The PAR-aPKC system: lessons in polarity

MARK2 regulates Golgi apparatus reorientation by phosphorylation of CAMSAP2 in directional cell migratio

The reorientation of the Golgi apparatus is crucial for cell migration and is regulated by multipolarity signals. A number of non-centrosomal microtubules anchor at the surface of the Golgi apparatus and play a vital role in the Golgi reorientation, but how the Golgi are regulated by polarity signals remains unclear. Calmodulin-regulated spectrin-associated protein 2 (CAMSAP2) is a protein that anchors microtubules to the Golgi, a cellular organelle. Our research indicates that CAMSAP2 is dynamically localized at the Golgi during its reorientation processing. Further research shows that CAMSAP2 is potentially regulated by a polarity signaling molecule called MARK2, which interacts with CAMSAP2. We used mass spectrometry to find that MARK2 phosphorylates CAMSAP2 at serine-835, which affects its interaction with the Golgi-associated protein USO1 but not with CG-NAP or CLASPs. This interaction is critical for anchoring microtubules to the Golgi during cell migration, altering microtubule polarity distribution, and aiding Golgi reorientation. Our study reveals an important signaling pathway in Golgi reorientation during cell migration, which can provide insights for research in cancer cell migration, immune response, and targeted drug development.

Asymmetric cell division of ALDH1-positive cancer stem cells generates glycolytic metabolically diverse cell populations

Metabolic heterogeneity in various cancer cells within a tumor causes resistance to medical therapies and promotes tumor recurrence and metastasis. However, the mechanisms by which tumors acquire metabolic heterogeneity are poorly understood. Here, we revealed that PKCλ-dependent asymmetric division of ALDH1-positive cancer stem cells (CSCs) led to an uneven distribution of glycolytic capacity, which is crucial for understanding metabolic heterogeneity within a tumor. The rate-limiting enzyme PFKP and the metabolic probe CDG in glycolysis codistributed with the ALDH1A3 protein during the post-cell division phase, highlighting a mechanism for acquiring metabolic diversity. PKCλ deficiency reduced the asymmetric distribution of these proteins in ALDH1high cells with high ALDH1 activity, suggesting a fundamental role for PKCλ in metabolic heterogeneity. We identified 28 distinct distribution patterns combining PFKP and CDG distributions, demonstrating the complexity of glycolytic heterogeneity. Furthermore, validation and prediction of cell distribution patterns via a probabilistic model confirmed that PKCλ deficiency diminished glycolytic diversity in individual cells within a cancer cell colony generated from an ALDH1-positive CSC. These findings suggest that PKCλ-dependent asymmetric cell division of ALDH1-positive CSCs is crucial for glycolytic heterogeneity in cancer cells within a tumor, potentially offering new therapeutic targets against tumor resistance and metastasis.

Comparing statistical learning methods for complex trait prediction from gene expression

Accurate prediction of complex traits is an important task in quantitative genetics. Genotypes have been used for trait prediction using a variety of methods such as mixed models, Bayesian methods, penalized regression methods, dimension reduction methods, and machine learning methods. Recent studies have shown that gene expression levels can produce higher prediction accuracy than genotypes. However, only a few prediction methods were tested in these studies. Thus, a comprehensive assessment of methods is needed to fully evaluate the potential of gene expression as a predictor of complex trait phenotypes. Here, we used data from the Drosophila Genetic Reference Panel (DGRP) to compare the ability of several existing statistical learning methods to predict starvation resistance and startle response from gene expression in the two sexes separately. The methods considered differ in assumptions about the distribution of gene effects-ranging from models that assume that every gene affects the trait to more sparse models-and their ability to capture gene-gene interactions. We also used functional annotation (i.e., Gene Ontology (GO)) as a source of biological information to inform prediction models. The results show that differences in prediction accuracy exist. For example, methods performing variable selection achieved higher prediction accuracy for starvation resistance in females, while they generally had lower accuracy for startle response in both sexes. Incorporating GO annotations further improved prediction accuracy for a few GO terms of biological significance. Biological significance extended to the genes underlying highly predictive GO terms. Notably, the Insulin-like Receptor (InR) was prevalent across methods and sexes for starvation resistance. For startle response, crumbs (crb) and imaginal disc growth factor 2 (Idgf2) were found for females and males, respectively. Our results confirmed the potential of transcriptomic prediction and highlighted the importance of selecting appropriate methods and strategies in order to achieve accurate predictions.

Perturbed cell cycle phase-dependent positioning and nuclear migration of retinal progenitors along the apico-basal axis underlie global retinal disorganization in the LCA8-like mouse model

Combined removal of Crb1 and Crb2 from the developing optic vesicle evokes cellular and laminar disorganization by disrupting the apical cell-cell adhesion in developing retinal epithelium. As a result, at postnatal stages, affected mouse retinas show temporarily thickened, coarsely laminated retinas in addition to functional deficits, including a severely abnormal electroretinogram and decreased visual acuity. These features are reminiscent of Leber congenital amaurosis 8, which is caused in humans by subsets of Crb1 mutations. However, the cellular basis of the abnormalities in retinal progenitor cells (RPCs) that lead to retinal disorganization is largely unknown. In this study, we analyze specific features of RPCs in mutant retinas, including maintenance of the progenitor pool, cell cycle progression, cell cycle phase-dependent nuclear positioning, cell survival, and generation of mature retinal cell types. We find crucial defects in the mutant RPCs. Upon removal of CRB1 and CRB2, apical structures of the RPCs, determined by markers of cilia and centrosomes, are basally shifted. In addition, the positioning of the somata of the M-phase cells, normally localized at the apical surface of the retinal epithelium, is basally shifted in a nearly randomized pattern along the apico-basal axis. Consequently, we propose that positioning of RPCs is desynchronized from cell cycle phase and largely randomized during embryonic development at E17.5. Because the resultant postmitotic cells inevitably lose positional information, the outer and inner nuclear layers (ONL and INL) fail to form from ONBL during neonatal development and retinal cells become mixed locally and globally. Additional results of the lost tissue polarity in Crb1/Crb2 dKO retinas include atypical formation of heterotopic cell patches containing photoreceptor cells in the ganglion cell layer and acellular patches filled with neural processes. Collectively, these changes lead to a mouse model of LCA8-like pathology. LCA8-like pathology differs substantially from the well-characterized, broad range of degeneration phenotypes that arise during the differentiation of photoreceptor and Muller glial cells in retinitis pigmentosa 12, a closely related disease caused by mutated human Crb1. Importantly, the present results suggest that Crb1/Crb2 serve indispensable functions in maintaining cell-cycle phase-dependent positioning of RPCs along the apico-basal axis, regulating cell cycle progression, and maintaining structural laminar integrity without significantly affecting the size of the RPC pools, generation of the subsets of the retinal cell types, or the distribution of cell cycle phases during RPC division. Taken together, these findings provide the crucial cellular basis of the thickening and severely disorganized lamination that are the unique features of the retinal abnormalities in LCA8 patients.

Synthetic Engineering of Cortical Polarity During Mitosis Using Designed Proteins

During asymmetric cell division, cortical polarity cues drive the polarization of the microtubule cytoskeleton to ensure the generation of two daughter cells with different fates. While this a critical process for development and tissue homeostasis, the underlying molecular mechanisms orchestrating those processes are not completely understood, especially in mammals. Here, we present an assay that allows the study of the molecular mechanisms driving mammalian asymmetric cell division in a high-throughput manner by capitalizing on protein design to engineer cortical polarity of virtually any protein of interest in otherwise unpolarized mammalian culture cells.

Signaling pathway regulators in preimplantation embryos

Embryonic development during the preimplantation stages is highly sensitive and critically dependent on the reception of signaling cues. The precise coordination of diverse pathways and signaling factors is essential for successful embryonic progression. Even minor disruptions in these factors can result in physiological dysfunction, fetal malformations, or embryonic arrest. This issue is particularly evident in assisted reproductive technologies, such as in vitro fertilization, where embryonic arrest is frequently observed. A detailed understanding of these pathways enhances insight into the fundamental mechanisms underlying cellular processes and their contributions to embryonic development. The significance of elucidating signaling pathways and their regulatory factors in preimplantation development cannot be overstated. The application of this knowledge in laboratory settings has the potential to support strategies for modeling developmental stages and diseases, drug screening, therapeutic discovery, and reducing embryonic arrest. Furthermore, using various factors, small molecules, and pharmacological agents can enable the development or optimization of culture media for enhanced embryonic viability. While numerous pathways influence preimplantation development, this study examines several critical signaling pathways in this contex.

Cell polarity proteins promote macropinocytosis in response to metabolic stress

Macropinocytosis has emerged as a scavenging pathway that cancer cells exploit to survive in a nutrient-deprived microenvironment. Tumor cells are especially reliant on glutamine for their survival, and in pancreatic ductal adenocarcinoma (PDAC) cells, glutamine deficiency can enhance the stimulation of macropinocytosis. Here, we identify the atypical protein kinase C (aPKC) enzymes, PKCζ and PKCι, as regulators of macropinocytosis. In normal epithelial cells, aPKCs associate with the scaffold proteins Par3 and Par6 to regulate cell polarity, affecting several targets, including the Par1 kinases and we find that each of these proteins is required for macropinocytosis. Mechanistically, aPKCs are regulated by EGFR signaling or by the transcription factor CREM to promote the Par3 relocation to microtubules, facilitating macropinocytosis in a dynein-dependent manner. Importantly, cell fitness impairment caused by aPKC depletion is rescued by the restoration of macropinocytosis and aPKCs support PDAC growth in vivo. Our findings enhance our understanding of the mechanistic underpinnings that control macropinocytic uptake in the context of metabolic stress.

Perturbation of mammary epithelial cell apicobasal polarity by RHBDF1-facilitated nuclear translocation of PKCζ

BACKGROUND

The establishment of apicobasal polarity in epithelial cells is of critical importance in morphogenesis of mammary gland and other secretive gland tissues. The demise of the polarity is a critical step in early stages of tumorigenesis such as in breast ductal carcinoma in situ. The underlying molecular mechanism thus warrants in-depth investigations.

RESULTS

Protein kinase C isoform ζ (PKCζ), which is highly expressed in breast cancer cells, accumulates in the nuclei of human mammary epithelial cells overexpressing human rhomboid family-1 (RHBDF1), an endoplasmic reticulum membrane protein. Nuclear translocation of PKCζ results in the failure of the formation of the cytosolic apicobasal polarity complex Par, of which PKCζ is an essential component. Additionally, enhanced nuclear translocation of PKCζ is accompanied by an inhibition of the expression of cell tight junction and adherens junction proteins and an increase of cell mobility. Mechanistically, RHBDF1 is able to interact with importin β1 and PKCζ and promote PKCζ phosphorylation. Consistently, treatment of RHBDF1-overexpressing cells with an inhibitor of PKCζ phosphorylation leads to restoration of apicobasal polarity and cell-cell junctions, as well as suppressed cell mobility.

CONCLUSIONS

RHBDF1-facilitated nuclear translocation of PKCζ is critically responsible for the dismantlement of epithelial cell apicobasal polarity, and thus may serve as a target in the development of therapeutic approaches against early stages of breast cancer.

Ca2+-PP2B-PSD-95 axis: A novel regulatory mechanism of the phosphorylation state of Serine 295 of PSD-95

The phosphorylation state of PSD-95 at Serine 295 (Ser295) is important for the regulation of synaptic plasticity. Although the activation of NMDA receptors (NMDARs), which initiates an intracellular calcium signaling cascade, decreases phosphorylated Ser295 (pS295) of PSD-95, the molecular mechanisms are not fully understood. We found that the calcium-activated protein phosphatase PP2B dephosphorylated pS295 not only in basal conditions but also in NMDAR-activated conditions in cultured neurons. The biochemical assay also revealed the dephosphorylation of pS295 by PP2B, consistently supporting the results obtained using neurons. The newly identified calcium signaling cascade "Ca2+-PP2B-PSD-95 axis" would play an important role in the molecular mechanism for NMDA receptor-dependent plasticity.

Spatial Transcriptomics Reveals the Temporal Architecture of the Seminiferous Epithelial Cycle and Precise Sertoli-Germ Synchronization

Spermatogenesis is characterized by the seminiferous epithelial cycle, a periodic pattern of germ cell differentiation with a wave-like progression along the length of seminiferous tubules. While key signaling and metabolic components of the cycle are known, the transcriptional changes across the cycle and the correlations between germ cell and somatic lineages remain undefined. Here, we use spatial transcriptomics via RNA SeqFISH+ to profile 2,638 genes in 216,090 cells in mouse testis and identify a periodic transcriptional pattern across tubules that precisely recapitulates the seminiferous epithelial cycle, enabling us to map cells to specific timepoints along the developmental cycle. Analyzing gene expression in somatic cells reveals that Sertoli cells exhibit a cyclic transcriptional profile closely synchronized with germ cell development while other somatic cells do not demonstrate such synchronization. Remarkably, in mouse testis with drug-induced ablation of germ cells, Sertoli cells independently maintain their cyclic transcriptional dynamics. By analyzing expression data, we identify an innate retinoic acid cycle, a network of transcription factors with cyclic activation, and signaling from germ cells that could interact with this network. Together, this work leverages spatial geometries for mapping the temporal dynamics and reveals a regulatory mechanism in spermatogenesis where Sertoli cells oscillate and coordinate with the cyclical progression of germ cell development.

Par3/bazooka binds NICD and promotes notch signaling during Drosophila development

The conserved bazooka (baz/par3) gene acts as a key regulator of asymmetrical cell divisions across the animal kingdom. Associated Par3/Baz-Par6-aPKC protein complexes are also well known for their role in the establishment of apical/basal cell polarity in epithelial cells. Here we define a novel, positive function of Baz/Par3 in the Notch pathway. Using Drosophila wing and eye development, we demonstrate that Baz is required for Notch signaling activity and optimal transcriptional activation of Notch target genes. Baz appears to act independently of aPKC in these contexts, as knockdown of aPKC does not cause Notch loss-of-function phenotypes. Using transgenic Notch constructs, our data positions Baz activity downstream of activating Notch cleavage steps and upstream of Su(H)/CSL transcription factor complex activity on Notch target genes. We demonstrate a biochemical interaction between NICD and Baz, suggesting that Baz is required for NICD activity before NICD binds to Su(H). Taken together, our data define a novel role of the polarity protein Baz/Par3, as a positive and direct regulator of Notch signaling through its interaction with NICD.

RhoGDI1 regulates cell-cell junctions in polarized epithelial cells

Cell-cell contact formation of polarized epithelial cells is a multi-step process that involves the co-ordinated activities of Rho family small GTPases. Consistent with the central role of Rho GTPases, a number of Rho guanine nucleotide exchange factors (GEFs) and Rho GTPase-activating proteins (GAPs) have been identified at cell-cell junctions at various stages of junction maturation. As opposed to RhoGEFs and RhoGAPs, the role of Rho GDP dissociation inhibitors (GDIs) during cell-cell contact formation is poorly understood. Here, we have analyzed the role of RhoGDI1/ARHGDIA, a member of the RhoGDI family, during cell-cell contact formation of polarized epithelial cells. Depletion of RhoGDI1 delays the development of linear cell-cell junctions and the formation of barrier-forming tight junctions. In addition, RhoGDI1 depletion impairs the ability of cells to stop migration in response to cell collision and increases the migration velocity of collectively migrating cells. We also find that the cell adhesion receptor JAM-A promotes the recruitment of RhoGDI1 to cell-cell contacts. Our findings implicate RhoGDI1 in various processes involving the dynamic reorganization of cell-cell junctions.

Cell polarity proteins promote macropinocytosis in response to metabolic stress

Macropinocytosis has emerged as a nutrient-scavenging pathway that cancer cells exploit to survive the nutrient-deprived conditions of the tumor microenvironment. Cancer cells are especially reliant on glutamine for their survival, and in pancreatic ductal adenocarcinoma (PDAC) cells, glutamine deficiency can enhance the stimulation of macropinocytosis, allowing the cells to escape metabolic stress through the production of extracellular-protein-derived amino acids. Here, we identify the atypical protein kinase C (aPKC) enzymes, PKCζ and PKCι as novel regulators of macropinocytosis. In normal epithelial cells, aPKCs are known to regulate cell polarity in association with the scaffold proteins Par3 and Par6, controlling the function of several targets, including the Par1 kinases. In PDAC cells, we identify that each of these cell polarity proteins are required for glutamine stress-induced macropinocytosis. Mechanistically, we find that the aPKCs are regulated by EGFR signaling or by the transcription factor CREM to promote the relocation of Par3 to microtubules, facilitating macropinocytosis in a dynein-dependent manner. Importantly, we determine that cell fitness impairment caused by aPKC depletion is rescued by the restoration of macropinocytosis and that aPKCs support PDAC growth in vivo. These results identify a previously unappreciated role for cell polarity proteins in the regulation of macropinocytosis and provide a better understanding of the mechanistic underpinnings that control macropinocytic uptake in the context of metabolic stress.

TMEM25 is a Par3-binding protein that attenuates claudin assembly during tight junction development

The tight junction (TJ) in epithelial cells is formed by integral membrane proteins and cytoplasmic scaffolding proteins. The former contains the claudin family proteins with four transmembrane segments, while the latter includes Par3, a PDZ domain-containing adaptor that organizes TJ formation. Here we show the single membrane-spanning protein TMEM25 localizes to TJs in epithelial cells and binds to Par3 via a PDZ-mediated interaction with its C-terminal cytoplasmic tail. TJ development during epithelial cell polarization is accelerated by depletion of TMEM25, and delayed by overexpression of TMEM25 but not by that of a C-terminally deleted protein, indicating a regulatory role of TMEM25. TMEM25 associates via its N-terminal extracellular domain with claudin-1 and claudin-2 to suppress their cis- and trans-oligomerizations, both of which participate in TJ strand formation. Furthermore, Par3 attenuates TMEM25-claudin association via binding to TMEM25, implying its ability to affect claudin oligomerization. Thus, the TJ protein TMEM25 appears to negatively regulate claudin assembly in TJ formation, which regulation is modulated by its interaction with Par3.

High expression of PKCλ and ALDH1A3 indicates a poor prognosis, and PKCλ is required for the asymmetric cell division of ALDH1A3-positive cancer stem cells in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is the cancer with the poorest prognosis. One of the major properties reflecting its poor prognosis is high-grade heterogeneity, which leads to insensitivity to anticancer treatments. Cancer stem cells (CSCs) acquire phenotypic heterogeneity, generating abnormally differentiated cells by asymmetric cell division. However, the detailed mechanism leading to phenotypic heterogeneity is largely unknown. Here, we showed that PDAC patients with co-upregulation of PKCλ and ALDH1A3 had the poorest clinical outcome. PKCλ knockdown by DsiRNA in the ALDH1high population of PDAC MIA-PaCa-2 cells attenuated the asymmetric distribution of the ALDH1A3 protein. To monitor asymmetric cell division of ALDH1A3-positive PDAC CSCs, we established stable Panc-1 PDAC clones expressing ALDH1A3-turboGFP (Panc-1-ALDH1A3-turboGFP cells). In addition to MIA-PaCa-2-ALDH1high cells, turboGFPhigh cells sorted from Panc-1-ALDH1A3-turboGFP cells showed asymmetric cell propagation of ALDH1A3 protein. PKCλ DsiRNA in Panc-1-ALDH1A3-turboGFP cells also attenuated the asymmetric distribution of ALDH1A3 protein. These results suggest that PKCλ regulates the asymmetric cell division of ALDH1A3-positive PDAC CSCs. Furthermore, Panc-1-ALDH1A3-turboGFP cells can be useful for the visualization and monitoring of CSC properties such as asymmetric cell division of ALDH1A3-positive PDAC CSCs in time-lapse imaging.

Polarity signaling balances epithelial contractility and mechanical resistance

Epithelia maintain a functional barrier during tissue turnover while facing varying mechanical stress. This maintenance requires both dynamic cell rearrangements driven by actomyosin-linked intercellular adherens junctions and ability to adapt to and resist extrinsic mechanical forces enabled by keratin filament-linked desmosomes. How these two systems crosstalk to coordinate cellular movement and mechanical resilience is not known. Here we show that in stratifying epithelia the polarity protein aPKCλ controls the reorganization from stress fibers to cortical actomyosin during differentiation and upward movement of cells. Without aPKC, stress fibers are retained resulting in increased contractile prestress. This aberrant stress is counterbalanced by reorganization and bundling of keratins, thereby increasing mechanical resilience. Inhibiting contractility in aPKCλ-/- cells restores normal cortical keratin networks but also normalizes resilience. Consistently, increasing contractile stress is sufficient to induce keratin bundling and enhance resilience, mimicking aPKC loss. In conclusion, our data indicate that keratins sense the contractile stress state of stratified epithelia and balance increased contractility by mounting a protective response to maintain tissue integrity.

Therapeutic Effectiveness of Anticancer Agents Targeting Different Signaling Molecules Involved in Asymmetric Division of Cancer Stem Cell

Intra-tumoral heterogeneity is maintained by cancer stem cells (CSCs) with dysregulated self-renewal and asymmetric cell division (ACD). According to the cancer stem cell theory, by ACD a CSC can generate two daughter progenies with different fates such as one cancer stem cell and one differentiated cell. Therefore, this type of mitotic division supports vital process of the maintenance of CSC population. But this CSC pool reservation by ACD complicates the treatment of cancer patients, as CSCs give rise to aggressive clones which are prone to metastasis and drug-insensitivity. Hence, identification of therapeutic modalities which can target ACD of cancer stem cell is an intriguing part of cancer research. In this review, other than the discussion about the extrinsic inducers of ACD role of different proteins, miRNAs and lncRNAs in this type of cell division is also mentioned. Other than these, mode of action of the proven and potential drugs targeting ACD of CSC is also discussed here.

A Role for Second Messengers in Axodendritic Neuronal Polarity

Neuronal polarization is a complex molecular process regulated by intrinsic and extrinsic mechanisms. Nerve cells integrate multiple extracellular cues to generate intracellular messengers that ultimately control cell morphology, metabolism, and gene expression. Therefore, second messengers' local concentration and temporal regulation are crucial elements for acquiring a polarized morphology in neurons. This review article summarizes the main findings and current understanding of how Ca2+, IP3, cAMP, cGMP, and hydrogen peroxide control different aspects of neuronal polarization, and highlights questions that still need to be resolved to fully understand the fascinating cellular processes involved in axodendritic polarization.

The physiological and pathological mechanisms of early embryonic development

Early embryonic development is a complex process. The zygote undergoes several rounds of division to form a blastocyst, and during this process, the zygote undergoes the maternal-to-zygotic transition to gain control of embryonic development and makes two cell fate decisions to differentiate into an embryonic and two extra-embryonic lineages. With the use of new molecular biotechnologies and animal models, we can now further study the molecular mechanisms of early embryonic development and the pathological causes of early embryonic arrest. Here, we first summarize the known molecular regulatory mechanisms of early embryonic development in mice. Then we discuss the pathological factors leading to the early embryonic arrest. We hope that this review will give researchers a relatively complete view of the physiology and pathology of early embryonic development.

Aberrant phosphorylation inactivates Numb in breast cancer causing expansion of the stem cell pool

Asymmetric cell division is a key tumor suppressor mechanism that prevents the uncontrolled expansion of the stem cell (SC) compartment by generating daughter cells with alternative fates: one retains SC identity and enters quiescence and the other becomes a rapidly proliferating and differentiating progenitor. A critical player in this process is Numb, which partitions asymmetrically at SC mitosis and inflicts different proliferative and differentiative fates in the two daughters. Here, we show that asymmetric Numb partitioning per se is insufficient for the proper control of mammary SC dynamics, with differential phosphorylation and functional inactivation of Numb in the two progeny also required. The asymmetric phosphorylation/inactivation of Numb in the progenitor is mediated by the atypical PKCζ isoform. This mechanism is subverted in breast cancer via aberrant activation of PKCs that phosphorylate Numb in both progenies, leading to symmetric division and expansion of the cancer SC compartment, associated with aggressive disease. Thus, Numb phosphorylation represents a target for breast cancer therapy.

Role of Cell-Cell Junctions in Oesophageal Squamous Cell Carcinoma

Cell-cell junctions comprise various structures, including adherens junctions, tight junctions, desmosomes, and gap junctions. They link cells to each other in tissues and regulate tissue homeostasis in critical cellular processes. Recent advances in cell-cell junction research have led to critical discoveries. Cell-cell adhesion components are important for the invasion and metastasis of tumour cells, which are not only related to cell-cell adhesion changes, but they are also involved in critical molecular signal pathways. They are of great significance, especially given that relevant molecular mechanisms are being discovered, there are an increasing number of emerging biomarkers, targeted therapies are becoming a future therapeutic concern, and there is an increased number of therapeutic agents undergoing clinical trials. Oesophageal squamous cell carcinoma (ESCC), the most common histological subtype of oesophageal cancer, is one of the most common cancers to affect epithelial tissue. ESCC progression is accompanied by the abnormal expression or localisation of components at cell-cell junctions. This review will discuss the recent scientific developments related to the molecules at cell-cell junctions and their role in ESCC to offer valuable insights for readers, provide a global view of the relationships between position, construction, and function, and give a reference for future mechanistic studies, diagnoses, and therapeutic developments.

A perspective on molecular signalling dysfunction, its clinical relevance and therapeutics in autism spectrum disorder

Intellectual disability (ID) and autism spectrum disorder (ASD) are neurodevelopmental disorders that have become a primary clinical and social concern, with a prevalence of 2-3% in the population. Neuronal function and behaviour undergo significant malleability during the critical period of development that is found to be impaired in ID/ASD. Human genome sequencing studies have revealed many genetic variations associated with ASD/ID that are further verified by many approaches, including many mouse and other models. These models have facilitated the identification of fundamental mechanisms underlying the pathogenesis of ASD/ID, and several studies have proposed converging molecular pathways in ASD/ID. However, linking the mechanisms of the pathogenic genes and their molecular characteristics that lead to ID/ASD has progressed slowly, hampering the development of potential therapeutic strategies. This review discusses the possibility of recognising the common molecular causes for most ASD/ID based on studies from the available models that may enable a better therapeutic strategy to treat ID/ASD. We also reviewed the potential biomarkers to detect ASD/ID at early stages that may aid in diagnosis and initiating medical treatment, the concerns with drug failure in clinical trials, and developing therapeutic strategies that can be applied beyond a particular mutation associated with ASD/ID.

Effects of hydrogen peroxide on endothelial function in three-dimensional hydrogel vascular model and regulation mechanism of polar protein Par3

Three-dimensional (3D) cell cultures better reflect the function of endothelial cells (ECs) than two-dimensional (2D) cultures. In recent years, studies have found that ECs cultured in a 3D luminal structure can mimic the biological characteristics and phenotypes of vascular ECs, thus making it more suitable for endothelial dysfunction research. In this study, we used a 3D model and 2D tissue culture polystyrene (TCP) to investigate the effects of cell polarity on hydrogen peroxide (H2O2)-induced endothelial dysfunction and its related mechanisms. We observed the cell morphology, oxidative stress, and barrier and endothelial function of human umbilical vein endothelial cells (HUVECs) in 3D and 2D cultures. We then used Illumina to detect the differentially expressed genes in the 3D-cultured HUVEC with and without H2O2 stimulation, using ClusterProfiler for Gene Ontology (GO) function enrichment analysis and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analysis of differentially expressed genes. Finally, we explored the role and mechanism of polar protein partitioning defective protein 3 (Par3) in the regulation of ECs. ECs were inoculated into the 3D hydrogel channel; after stimulation with H2O2, the morphology of HUVECs changed, the boundary was blurred, the expression of intercellular junction proteins decreased, and the barrier function of the EC layer was damaged. 3D culture increased the oxidative stress response of cells stimulated by H2O2 compared to 2D TCPs. The polarity-related protein Par3 and cell division control protein 42 (CDC42) were screened using bioinformatics analysis, and western blotting was used to verify the results. Par3 knockdown significantly suppressed claudin1 (CLDN1) and vascular endothelial cadherin (VE-cadherin). These results suggest that the polar protein Par3 can protect H2O2-induced vascular ECs from damage by regulating CLDN1 and VE-cadherin.

VEGFR endocytosis: Implications for angiogenesis

The binding of vascular endothelial growth factor (VEGF) superfamily to VEGF receptor tyrosine kinases (VEGFRs) and co-receptors regulates vasculogenesis, angiogenesis and lymphangiogenesis. A recurring theme is that dysfunction in VEGF signaling promotes pathological angiogenesis, an important feature of cancer and pro-inflammatory disease states. Endocytosis of basal (resting) or activated VEGFRs facilitates signal attenuation and endothelial quiescence. However, increasing evidence suggest that activated VEGFRs can continue to signal from intracellular compartments such as endosomes. In this chapter, we focus on the evolving link between VEGFR endocytosis, signaling and turnover and the implications for angiogenesis. There is much interest in how such understanding of VEGFR dynamics can be harnessed therapeutically for a wide range of human disease states.

Dual Function of Par3 in Tumorigenesis

Cell maintenance and the establishment of cell polarity involve complicated interactions among multiple protein complexes as well as the regulation of different signaling pathways. As an important cell polarity protein, Par3 is evolutionarily conserved and involved in tight junction formation as well as tumorigenesis. In this review, we aimed to explore the function of Par3 in tumorigenesis. Research has shown that Par3 exhibits dual functions in human cancers, both tumor-promoting and tumor-suppressive. Here, we focus on the activities of Par3 in different stages and types of tumors, aiming to offer a new perspective on the molecular mechanisms that regulate the functions of Par3 in tumor development. Tumor origin, tumor microenvironment, tumor type, cell density, cell–cell contact, and the synergistic effect of Par3 and other tumor-associated signaling pathways may be important reasons for the dual function of Par3. The important role of Par3 in mammalian tumorigenesis and potential signaling pathways is context dependent.

Rho and Rab Family Small GTPases in the Regulation of Membrane Polarity in Epithelial Cells

Membrane polarity, defined as the asymmetric distribution of lipids and proteins in the plasma membrane, is a critical prerequisite for the development of multicellular tissues, such as epithelia and endothelia. Membrane polarity is regulated by polarized trafficking of membrane components to specific membrane domains and requires the presence of intramembrane diffusion barriers that prevent the intermixing of asymmetrically distributed membrane components. This intramembrane diffusion barrier is localized at the tight junctions (TJs) in these cells. Both the formation of cell-cell junctions and the polarized traffic of membrane proteins and lipids are regulated by Rho and Rab family small GTPases. In this review article, we will summarize the recent developments in the regulation of apico-basal membrane polarity by polarized membrane traffic and the formation of the intramembrane diffusion barrier in epithelial cells with a particular focus on the role of Rho and Rab family small GTPases.

Self-Sustained Regulation or Self-Perpetuating Dysregulation: ROS-dependent HIF-YAP-Notch Signaling as a Double-Edged Sword on Stem Cell Physiology and Tumorigenesis

Organ development, homeostasis, and repair often rely on bidirectional, self-organized cell-niche interactions, through which cells select cell fate, such as stem cell self-renewal and differentiation. The niche contains multiplexed chemical and mechanical factors. How cells interpret niche structural information such as the 3D topology of organs and integrate with multiplexed mechano-chemical signals is an open and active research field. Among all the niche factors, reactive oxygen species (ROS) have recently gained growing interest. Once considered harmful, ROS are now recognized as an important niche factor in the regulation of tissue mechanics and topology through, for example, the HIF-YAP-Notch signaling pathways. These pathways are not only involved in the regulation of stem cell physiology but also associated with inflammation, neurological disorder, aging, tumorigenesis, and the regulation of the immune checkpoint molecule PD-L1. Positive feedback circuits have been identified in the interplay of ROS and HIF-YAP-Notch signaling, leading to the possibility that under aberrant conditions, self-organized, ROS-dependent physiological regulations can be switched to self-perpetuating dysregulation, making ROS a double-edged sword at the interface of stem cell physiology and tumorigenesis. In this review, we discuss the recent findings on how ROS and tissue mechanics affect YAP-HIF-Notch-PD-L1 signaling, hoping that the knowledge can be used to design strategies for stem cell-based and ROS-targeting therapy and tissue engineering.

MicroRNAs as the critical regulators of cell migration and invasion in thyroid cancer

Thyroid cancer (TC) is one of the most frequent endocrine malignancies that is more common among females. Tumor recurrence is one of the most important clinical manifestations in differentiated TC which is associated with different factors including age, tumor size, and histological features. Various molecular processes such as genetic or epigenetic modifications and non-coding RNAs are also involved in TC progression and metastasis. The epithelial-to-mesenchymal transition (EMT) is an important biological process during tumor invasion and migration that affects the initiation and transformation of early-stage tumors into invasive malignancies. A combination of transcription factors, growth factors, signaling pathways, and epigenetic regulations affect the thyroid cell migration and EMT process. MicroRNAs (miRNAs) are important molecular factors involved in tumor metastasis by regulation of EMT-activating signaling pathways. Various miRNAs are involved in the signaling pathways associated with TC metastasis which can be used as diagnostic and therapeutic biomarkers. Since, the miRNAs are sensitive, specific, and non-invasive, they can be suggested as efficient and optimal biomarkers of tumor invasion and metastasis. In the present review, we have summarized all of the miRNAs which have been significantly involved in thyroid tumor cells migration and invasion. We also categorized all of the reported miRNAs based on their cellular processes to clarify the molecular role of miRNAs during thyroid tumor cell migration and invasion. This review paves the way of introducing a non-invasive diagnostic and prognostic panel of miRNAs in aggressive and metastatic TC patients.

DAPLE orchestrates apical actomyosin assembly from junctional polarity complexes

Establishment of apicobasal polarity and the organization of the cytoskeleton must operate coordinately to ensure proper epithelial cell shape and function. However, the precise molecular mechanisms by which polarity complexes directly instruct the cytoskeletal machinery to determine cell shape are poorly understood. Here, we define a mechanism by which the PAR polarity complex (PAR3–PAR6–aPKC) at apical cell junctions leads to efficient assembly of the apical actomyosin network to maintain epithelial cell morphology. We found that the PAR polarity complex recruits the protein DAPLE to apical cell junctions, which in turn triggers a two-pronged mechanism that converges upon assembly of apical actomyosin. More specifically, DAPLE directly recruits the actin-stabilizing protein CD2AP to apical junctions and, concomitantly, activates heterotrimeric G protein signaling in a GPCR-independent manner to favor RhoA-myosin activation. These observations establish DAPLE as a direct molecular link between junctional polarity complexes and the formation of apical cytoskeletal assemblies that support epithelial cell shape.

PKC-ζ Aggravates Doxorubicin-Induced Cardiotoxicity by Inhibiting Wnt/β-Catenin Signaling

Doxorubicin (Dox) is a chemotherapeutic drug used to treat a wide range of cancers, but its clinical application is limited due to its cardiotoxicity. Protein kinase C-ζ (PKC-ζ) is a serine/threonine kinase belonging to atypical protein kinase C (PKC) subfamily, and is activated by its phosphorylation. We and others have reported that PKC-ζ induced cardiac hypertrophy by activating the inflammatory signaling pathway. This study focused on whether PKC-ζ played an important role in Dox-induced cardiotoxicity. We found that PKC-ζ phosphorylation was increased by Dox treatment in vivo and in vitro. PKC-ζ overexpression exacerbated Dox-induced cardiotoxicity. Conversely, knockdown of PKC-ζ by siRNA relieved Dox-induced cardiotoxicity. Similar results were observed when PKC-ζ enzyme activity was inhibited by its pseudosubstrate inhibitor, Myristoylated. PKC-ζ interacted with β-catenin and inhibited Wnt/β-catenin signaling pathway. Activation of Wnt/β-catenin signaling by LiCl protected against Dox-induced cardiotoxicity. The Wnt/β-catenin inhibitor XAV-939 aggravated Dox-caused decline of β-catenin and cardiomyocyte apoptosis and mitochondrial damage. Moreover, activation of Wnt/β-catenin suppressed aggravation of Dox-induced cardiotoxicity due to PKC-ζ overexpression. Taken together, our study revealed that inhibition of PKC-ζ activity was a potential cardioprotective approach to preventing Dox-induced cardiac injury.

Polarity protein Par3 sensitizes breast cancer to paclitaxel by promoting cell cycle arrest

PURPOSE

Paclitaxel, belongs to tubulin-binding agents (TBAs), shows a great efficacy against breast cancer via stabilizing microtubules. Drug resistance limits its clinical application. Here we aimed to explore a role of Polarity protein Par3 in improving paclitaxel effectiveness.

METHODS

Breast cancer specimens from 45 patients were collected to study the relationship between Par3 expression and paclitaxel efficacy. The Kaplan-Meier method was used for survival analysis. Cell viability was measured in breast cancer cells (SK-BR-3 and T-47D) with Par3 over-expression or knockdown. The flow cytometry assays were performed to measure cell apoptosis and cell cycle. BrdU incorporation assay and Hoechst 33,258 staining were performed to measure cell proliferation and cell apoptosis, respectively. Immunofluorescence was used to detect microtubule structures.

RESULTS

Par3 expression was associated with good response of paclitaxel in breast cancer patients. Consistently, Par3 over-expression significantly sensitized breast cancer cells to paclitaxel by promoting cell apoptosis and reducing cell proliferation. In Par3 overexpressing cells upon paclitaxel treatment, we observed intensified cell cycle arrests at metaphase. Further exploration showed that Par3 over-expression stabilized microtubules of breast cancer cells in response to paclitaxel and resists to microtubules instability induced by nocodazole, a microtubule-depolymerizing agent.

CONCLUSION

Par3 facilitates polymeric forms of tubulin and stabilizes microtubule structure, which aggravates paclitaxel-induced delay at the metaphase-anaphase transition, leading to proliferation inhibition and apoptosis of breast cancer cells. Par3 has a potential role in sensitizing breast cancer cells to paclitaxel, which may provide a more precise assessment of individual treatment and novel therapeutic targets.

Wnt/β-Catenin Signaling Stabilizes Hemidesmosomes in Keratinocytes

Hemidesmosomes (HDs) are adhesion complexes that promote epithelial-stromal attachment in stratified and complex epithelia, including the epidermis. In various biological processes, such as differentiation and migration of epidermal keratinocytes during wound healing or carcinoma invasion, quick assembly and disassembly of HDs are prerequisites. In this study, we show that inhibition of Wnt/β-catenin signaling disturbs HD organization in keratinocytes. Screening with inhibitors identified the depletion of HD components and HD-like structures through Wnt inhibition, but keratinocyte differentiation was not affected. Wnt inhibition significantly diminished plectin and type XVII collagen expression in the basal side of Wnt-inhibited cells and the dermo-epidermal junction of the Wnt-inactive murine basal epidermis. Similar to Wnt inhibition, PLEC-knockout cells or cells with plectin-type XVII collagen binding defects showed type XVII collagen reduction in the basal side of the cells, implying the possible involvement of Wnt/β-catenin signaling in HD assembly. Atypical protein kinase C inhibition ameliorated the phenotypes of Wnt-inhibited cells. These findings show that Wnt/β-catenin signaling regulates the localization of HD components in keratinocytes and that the atypical protein kinase C pathway is involved in Wnt inhibition‒induced HD disarrangement. Our study suggests that the Wnt signaling pathway could be a potential therapeutic target for treating HD-defective diseases, such as epidermolysis bullosa.

Basolateral protein Scribble binds phosphatase PP1 to establish a signaling network maintaining apicobasal polarity

Scribble, a member of the LAP protein family, contributes to the apicobasal polarity (ABP) of epithelial cells. The LAP-unique region of these proteins, which is essential and sufficient for ABP, includes a conserved Leucine-Rich Repeat (LRR) domain. The major binding partners of this region that could regulate ABP remain unknown. Here, using proteomics, native gel electrophoresis, and site-directed mutagenesis, we show that the concave surface of LRR domain in Scribble participates in three types of mutually exclusive interactions-(i) homodimerization, serving as an auto-inhibitory mechanism; (ii) interactions with a diverse set of polarity proteins, such as Llgl1, Llgl2, EPB41L2, and EPB41L5, which produce distinct multiprotein complexes; and (iii) a direct interaction with the protein phosphatase, PP1. Analogy with the complex between PP1 and LRR domain of SDS22, a well-studied PP1 regulator, suggests that the Scibble-PP1 complex stores a latent form of PP1 in the basolateral cell cortex. Such organization may generate a dynamic signaling network wherein PP1 could be dispatched from the complex with Scribble to particular protein ligands, achieving fast dephosphorylation kinetics.

Hepatocyte polarity establishment and apical lumen formation are organized by Par3, Cdc42, and aPKC in conjunction with Lgl

Hepatocytes differ from columnar epithelial cells by their multipolar organization, which follows the initial formation of central lumen-sharing clusters of polarized cells as observed during liver development and regeneration. The molecular mechanism for hepatocyte polarity establishment, however, has been comparatively less studied than those for other epithelial cell types. Here, we show that the tight junction protein Par3 organizes hepatocyte polarization via cooperating with the small GTPase Cdc42 to target atypical protein kinase C (aPKC) to a cortical site near the center of cell-cell contacts. In 3D Matrigel culture of human hepatocytic HepG2 cells, which mimics a process of liver development and regeneration, depletion of Par3, Cdc42, or aPKC results in an impaired establishment of apicobasolateral polarity and a loss of subsequent apical lumen formation. The aPKC activity is also required for bile canalicular (apical) elongation in mouse primary hepatocytes. The lateral membrane-associated proteins Lgl1 and Lgl2, major substrates of aPKC, seem to be dispensable for hepatocyte polarity establishment because Lgl-depleted HepG2 cells are able to form a single apical lumen in 3D culture. On the other hand, Lgl depletion leads to lateral invasion of aPKC, and overexpression of Lgl1 or Lgl2 prevents apical lumen formation, indicating that they maintain proper lateral integrity. Thus, hepatocyte polarity establishment and apical lumen formation are organized by Par3, Cdc42, and aPKC; Par3 cooperates with Cdc42 to recruit aPKC, which plays a crucial role in apical membrane development and regulation of the lateral maintainer Lgl.

Otic Neurogenesis in Xenopus laevis: Proliferation, Differentiation, and the Role of Eya1

Using immunostaining and confocal microscopy, we here provide the first detailed description of otic neurogenesis in Xenopus laevis. We show that the otic vesicle comprises a pseudostratified epithelium with apicobasal polarity (apical enrichment of Par3, aPKC, phosphorylated Myosin light chain, N-cadherin) and interkinetic nuclear migration (apical localization of mitotic, pH3-positive cells). A Sox3-immunopositive neurosensory area in the ventromedial otic vesicle gives rise to neuroblasts, which delaminate through breaches in the basal lamina between stages 26/27 and 39. Delaminated cells congregate to form the vestibulocochlear ganglion, whose peripheral cells continue to proliferate (as judged by EdU incorporation), while central cells differentiate into Islet1/2-immunopositive neurons from stage 29 on and send out neurites at stage 31. The central part of the neurosensory area retains Sox3 but stops proliferating from stage 33, forming the first sensory areas (utricular/saccular maculae). The phosphatase and transcriptional coactivator Eya1 has previously been shown to play a central role for otic neurogenesis but the underlying mechanism is poorly understood. Using an antibody specifically raised against Xenopus Eya1, we characterize the subcellular localization of Eya1 proteins, their levels of expression as well as their distribution in relation to progenitor and neuronal differentiation markers during otic neurogenesis. We show that Eya1 protein localizes to both nuclei and cytoplasm in the otic epithelium, with levels of nuclear Eya1 declining in differentiating (Islet1/2+) vestibulocochlear ganglion neurons and in the developing sensory areas. Morpholino-based knockdown of Eya1 leads to reduction of proliferating, Sox3- and Islet1/2-immunopositive cells, redistribution of cell polarity proteins and loss of N-cadherin suggesting that Eya1 is required for maintenance of epithelial cells with apicobasal polarity, progenitor proliferation and neuronal differentiation during otic neurogenesis.

Cell fate determination and Hippo signaling pathway in preimplantation mouse embryo

First cell fate determination plays crucial roles in cell specification during early phases of embryonic development. Three classical concepts have been proposed to explain the lineage specification mechanism of the preimplantation embryo: inside-outside, pre-patterning, and polarity models. Transcriptional effectors of the Hippo signal pathway are YAP and TAZ activators that can create a shuttle between the cytoplasm and the nucleus. Despite different localizations of YAP in the cell, it determines the fate of ICM and TE. How the decisive cue driving factors that determine YAP localization are coordinated remains a central unanswered question. How can an embryonic cell find its position? The objective of this review is to summarize the molecular and mechanical aspects in cell fate decision during mouse preimplantation embryonic development. The findings will reveal the relationship between cell-cell adhesion, cell polarity, and determination of cell fate during early embryonic development in mice and elucidate the inducing/inhibiting mechanisms that are involved in cell specification following zygotic genome activation and compaction processes. With future studies, new biophysical and chemical cues in the cell fate determination will impart significant spatiotemporal effects on early embryonic development. The achieved knowledge will provide important information to the development of new approaches to be used in infertility treatment and increase the success of pregnancy.

Inheritance and flexibility of cell polarity: a clue for understanding human brain development and evolution

Cell polarity is fundamentally important for understanding brain development. Here, we hypothesize that the inheritance and flexibility of cell polarity during neocortex development could be implicated in neocortical evolutionary expansion. Molecular and morphological features of cell polarity may be inherited from one type of progenitor cell to the other and finally transmitted to neurons. Furthermore, key cell types, such as basal progenitors and neurons, exhibit a highly flexible polarity. We suggest that both inheritance and flexibility of cell polarity are implicated in the amplification of basal progenitors and tangential dispersion of neurons, which are key features of the evolutionary expansion of the neocortex.

Summary: We suggest that the inheritance and flexibility of cell polarity are implicated in the evolutionary expansion of the developing neocortex by promoting the amplification of neural progenitors and tangential migration of neurons.

Phase Separation in Cell Polarity

Cells are biochemically and morphologically polarized, which allows them to produce different cell shapes for various functions. Remarkably, some polarity protein complexes are asymmetrically recruited and concentrated on limited membrane regions, which is essential for the establishment and maintenance of diverse cell polarity. Though the components and mutual interactions within these protein complexes have been extensively investigated, how these proteins autonomously concentrate at local membranes and whether they have the same organization mechanism in the condensed assembly as that in aqueous solution remain elusive. A number of recent studies suggest that these highly concentrated polarity protein assemblies are membraneless biomolecular condensates which form through liquid-liquid phase separation (LLPS) of specific proteins. In this perspective, we summarize the LLPS-driven condensed protein assemblies found in asymmetric cell division, epithelial cell polarity, and neuronal synapse formation and function. These findings suggest that LLPS may be a general strategy for cells to achieve local condensation of specific proteins, thus establishing cell polarity.

SCRIB Promotes Proliferation and Metastasis by Targeting Hippo/YAP Signalling in Colorectal Cancer

The complex in which scribble planar cell polarity protein (SCRIB) is located is one of the three main polar protein complexes that play an important role in maintaining epithelial polarity and affecting tumour growth. However, the role of SCRIB in colorectal cancer (CRC) remains largely unknown. This study used date from The Cancer Genome Atlas (TCGA) and clinical samples to determine the expression of SCRIB in CRC and explored its mechanism through bioinformatics analysis and in vivo and in vitro experiments. In this study, SCRIB was found to be highly expressed in CRC patients, and it was often associated with malignant characteristics, such as proliferation, apoptosis, and epithelial-mesenchymal transition (EMT). Furthermore, we found that SCRIB may interact with the Hippo signalling pathway and affect the phosphorylation of YAP and its distribution inside and outside of the nucleus. We concluded that increased expression of SCRIB is likely to inhibit the Hippo signalling pathway by promoting YAP phosphorylation. This role of SCRIB in the progression of CRC provides an important information for the treatment of CRC.

Genetic causes of preimplantation embryo developmental failure

Embryo development requires orchestrated events, finely regulated at the molecular and cellular level by mechanisms which are progressively emerging from animal studies. With progress in genetic technologies-such as genome editing and single-cell RNA analysis-we can now assess embryo gene expression with increased precision and gain new insights into complex processes until recently difficult to explore. Multiple genes and regulative pathways have been identified for each developmental stage. We have learned that embryos with undisturbed and timely gene expression have higher chances of successful development. For example, selected genes are highly expressed during the first stages, being involved in cell adhesion, cell cycle, and regulation of transcription; other genes are instead crucial for lineage specification and therefore expressed at later stages. Due to ethical constraints, studies on human embryos remain scarce, mainly descriptive, and unable to provide functional evidence. This highlights the importance of animal studies as basic knowledge to test and appraise in a clinical context. In this review, we report on preimplantation development with a focus on genes whose impairment leads to developmental arrest. Preconceptional genetic screening could identify loss-of-function mutations of these genes; thereby, novel biomarkers of embryo quality could be adopted to improve diagnosis and treatment of infertility.

A polybasic domain in aPKC mediates Par6-dependent control of membrane targeting and kinase activity

Mechanisms coupling the atypical PKC (aPKC) kinase activity to its subcellular localization are essential for cell polarization. Unlike other members of the PKC family, aPKC has no well-defined plasma membrane (PM) or calcium binding domains, leading to the assumption that its subcellular localization relies exclusively on protein–protein interactions. Here we show that in both Drosophila and mammalian cells, the pseudosubstrate region (PSr) of aPKC acts as a polybasic domain capable of targeting aPKC to the PM via electrostatic binding to PM PI4P and PI(4,5)P₂. However, physical interaction between aPKC and Par-6 is required for the PM-targeting of aPKC, likely by allosterically exposing the PSr to bind PM. Binding of Par-6 also inhibits aPKC kinase activity, and such inhibition can be relieved through Par-6 interaction with apical polarity protein Crumbs. Our data suggest a potential mechanism in which allosteric regulation of polybasic PSr by Par-6 couples the control of both aPKC subcellular localization and spatial activation of its kinase activity.

Polarity scaffolds signaling in epithelial cell permeability

As an integral part of the innate immune system, the epithelial membrane is exposed to an array of insults that may trigger an immune response. One of the immune system's main functions is to regulate the level of communications between the mucosa and the lumen of various tissues. While it is clear that inhaled or ingested substances, or microorganisms may induce changes that affect the epithelial barrier in various ways, the proteins involved in the signaling cascades and physiological events leading to the regulation and maintenance of the barrier are not always well characterized. We review here some of the signaling components involved in regulating the barrier's paracellular permeability, and their potential effects on the activation of an immune response. While an effective immune response must be launched against pathogenic insults, tolerance must also be maintained for non-pathogenic antigens such as those in the commensal flora or for endogenous metabolites. Along with other members of the innate and adaptive immunity, the endocannabinoid system also plays an instrumental role in maintaining the balance between inflammation and tolerance. We discuss the potential effects of endo- and phytocannabinoids on epithelial permeability and how the dysregulation of this system could be involved in diseases and targeted for therapy.

Par3/integrin β1 regulates embryo adhesion via changing endometrial luminal epithelium polarity†

The objective is to investigate the pathophysiological significance of Par3 and integrin β1 with regard to the functionality of the endometrial luminal epithelium (LE). Design: laboratory study; setting: university research laboratory. Analysis involved endometrial aspirates and endometrial adenocarcinoma cells (HEC-1A) and endometrial carcinoma cells (RL95-2). We first examined the expression and localization of Par3 and integrin β1 in HEC-1A cells and RL95-2 cells. Then we knocked down Par3 and integrin β1 in HEC-1A cells and RL95-2 cells, respectively, and found that Par3/integrin β1 affected embryo adhesion by regulating the intercellular tight junctions' (TJs') structure and thus the polarity of the endometrial LE. These findings were also confirmed in the endometrium specimens from human and mice. The main outcome measures were the expression and localization of Par3 and integrin β1 in the endometrial epithelial cell lines and endometrium specimens and the regulations of Par3 and integrin β1 on TJs, polarity, and embryo adhesion. Following the knockdown of Par3 in HEC-1A cells, there was a reduction in the complexity of the TJs and cell polarity, and the adhered blastocysts number was significantly increased. However, the reduction of integrin β1 in RL95-2 cells resulted in effects that directly opposed those following the knockdown of Par3 in HEC-1A cells. Estrogen and progesterone reduced the expression of Par3 and promoted the expression of integrin β1 in HEC-1A cells. Par3/integrin β1 regulates embryo adhesion by regulating intercellular TJs' structure and polarity of endometrial LE under the action of ovarian hormones.

The cell polarity kinase Par1b/MARK2 activation selects specific NF-kB transcripts via phosphorylation of core mediator Med17/TRAP80

Par1b/MARK2 is a Ser/Thr kinase with pleiotropic effects that participates in the generation of apico-basal polarity in Caenorhabditis elegans. It is phosphorylated by atypical PKC(ι/λ) in Thr595 and inhibited. Because previous work showed a decrease in atypical protein kinase C (aPKC) activity under proinflammatory conditions, we analyzed the hypothesis that the resulting decrease in Thr595-MARK2 with increased kinase activity may also participate in innate immunity. We confirmed that pT595-MARK2 was decreased under inflammatory stimulation. The increase in MARK2 activity was verified by Par3 delocalization and rescue with a specific inhibitor. MARK2 overexpression significantly enhanced the transcriptional activity of NF-kB for a subset of transcripts. It also resulted in phosphorylation of a single band (∼Mr 80,000) coimmunoprecipitating with RelA, identified as Med17. In vitro phosphorylation showed direct phosphorylation of Med17 in Ser152 by recombinant MARK2. Expression of S152D-Med17 mimicked the effect of MARK2 activation on downstream transcriptional regulation, which was antagonized by S152A-Med17. The decrease in pThr595 phosphorylation was validated in aPKC-deficient mouse jejunal mucosae. The transcriptional effects were confirmed in transcriptome analysis and transcript enrichment determinations in cells expressing S152D-Med17. We conclude that theMARK2-Med17 axis represents a novel form of cross-talk between polarity signaling and transcriptional regulation including, but not restricted to, innate immunity responses.

Equivocal, explicit and emergent actions of PKC isoforms in cancer

The maturing mutational landscape of cancer genomes, the development and application of clinical interventions and evolving insights into tumour-associated functions reveal unexpected features of the protein kinase C (PKC) family of serine/threonine protein kinases. These advances include recent work showing gain or loss-of-function mutations relating to driver or bystander roles, how conformational constraints and plasticity impact this class of proteins and how emergent cancer-associated properties may offer opportunities for intervention. The profound impact of the tumour microenvironment, reflected in the efficacy of immune checkpoint interventions, further prompts to incorporate PKC family actions and interventions in this ecosystem, informed by insights into the control of stromal and immune cell functions. Drugging PKC isoforms has offered much promise, but when and how is not obvious.

Type XVII collagen interacts with the aPKC-PAR complex and maintains epidermal cell polarity

Type XVII collagen (COL17) is a transmembrane protein expressed in the basal epidermis. COL17 serves as a niche for epidermal stem cells, and although its reduction has been implicated in altering cell polarity and ageing of the epidermis, it is unknown how COL17 affects epidermal cell polarity. Here, we uncovered COL17 as a binding partner of the aPKC-PAR complex, which is a key regulating factor of cell polarity. Immunoprecipitation-immunoblot assay and protein-protein binding assay revealed that COL17 interacts with aPKC and PAR3. COL17 deficiency or epidermis-specific aPKCλ deletion destabilized PAR3 distribution in the epidermis, while aPKCζ knockout did not. Asymmetrical cell division was pronounced in COL17-null neonatal paw epidermis. These results show that COL17 is pivotal for maintaining epidermal cell polarity. Our study highlights the previously unrecognized role of COL17 in the basal keratinocytes.

RAS-mediated suppression of PAR3 and its effects on SCC initiation and tissue architecture occur independently of hyperplasia

Proper epithelial development and homeostasis depends on strict control of oriented cell division. Current evidence shows that this process is regulated by intrinsic polarity factors and external spatial cues. Owing to the lack of an appropriate model system that can recapitulate the architecture of the skin, deregulation of spindle orientation in human epithelial carcinoma has never been investigated. Here, using an inducible model of human squamous cell carcinoma (SCC), we demonstrate that RAS-dependent suppression of PAR3 (encoded by PARD3) accelerates epithelial disorganization during early tumorigenesis. Diminished PAR3 led to loss of E-cadherin-mediated cell adhesion, which in turn contributed to misoriented cell division. Pharmacological inhibition of the MAPK pathway downstream of RAS activation reversed the defects in PAR3 expression, E-cadherin-mediated cell adhesion and mitotic spindle orientation. Thus, temporal analysis of human neoplasia provides a powerful approach to study cellular and molecular transformations during early oncogenesis, which allowed identification of PAR3 as a critical regulator of tissue architecture during initial human SCC development.

Phosphorylation and dephosphorylation of Ser852 and Ser889 control the clustering, localization and function of PAR3

Cell polarity is essential for various asymmetric cellular events, and the partitioning defective (PAR) protein PAR3 (encoded by PARD3 in mammals) plays a unique role as a cellular landmark to establish polarity. In epithelial cells, PAR3 localizes at the subapical border, such as the tight junction in vertebrates, and functions as an apical determinant. Although we know a great deal about the regulators of PAR3 localization, how PAR3 is concentrated and localized to a specific membrane domain remains an important question to be clarified. In this study, we demonstrate that ASPP2 (also known as TP53BP2), which controls PAR3 localization, links PAR3 and protein phosphatase 1 (PP1). The ASPP2-PP1 complex dephosphorylates a novel phosphorylation site, Ser852, of PAR3. Furthermore, Ser852- or Ser889-unphosphorylatable PAR3 mutants form protein clusters, and ectopically localize to the lateral membrane. Concomitance of clustering and ectopic localization suggests that PAR3 localization is a consequence of local clustering. We also demonstrate that unphosphorylatable forms of PAR3 exhibited a low molecular turnover and failed to coordinate rapid reconstruction of the tight junction, supporting that both the phosphorylated and dephosphorylated states are essential for the functional integrity of PAR3.