The Rho family GEF FARP2 is activated by aPKCι to control tight junction formation and polarity

Spatial Transcriptomics and Proteomics Profiling After Ischemic Stroke Reperfusion: Insights Into Vascular Alterations

BACKGROUND

More than half of patients with ischemic stroke experience futile reperfusion, increasing the risk of death and disabilities despite a successful recanalization. The reason behind this is debated, and we aim to investigate cerebrovascular changes toward a broader understanding of these conditions. We hypothesize that ischemic stroke reperfusion modifies the expression profile in the microvasculature in a spatial manner toward peri-infarct brain edema and circulatory failure.

METHODS

We investigated the early (24-hour) changes in spatial gene expression in the brain parenchymal endothelial cells and mural cells following ischemia stroke reperfusion in 13- to 14-week-old C57BL/6JRj male mice (n=5). Ischemia was induced by occlusion of the middle cerebral artery for 60 minutes, and Nissl staining was used to validate infarct size. Spatial transcriptomics complemented by bulk proteomics was conducted in the peri-infarct cortex region and validated with immunohistochemical semiquantification of proteins of interest. To avoid individual biological variations, changes in the peri-infarct cortex region were expressed relatively to the matching contralateral hemisphere region.

RESULTS

Ischemic stroke reperfusion impaired the blood-brain barrier integrity through junctional Cldn5 (claudin-5) downregulation, changes of the actin cytoskeleton adhesion, and high expression of the proinflammatory Il-6 (interleukin-6). Molecules important for extracellular Ca2+ influx and intracellular Ca2+ release, Cacna1e (R-type Ca2+ channels), Orai2, Ryr3, Itpr1, and Itpka (inositol-trisphosphate 3-kinase A), were markedly reduced. Furthermore, reduced Grm5 (glutamate receptor 5) associated with upregulated Nfatc3 and Stat3 implicates suppression of the contractile phenotype, suggesting reduced poststroke vascular resistance due to loss of mural cell tone. The complete spatial transcriptomics map over the ipsilateral and contralateral hemispheres is available online as a Web tool.

CONCLUSIONS

Emphasizing the spatial molecular pattern behind blood-brain barrier disruption and loss of the vascular tone in the acute phase following ischemic stroke reperfusion suggests the gene expression contribution for a therapeutic target in ischemia-reperfusion abnormalities.

PARD6A promotes lung adenocarcinoma cell proliferation and invasion through Serpina3

Par6α encoded by PARD6A is a member of the PAR6 family and is reported to promote cancer initiation and progression. PARD6A is frequently upregulated in different types of cancers, but its regulatory role in lung cancer progression is yet to be established. In this study, we analyzed the PARD6A expression in biopsies from lung adenocarcinoma (LUAD) patients, and the survival probability using LUAD tissue microarray (TMA) and online datasets from TCGA and GEO. We conducted in vitro and in vivo assays to assess the role of PARD6A in regulating lung cancer progression, including proliferation, wound healing, transwell, RNA-seq, and subcutaneous tumor mice models. Our findings revealed that PARD6A is highly expressed in cancer tissues from LUAD patients and is associated with poor prognosis in LUAD patients. In vitro assays showed that PARD6A promoted cell proliferation, migration, and invasion. The transcriptome sequencing identified Serpina3 as one of the key downstream molecules of PARD6A. Ectopic expression of Serpina3 rescued impaired proliferation, migration, and invasion in PARD6A-knocking down H1299 cells, whereas silencing Serpina3 impeded enhanced proliferation, migration, and invasion in PARD6A-overexpressing H1975 cells. Our findings suggest that PARD6A promotes lung cancer progression by inducing Serpina3, which may be a promising therapeutic target.

Into the fold: advances in understanding aPKC membrane dynamics

Atypical protein kinase Cs (aPKCs) are part of the PKC family of protein kinases and are atypical because they don't respond to the canonical PKC activators diacylglycerol (DAG) and Ca2+. They are central to the organization of polarized cells and are deregulated in several cancers. aPKC recruitment to the plasma membrane compartment is crucial to their encounter with substrates associated with polarizing functions. However, in contrast with other PKCs, the mechanism by which atypical PKCs are recruited there has remained elusive until recently. Here, we bring aPKC into the fold, summarizing recent reports on the direct recruitment of aPKC to membranes, providing insight into seemingly discrepant findings and integrating them with existing literature.

DjFARP Contributes to the Regeneration and Maintenance of the Brain through Activation of DjRac1 in Dugesia japonica

FERM, RhoGEF, and Pleckstrin domain protein (FARP) mediated RhoGTPase pathways are involved in diverse biological processes, such as neuronal development and tumorigenesis. However, little is known about their role in neural regeneration. We uncovered for the first time that FARP-Rac1 signaling plays an important role in neural regeneration in Dugesia japonica, a planarian that possesses unparalleled regenerative capacities. The planarian FARP homolog DjFARP was primarily expressed in both intact and regenerating brain and pharynx tissue. Functional studies suggested that downregulation of DjFARP with dsRNA in Dugesia japonica led to smaller brain sizes, defects in brain lateral branches, and loss of cholinergic, GABAergic, and dopaminergic neurons in both intact and regenerating animals. Moreover, the Rho GTPase DjRac1 was shown to play a similar role in neural regeneration and maintenance. Rac1 activation assay showed that DjFARP acts as a guanine nucleotide exchange factor (GEF) for DjRac1. Together, these findings indicate that the brain defects seen in DjFARP knockdown animals may be attributable to DjRac1 inactivation. In conclusion, our study demonstrated that DjFARP-DjRac1 signaling was required for the maintenance and proper regeneration of the brain in Dugesia japonica.

Control of atypical PKCι membrane dissociation by tyrosine phosphorylation within a PB1-C1 interdomain interface

Atypical PKCs are cell polarity kinases that operate at the plasma membrane where they function within multiple molecular complexes to contribute to the establishment and maintenance of polarity. In contrast to the classical and novel PKCs, atypical PKCs do not respond to diacylglycerol cues to bind the membrane compartment. Until recently, it was not clear how aPKCs are recruited; whether aPKCs can directly interact with membranes or whether they are dependent on other protein interactors to do so. Two recent studies identified the pseudosubstrate region and the C1 domain as direct membrane interaction modules; however, their relative importance and coupling are unknown. We combined molecular modeling and functional assays to show that the regulatory module of aPKCι, comprising the PB1 pseudosubstrate and C1 domains, forms a cooperative and spatially continuous invariant membrane interaction platform. Furthermore, we show the coordinated orientation of membrane-binding elements within the regulatory module requires a key PB1-C1 interfacial β-strand (beta-strand linker). We show this element contains a highly conserved Tyr residue that can be phosphorylated and that negatively regulates the integrity of the regulatory module, leading to membrane release. We thus expose a hitherto unknown regulatory mechanism of aPKCι membrane binding and release during cell polarization.

Comparative transcriptome analysis provides insight into the molecular targets and signaling pathways of deer TGF-1 regulating chondrocytes proliferation and differentiation

BACKGROUND

Chondrocytes are the only cell components in the cartilage, which has the poor regeneration ability. Thus, repairing damaged cartilage remains a huge challenge. Sika deer antlers are mainly composed of cartilaginous tissues that have an astonishing capacity for repair and renewal. Our previous study has demonstrated the transforming growth factor β (TGF-β1) is considered to be a key molecule involved in rapid growth, with the strongest expression in the cartilage layer. However, it remains to be clarified whether deer TGF-β1 has significantly different function from other species such as mouse, and what is the molecular mechanism of regulating cartilage growth.

METHODS

Primary chondrocytes was collected from new born mouse rib cartilage. The effect of TGF-β1 on primary chondrocytes viability was elucidated by RNA sequencing (RNA-seq) technology combined with validation methods such as quantitative real-time polymerase chain reaction (qRT-PCR) and immunofluorescence assay (IFA). Differential expression genes were identified using the DEGseq package.

RESULTS

Our results demonstrated that the overexpression of deer TGF-β1 possibly promoted chondrocyte proliferation and extracellular matrix (ECM) synthesis, while simultaneously suppressing chondrocyte differentiation through regulating transcription factors, growth factors, ECM related genes, proliferation and differentiation marker genes, such as Comp, Fgfr3, Atf4, Stat1 etc., and signaling pathways such as the MAPK signaling pathway, inflammatory mediator regulation of TRP channels etc. In addition, by comparing the amino acid sequence and structures between the deer TGF-β1 and mouse TGF-β1, we found that deer TGF-β1 and mouse TGF-β1 proteins are mainly structurally different in arm domains, which is the main functional domain. Phenotypic identification results showed that deer TGF-β1 may has stronger function than mouse TGF-β1.

CONCLUSION

​These results suggested that deer TGF-β1 has the ability to promote chondrogenesis by regulating chondrocyte proliferation, differentiation and ECM synthesis. This study provides insights into the molecular mechanisms underlying the effects of deer TGF-β1 on chondrocyte viability.

Separable mechanisms drive local and global polarity establishment in the Caenorhabditiselegans intestinal epithelium

Apico-basolateral polarization is essential for epithelial cells to function as selective barriers and transporters, and to provide mechanical resilience to organs. Epithelial polarity is established locally, within individual cells to establish distinct apical, junctional and basolateral domains, and globally, within a tissue where cells coordinately orient their apico-basolateral axes. Using live imaging of endogenously tagged proteins and tissue-specific protein depletion in the Caenorhabditiselegans embryonic intestine, we found that local and global polarity establishment are temporally and genetically separable. Local polarity is initiated prior to global polarity and is robust to perturbation. PAR-3 is required for global polarization across the intestine but local polarity can arise in its absence, as small groups of cells eventually established polarized domains in PAR-3-depleted intestines in a HMR-1 (E-cadherin)-dependent manner. Despite the role of PAR-3 in localizing PKC-3 to the apical surface, we additionally found that PAR-3 and PKC-3/aPKC have distinct roles in the establishment and maintenance of local and global polarity. Taken together, our results indicate that different mechanisms are required for local and global polarity establishment in vivo.

A Scribble/Cdep/Rac pathway controls follower-cell crawling and cluster cohesion during collective border-cell migration

Collective cell movements drive normal development and metastasis. Drosophila border cells move as a cluster of 6-10 cells, where the role of the Rac GTPase in migration was first established. In border cells, as in most migratory cells, Rac stimulates leading-edge protrusion. Upstream Rac regulators in leaders have been identified; however, the regulation and function of Rac in follower border cells is unknown. Here, we show that all border cells require Rac, which promotes follower-cell motility and is important for cluster compactness and movement. We identify a Rac guanine nucleotide exchange factor, Cdep, which also regulates follower-cell movement and cluster cohesion. Scribble, Discs large, and Lethal giant larvae localize Cdep basolaterally and share phenotypes with Cdep. Relocalization of Cdep::GFP partially rescues Scribble knockdown, suggesting that Cdep is a major downstream effector of basolateral proteins. Thus, a Scrib/Cdep/Rac pathway promotes cell crawling and coordinated, collective migration in vivo.

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.

Rac-GEF/Rac Signaling and Metastatic Dissemination in Lung Cancer

Lung cancer is the leading cause of cancer-related deaths worldwide, with non-small cell lung cancer (NSCLC) representing ∼85% of new diagnoses. The disease is often detected in an advanced metastatic stage, with poor prognosis and clinical outcome. In order to escape from the primary tumor, cancer cells acquire highly motile and invasive phenotypes that involve the dynamic reorganization of the actin cytoskeleton. These processes are tightly regulated by Rac1, a small G-protein that participates in the formation of actin-rich membrane protrusions required for cancer cell motility and for the secretion of extracellular matrix (ECM)-degrading proteases. In this perspective article we focus on the mechanisms leading to aberrant Rac1 signaling in NSCLC progression and metastasis, highlighting the role of Rac Guanine nucleotide Exchange Factors (GEFs). A plausible scenario is that specific Rac-GEFs activate discrete intracellular pools of Rac1, leading to unique functional responses in the context of specific oncogenic drivers, such as mutant EGFR or mutant KRAS. The identification of dysregulated Rac signaling regulators may serve to predict critical biomarkers for metastatic disease in lung cancer patients, ultimately aiding in refining patient prognosis and decision-making in the clinical setting.

Autoactivation of small GTPases by the GEF-effector positive feedback modules

Small GTPases are organizers of a plethora of cellular processes. The time and place of their activation are tightly controlled by the localization and activation of their regulators, guanine-nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Remarkably, in some systems, the upstream regulators of GTPases are also found downstream of their activity. Resulting feedback loops can generate complex spatiotemporal dynamics of GTPases with important functional consequences. Here we discuss the concept of positive autoregulation of small GTPases by the GEF-effector feedback modules and survey recent developments in this exciting area of cell biology.

Regulation of Cdc42 and its effectors in epithelial morphogenesis

Cdc42 - a member of the small Rho GTPase family - regulates cell polarity across organisms from yeast to humans. It is an essential regulator of polarized morphogenesis in epithelial cells, through coordination of apical membrane morphogenesis, lumen formation and junction maturation. In parallel, work in yeast and Caenorhabditis elegans has provided important clues as to how this molecular switch can generate and regulate polarity through localized activation or inhibition, and cytoskeleton regulation. Recent studies have revealed how important and complex these regulations can be during epithelial morphogenesis. This complexity is mirrored by the fact that Cdc42 can exert its function through many effector proteins. In epithelial cells, these include atypical PKC (aPKC, also known as PKC-3), the P21-activated kinase (PAK) family, myotonic dystrophy-related Cdc42 binding kinase beta (MRCKβ, also known as CDC42BPB) and neural Wiskott-Aldrich syndrome protein (N-WASp, also known as WASL). Here, we review how the spatial regulation of Cdc42 promotes polarity and polarized morphogenesis of the plasma membrane, with a focus on the epithelial cell type.

First person – Mathias Cobbaut and Ahmed Elbediwy

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Mathias Cobbaut and Ahmed Elbediwy are co-first authors on ‘The Rho family GEF FARP2 is activated by aPKCι to control tight junction formation and polarity’, published in JCS. Mathias is a postdoc in the lab of Prof. Peter Parker at The Francis Crick Institute, London, investigating protein kinase regulation/biochemistry and the functional role of protein kinase signaling. Ahmed is a lecturer at Kingston University, investigating cancer biology, polarity and signaling.