Sticking Around: Short-Range Activity of Wnt Ligands

A WNT4- and DKK3-driven canonical to noncanonical Wnt signaling switch controls multiciliogenesis

Multiciliated cells contain hundreds of cilia whose directional movement powers the mucociliary clearance of the airways, a vital host defense mechanism. Multiciliated cell specification requires canonical Wnt signaling, which then must be turned off. Next, ciliogenesis and polarized ciliary orientation are regulated by noncanonical Wnt/planar cell polarity (Wnt/PCP) signaling. The mechanistic relationship between the Wnt pathways is unknown. We show that DKK3, a secreted canonical Wnt regulator and WNT4, a noncanonical Wnt ligand act together to facilitate a canonical to noncanonical Wnt signaling switch during multiciliated cell formation. In primary human airway epithelial cells, DKK3 and WNT4 CRISPR knockout blocks, whereas ectopic expression promotes, multiciliated cell formation by inhibiting canonical Wnt signaling. Wnt4 and Dkk3 single-knockout mice also display defective ciliated cells. DKK3 and WNT4 are co-secreted from basal stem cells and act directly on multiciliated cells via KREMEN1 and FZD6, respectively. We provide a novel mechanism that links specification to cilium biogenesis and polarization for proper multiciliated cell formation.

Gone with the Wnt(less): a mechanistic perspective on the journey of Wnt

Wnts are short-range signaling proteins, expressed in all metazoans from sponges to humans, critical for cell development and fate. There are 19 different Wnts in the human genome with varying expression levels and patterns, and post-translational modifications. Common to essentially all Wnts is the palmitoleation of a conserved serine by the O-acyltransferase PORCN in the endoplasmic reticulum (ER). All lipidated Wnts then bind a dedicated carrier Wntless (WLS), endowed with the task of transporting them from the ER to the plasma membrane, and ultimately facilitating their release to receptors on the Wnt-receiving cell to initiate signaling. Here, we will focus on the WLS-mediated transport step. There are currently two published structures, both obtained by single-particle cryo-electron microscopy of the Wnt/WLS complex: human Wnt8A-bound and human Wnt3A-bound WLS. We analyze the two Wnt/WLS structures - remarkably similar despite the sequence similarity between Wnt8A and Wnt3A being only ∼39% - to begin to understand the conserved nature of this binding mechanism, and ultimately how one carrier can accommodate a family of 19 different Wnts. By comparing how Wnt associates with WLS with how it binds to PORCN and FZD receptors, we can begin to speculate on mechanisms of Wnt transfer from PORCN to WLS, and from WLS to FZD, thus providing molecular-level insight into these essential steps of the Wnt signaling pathway.

The multidimensional role of the Wnt/β-catenin signaling pathway in human malignancies

Several signaling pathways have been identified as important for developmental processes. One of such important cascades is the Wnt/β-catenin signaling pathway, which can regulate various physiological processes such as embryonic development, tissue homeostasis, and tissue regeneration; while its dysregulation is implicated in several pathological conditions especially cancers. Interestingly, deregulation of the Wnt/β-catenin pathway has been reported to be closely associated with initiation, progression, metastasis, maintenance of cancer stem cells, and drug resistance in human malignancies. Moreover, several genetic and experimental models support the inhibition of the Wnt/β-catenin pathway to answer the key issues related to cancer development. The present review focuses on different regulators of Wnt pathway and how distinct mutations, deletion, and amplification in these regulators could possibly play an essential role in the development of several cancers such as colorectal, melanoma, breast, lung, and leukemia. Additionally, we also provide insights on diverse classes of inhibitors of the Wnt/β-catenin pathway, which are currently in preclinical and clinical trial against different cancers.

Pluripotency state regulates cytoneme selectivity and self-organization of embryonic stem cells

To coordinate cell fate with changes in spatial organization, stem cells (SCs) require specific and adaptable systems of signal exchange and cell-to-cell communication. Pluripotent embryonic stem cells (ESCs) use cytonemes to pair with trophoblast stem cells (TSCs) and form synthetic embryonic structures in a Wnt-dependent manner. How these interactions vary with pluripotency states remains elusive. Here we show that ESC transition to an early primed ESC (pESC) state reduces their pairing with TSCs and impairs synthetic embryogenesis. pESCs can activate the Wnt/β-catenin pathway in response to soluble Wnt ligands, but their cytonemes form unspecific and unstable interactions with localized Wnt sources. This is due to an impaired crosstalk between Wnt and glutamate receptor activity and reduced generation of Ca2+ transients on the cytonemes upon Wnt source contact. Induced iGluR activation can partially restore cytoneme function in pESCs, while transient overexpression of E-cadherin improves pESC-TSC pairing. Our results illustrate how changes in pluripotency state alter the mechanisms SCs use to self-organize.

Targeting the Versatile Wnt/β-Catenin Pathway in Cancer Biology and Therapeutics: From Concept to Actionable Strategy

This expert review offers a critical synthesis of the latest insights and approaches at targeting the Wnt/β-catenin pathway in various cancers such as colorectal cancer, melanoma, leukemia, and breast and lung cancers. Notably, from organogenesis to cancer, the Wnt/β-catenin signaling displays varied and highly versatile biological functions in animals, with virtually all tissues requiring the Wnt/β-catenin signaling in one way or the other. Aberrant expression of the members of the Wnt/β-catenin has been implicated in many pathological conditions, particularly in human cancers. Mutations in the Wnt/β-catenin pathway genes have been noted in diverse cancers. Biochemical and genetic data support the idea that inhibition of Wnt/β-catenin signaling is beneficial in cancer therapeutics. The interaction of this important pathway with other signaling systems is also noteworthy, but remains as an area for further research and discovery. In addition, formation of different complexes by components of the Wnt/β-catenin pathway and the precise roles of these complexes in the cytoplasmic milieu are yet to be fully elucidated. This article highlights the latest medical technologies in imaging, single-cell omics, use of artificial intelligence (e.g., machine learning techniques), genome sequencing, quantum computing, molecular docking, and computational softwares in modeling interactions between molecules and predicting protein-protein and compound-protein interactions pertinent to the biology and therapeutic value of the Wnt/β-catenin signaling pathway. We discuss these emerging technologies in relationship to what is currently needed to move from concept to actionable strategies in translating the Wnt/β-catenin laboratory discoveries to Wnt-targeted cancer therapies and diagnostics in the clinic.

Robust Wnt signaling is maintained by a Wg protein gradient and Fz2 receptor activity in the developing Drosophila wing

Wnts are secreted proteins that regulate cell fate during development of all metazoans. Wnt proteins were proposed to spread over several cells to activate signaling directly at a distance. In the Drosophila wing epithelium, an extracellular gradient of the Wnt1 homolog Wingless (Wg) was observed extending over several cells away from producing cells. Surprisingly, however, it was also shown that a membrane-tethered Neurotactin-Wg fusion protein (NRT-Wg) can largely replace endogenous Wg, leading to proper patterning of the wing. Therefore, the functional range of Wg and whether Wg spreading is required for correct tissue patterning remains controversial. Here, by capturing secreted Wg on cells away from the source, we show that Wg acts over a distance of up to 11 cell diameters to induce signaling. Furthermore, cells located outside the reach of extracellular Wg depend on the Frizzled2 receptor to maintain signaling. Frizzled2 expression is increased in the absence of Wg secretion and is required to maintain signaling and cell survival in NRT-wg wing discs. Together, these results provide insight into the mechanisms by which robust Wnt signaling is achieved in proliferating tissues.

Essential long-range action of Wingless/Wnt in adult intestinal compartmentalization

Signal transduction activated by Wingless/Wnt ligands directs cell proliferation and fate specification in metazoans, and its overactivation underlies the development of the vast majority of colorectal cancers. In the conventional model, the secretion and movement of Wingless to cells distant from its source of synthesis are essential for long-range signaling in tissue patterning. However, this model was upended recently by an unanticipated finding: replacement of wild-type Drosophila Wingless with a membrane-tethered form produced viable adults with largely normal external morphology, which suggested that Wingless secretion and movement are dispensable for tissue patterning. Herein, we tested this foundational principle in the adult intestine, where Wingless signaling gradients coincide with all major boundaries between compartments. We find that the critical roles of Wingless during adult intestinal development, which include regulation of target gene activation, boundary formation, stem cell proliferation, epithelial cell fate specification, muscle differentiation, gut folding, and signaling crosstalk with the Decapentaplegic pathway, are all disrupted by Wingless tethering. These findings provide new evidence that supports the requirement for the direct, long-range action of Wingless in tissue patterning, with relevance for animal development, tissue homeostasis and Wnt-driven disease.

A ZNRF3-dependent Wnt/β-catenin signaling gradient is required for adrenal homeostasis

The transmembrane E3 ubiquitin ligases ZNRF3 and RNF43 antagonize Wnt signaling by promoting degradation of frizzled receptors. Here, Basham et al. demonstrate that adrenocortical-specific loss of ZNRF3, but not RNF43, results in adrenal hyperplasia that depends on Porcupine-mediated Wnt ligand secretion.

Spatiotemporal control of Wnt signaling is essential for the development and homeostasis of many tissues. The transmembrane E3 ubiquitin ligases ZNRF3 (zinc and ring finger 3) and RNF43 (ring finger protein 43) antagonize Wnt signaling by promoting degradation of frizzled receptors. ZNRF3 and RNF43 are frequently inactivated in human cancer, but the molecular and therapeutic implications remain unclear. Here, we demonstrate that adrenocortical-specific loss of ZNRF3, but not RNF43, results in adrenal hyperplasia that depends on Porcupine-mediated Wnt ligand secretion. Furthermore, we discovered a Wnt/β-catenin signaling gradient in the adrenal cortex that is disrupted upon loss of ZNRF3. Unlike β-catenin gain-of-function models, which induce high Wnt/β-catenin activation and expansion of the peripheral cortex, ZNRF3 loss triggers activation of moderate-level Wnt/β-catenin signaling that drives proliferative expansion of only the histologically and functionally distinct inner cortex. Genetically reducing β-catenin dosage significantly reverses the ZNRF3-deficient phenotype. Thus, homeostatic maintenance of the adrenal cortex is dependent on varying levels of Wnt/β-catenin activation, which is regulated by ZNRF3.

An atlas of Wnt activity during embryogenesis in Xenopus tropicalis

Wnt proteins form a family of highly conserved secreted molecules that are critical mediators of cell-cell signaling during embryogenesis. Partial data on Wnt activity in different tissues and at different stages have been reported in frog embryos. Our objective here is to provide a coherent and detailed description of Wnt activity throughout embryo development. Using a transgenic Xenopus tropicalis line carrying a Wnt-responsive reporter sequence, we depict the spatial and temporal dynamics of canonical Wnt activity during embryogenesis. We provide a comprehensive series of in situ hybridization in whole-mount embryos and in cross-sections, from gastrula to tadpole stages, with special focus on neural tube, retina and neural crest cell development. This collection of patterns will thus constitute a valuable resource for developmental biologists to picture the dynamics of Wnt activity during development.

Coupling of apical-basal polarity and PCP to interpret the Wnt signaling gradient and orient feather branch

To sense a global directional cue and orient cell growth is crucial in tissue morphogenesis. An anterior-posterior gradient of Wnt signaling controls the helical growth of feather branches (barbs), thus the formation of bilateral feathers. However, it remains unclear how the keratinocytes sense this gradient and orient barb growth. Here we show that due to feather branching, the global Wnt gradient is subdivided into periodic barbs. Within each barb, the anterior barbule plate cells tilt before the posterior cells. The core PCP gene Prickle1 is involved, as knockdown of its expression resulted in no cell shape change and no barb tilting. Furthermore, perturbation of the Wnt gradient leads to diffusive Prickle1 expression, and loss of barb orientation. Finally, the asymmetric distribution of Wnt6/Fzd10 is coordinated by the apical-basal polarity of the barbule plate keratinocytes, which is in turn regulated by the Par3/aPKC machinery. Our data elucidate a new mechanism through which the global Wnt signaling gradient is interpreted locally to construct complex spatial forms.

Patients Taking Antihistamines and Their Effects on Driving

Sleepiness is known as one of the side effects of antihistamines, and impaired performance caused by these drugs has become problematic. Among the 13 second-generation antihistamines causing sleepiness to some extent, the package inserts of 8 drugs prohibit driving, 3 stress driving with care, and 2 give no driving-related warning. It was confirmed that the description did not necessarily reflect the results of the standard deviation of lateral position measurement study, which is considered the most effective study for evaluating the effects of drugs on automobile driving. Do these descriptions reflect actual patients' sleepiness? According to a questionnaire survey involving 2000 individuals taking second-generation antihistamines, 7.3% of respondents answered that they had always become sleepy after taking antihistamines (3.1-12.5% according to the type of antihistamine), 32.8% (27.8-45.8%) had become sleepy sometimes, 9.1% (3.1-15.8%) had previously become sleepy but not anymore, and 40.9% (27.1-49.1%) had never become sleepy. In addition, 10.3% (2.4-21.1%) reported intolerable sleepiness. Patients who had experience of receiving pharmaceutical education from pharmacists numbered 1296 (64.8%), and 80.2% of them had also received driving-related explanations, which included the prohibition of driving (32.8%), stressing the need to drive with care (54.7%), and the prohibition of medication before driving (12.0%). Concerning these explanations, the proportion who paid attention on a daily basis, paid slight attention, and paid no attention was 36.7, 31.2, and 32.1%, respectively. To provide effective and safe pharmacotherapy for the increasing number of patients taking antihistamines, pharmacists should ideally improve pharmaceutical education.

Wnt signaling in cancer

Wnt signaling is one of the key cascades regulating development and stemness, and has also been tightly associated with cancer. The role of Wnt signaling in carcinogenesis has most prominently been described for colorectal cancer, but aberrant Wnt signaling is observed in many more cancer entities. Here, we review current insights into novel components of Wnt pathways and describe their impact on cancer development. Furthermore, we highlight expanding functions of Wnt signaling for both solid and liquid tumors. We also describe current findings how Wnt signaling affects maintenance of cancer stem cells, metastasis and immune control. Finally, we provide an overview of current strategies to antagonize Wnt signaling in cancer and challenges that are associated with such approaches.