Regulation of Hippo signaling pathway in cancer: A MicroRNA perspective

Recent studies have suggested that Hippo signaling is not only involved in controlling organ size in Drosophila but can also regulate cell proliferation, tissue homeostasis, differentiation, apoptosis and regeneration. Any dysregulation of Hippo signaling, especially the hyper activation of its downstream effectors YAP/TAZ, can lead to uncontrolled cell proliferation and malignant transformation. In majority of cancers, expression of YAP/TAZ is extremely high and this increased expression of YAP/TAZ has been shown to be an independent predictor of prognosis and indicator of increased cell proliferation, metastasis and poor survival. In this review, we have summarized the most recent findings about the cross talk of Hippo signaling pathway with other signaling pathways and its regulation by different miRNAs in various cancer types. Recent evidence has suggested that Hippo pathway is also involved in mediating the resistance of different cancer cells to chemotherapeutic drugs and in a few cancer types, this is brought about by regulating miRNAs. Therefore, the delineation of the underlying mechanisms regulating the chemotherapeutic resistance might help in developing better treatment options. This review has attempted to provide an overview of different drugs/options which can be utilized to target oncogenic YAP/TAZ proteins for therapeutic interventions.     

Hippo信号对卵巢生殖干细胞增殖及卵巢功能的影响

已有研究表明,Hippo信号通路对干细胞的自我更新和分化至关重要,且Hippo信号通路在调控卵泡生长中起重要作用,然而,目前关于Hippo通路对卵巢生殖干细胞的增殖和分化以及卵巢功能重塑的影响相关的研究较少。为了明确Hippo信号通路效应因子YAP1与卵巢生殖干细胞体外增殖分化的关系,以及Hippo信号通路对卵巢癌的主要功能。我们采用两步法酶促分离和磁性分离技术分别鉴定卵巢生殖干细胞,通过测定MVH和OCT4标记物的表达,然后选择YAP1作为Hippo信号通路的主要效应分子,作为研究的靶基因。将含有过表达的YAP1或YAP1靶向的shRNA的慢病毒转导入卵巢生殖干细胞中。通过将过表达YAP1或YAP1 shRNA的慢病毒载体微量注射到不育小鼠模型中,观察调节Hippo信号通路对卵巢的增殖、分化和内分泌功能的影响。研究结果表明,在分离的卵巢生殖干细胞中观察到YAP1和MVH的共表达。与对照组相比,过表达YAP1的卵巢生殖干细胞中MVH和OCT4表达水平显著增加。而YAP1敲低后,MVH和OCT4水平显著降低;不育小鼠模型中YAP1过表达15 d后,E2和FSH含量显著升高,而YAP1 shRNA表达后,小鼠血清E2和FSH含量显著降低。YAP1可用于调控卵巢生殖干细胞的增殖和分化以及小鼠的卵巢功能。本研究表明,Hippo信号通路可能是调控卵巢功能重建的一个新的分子靶点。     

Hippo信号通路在肺发育、再生和疾病中的功能

哺乳动物肺对于血液与外部环境之间的气体交换至关重要。而肺相关的疾病是现代人死亡的主要原因之一。肺的发育、再生和相关疾病的研究对临床治疗具有重要的指导作用。研究发现,Hippo信号通路参与细胞增殖与分化的调控、器官大小的控制,以及机械力的感应和传递。Hippo信号通路中的核心转录调控分子YAP/TAZ在肺部的多种细胞中均有表达,其表达及定位的变化在肺发育与再生中发挥着重要的调控作用。本文主要介绍了Hippo信号通路在肺生长发育中的功能及其与肺纤维化、肺癌的关系,并从肺泡力学和肺泡相关免疫两个角度对Hippo信号通路潜在的功能进行了展望。     

Regulation of Hippo pathway components by FSH in testis

The transition of testicular Sertoli cells (Sc) from a proliferative state during infancy to a non proliferative functionally mature state at the onset of puberty is essential for proper spermatogenic progression. The Hippo signaling pathway is a conserved growth control pathway that has been shown to play a crucial role in regulating proliferation and differentiation of different cell types. However, the expression pattern of the pathway components relative to proliferative infant Sc and functionally mature pubertal Sc is not known. In this study, we show that the Hippo pathway components are differentially expressed in infant and pubertal rat Sc. Interestingly, Hippo transducer- YAP was found to be significantly up-regulated in pubertal Sc as compared to infant Sc. Follicle stimulating hormone (FSH) was found to up-regulate Yap expression in pubertal Sc but not in infant Sc. Moreover, FSH induced the phosphorylation of YAP at Ser 127 residue (which is associated with its inactivation) in pubertal Sc. This indicated negative regulation of YAP by FSH mediated signaling in pubertal Sc. Our results demonstrated the differential expression of Hippo pathway genes in infant and pubertal Sc and also established an important role of FSH in regulating YAP expression and phosphorylation in Sc.     

The Hippo–YAP pathway regulates the proliferation of alveolar epithelial progenitors after acute lung injury

Regeneration of pulmonary epithelial cells plays an important role in the recovery of acute lung injury (ALI), which is defined by pulmonary epithelial cell death. However, the mechanism of the regenerative capacity of alveolar epithelial cells is unknown. Using a lung injury mouse model induced by hemorrhagic shock and lipopolysaccharide, a protein mass spectrometry‐based high‐throughput screening and linage tracing technology to mark alveolar epithelial type 2 cells (AEC2s), we analyzed the mechanism of alveolar epithelial cells proliferation. We demonstrated that the expression of Hippo‐yes‐associated protein 1 (YAP1) key proteins were highly consistent with the regularity of the proliferation of alveolar epithelial type 2 cells after ALI. Furthermore, the results showed that YAP1+ cells in lung tissue after ALI were mainly Sftpc lineage‐labeled AEC2s. An in vitro proliferation assay of AEC2s demonstrated that AEC2 proliferation was significantly inhibited by both YAP1 small interfering RNA and Hippo inhibitor. These findings revealed that YAP functioned as a key regulator to promote AEC2s proliferation, with the Hippo signaling pathway playing a pivotal role in this process.     

CD44 acts through RhoA to regulate YAP signaling

The Hippo pathway plays an important role in both physical and pathogenesis processes. As crucial downstream effectors of Hippo pathway, YAP is inhibited by Lats1/2 through phosphorylation. However, upstream signals that regulate the Hippo pathway have been still poorly understood. Here, we found that knockdown of CD44 reduced YAP expression and nuclear localization, but nearly had no effect on its upstream effectors, Mst1 and Lats1. Downregulated CD44 expression also significantly decreased the expression of YAP downstream effectors CTGF, Cyr61 and EDN1 at mRNA level. Our next study showed that knockdown of CD44 inhibited RhoA expression, which was consistent with RhoA knockdown mediated YAP downregulation. Furthermore, we demonstrated that over expression of the constitutively active RhoA (RhoA-V14) could block the YAP expression decrease mediated by CD44 knockdown. Moreover, downregulation of CD44 significantly promoted cell apoptosis and inhibited cell proliferation, cell cycle progression and migration, which were consistent with the effects of RNAi-mediated YAP knockdown in both A549 and HepG2 cells. Overall, data are presented showing that CD44 could act through RhoA signaling to regulate YAP expression and this study also provide new insights into the regulatory mechanisms of the Hippo–YAP pathway.     

Hippo Signaling Mediates Proliferation,Invasiveness, and Metastatic Potential of Clear Cell Renal Cell Carcinoma

Recent work has identified dysfunctional Hippo signaling to be involved in maintenance and progression of various human cancers, although data on clear cell renal cell carcinoma (ccRCC) have been limited. Here, we provide evidence implicating aberrant Hippo signaling in ccRCC proliferation, invasiveness, and metastatic potential. Nuclear overexpression of the Hippo target Yes-associated protein (YAP) was found in a subset of patients with ccRCC. Immunostaining was particularly prominent at the tumor margins and highlighted neoplastic cells invading the tumor-adjacent stroma. Short hairpin RNA-mediated knockdown of YAP significantly inhibited proliferation, migration, and anchorage-independent growth of ccRCC cells in soft agar and led to significantly reduced murine xenograft growth. Microarray analysis of YAP knockdown versus mock-transduced ccRCC cells revealed down-regulation of endothelin 1, endothelin 2, cysteine-rich, angiogenic inducer, 61 (CYR61), and c-Myc in ccRCC cells as well as up-regulation of the cell adhesion molecule cadherin 6. Signaling pathway impact analysis revealed activation of the p53 signaling and cell cycle pathways as well as inhibition of mitogen-activated protein kinase signaling on YAP down-regulation. Our data suggest CYR61 and c-Myc as well as signaling through the endothelin axis as bona fide downstream effectors of YAP and establish aberrant Hippo signaling as a potential therapeutic target in ccRCC.     

YAP‐TEAD signaling promotes basal cell carcinoma development via a c‐JUN/AP1 axis

The mammalian Hippo signaling pathway, through its effectors YAP and TAZ, coerces epithelial progenitor cell expansion for appropriate tissue development or regeneration upon damage. Its ability to drive rapid tissue growth explains why many oncogenic events frequently exploit this pathway to promote cancer phenotypes. Indeed, several tumor types including basal cell carcinoma (BCC) show genetic aberrations in the Hippo (or YAP/TAZ) regulators. Here, we uncover that while YAP is dispensable for homeostatic epidermal regeneration, it is required for BCC development. Our clonal analyses further demonstrate that the few emerging Yap‐null dysplasia have lower fitness and thus are diminished as they progress to invasive BCC. Mechanistically, YAP depletion in BCC tumors leads to effective impairment of the JNK‐JUN signaling, a well‐established tumor‐driving cascade. Importantly, in this context, YAP does not influence canonical Wnt or Hedgehog signaling. Overall, we reveal Hippo signaling as an independent promoter of BCC pathogenesis and thereby a viable target for drug‐resistant BCC.     

YAP参与调控细胞上皮-间充质转化的研究进展

上皮-间充质转化(epithelial-mesenchymal transition,EMT)是上皮来源细胞在各种理化因素作用下经历表型转化获得间充质样细胞表型的过程.研究表明,有多种信号分子参与EMT的发生,并在胚胎发育、器官损伤修复和肿瘤的发生发展过程中起着关键作用.Yes相关蛋白(yes-associated protein,YAP)作为Hippo信号通路的下游效应分子,被广泛报道参与EMT的进程,调控多种基因的表达,起到调节细胞增殖、凋亡、器官发育和修复等作用.最新研究表明,YAP活性的变化直接介导肿瘤细胞的迁移和侵袭等能力的变化,而这些变化都伴随着EMT的发生.因此,YAP蛋白跟EMT的发生密切相关.本文就近年来关于YAP调控组织发育、器官纤维化及在肿瘤发生发展中的作用,以及相关分子机制的研究进行综述,并将阐明其与EMT之间的相互关系,以期为EMT的研究提供新的视角,进而为相关疾病的治疗提供新的分子靶点和诊断治疗策略.     

Bone marrow-derived fibroblast growth factor-2 induces glial cell proliferation in the regenerating peripheral nervous system

ABSTRACT: BACKGROUND: Among the essential biological roles of bone marrow-derived cells, secretion of many soluble factors is included and these small molecules can act upon specific receptors present in many tissues including the nervous system. Some of the released molecules can induce proliferation of Schwann cells (SC), satellite cells and lumbar spinal cord astrocytes during early steps of regeneration in a rat model of sciatic nerve transection. These are the major glial cell types that support neuronal survival and axonal growth following peripheral nerve injury. Fibroblast growth factor-2 (FGF-2) is the main mitogenic factor for SCs and is released in large amounts by bone marrow-derived cells, as well as by growing axons and endoneurial fibroblasts during development and regeneration of the peripheral nervous system (PNS). RESULTS: Here we show that bone marrow-derived cell treatment induce an increase in the expression of FGF-2 in the sciatic nerve, dorsal root ganglia and the dorsolateral (DL) region of the lumbar spinal cord (LSC) in a model of sciatic nerve transection and connection into a hollow tube. SCs in culture in the presence of bone marrow derived conditioned media (CM) resulted in increased proliferation and migration. This effect was reduced when FGF-2 was neutralized by pretreating BMMC or CM with a specific antibody. The increased expression of FGF-2 was validated by RT-PCR and immunocytochemistry in co-cultures of bone marrow derived cells with sciatic nerve explants and regenerating nerve tissue respectivelly. CONCLUSION: We conclude that FGF-2 secreted by BMMC strongly increases early glial proliferation, which can potentially improve PNS regeneration.