Integrin signalling regulates YAP and TAZ to control skin homeostasis

YAP Expression is Related to the Aggressive Behavior of Odontogenic Cysts

OBJECTIVE

 Yes-associated protein (YAP) and Ki-67 are known to be involved in cell proliferation. While their overexpression is associated with aggressive behaviors in oral squamous cell carcinoma (OSCC), their roles in odontogenic cysts have not been thoroughly investigated. Therefore, this study aimed to evaluate the immunohistochemical expression of YAP and Ki-67 in odontogenic cysts.

MATERIAL AND METHODS

 Tissue samples included 12 radicular cysts, 10 dentigerous cysts, 9 odontogenic keratocysts, and 9 normal oral mucosa specimens. Immunohistochemical analysis was conducted both manually and using ImageJ software for comparison.

STATISTICAL ANALYSIS

 The Kruskal-Wallis, followed by the Mann-Whitney U-test was used to assess the differences in the YAP and Ki-67 immunoexpression levels among various group lesions. The correlation between those two proteins in individual groups was tested by Spearman correlation. A p-value of less than 0.05 was considered statistically significant. SPSS software version 25.0 was used.

RESULTS

 There was a strong nuclear staining of YAP in basal and superficial cells and an intense cytoplasmic YAP positivity in odontogenic keratocysts, whereas a weaker YAP staining in both the nucleus and cytoplasm throughout the epithelial thickness was observed in dentigerous cyst, radicular cyst, and normal oral mucosa, respectively. YAP expression differed significantly in all odontogenic cysts compared with normal oral mucosa (p < 0.05). Ki-67 expression was notably higher in odontogenic keratocysts relative to other cysts and normal oral mucosa. Although no statistically significant correlation was found between YAP and Ki-67 across the groups, both proteins displayed similar positive trends in odontogenic keratocysts.

CONCLUSION

 These findings suggest that YAP activation may be related to the proliferative behavior of odontogenic cysts, especially in more aggressive lesions, but less likely to influence the inflammatory cysts. This insight could improve understanding of their pathogenesis and pave the way for new diagnostic and therapeutic approaches.

EDA Fibronectin Microarchitecture and YAP Translocation during Wound Closure

Fibronectin (Fn) is an extracellular matrix glycoprotein with mechanosensitive structure-function. Extra domain A (EDA) Fn, a Fn isoform, is not present in adult tissue but is required for tissue repair. Curiously, EDA Fn is linked to both regenerative and fibrotic tissue repair. Given that Fn mechanoregulates cell behavior, EDA Fn organization during wound closure might play a role in mediating these differing responses. One mechanism by which cells sense and respond to their microenvironment is by activating a transcriptional coactivator, yes-associated protein (YAP). Interestingly, YAP activity is not only required for wound closure but similarly linked to both regenerative and fibrotic repair. Therefore, this study aims to evaluate how, during normal and fibrotic wound closure, EDA Fn organization might modulate YAP translocation by culturing human dermal fibroblasts on polydimethylsiloxane substrates mimicking normal (soft: 18 kPa) and fibrotic (stiff: 146 kPa) wounded skin. On stiffer substrates mimicking fibrotic wounds, fibroblasts assembled an aligned EDA Fn matrix comprising thinner fibers, suggesting increased microenvironmental tension. To evaluate if cell binding to the EDA domain of Fn was essential to overall matrix organization, fibroblasts were treated with Irigenin, which inhibits binding to the EDA domain within Fn. Blocking adhesion to EDA led to randomly organized EDA Fn matrices with thicker fibers, suggesting reduced microenvironmental tension even during fibrotic wound closure. To evaluate whether YAP signaling plays a role in EDA Fn organization, fibroblasts were treated with CA3, which suppresses YAP activity in a dose-dependent manner. Treatment with CA3 also led to randomly organized EDA Fn matrices with thicker fibers, suggesting a potential connected mechanism of reducing tension during fibrotic wound closure. Next, YAP activity was assessed to evaluate the impact of EDA Fn organization. Interestingly, fibroblasts migrating on softer substrates mimicking normal wounds increased YAP activity, but on stiffer substrates, they decreased YAP activity. When fibroblasts on stiffer substrates were treated with Irigenin or CA3, fibroblasts increased YAP activity. These results suggest that there may be disrupted signaling between EDA Fn organization and YAP translocation during fibrotic wound closure that could be restored when reestablishing normal EDA Fn matrix organization to instead drive regenerative wound repair.

The integrin repertoire drives YAP-dependent epithelial:stromal interactions during injury of the kidney glomerulus

The kidney glomerulus is a filtration barrier in which capillary loop architecture depends on epithelial-stromal interactions between podocytes and mesangial cells. Podocytes are terminally differentiated cells within the glomerulus that express YAP and TAZ. Here we test the hypotheses that YAP and TAZ are required in podocytes to maintain capillary loop architecture and that shifts in the integrin repertoire during podocyte injury affect transcriptional activity of YAP and TAZ. Loss of YAP in podocytes of adult mice renders them more sensitive to injury, whereas loss of both YAP and TAZ in podocytes rapidly compromises the filtration barrier. α3β1 and αvβ5 are two prominent integrins on murine podocytes. Podocyte injury or loss of α3β1 leads to increased abundance of αvβ5 and nuclear localization of YAP. In vitro, blockade of αvβ5 decreases nuclear YAP. Increased αv integrins are found in human kidney disease. Thus, our studies demonstrate the crucial regulatory interplay between cell adhesion and transcriptional regulation as an important determinant of human disease.

Comparative proteomic analysis of the telogen-to-anagen transition in cashmere goat secondary hair follicles

Secondary hair follicles (SHFs) in cashmere goats produce high-value cashmere fibers, which cyclic regulation is critical for optimizing cashmere yield and quality. This study explores the phenotypic changes and differential protein expression profiles involved in the telogen-to-anagen transition of SHFs. Through histological observations, proteomic analyses, and immunohistochemical validation, we identified key molecular features and regulatory pathways underlying SHF cyclic renewal. Histological analysis showed that telogen-phase SHFs exhibit a reduced volume, decreased dermal papilla cell (DPC) and hair matrix cell (HMC) activity, compact structure, and superficial localization in the dermis. Anagen-phase SHFs exhibit significantly increased volume, deeper dermal penetration, and active cell proliferation. Proteomic analysis identified 3,654 proteins in skin samples, with 458 differentially expressed proteins (DEPs) significantly associated with biological processes such as cell adhesion, signal transduction, protein synthesis, and metabolism. These DEPs were enriched in key regulatory pathways, including Notch, Wnt, Jak-STAT, PI3K-Akt, and ECM-receptor interaction. Protein-protein interaction analysis identified A Disintegrin and Metalloproteinase Domain 17 (ADAM17), Secreted Frizzled-Related Protein 1 (SFRP1), and Protein Phosphatase 1 Catalytic Subunit Alpha (PPP1CA) as core regulators of SHF cyclic transitions. Validation by RT-qPCR, Western blot, and immunohistochemical analyses confirmed that ADAM17, SFRP1, and PPP1CA were predominantly localized in functional regions, including the outer root sheath (ORS), dermal papilla (DP), and hair matrix (HM). Their expression levels were significantly enhanced during anagen. ADAM17 is suggested to promote the growth of SHFs by regulating ORS cells proliferation and mediating signal transduction in DPCs, while SFRP1, as a modulator of the Wnt signaling pathway, likely supports SHFs growth and regeneration by modulating the activity of Secondary hair follicle stem cells (SHFSCs) and promoting the differentiation of HMCs. PPP1CA may enhance cell proliferation and metabolic activity by modulating phosphorylation states. In conclusion, this study identifies key molecular factors and pathways driving the telogen-to-anagen transition in cashmere goat SHFs. It emphasizes the roles of ADAM17, SFRP1, and PPP1CA in SHF renewal and offers insights into SHF development mechanisms and cashmere fiber improvement.

The regenerative wound healing effects and molecular mechanism of Isaria cicadae Miquel rice fermentation extract

Human skin wounds primarily heal through reparative wound healing without pilosebaceous units or other appendages, rather than regenerative wound healing. Hair follicle (HF) regeneration is a significant challenge for skin wound healing. The effects and underlying mechanisms of Isaria cicadae Miquel rice fermentation extract (IMFRE) remain unclear, although it has anti-inflammatory, antioxidant, and reparative effects on oxidative damage in keratinocytes. We assessed the regenerative wound healing ability of IMFRE and its related molecular mechanisms through experimental validation and network pharmacology analysis. Our findings suggest that IMFRE could be an important potential solution for regenerative wound healing of skin hair follicle by utilizing the Hippo pathway regulatory mechanism. KEY POINTS: • IMFRE was found to significantly enhance the wound healing rate of mouse skin. • CK15 and CD34 were significantly increased by high-dose IMFRE intervention. • IMFRE could inhibit EGFR, GPCR, and Integrin expression.

Extracellular Matrix Stiffness Modulates Myopia Scleral Remodeling Through Integrin/F-Actin/YAP Axis

Purpose

Scleral extracellular matrix (ECM) remodeling and weakened scleral stiffness are characteristic of myopia. The purpose of this study was to investigate the precise underlying mechanisms of scleral remodeling regulated by mechanical signals emanating from the ECM.

Methods

The expression and regulation of YES-associated protein (YAP) were confirmed in human samples or guinea pig myopia models by Western blot (WB) or ELISA. To mimic the biomechanical microenvironment associated with myopia, stiff (50 kPa) and soft (8 kPa) substrates were established. The underlying mechanisms were further investigated by quantitative real-time RT-PCR, WB, and fluorescence staining in cells treated with siRNAs, plasmids or inhibitors. In vivo, a YAP activator, inhibitor and F-actin polymerization facilitator were applied to evaluate their therapeutic significance for myopia.

Results

Our findings revealed that YAP expression is decreased in the sclera of guinea pigs and humans with myopia. Under mechanical stimuli, YAP functions as a mediator, transducing mechanical signals and modulating collagen expression. Furthermore, integrin α1β1 acts as a regulator of YAP and operates through modification of the F-actin cytoskeleton. Specifically, in response to mechanical forces, integrin α1β1 modulates F-actin restructuring. This modified actin cytoskeletal architecture subsequently facilitates the nuclear translocation of YAP, ultimately leading to the suppression of COL1A1 expression.

Conclusions

Our results suggest that the integrin α1β1-F-actin-YAP-COL1A1 axis constitutes a vital regulatory mechanism intrinsically associated with the pathogenesis of myopia.

KANK1 promotes breast cancer development by compromising Scribble-mediated Hippo activation

KANK1 is expressed in epithelial cells and connects focal adhesions with the adjacent cortical microtubule stabilizing complex. Although KANK1 was shown to suppress cancer cell growth in vitro, TCGA database points to high KANK1 levels associated with poor prognosis in a wide spectrum of human malignancies. Here, we address this discrepancy and report that KANK1 promotes proliferation and survival of PyMT-transformed mammary tumor cells in vivo. Mechanistically, KANK1 localizes to the basal side of basement membrane (BM)-attached transformed luminal epithelial cells. When these cells lose the contact with the BM and disassemble integrin adhesions, KANK1 is found at cell-cell junctions where it competes with the polarity and tumor suppressor Scribble for NOS1AP binding, which curbs the ability of Scribble to promote Hippo pathway activity. The consequences are stabilization and nuclear accumulation of TAZ, growth and survival of tumor cells and elevated breast cancer development.

Stromal softness confines pancreatic cancer growth through lysosomal-cathepsin mediated YAP1 degradation

The progression and malignancy of many tumors are associated with increased tissue stiffness. Conversely, the oncogenically transformed cells can be confined in soft stroma. Yet, the underlying mechanisms by which soft matrix confines tumorigenesis and metastasis remain elusive. Here, we show that pancreatic cancer cells are suppressed in the soft extracellular matrix, which is associated with YAP1 degradation through autophagic-lysosomal pathway rather than Hippo signal mediated proteasome pathway. In the soft stroma, PTEN is upregulated and activated, which consequently promotes lysosomal biogenesis, leading to the activation of cysteine-cathepsins for YAP1 degradation. In vitro, purified cathepsin L can directly digest YAP1 under acidic conditions. Lysosomal stress, either caused by chloroquine or overexpression of cystatin A/B, results in YAP1 accumulation and malignant transformation. Likewise, liver fibrosis induced stiffness can promote malignant potential in mice. Clinical data show that down-regulation of lysosomal biogenesis is associated with pancreatic fibrosis and stiffness, YAP1 accumulation, and poor prognosis in PDAC patients. Together, our findings suggest that soft stroma triggers lysosomal flux-mediated YAP1 degradation and induces cancer cell dormancy.

ETS1 Expression in Diabetic Foot Ulcers: Implications for Fibroblast Phenotype and Wound Healing Through the PP2A/YAP Pathway

Objective

Diabetic foot ulcers (DFUs) are a serious complication of diabetes, characterized by impaired wound healing and high morbidity and mortality risks. While ETS1 is known to influence fibroblast pathological remodeling, its specific role in DFU and fibroblast wound healing remains unclear.

Methods

Skin tissue samples from DFU patients were categorized by Wagner grades to analyze ETS1 expression. Primary fibroblasts derived from diabetes mellitus wound (DMFBs) were collected from wound margins to test migration ability and analyze cell phenotype by immunofluorescence; they were further treated with siETS1 and the ETS1 inhibitor YK-4-279. Techniques including Western blotting, quantitative Real-Time PCR (qRT-PCR), and immunofluorescence were used to assess the expressionof ETS1, Collagen I, and phenotype in DMFBs. Additionally, the binding sites between human ETS1 and the PP2A promoter were predicted by the UCSC and JASPAR databases. It intended to explore the negative transcriptional regulation of PP2A by ETS1 and its implications in fibroblast function and wound healing.

Results

Fibroblasts derived from Wagner Grades II-IV exhibit differences in cell morphology, migratory ability, and phenotype. Our findings indicate a significant upregulation of ETS1 in Wagner III and IV. The downregulation of ETS1 was observed to enhance DMFB migration and increase the expression of Collagen I and α-SMA. These changes suggest a potential mechanism by which PP2A regulates the YAP/Hippo pathway in diabetic wound healing.

Conclusion

ETS1 appears to impede the repair processes in DFUs, likely through the negative regulation of PP2A, affecting fibroblast function and wound healing.

HPV18 E7 inhibits LATS1 kinase and activates YAP1 by degrading PTPN14

High-risk human papillomavirus (HPV) oncoproteins inactivate cellular tumor suppressors to reprogram host cell signaling pathways. HPV E7 proteins bind and degrade the tumor suppressor PTPN14, thereby promoting the nuclear localization of the YAP1 oncoprotein and inhibiting keratinocyte differentiation. YAP1 is a transcriptional coactivator that drives epithelial cell stemness and self-renewal. YAP1 activity is inhibited by the highly conserved Hippo pathway, which is frequently inactivated in human cancers. MST1/2 and LATS1/2 kinases form the core of the Hippo kinase cascade. Active LATS1 kinase is phosphorylated on threonine 1079 and inhibits YAP1 by phosphorylating it on amino acids including serine 127. Here, we tested the effect of high-risk (carcinogenic) HPV18 E7 on Hippo pathway activity. We found that either PTPN14 knockout or PTPN14 degradation by HPV18 E7 decreased the phosphorylation of LATS1 T1079 and YAP1 S127 in human keratinocytes and inhibited keratinocyte differentiation. Conversely, PTPN14-dependent differentiation required LATS kinases and certain PPxY motifs in PTPN14. Neither MST1/2 kinases nor the putative PTPN14 phosphatase active sites were required for PTPN14 to promote differentiation. Together, these data support that PTPN14 inactivation or degradation of PTPN14 by HPV18 E7 reduce LATS1 activity, promoting active YAP1 and inhibiting keratinocyte differentiation.IMPORTANCEThe Hippo kinase cascade inhibits YAP1, an oncoprotein and driver of cell stemness and self-renewal. There is mounting evidence that the Hippo pathway is targeted by tumor viruses including human papillomavirus. The high-risk HPV E7 oncoprotein promotes YAP1 nuclear localization and the carcinogenic activity of high-risk HPV E7 requires YAP1 activity. Blocking HPV E7-dependent YAP1 activation could inhibit HPV-mediated carcinogenesis, but the mechanism by which HPV E7 activates YAP1 has not been elucidated. Here we report that by degrading the tumor suppressor PTPN14, HPV18 E7 inhibits LATS1 kinase, reducing inhibitory phosphorylation on YAP1. These data support that an HPV oncoprotein can inhibit Hippo signaling to activate YAP1 and strengthen the link between PTPN14 and Hippo signaling in human epithelial cells.

The Hippo signalling pathway in bone homeostasis: Under the regulation of mechanics and aging

The Hippo signalling pathway is a conserved kinase cascade that orchestrates diverse cellular processes, such as proliferation, apoptosis, lineage commitment and stemness. With the onset of society ages, research on skeletal aging-mechanics-bone homeostasis has exploded. In recent years, aging and mechanical force in the skeletal system have gained groundbreaking research progress. Under the regulation of mechanics and aging, the Hippo signalling pathway has a crucial role in the development and homeostasis of bone. We synthesize the current knowledge on the role of the Hippo signalling pathway, particularly its downstream effectors yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), in bone homeostasis. We discuss the regulation of the lineage specification and function of different skeletal cell types by the Hippo signalling pathway. The interactions of the Hippo signalling pathway with other pathways, such as Wnt, transforming growth factor beta and nuclear factor kappa-B, are also mentioned because of their importance for modulating bone homeostasis. Furthermore, YAP/TAZ have been extensively studied as mechanotransducers. Due to space limitations, we focus on reviewing how mechanical forces and aging influence cell fate, communications and homeostasis through a dysregulated Hippo signalling pathway.

EDA Fibronectin Microarchitecture and YAP Translocation During Wound Closure

Fibronectin (Fn) is an extracellular matrix glycoprotein with mechanosensitive structure-function. EDA Fn, a Fn isoform, is not present in adult tissue but is required for tissue repair. Curiously, EDA Fn is linked to both regenerative and fibrotic tissue repair. Given that Fn mechanoregulates cell behavior, Fn EDA organization during wound closure might play a role in mediating these differing responses. One mechanism by which cells sense and respond to their microenvironment is by activating a transcriptional co-activator, Yes-associated protein (YAP). Interestingly, YAP activity is not only required for wound closure, but similarly linked to both regenerative and fibrotic repair. Therefore, this study aims to evaluate how, during normal and fibrotic wound closure, EDA Fn organization might modulate YAP translocation by culturing human dermal fibroblasts on polydimethylsiloxane (PDMS) substrates mimicking normal (soft: 18 kPa) and fibrotic (stiff: 146 kPa) wounded skin. On stiffer substrates mimicking fibrotic wounds, fibroblasts assembled an aligned EDA Fn matrix comprising thinner fibers, suggesting increased microenvironmental tension. To evaluate if cell binding to the EDA domain of Fn was essential to overall matrix organization, fibroblasts were treated with Irigenin, which inhibits binding to the EDA domain within Fn. Blocking adhesion to EDA led to randomly organized EDA Fn matrices with thicker fibers, suggesting reduced microenvironmental tension even during fibrotic wound closure. To evaluate if YAP signaling plays a role in EDA Fn organization, fibroblasts were treated with CA3, which suppresses YAP activity in a dose-dependent manner. Treatment with CA3 also led to randomly organized EDA Fn matrices with thicker fibers, suggesting a potential connected mechanism of reducing tension during fibrotic wound closure. Next, YAP activity was assessed to evaluate the impact of EDA Fn organization. Interestingly, fibroblasts migrating on softer substrates mimicking normal wounds increased YAP activity but on stiffer substrates, decreased YAP activity. When fibroblasts on stiffer substrates were treated with Irigenin or CA3, fibroblasts increased YAP activity. These results suggest there may be disrupted signaling between EDA Fn organization and YAP translocation during fibrotic wound closure that could be restored when reestablishing normal EDA Fn matrix organization to instead drive regenerative wound repair.

Hypoxia and Foxn1 alter the proteomic signature of dermal fibroblasts to redirect scarless wound healing to scar-forming skin wound healing in Foxn1-/- mice

BACKGROUND

Foxn1-/- deficient mice are a rare model of regenerative skin wound healing among mammals. In wounded skin, the transcription factor Foxn1 interacting with hypoxia-regulated factors affects re-epithelialization, epithelial-mesenchymal transition (EMT) and dermal white adipose tissue (dWAT) reestablishment and is thus a factor regulating scar-forming/reparative healing. Here, we hypothesized that transcriptional crosstalk between Foxn1 and Hif-1α controls the switch from scarless (regenerative) to scar-present (reparative) skin wound healing. To verify this hypothesis, we examined (i) the effect of hypoxia/normoxia and Foxn1 signalling on the proteomic signature of Foxn1-/- (regenerative) dermal fibroblasts (DFs) and then (ii) explored the effect of Hif-1α or Foxn1/Hif-1α introduced by a lentiviral (LV) delivery vector to injured skin of regenerative Foxn1-/- mice with particular attention to the remodelling phase of healing.

RESULTS

We showed that hypoxic conditions and Foxn1 stimulation modified the proteome of Foxn1-/- DFs. Hypoxic conditions upregulated DF protein profiles, particularly those related to extracellular matrix (ECM) composition: plasminogen activator inhibitor-1 (Pai-1), Sdc4, Plod2, Plod1, Lox, Loxl2, Itga2, Vldlr, Ftl1, Vegfa, Hmox1, Fth1, and F3. We found that Pai-1 was stimulated by hypoxic conditions in regenerative Foxn1-/- DFs but was released by DFs to the culture media exclusively upon hypoxia and Foxn1 stimulation. We also found higher levels of Pai-1 protein in DFs isolated from Foxn1+/+ mice (reparative/scar-forming) than in DFs isolated from Foxn1-/- (regenerative/scarless) mice and triggered by injury increase in Foxn1 and Pai-1 protein in the skin of mice with active Foxn1 (Foxn1+/+ mice). Then, we demonstrated that the introduction of Foxn1 and Hif-1α via lentiviral injection into the wounded skin of regenerative Foxn1-/- mice activates reparative/scar-forming healing by increasing the wounded skin area and decreasing hyaluronic acid deposition and the collagen type III to I ratio. We also identified a stimulatory effect of LV-Foxn1 + LV-Hif-1α injection in the wounded skin of Foxn1-/- mice on Pai-1 protein levels.

CONCLUSIONS

The present data highlight the effect of hypoxia and Foxn1 on the protein profile and functionality of regenerative Foxn1-/- DFs and demonstrate that the introduction of Foxn1 and Hif-1α into the wounded skin of regenerative Foxn1-/- mice activates reparative/scar-forming healing.

Restoring mechanophenotype reverts malignant properties of ECM-enriched vocal fold cancer

Increased extracellular matrix (ECM) and matrix stiffness promote solid tumor progression. However, mechanotransduction in cancers arising in mechanically active tissues remains underexplored. Here, we report upregulation of multiple ECM components accompanied by tissue stiffening in vocal fold cancer (VFC). We compare non-cancerous (NC) and patient-derived VFC cells - from early (mobile, T1) to advanced-stage (immobile, T3) cancers - revealing an association between VFC progression and cell-surface receptor heterogeneity, reduced laminin-binding integrin cell-cell junction localization and a flocking mode of collective cell motility. Mimicking physiological movement of healthy vocal fold tissue (stretching/vibration), decreases oncogenic nuclear β-catenin and YAP levels in VFC. Multiplex immunohistochemistry of VFC tumors uncovered a correlation between ECM content, nuclear YAP and patient survival, concordant with VFC sensitivity to YAP-TEAD inhibitors in vitro. Our findings present evidence that VFC is a mechanically sensitive malignancy and restoration of tumor mechanophenotype or YAP/TAZ targeting, represents a tractable anti-oncogenic therapeutic avenue for VFC.

Crk mediates Csk-Hippo signaling independently of Yap tyrosine phosphorylation to induce cell extrusion

Src family kinases (SFKs), including Src, Fyn and Yes, play important roles in development and cancer. Despite being first discovered as the Yes-associated protein, the regulation of Yap by SFKs remains poorly understood. Here, through single-cell analysis and genetic lineage tracing, we show that the pan-epithelial ablation of C-terminal Src kinase (Csk) in the lacrimal gland unleashes broad Src signaling but specifically causes extrusion and apoptosis of acinar progenitors at a time when they are shielded by myoepithelial cells from the basement membrane. Csk mutants can be phenocopied by constitutively active Yap and rescued by deleting Yap or Taz, indicating a significant functional overlap between Src and Yap signaling. Although Src-induced tyrosine phosphorylation has long been believed to regulate Yap activity, we find that mutating these tyrosine residues in both Yap and Taz fails to perturb mouse development or alleviate the Csk lacrimal gland phenotype. In contrast, Yap loses Hippo signaling-dependent serine phosphorylation and translocates into the nucleus in Csk mutants. Further chemical genetics studies demonstrate that acute inhibition of Csk enhances Crk/CrkL phosphorylation and Rac1 activity, whereas removing Crk/CrkL or Rac1/Rap1 ameliorates the Csk mutant phenotype. These results show that Src controls Hippo-Yap signaling through the Crk/CrkL-Rac/Rap axis to promote cell extrusion.

HPV18 E7 inhibits LATS1 kinase and activates YAP1 by degrading PTPN14

High-risk human papillomavirus (HPV) oncoproteins inactivate cellular tumor suppressors to reprogram host cell signaling pathways. HPV E7 proteins bind and degrade the tumor suppressor PTPN14, thereby promoting the nuclear localization of the YAP1 oncoprotein and inhibiting keratinocyte differentiation. YAP1 is a transcriptional coactivator that drives epithelial cell stemness and self-renewal. YAP1 activity is inhibited by the highly conserved Hippo pathway, which is frequently inactivated in human cancers. MST1/2 and LATS1/2 kinases form the core of the Hippo kinase cascade. Active LATS1 kinase is phosphorylated on threonine 1079 and inhibits YAP1 by phosphorylating it on amino acids including serine 127. Here, we tested the effect of high-risk (carcinogenic) HPV18 E7 on Hippo pathway activity. We found that either PTPN14 knockout or PTPN14 degradation by HPV18 E7 decreased phosphorylation of LATS1 T1079 and YAP1 S127 in human keratinocytes and inhibited keratinocyte differentiation. Conversely, PTPN14-dependent differentiation required LATS kinases and certain PPxY motifs in PTPN14. Neither MST1/2 kinases nor the putative PTPN14 phosphatase active site were required for PTPN14 to promote differentiation. Taken together, these data support that PTPN14 inactivation or degradation of PTPN14 by HPV18 E7 reduce LATS1 activity, promoting active YAP1 and inhibiting keratinocyte differentiation.

A YAP-centered mechanotransduction loop drives collective breast cancer cell invasion

Dense and aligned Collagen I fibers are associated with collective cancer invasion led by protrusive tumor cells, leader cells. In some breast tumors, a population of cancer cells (basal-like cells) maintain several epithelial characteristics and express the myoepithelial/basal cell marker Keratin 14 (K14). Emergence of leader cells and K14 expression are regarded as interconnected events triggered by Collagen I, however the underlying mechanisms remain unknown. Using breast carcinoma organoids, we show that Collagen I drives a force-dependent loop, specifically in basal-like cancer cells. The feed-forward loop is centered around the mechanotransducer Yap and independent of K14 expression. Yap promotes a transcriptional program that enhances Collagen I alignment and tension, which further activates Yap. Active Yap is detected in invading breast cancer cells in patients and required for collective invasion in 3D Collagen I and in the mammary fat pad of mice. Our work uncovers an essential function for Yap in leader cell selection during collective cancer invasion.

YAP and TAZ differentially regulate postnatal cortical progenitor proliferation and astrocyte differentiation

WW domain-containing transcription regulator 1 (WWTR1, referred to here as TAZ) and Yes-associated protein (YAP, also known as YAP1) are transcriptional co-activators traditionally studied together as a part of the Hippo pathway, and are best known for their roles in stem cell proliferation and differentiation. Despite their similarities, TAZ and YAP can exert divergent cellular effects by differentially interacting with other signaling pathways that regulate stem cell maintenance or differentiation. In this study, we show in mouse neural stem and progenitor cells (NPCs) that TAZ regulates astrocytic differentiation and maturation, and that TAZ mediates some, but not all, of the effects of bone morphogenetic protein (BMP) signaling on astrocytic development. By contrast, both TAZ and YAP mediate the effects on NPC fate of β1-integrin (ITGB1) and integrin-linked kinase signaling, and these effects are dependent on extracellular matrix cues. These findings demonstrate that TAZ and YAP perform divergent functions in the regulation of astrocyte differentiation, where YAP regulates cell cycle states of astrocytic progenitors and TAZ regulates differentiation and maturation from astrocytic progenitors into astrocytes.

Roles for epithelial integrin α3β1 in regulation of the microenvironment during normal and pathological tissue remodeling

Integrin receptors for the extracellular matrix activate intracellular signaling pathways that are critical for tissue development, homeostasis, and regeneration/repair, and their loss or dysregulation contributes to many developmental defects and tissue pathologies. This review will focus on tissue remodeling roles for integrin α3β1, a receptor for laminins found in the basement membranes (BMs) that underlie epithelial cell layers. As a paradigm, we will discuss literature that supports a role for α3β1 in promoting ability of epidermal keratinocytes to modify their tissue microenvironment during skin development, wound healing, or tumorigenesis. Preclinical and clinical studies have shown that this role depends largely on ability of α3β1 to govern the keratinocyte's repertoire of secreted proteins, or the "secretome," including 1) matrix proteins and proteases involved in matrix remodeling and 2) paracrine-acting growth factors/cytokines that stimulate other cells with important tissue remodeling functions (e.g., endothelial cells, fibroblasts, inflammatory cells). Moreover, α3β1 signaling controls gene expression that helps epithelial cells carry out these functions, including genes that encode secreted matrix proteins, proteases, growth factors, or cytokines. We will review what is known about α3β1-dependent gene regulation through both transcription and posttranscriptional mRNA stability. Regarding the latter, we will discuss examples of α3β1-dependent alternative splicing (AS) or alternative polyadenylation (APA) that prevents inclusion of cis-acting mRNA sequences that would otherwise target the transcript for degradation via nonsense-mediated decay or destabilizing AU-rich elements (AREs) in the 3'-untranslated region (3'-UTR). Finally, we will discuss prospects and anticipated challenges of exploiting α3β1 as a clinical target for the treatment of cancer or wound healing.

Dermal stiffness governs the topography of the epidermis and the underlying basement membrane in young and old human skin

The epidermis is a stratified epithelium that forms the outer layer of the skin. It is composed primarily of keratinocytes and is constantly renewed by the proliferation of stem cells and their progeny that undergo terminal differentiation as they leave the basal layer and migrate to the skin surface. Basal keratinocytes rest on a basement membrane composed of an extracellular matrix that controls their fate via integrin-mediated focal adhesions and hemidesmosomes which are critical elements of the epidermal barrier and promote its regenerative capabilities. The distribution of basal cells with optimal activity provides the basement membrane with its characteristic undulating shape; this configuration disappears with age, leading to epidermal weakness. In this study, we present an in-depth imaging analysis of basal keratinocyte anchorage in samples of human skin from participants across the age spectrum. Our findings reveal that skin aging is associated with the depletion of hemidesmosomes that provide crucial support for stem cell maintenance; their depletion correlates with the loss of the characteristic basement membrane structure. Atomic force microscopy studies of skin and in vitro experiments revealed that the increase in tissue stiffness observed with aging triggers mechanical signals that alter the basement membrane structure and reduce the extent of basal keratinocyte anchorage, forcing them to differentiate. Genomic analysis revealed that epidermal aging was associated with mechanical induction of the transcription factor Krüppel-like factor 4. The altered mechanical properties of tissue being a new hallmark of aging, our work opens new avenues for the development of skin rejuvenation strategies.

ECM and epithelial stem cells: the scaffold of destiny

Adult stem cells play a critical role in maintaining tissue homeostasis and promoting longevity. The intricate organization and presence of common markers among adult epithelial stem cells in the intestine, lung, and skin serve as hallmarks of these cells. The specific location pattern of these cells within their respective organs highlights the significance of the niche in which they reside. The extracellular matrix (ECM) not only provides physical support but also acts as a reservoir for various biochemical and biophysical signals. We will consider differences in proliferation, repair, and regenerative capacities of the three epithelia and review how environmental cues emerging from the niche regulate cell fate. These cues are transduced via mechanosignaling, regulating gene expression, and bring us to the concept of the fate scaffold. Understanding both the analogies and discrepancies in the mechanisms that govern stem cell fate in various organs can offer valuable insights for rejuvenation therapy and tissue engineering.

YAP/TAZ as Molecular Targets in Skeletal Muscle Atrophy and Osteoporosis

Skeletal muscles and bones are closely connected anatomically and functionally. Age-related degeneration in these tissues is associated with physical disability in the elderly and significantly impacts their quality of life. Understanding the mechanisms of age-related musculoskeletal tissue degeneration is crucial for identifying molecular targets for therapeutic interventions for skeletal muscle atrophy and osteoporosis. The Hippo pathway is a recently identified signaling pathway that plays critical roles in development, tissue homeostasis, and regeneration. The Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key downstream effectors of the mammalian Hippo signaling pathway. This review highlights the fundamental roles of YAP and TAZ in the homeostatic maintenance and regeneration of skeletal muscles and bones. YAP/TAZ play a significant role in stem cell function by relaying various environmental signals to stem cells. Skeletal muscle atrophy and osteoporosis are related to stem cell dysfunction or senescence triggered by YAP/TAZ dysregulation resulting from reduced mechanosensing and mitochondrial function in stem cells. In contrast, the maintenance of YAP/TAZ activation can suppress stem cell senescence and tissue dysfunction and may be used as a basis for the development of potential therapeutic strategies. Thus, targeting YAP/TAZ holds significant therapeutic potential for alleviating age-related muscle and bone dysfunction and improving the quality of life in the elderly.

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.

Ablation of integrin-mediated cell-collagen communication alleviates fibrosis

OBJECTIVES

Activation of fibroblasts is a hallmark of fibrotic processes. Besides cytokines and growth factors, fibroblasts are regulated by the extracellular matrix environment through receptors such as integrins, which transduce biochemical and mechanical signals enabling cells to mount appropriate responses according to biological demands. The aim of this work was to investigate the in vivo role of collagen-fibroblast interactions for regulating fibroblast functions and fibrosis.

METHODS

Triple knockout (tKO) mice with a combined ablation of integrins α1β1, α2β1 and α11β1 were created to address the significance of integrin-mediated cell-collagen communication. Properties of primary dermal fibroblasts lacking collagen-binding integrins were delineated in vitro. Response of the tKO mice skin to bleomycin induced fibrotic challenge was assessed.

RESULTS

Triple integrin-deficient mice develop normally, are transiently smaller and reveal mild alterations in mechanoresilience of the skin. Fibroblasts from these mice in culture show defects in cytoskeletal architecture, traction stress generation, matrix production and organisation. Ablation of the three integrins leads to increased levels of discoidin domain receptor 2, an alternative receptor recognising collagens in vivo and in vitro. However, this overexpression fails to compensate adhesion and spreading defects on collagen substrates in vitro. Mice lacking collagen-binding integrins show a severely attenuated fibrotic response with impaired mechanotransduction, reduced collagen production and matrix organisation.

CONCLUSIONS

The data provide evidence for a crucial role of collagen-binding integrins in fibroblast force generation and differentiation in vitro and for matrix deposition and tissue remodelling in vivo. Targeting fibroblast-collagen interactions might represent a promising therapeutic approach to regulate connective tissue deposition in fibrotic diseases.

Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.

Integrin signaling in cancer: bidirectional mechanisms and therapeutic opportunities

Integrins are transmembrane receptors that possess distinct ligand-binding specificities in the extracellular domain and signaling properties in the cytoplasmic domain. While most integrins have a short cytoplasmic tail, integrin β4 has a long cytoplasmic tail that can indirectly interact with the actin cytoskeleton. Additionally, 'inside-out' signals can induce integrins to adopt a high-affinity extended conformation for their appropriate ligands. These properties enable integrins to transmit bidirectional cellular signals, making it a critical regulator of various biological processes.Integrin expression and function are tightly linked to various aspects of tumor progression, including initiation, angiogenesis, cell motility, invasion, and metastasis. Certain integrins have been shown to drive tumorigenesis or amplify oncogenic signals by interacting with corresponding receptors, while others have marginal or even suppressive effects. Additionally, different α/β subtypes of integrins can exhibit opposite effects. Integrin-mediated signaling pathways including Ras- and Rho-GTPase, TGFβ, Hippo, Wnt, Notch, and sonic hedgehog (Shh) are involved in various stages of tumorigenesis. Therefore, understanding the complex regulatory mechanisms and molecular specificities of integrins are crucial to delaying cancer progression and suppressing tumorigenesis. Furthermore, the development of integrin-based therapeutics for cancer are of great importance.This review provides an overview of integrin-dependent bidirectional signaling mechanisms in cancer that can either support or oppose tumorigenesis by interacting with various signaling pathways. Finally, we focus on the future opportunities for emergent therapeutics based on integrin agonists. Video Abstract.

Musculoskeletal defects associated with myosin heavy chain-embryonic loss of function are mediated by the YAP signaling pathway

Mutations in MYH3, the gene encoding the developmental myosin heavy chain-embryonic (MyHC-embryonic) skeletal muscle-specific contractile protein, cause several congenital contracture syndromes. Among these, recessive loss-of-function MYH3 mutations lead to spondylocarpotarsal synostosis (SCTS), characterized by vertebral fusions and scoliosis. We find that Myh3 germline knockout adult mice display SCTS phenotypes such as scoliosis and vertebral fusion, in addition to reduced body weight, muscle weight, myofiber size, and grip strength. Myh3 knockout mice also exhibit changes in muscle fiber type, altered satellite cell numbers and increased muscle fibrosis. A mass spectrometric analysis of embryonic skeletal muscle from Myh3 knockouts identified integrin signaling and cytoskeletal regulation as the most affected pathways. These pathways are closely connected to the mechanosensing Yes-associated protein (YAP) transcriptional regulator, which we found to be significantly activated in the skeletal muscle of Myh3 knockout mice. To test whether increased YAP signaling might underlie the musculoskeletal defects in Myh3 knockout mice, we treated these mice with CA3, a small molecule inhibitor of YAP signaling. This led to increased muscle fiber size, rescue of most muscle fiber type alterations, normalization of the satellite cell marker Pax7 levels, increased grip strength, reduced fibrosis, and decline in scoliosis in Myh3 knockout mice. Thus, increased YAP activation underlies the musculoskeletal defects seen in Myh3 knockout mice, indicating its significance as a key pathway to target in SCTS and other MYH3-related congenital syndromes.

Small intestinal submucosa promotes angiogenesis via the Hippo pathway to improve vaginal repair

Vaginal reconstruction has incorporated the use of gastrointestinal segments for decades, but the technique is inevitably associated with complications. Tissue-engineering techniques, however, have brought great hope for vaginal reconstruction. This study aimed to evaluate the utility of small intestinal submucosa (SIS) in reconstructing clinically significant large vaginal defects in a porcine model and to investigate the role of the Hippo pathway in the vascular remodeling process. The composition and mechanical properties of SIS were characterized. Full-thickness vaginal defects were established in 10 minipig donors, with 4 cm lengths removed and replaced by an equal sized SIS scaffolds. The neovaginas were subjected to macroscopic, histological, immunohistochemical and molecular evaluations at 4 and 12 weeks after the surgery. Four weeks after the operation, extracellular matrix reorganization and complete coverage of the surface of the luminal matrix by vaginal epithelium were observed, accompanied by the formation of a microvascular network and the regeneration of smooth muscles, albeit disorderly arranged. Twelve weeks after implantation, enhancements were seen in the formation of the multi-layered squamous epithelium, angiogenesis, and large muscle bundle formation in the vagina. Additionally, the expression levels of angiogenesis-related proteins, proliferation-related proteins and Hippo pathway-related proteins in the neovagina were significantly increased. These results indicate that SIS could be used to reconstruct large vaginal defects and that the vascular remodeling process is potentially regulated by the Hippo pathway.

Cellular mechanotransduction in health and diseases: from molecular mechanism to therapeutic targets

Cellular mechanotransduction, a critical regulator of numerous biological processes, is the conversion from mechanical signals to biochemical signals regarding cell activities and metabolism. Typical mechanical cues in organisms include hydrostatic pressure, fluid shear stress, tensile force, extracellular matrix stiffness or tissue elasticity, and extracellular fluid viscosity. Mechanotransduction has been expected to trigger multiple biological processes, such as embryonic development, tissue repair and regeneration. However, prolonged excessive mechanical stimulation can result in pathological processes, such as multi-organ fibrosis, tumorigenesis, and cancer immunotherapy resistance. Although the associations between mechanical cues and normal tissue homeostasis or diseases have been identified, the regulatory mechanisms among different mechanical cues are not yet comprehensively illustrated, and no effective therapies are currently available targeting mechanical cue-related signaling. This review systematically summarizes the characteristics and regulatory mechanisms of typical mechanical cues in normal conditions and diseases with the updated evidence. The key effectors responding to mechanical stimulations are listed, such as Piezo channels, integrins, Yes-associated protein (YAP) /transcriptional coactivator with PDZ-binding motif (TAZ), and transient receptor potential vanilloid 4 (TRPV4). We also reviewed the key signaling pathways, therapeutic targets and cutting-edge clinical applications of diseases related to mechanical cues.

Regulation of Photosensitivity by the Hippo Pathway in Lupus Skin

OBJECTIVE

Photosensitivity is one of the most common manifestations of systemic lupus erythematosus (SLE), yet its pathogenesis is not well understood. The normal-appearing epidermis of patients with SLE exhibits increased ultraviolet B (UVB)-driven cell death that persists in cell culture. Here, we investigated the role of epigenetic modification and Hippo signaling in enhanced UVB-induced apoptosis seen in SLE keratinocytes.

METHODS

We analyzed DNA methylation in cultured keratinocytes from SLE patients compared to keratinocytes from healthy controls (n = 6/group). Protein expression was validated in cultured keratinocytes using immunoblotting and immunofluorescence. An immortalized keratinocyte line overexpressing WWC1 was generated via lentiviral vector. WWC1-driven changes were inhibited using a large tumor suppressor kinase 1/2 (LATS1/2) inhibitor (TRULI) and small interfering RNA (siRNA). The interaction between the Yes-associated protein (YAP) and the transcriptional enhancer associate domain (TEAD) was inhibited by overexpression of an N/TERT cell line expressing a tetracycline-inducible green fluorescent protein-tagged protein that inhibits YAP-TEAD binding (TEADi). Apoptosis was assessed using cleaved caspase 3/7 and TUNEL staining.

RESULTS

Hippo signaling was the top differentially methylated pathway in SLE versus control keratinocytes. SLE keratinocytes (n = 6) showed significant hypomethylation (Δβ = -0.153) and thus overexpression of the Hippo regulator WWC1 (P = 0.002). WWC1 overexpression increased LATS1/2 kinase activation, leading to YAP cytoplasmic retention and altered proapoptotic transcription in SLE keratinocytes. Accordingly, UVB-mediated apoptosis in keratinocytes could be enhanced by WWC1 overexpression or YAP-TEAD inhibition, mimicking SLE keratinocytes. Importantly, inhibition of LATS1/2 with either the chemical inhibitor TRULI or siRNA effectively eliminated enhanced UVB-apoptosis in SLE keratinocytes.

CONCLUSION

Our work unravels a novel driver of photosensitivity in SLE: overactive Hippo signaling in SLE keratinocytes restricts YAP transcriptional activity, leading to shifts that promote UVB apoptosis.

A comprehensive review of stroke-related signaling pathways and treatment in western medicine and traditional Chinese medicine

This review provides insight into the complex network of signaling pathways and mechanisms involved in stroke pathophysiology. It summarizes the historical progress of stroke-related signaling pathways, identifying potential interactions between them and emphasizing that stroke is a complex network disease. Of particular interest are the Hippo signaling pathway and ferroptosis signaling pathway, which remain understudied areas of research, and are therefore a focus of the review. The involvement of multiple signaling pathways, including Sonic Hedgehog (SHH), nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE), hypoxia-inducible factor-1α (HIF-1α), PI3K/AKT, JAK/STAT, and AMPK in pathophysiological mechanisms such as oxidative stress and apoptosis, highlights the complexity of stroke. The review also delves into the details of traditional Chinese medicine (TCM) therapies such as Rehmanniae and Astragalus, providing an analysis of the recent status of western medicine in the treatment of stroke and the advantages and disadvantages of TCM and western medicine in stroke treatment. The review proposes that since stroke is a network disease, TCM has the potential and advantages of a multi-target and multi-pathway mechanism of action in the treatment of stroke. Therefore, it is suggested that future research should explore more treasures of TCM and develop new therapies from the perspective of stroke as a network disease.

A Yap-dependent mechanoregulatory program sustains cell migration for embryo axis assembly

The assembly of the embryo's primary axis is a fundamental landmark for the establishment of the vertebrate body plan. Although the morphogenetic movements directing cell convergence towards the midline have been described extensively, little is known on how gastrulating cells interpret mechanical cues. Yap proteins are well-known transcriptional mechanotransducers, yet their role in gastrulation remains elusive. Here we show that the double knockout of yap and its paralog yap1b in medaka results in an axis assembly failure, due to reduced displacement and migratory persistence in mutant cells. Accordingly, we identified genes involved in cytoskeletal organization and cell-ECM adhesion as potentially direct Yap targets. Dynamic analysis of live sensors and downstream targets reveal that Yap is acting in migratory cells, promoting cortical actin and focal adhesions recruitment. Our results indicate that Yap coordinates a mechanoregulatory program to sustain intracellular tension and maintain the directed cell migration for embryo axis development.

Epstein-Barr virus LMP1 protein promotes proliferation and inhibits differentiation of epithelial cells via activation of YAP and TAZ

Latent Epstein-Barr virus (EBV) infection promotes undifferentiated nasopharyngeal carcinomas (NPCs) in humans, but the mechanism(s) for this effect has been difficult to study because EBV cannot transform normal epithelial cells in vitro and the EBV genome is often lost when NPC cells are grown in culture. Here we show that the latent EBV protein, LMP1 (Latent membrane protein 1), induces cellular proliferation and inhibits spontaneous differentiation of telomerase-immortalized normal oral keratinocytes (NOKs) in growth factor-deficient conditions by increasing the activity of the Hippo pathway effectors, YAP (Yes-associated protein) and TAZ (Transcriptional coactivator with PDZ-binding motif). We demonstrate that LMP1 enhances YAP and TAZ activity in NOKs both by decreasing Hippo pathway-mediated serine phosphorylation of YAP and TAZ and increasing Src kinase-mediated Y357 phosphorylation of YAP. Furthermore, knockdown of YAP and TAZ is sufficient to reduce proliferation and promote differentiation in EBV-infected NOKs. We find that YAP and TAZ are also required for LMP1-induced epithelial-to-mesenchymal transition. Importantly, we demonstrate that ibrutinib (an FDA-approved BTK inhibitor that blocks YAP and TAZ activity through an off-target effect) restores spontaneous differentiation and inhibits proliferation of EBV-infected NOKs at clinically relevant doses. These results suggest that LMP1-induced YAP and TAZ activity contributes to the development of NPC.

Optogenetic control of YAP can enhance the rate of wound healing

BACKGROUND

Tissues need to regenerate to restore function after injury. Yet, this regenerative capacity varies significantly between organs and between species. For example, in the heart, some species retain full regenerative capacity throughout their lifespan but human cardiac cells display a limited ability to repair the injury. After a myocardial infarction, the function of cardiomyocytes is impaired and reduces the ability of the heart to pump, causing heart failure. Therefore, there is a need to restore the function of an injured heart post myocardial infarction. We investigate in cell culture the role of the Yes-associated protein (YAP), a transcriptional co-regulator with a pivotal role in growth, in driving repair after injury.

METHODS

We express optogenetic YAP (optoYAP) in three different cell lines. We characterised the behaviour and function of optoYAP using fluorescence imaging and quantitative real-time PCR of downstream YAP target genes. Mutant constructs were generated using site-directed mutagenesis. Nuclear localised optoYAP was functionally tested using wound healing assay.

RESULTS

Utilising optoYAP, which enables precise control of pathway activation, we show that YAP induces the expression of downstream genes involved in proliferation and migration. optoYAP can increase the speed of wound healing in H9c2 cardiomyoblasts. Interestingly, this is not driven by an increase in proliferation, but by collective cell migration. We subsequently dissect specific phosphorylation sites in YAP to identify the molecular driver of accelerated healing.

CONCLUSIONS

This study shows that optogenetic YAP is functional in H9c2 cardiomyoblasts and its controlled activation can potentially enhance wound healing in a range of conditions.

Inflammation modulates intercellular adhesion and mechanotransduction in human epidermis via ROCK2

Aberrant mechanotransduction and compromised epithelial barrier function are associated with numerous human pathologies including inflammatory skin disorders. However, the cytoskeletal mechanisms regulating inflammatory responses in the epidermis are not well understood. Here we addressed this question by inducing a psoriatic phenotype in human keratinocytes and reconstructed human epidermis using a cytokine stimulation model. We show that the inflammation upregulates the Rho-myosin II pathway and destabilizes adherens junctions (AJs) promoting YAP nuclear entry. The integrity of cell-cell adhesion but not the myosin II contractility per se is the determinative factor for the YAP regulation in epidermal keratinocytes. The inflammation-induced disruption of AJs, increased paracellular permeability, and YAP nuclear translocation are regulated by ROCK2, independently from myosin II activation. Using a specific inhibitor KD025, we show that ROCK2 executes its effects via cytoskeletal and transcription-dependent mechanisms to shape the inflammatory response in the epidermis.

Recent advances in the role of Yes-associated protein in dermatosis

BACKGROUND

Dermatosis is a general term for diseases of the skin and skin appendages including scleroderma, psoriasis, bullous disease, atopic dermatitis, basal cell carcinoma, squamous cell carcinoma, and melanoma. These diseases affect millions of individuals globally and are a serious public health concern. However, the pathogenesis of skin diseases is not fully understood, and treatments are not optimal. Yes-associated protein (YAP) is a transcriptional coactivator that plays a role in the regulation of gene transcription and signal transduction.

AIMS

To study the role of Yes-associated protein in skin diseases.

MATERIALS AND METHODS

The present review summarizes recent advances in our understanding of the role of YAP in skin diseases, current treatments that target YAP, and potential avenues for novel therapies.

RESULTS

Abnormal YAP expression has been implicated in occurrence and development of dermatosis. YAP regulates the cell homeostasis, proliferation, differentiation, apoptosis, angiopoiesis, and epithelial-to-mesenchymal transition, among other processes. As well as, it serves as a potential target in many biological processes for treating dermatosis.

CONCLUSIONS

The effects of YAP on the skin are complex and require multidimensional investigational approaches. YAP functions as an oncoprotein that can promote the occurrence and development of cancer, but there is currently limited information on the therapeutic potential of YAP inhibition for cancer treatment. Additional studies are also needed to clarify the role of YAP in the development and maturation of dermal fibroblasts; skin barrier function, homeostasis, aging, and melanin production; and dermatosis.

Cold atmospheric microwave plasma (CAMP) stimulates dermal papilla cell proliferation by inducing β-catenin signaling

Hair loss or alopecia is an unpleasant symptom that exacerbates an individual's self-esteem and requires appropriate treatment. The Wnt/β-catenin signaling is a central pathway that promotes dermal papilla induction and keratinocyte proliferation during hair follicle renewal. GSK-3β inactivated by its upstream Akt and ubiquitin-specific protease 47 (USP47) has been shown to inhibit β-catenin degradation. The cold atmospheric microwave plasma (CAMP) is microwave energy enriched with mixtures of radicals. CAMP has been reported to have antibacterial and antifungal activities with wound healing activity against skin infection; however, the effect of CAMP on hair loss treatment has not been reported. We aimed to investigate the effect of CAMP on promoting hair renewal in vitro and to elucidate the molecular mechanism, targeting β-catenin signaling and YAP/TAZ, the co-activators in the Hippo pathway, in human dermal papilla cells (hDPCs). We also evaluated plasma effects on the interaction between hDPCs and HaCaT keratinocytes. The hDPCs were treated with plasma-activating media (PAM) or gas-activating media (GAM). The biological outcomes were determined by MTT assay, qRT-PCR, western blot analysis, immunoprecipitation, and immunofluorescence. We found that β-catenin signaling and YAP/TAZ were significantly increased in PAM-treated hDPCs. PAM treatment also induced β-catenin translocation and inhibited β-catenin ubiquitination by activating Akt/GSK-3β signaling and upregulating USP47 expression. In addition, hDPCs were more aggregated with keratinocytes in PAM-treated cells compared with control. HaCaT cells cultured in a conditioned medium derived from PAM-treated hDPCs exhibited an enhancing effect on activating YAP/TAZ and β-catenin signaling. These findings suggested that CAMP may be a new therapeutic alternative for alopecic treatment.

Atherosclerosis and endothelial mechanotransduction: current knowledge and models for future research

Endothelium health is essential to the regulation of physiological vascular functions. Because of the critical capability of endothelial cells (ECs) to sense and transduce chemical and mechanical signals in the local vascular environment, their dysfunction is associated with a vast variety of vascular diseases and injuries, especially atherosclerosis and subsequent cardiovascular diseases. This review describes the mechanotransduction events that are mediated through ECs, the EC subcellular components involved, and the pathways reported to be potentially involved. Up-to-date research efforts involving in vivo animal models and in vitro biomimetic models are also discussed, including their advantages and drawbacks, with recommendations on future modeling approaches to aid the development of novel therapies targeting atherosclerosis and related cardiovascular diseases.

Effect of cold atmospheric microwave plasma (CAMP) on wound healing in canine keratinocytes

Cutaneous wound healing is a biological process that occurs upon skin injury and involves different mechanisms to repair tissue damage. Improper healing or prolonged curation period of wound lesions may induce unpleasant complications. Cold atmospheric microwave plasma (CAMP) is an upcoming medical therapeutic option for skin infection and wound treatment. However, the molecular mechanisms of CAMP-mediated canine wound healing are not well characterized. Wound-healing activity was examined to elucidate the biological effects and molecular mechanisms of CAMP. Canine keratinocytes (CPEKs) were treated using CAMP, and their wound-healing activities were evaluated. The molecular mechanisms of that effect were examined, based on RNA-Seq analysis data, and verified using immunoblotting and polymerase chain reaction. It was found that the CAMP-treated cells exhibited a significant increase in cell migration evaluated by scratch assay in human keratinocytes (HaCaT) and canine keratinocytes (CPEK). Additionally, CAMP-treated CPEK cells showed a significant positive effect on cell invasion. The RNA-Seq data revealed that CAMP alters different genes and pathways in CPEK cells. Gene expression involved in the cell cycle, cell proliferation, angiogenesis, cell adhesion, and wound healing was upregulated in CAMP-treated cells compared with gas-activated media used as a control. The Hippo pathway was also analyzed, and the protein and mRNA levels of YAP were significantly increased in CAMP-treated cells. CAMP-treated CPEK cells indicated the downregulation of E-cadherin and upregulation of vimentin, Snail, and Slug at transcription and translation levels, contributing to a favorable effect on cell migration. Our findings suggested that CAMP treatment provided beneficial effects on the curative wound process through the induction of genes involved in wound healing, promotion of EMT, and increase in the molecular targets in the Hippo signaling pathway.

Extracellular matrix stiffness mediates uterine repair via the Rap1a/ARHGAP35/RhoA/F-actin/YAP axis

The integrity of the structure and function of the endometrium is essential for the maintenance of fertility. However, the repair mechanisms of uterine injury remain largely unknown. Here, we showed that the disturbance of mechanical cue homeostasis occurs after uterine injury. Applying a multimodal approach, we identified YAP as a sensor of biophysical forces that drives endometrial regeneration. Through protein activation level analysis of the combinatorial space of mechanical force strength and of the presence of particular kinase inhibitors and gene silencing reagents, we demonstrated that mechanical cues related to extracellular matrix rigidity can turn off the Rap1a switch, leading to the inactivation of ARHGAP35and then induced activation of RhoA, which in turn depends on the polymerization of the agonist protein F-actin to activate YAP. Further study confirmed that mechanotransduction significantly accelerates remodeling of the uterus by promoting the proliferation of endometrial stromal cells in vitro and in vivo. These studies provide new insights into the dynamic regulatory mechanisms behind uterine remodeling and the function of mechanotransduction. Video Abstract.

Collagen type I-mediated mechanotransduction controls epithelial cell fate conversion during intestinal inflammation

BACKGROUND

The emerging concepts of fetal-like reprogramming following tissue injury have been well recognized as an important cue for resolving regenerative mechanisms of intestinal epithelium during inflammation. We previously revealed that the remodeling of mesenchyme with collagen fibril induces YAP/TAZ-dependent fate conversion of intestinal/colonic epithelial cells covering the wound bed towards fetal-like progenitors. To fully elucidate the mechanisms underlying the link between extracellular matrix (ECM) remodeling of mesenchyme and fetal-like reprogramming of epithelial cells, it is critical to understand how collagen type I influence the phenotype of epithelial cells. In this study, we utilize collagen sphere, which is the epithelial organoids cultured in purified collagen type I, to understand the mechanisms of the inflammatory associated reprogramming. Resolving the entire landscape of regulatory networks of the collagen sphere is useful to dissect the reprogrammed signature of the intestinal epithelium.

METHODS

We performed microarray, RNA-seq, and ATAC-seq analyses of the murine collagen sphere in comparison with Matrigel organoid and fetal enterosphere (FEnS). We subsequently cultured human colon epithelium in collagen type I and performed RNA-seq analysis. The enriched genes were validated by gene expression comparison between published gene sets and immunofluorescence in pathological specimens of ulcerative colitis (UC).

RESULTS

The murine collagen sphere was confirmed to have inflammatory and regenerative signatures from RNA-seq analysis. ATAC-seq analysis confirmed that the YAP/TAZ-TEAD axis plays a central role in the induction of the distinctive signature. Among them, TAZ has implied its relevant role in the process of reprogramming and the ATAC-based motif analysis demonstrated not only Tead proteins, but also Fra1 and Runx2, which are highly enriched in the collagen sphere. Additionally, the human collagen sphere also showed a highly significant enrichment of both inflammatory and fetal-like signatures. Immunofluorescence staining confirmed that the representative genes in the human collagen sphere were highly expressed in the inflammatory region of ulcerative colitis.

CONCLUSIONS

Collagen type I showed a significant influence in the acquisition of the reprogrammed inflammatory signature in both mice and humans. Dissection of the cell fate conversion and its mechanisms shown in this study can enhance our understanding of how the epithelial signature of inflammation is influenced by the ECM niche.

The Hippo signalling pathway and its implications in human health and diseases

As an evolutionarily conserved signalling network, the Hippo pathway plays a crucial role in the regulation of numerous biological processes. Thus, substantial efforts have been made to understand the upstream signals that influence the activity of the Hippo pathway, as well as its physiological functions, such as cell proliferation and differentiation, organ growth, embryogenesis, and tissue regeneration/wound healing. However, dysregulation of the Hippo pathway can cause a variety of diseases, including cancer, eye diseases, cardiac diseases, pulmonary diseases, renal diseases, hepatic diseases, and immune dysfunction. Therefore, therapeutic strategies that target dysregulated Hippo components might be promising approaches for the treatment of a wide spectrum of diseases. Here, we review the key components and upstream signals of the Hippo pathway, as well as the critical physiological functions controlled by the Hippo pathway. Additionally, diseases associated with alterations in the Hippo pathway and potential therapies targeting Hippo components will be discussed.

The Regulation of the Hippo Pathway by Intercellular Junction Proteins

The Hippo pathway is an evolutionarily conserved pathway that serves to promote cell death and differentiation while inhibiting cellular proliferation across species. The downstream effectors of this pathway, yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), are considered vital in promoting the output of the Hippo pathway, with activation of upstream kinases negatively regulating YAP/TAZ activity. The upstream regulation of the Hippo pathway is not entirely understood on a molecular level. However, several studies have shown that numerous cellular and non-cellular mechanisms such as cell polarity, contact inhibition, soluble factors, mechanical forces, and metabolism can convey external stimuli to the intracellular kinase cascade, promoting the activation of key components of the Hippo pathway and therefore regulating the subcellular localisation and protein activity of YAP/TAZ. This review will summarise what we have learnt about the role of intercellular junction-associated proteins in the activation of this pathway, including adherens junctions and tight junctions, and in particular our latest findings about the desmosomal components, including desmoglein-3 (DSG3), in the regulation of YAP signalling, phosphorylation, and subcellular translocation.

IL-38 orchestrates proliferation and differentiation in human keratinocytes

Interleukin (IL)-38 is a member of the IL-1 cytokine family with reported anti-inflammatory activity. The highest constitutive IL-38 expression is detected in the skin, where it is mainly produced by differentiating keratinocytes. However, little data are available regarding its biological functions. In this study, we investigated the role of IL-38 in skin physiology. We demonstrate here that dermal fibroblasts and epithelial cells of skin appendages, such as eccrine sweat glands and sebaceous glands, also express IL-38. Next, using two- and three-dimensional cell cultures, we show that endogenous expression of IL-38 correlates with keratinocyte differentiation and its ectopic overexpression inhibits keratinocyte proliferation and enhances differentiation. Accordingly, immunohistochemical analysis revealed downregulation of IL-38 in skin pathologies characterized by keratinocyte hyperproliferation, such as psoriasis and basal or squamous cell carcinoma. Finally, intracellular IL-38 can shuttle between the nucleus and the cytoplasm and its overexpression modulates the activity of the transcription regulators YAP and ID1. Our results indicate that IL-38 can act independently from immune system activation and suggest that it may affect the epidermis directly by decreasing proliferation and promoting differentiation of keratinocytes. These data suggest an important role of keratinocyte-derived IL-38 in skin homeostasis and pathologies characterized by epidermal alterations.

The Role of Hippo Signaling Pathway and ILK in the Pathophysiology of Human Hypertrophic Scars and Keloids: An Immunohistochemical Investigation

BACKGROUND

Keloids and hypertrophic scars are characterized by abnormal fibroblast activation and proliferation. While their molecular pathogenesis remains unclear, myofibroblasts have been associated with their development. Hippo pathway effectors YAP/TAZ promote cell proliferation and matrix stiffening. Integrin-linked kinase (ILK), a central component of focal adhesions that mediates cell-matrix interactions, has been linked to tissue repair and fibrosis. The aim of this study was to investigate the expression of key Hippo pathway molecules and ILK in hypertrophic scars and keloids.

METHODS

YAP/TAZ, TEAD4, ILK and a-SMA expression were evaluated by immunohistochemistry in keloids (n = 55), hypertrophic scars (n = 38) and normal skin (n = 14).

RESULTS

The expression of YAP/TAZ, TEAD4, ILK and a-SMA was higher in fibroblasts of keloids compared to hypertrophic scars while negative in normal skin. There was a significant positive correlation between the expression of ILK and Hippo pathway effectors.

CONCLUSIONS

Our results suggest that the deregulation of Hippo signaling and ILK are implicated in keloid and hypertrophic scar formation.

Mechanotransduction in skin wound healing and scar formation: Potential therapeutic targets for controlling hypertrophic scarring

Hypertrophic scarring (HTS) is a major source of morbidity after cutaneous injury. Recent studies indicate that mechanical force significantly impacts wound healing and skin regeneration which opens up a new direction to combat scarring. Hence, a thorough understanding of the underlying mechanisms is essential in the development of efficacious scar therapeutics. This review provides an overview of the current understanding of the mechanotransduction signaling pathways in scar formation and some strategies that offload mechanical forces in the wounded region for scar prevention and treatment.

Targeting the Hippo/YAP/TAZ signalling pathway: Novel opportunities for therapeutic interventions into skin cancers

Skin cancers are by far the most frequently diagnosed human cancers. The closely related transcriptional co-regulator proteins YAP and TAZ (WWTR1) have emerged as important drivers of tumour initiation, progression and metastasis in melanoma and non-melanoma skin cancers. YAP/TAZ serve as an essential signalling hub by integrating signals from multiple upstream pathways. In this review, we summarize the roles of YAP/TAZ in skin physiology and tumorigenesis and discuss recent efforts of therapeutic interventions that target YAP/TAZ in in both preclinical and clinical settings, as well as their prospects for use as skin cancer treatments.

Airway basal cells show a dedifferentiated KRT17highPhenotype and promote fibrosis in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal disease with limited treatment options. In this study, we focus on the properties of airway basal cells (ABC) obtained from patients with IPF (IPF-ABC). Single cell RNA sequencing (scRNAseq) of bronchial brushes revealed extensive reprogramming of IPF-ABC towards a KRT17high PTENlow dedifferentiated cell type. In the 3D organoid model, compared to ABC obtained from healthy volunteers, IPF-ABC give rise to more bronchospheres, de novo bronchial structures resembling lung developmental processes, induce fibroblast proliferation and extracellular matrix deposition in co-culture. Intratracheal application of IPF-ABC into minimally injured lungs of Rag2-/- or NRG mice causes severe fibrosis, remodeling of the alveolar compartment, and formation of honeycomb cyst-like structures. Connectivity MAP analysis of scRNAseq of bronchial brushings suggested that gene expression changes in IPF-ABC can be reversed by SRC inhibition. After demonstrating enhanced SRC expression and activity in these cells, and in IPF lungs, we tested the effects of saracatinib, a potent SRC inhibitor previously studied in humans. We demonstrate that saracatinib modified in-vitro and in-vivo the profibrotic changes observed in our 3D culture system and novel mouse xenograft model.

On modeling the multiscale mechanobiology of soft tissues: Challenges and progress

Tissues grow and remodel in response to mechanical cues, extracellular and intracellular signals experienced through various biological events, from the developing embryo to disease and aging. The macroscale response of soft tissues is typically nonlinear, viscoelastic anisotropic, and often emerges from the hierarchical structure of tissues, primarily their biopolymer fiber networks at the microscale. The adaptation to mechanical cues is likewise a multiscale phenomenon. Cell mechanobiology, the ability of cells to transform mechanical inputs into chemical signaling inside the cell, and subsequent regulation of cellular behavior through intra- and inter-cellular signaling networks, is the key coupling at the microscale between the mechanical cues and the mechanical adaptation seen macroscopically. To fully understand mechanics of tissues in growth and remodeling as observed at the tissue level, multiscale models of tissue mechanobiology are essential. In this review, we summarize the state-of-the art modeling tools of soft tissues at both scales, the tissue level response, and the cell scale mechanobiology models. To help the interested reader become more familiar with these modeling frameworks, we also show representative examples. Our aim here is to bring together scientists from different disciplines and enable the future leap in multiscale modeling of tissue mechanobiology.