The principal cell of the kidney collecting duct is one of the most highly regulated epithelial cell types in vertebrates. The effects of hormonal, autocrine, and paracrine factors to regulate principal cell transport processes are central to the maintenance of fluid and electrolyte balance in the face of wide variations in food and water intake. In marked contrast with the epithelial cells lining the proximal tubule, the collecting duct is electrically tight, and ion and osmotic gradients can be very high. The central role of principal cells in salt and water transport is reflected by their defining transporters-the epithelial Na 1 channel (ENaC), the renal outer medullary K 1 channel, and the aquaporin 2 (AQP2) water channel. The coordinated regulation of ENaC by aldosterone, and AQP2 by arginine vasopressin (AVP) in principal cells is essential for the control of plasma Na 1 and K 1 concentrations, extracellular fluid volume, and BP. In addition to these essential hormones, additional neuronal, physical, and chemical factors influence Na 1 , K 1 , and water homeostasis. Notably, a variety of secreted paracrine and autocrine agents such as bradykinin, ATP, endothelin, nitric oxide, and prostaglandin E 2 counterbalance and limit the natriferic effects of aldosterone and the water-retaining effects of AVP. Considerable recent progress has improved our understanding of the transporters, receptors, second messengers, and signaling events that mediate principal cell responses to changing environments in health and disease. This review primarily addresses the structure and function of the key transporters and the complex interplay of regulatory factors that modulate principal cell ion and water transport.

The steroid hormone aldosterone stimulates sodium (Na ؉ ) transport in tight epithelia by altering the expression of target genes that regulate the activity and trafficking of the epithelial sodium channel (ENaC Hormone-regulated sodium (Na ϩ ) transport in tight epithelia is essential for the control of circulatory volume, blood pressure, and extracellular fluid composition in vertebrates. The epithelial Na ϩ channel, ENaC, 5 constitutes the rate-limiting step for Na ϩ transport, and its activity, trafficking, and expression are important targets of regulation, most notably by the mineralocorticoid hormone aldosterone, which acts primarily through the mineralocorticoid receptor to alter the transcription of a set of target genes (1). Several studies using candidate gene approaches (2, 3) or unbiased screens (4 -8) have been undertaken to discern the mechanistic basis of aldosterone action. As with other steroid-regulated processes (9), two major classes of target genes have been identified: early and late. Early response genes appear to be required for initiation of the response, whereas the late response genes participate in consolidation (10). The latter include components of the ion transport machinery itself (for example, ENaC subunits and subunits of the Na,KATPase) and genes that encode regulatory proteins that likely act to limit the extent of the aldosterone response (for example, activators of the mitogen-activated protein kinase cascade, such as epidermal growth factor (EGF) or its receptor, epidermal growth factor receptor (11). The former category encodes primarily signaling molecules, implicated in pathways that control ENaC activity and/or trafficking (1). The best characterized of these targets is the serine-threonine kinase serum-and glucocorticoid-induced kinase-1 (SGK1) (1), which acts to increase apical membrane ENaC, at least in part, by inhibiting the ubiquitin ligase Nedd4Ϫ2, itself a modulator of ENaC trafficking and degradation (12, 13). Recently, several lines of evidence have suggested that aldosteroneregulated mediators other than SGK1 provide stimulatory input into this system (1). Most notably, although SGK1 knock-out mice have aldosterone resistance, their phenotype is substantially less severe than that of either mineralocorticoid receptor or ␣ENaC knock-out mice (1, 14) or of adrenalectomized wild type animals (15), suggesting that renal ENaC function and renal mineralocorticoid action are partially but not completely dependent on SGK1. The observation that short term aldosterone treatment induces an accumulation of SGK1 in the entire aldosterone-sensitive distal nephron, whereas the apical insertion of ENaC takes place only in the connecting tubule and early collecting duct, indicates that other factors are probably required as well to drive ENaC cell surface expression and activity and, thus, Na ϩ reabsorption (15). It is also notable that inhibitors of phosphatidylinositol 3Ј-kinase (which is responsible for activation of SGK1) do not completely abolish aldosterone-induced Na ...

Highlights d Unsupervised clustering revealed subtype with EMT and phosphoprotein signatures d Potential therapeutic vulnerabilities included survivin, NSD3, LSD1, and EZH2 d Rb phosphorylation nominated as a biomarker for trials with CDK4/6 inhibitors d Detailed immune landscape analysis highlighted targetable points of immuneregulation

The epithelial-to-mesenchymal transition (EMT) plays a critical role during normal development and in cancer progression. EMT is induced by various signaling pathways, including TGF-β, BMP, Wnt–β-catenin, NOTCH, Shh, and receptor tyrosine kinases. In this study, we performed single-cell RNA sequencing on MCF10A cells undergoing EMT by TGF-β1 stimulation. Our comprehensive analysis revealed that cells progress through EMT at different paces. Using pseudotime clustering reconstruction of gene-expression profiles during EMT, we found sequential and parallel activation of EMT signaling pathways. We also observed various transitional cellular states during EMT. We identified regulatory signaling nodes that drive EMT with the expression of important microRNAs and transcription factors. Using a random circuit perturbation methodology, we demonstrate that the NOTCH signaling pathway acts as a key driver of TGF-β–induced EMT. Furthermore, we demonstrate that the gene signatures of pseudotime clusters corresponding to the intermediate hybrid EMT state are associated with poor patient outcome. Overall, this study provides insight into context-specific drivers of cancer progression and highlights the complexities of the EMT process.

Background The epithelial-mesenchymal transition (EMT) enables dissociation of tumour cells from the primary tumour mass, invasion through the extracellular matrix, intravasation into blood vessels and colonisation of distant organs. Cells that revert to the epithelial state via the mesenchymal-epithelial transition cause metastases, the primary cause of death in cancer patients. EMT also empowers cancer cells with stem-cell properties and induces resistance to chemotherapeutic drugs. Understanding the driving factors of EMT is critical for the development of effective therapeutic interventions. Methods This manuscript describes the generation of a database containing EMT gene signatures derived from cell lines, patient-derived xenografts and patient studies across cancer types and multiomics data and the creation of a web-based portal to provide a comprehensive analysis resource. Results EMTome incorporates (i) EMT gene signatures; (ii) EMT-related genes with multiomics features across different cancer types; (iii) interactomes of EMT-related genes (miRNAs, transcription factors, and proteins); (iv) immune profiles identified from The Cancer Genome Atlas (TCGA) cohorts by exploring transcriptomics, epigenomics, and proteomics, and drug sensitivity and (iv) clinical outcomes of cancer cohorts linked to EMT gene signatures. Conclusion The web-based EMTome portal is a resource for primary and metastatic tumour research publicly available at www.emtome.org.