated view of YAP/TAZ's biological functions, discuss ongoing controversies, and offer perspectives on specific debated topics in this rapidly evolving field.