Lysosomes are required for early dorsal signaling in the Xenopus embryo

Wnt signaling in cell adhesion, development, and colon cancer

Wnt signaling is essential for embryonic development, influencing processes such as axis formation, cell proliferation and differentiation, cell fate decisions, and axon guidance. It also plays a role in maintaining tissue homeostasis in adult organisms. The loss of normal cell polarity and adhesion caused by Wnt signaling activation is a fundamental step for tumor progression and metastasis. Activating the canonical Wnt pathway is a driving force in many human cancers, especially colorectal, hepatocellular, and mammary carcinomas. Wnt causes the stabilization and nuclear transport of newly synthesized transcriptional regulator β-catenin. The generally accepted view is that the canonical effects of Wnt growth factors are caused by the transcription of β-catenin target genes. Here, we review recent findings that indicate Wnt is a regulator of many other cellular physiological activities, such as macropinocytosis, endosome trafficking, protein stability, focal adhesions, and lysosomal activity. Some of these regulatory responses occur within minutes and do not require new protein synthesis, indicating that there is much more to Wnt beyond the well-established transcriptional role of β-catenin. The main conclusion that emerges from these studies is that in basal cell conditions, the activity of the key protein kinase GSK3, which is inhibited by Wnt pathway activation, normally represses the actin machinery that orchestrates macropinocytosis with implications in cancer. These contributions expand our understanding of the multifaceted roles of Wnt signaling in cellular processes, development, and cancer, providing insights into potential therapeutic targets and strategies.

Interactions between genistein and Wnt pathway in colon adenocarcinoma and early embryos

The Wnt signaling pathway is one of the most ancient and pivotal signaling cascades, governing diverse processes in development and cancer regulation. Within the realm of cancer treatment, genistein emerges as a promising candidate due to its multifaceted modulation of various signaling pathways, including the Wnt pathway. Despite promising preclinical studies, the precise mechanisms underlying genistein's therapeutic effects via Wnt modulation remain elusive. In this study, we unveil novel insights into the therapeutic mechanisms of genistein by elucidating its inhibitory effects on Wnt signaling through macropinocytosis. Additionally, we demonstrate its capability to curtail cell growth, proliferation, and lysosomal activity in the SW480 colon adenocarcinoma cell model. Furthermore, our investigation extends to the embryonic context, where genistein influences gene regulatory networks governed by endogenous Wnt pathways. Our findings shed light on the intricate interplay between genistein, Wnt signaling, membrane trafficking, and gene regulation, paving the way for further exploration of genistein's therapeutic potential in cancer treatment strategies.

Na,K-ATPase activity promotes macropinocytosis in colon cancer via Wnt signaling

Recent research has shown that membrane trafficking plays an important role in canonical Wnt signaling through sequestration of the β-catenin destruction complex inside multivesicular bodies (MVBs) and lysosomes. In this study, we introduce Ouabain, an inhibitor of the Na,K-ATPase pump that establishes electric potentials across membranes, as a potent inhibitor of Wnt signaling. We find that Na,K-ATPase levels are elevated in advanced colon carcinoma, that this enzyme is elevated in cancer cells with constitutively activated Wnt pathway and is activated by GSK3 inhibitors that increase macropinocytosis. Ouabain blocks macropinocytosis, which is an essential step in Wnt signaling, probably explaining the strong effects of Ouabain on this pathway. In Xenopus embryos, brief Ouabain treatment at the 32-cell stage, critical for the earliest Wnt signal in development-inhibited brains, could be reversed by treatment with Lithium chloride, a Wnt mimic. Inhibiting membrane trafficking may provide a way of targeting Wnt-driven cancers.

A maternal dorsoventral prepattern revealed by an asymmetric distribution of ventralizing molecules before fertilization in Xenopus laevis

The establishment of the embryonic dorsoventral axis in Xenopus occurs when the radial symmetry around the egg's animal-vegetal axis is broken to give rise to the typical symmetry of Bilaterians. We have previously shown that the Notch1 protein is ventrally enriched during early embryogenesis in Xenopus laevis and zebrafish and exerts ventralizing activity through β-Catenin destabilization and the positive regulation of ventral center genes in X. laevis. These findings led us to further investigate when these asymmetries arise. In this work, we show that the asymmetrical distribution of Notch1 protein and mRNA precedes cortical rotation and even fertilization in X. laevis. Moreover, we found that in unfertilized eggs transcripts encoded by the ventralizing gene bmp4 are also asymmetrically distributed in the animal hemisphere and notch1 transcripts accumulate consistently on the same side of the eccentric maturation point. Strikingly, a Notch1 asymmetry orthogonal to the animal-vegetal axis appears during X. laevis oogenesis. Thus, we show for the first time a maternal bias in the distribution of molecules that are later involved in ventral patterning during embryonic axialization, strongly supporting the hypothesis of a dorsoventral prepattern or intrinsic bilaterality of Xenopus eggs before fertilization.

Strategies to decrease inequalities in cancer therapeutics, care and prevention: Proceedings on a conference organized by the Pontifical Academy of Sciences and the European Academy of Cancer Sciences, Vatican City, February 23-24, 2023

Analyses of inequalities related to prevention and cancer therapeutics/care show disparities between countries with different economic standing, and within countries with high Gross Domestic Product. The development of basic technological and biological research provides clinical and prevention opportunities that make their implementation into healthcare systems more complex, mainly due to the growth of Personalized/Precision Cancer Medicine (PCM). Initiatives like the USA-Cancer Moonshot and the EU-Mission on Cancer and Europe's Beating Cancer Plan are initiated to boost cancer prevention and therapeutics/care innovation and to mitigate present inequalities. The conference organized by the Pontifical Academy of Sciences in collaboration with the European Academy of Cancer Sciences discussed the inequality problem, dependent on the economic status of a country, the increasing demands for infrastructure supportive of innovative research and its implementation in healthcare and prevention programs. Establishing translational research defined as a coherent cancer research continuum is still a challenge. Research has to cover the entire continuum from basic to outcomes research for clinical and prevention modalities. Comprehensive Cancer Centres (CCCs) are of critical importance for integrating research innovations to preclinical and clinical research, as for ensuring state-of-the-art patient care within healthcare systems. International collaborative networks between CCCs are necessary to reach the critical mass of infrastructures and patients for PCM research, and for introducing prevention modalities and new treatments effectively. Outcomes and health economics research are required to assess the cost-effectiveness of new interventions, currently a missing element in the research portfolio. Data sharing and critical mass are essential for innovative research to develop PCM. Despite advances in cancer research, cancer incidence and prevalence is growing. Making cancer research infrastructures accessible for all patients, considering the increasing inequalities, requires science policy actions incentivizing research aimed at prevention and cancer therapeutics/care with an increased focus on patients' needs and cost-effective healthcare.

The early dorsal signal in vertebrate embryos requires endolysosomal membrane trafficking

Fertilization triggers cytoplasmic movements in the frog egg that lead in mysterious ways to the stabilization of β-catenin on the dorsal side of the embryo. The novel Huluwa (Hwa) transmembrane protein, identified in China, is translated specifically in the dorsal side, acting as an egg cytoplasmic determinant essential for β-catenin stabilization. The Wnt signaling pathway requires macropinocytosis and the sequestration inside multivesicular bodies (MVBs, the precursors of endolysosomes) of Axin1 and Glycogen Synthase Kinase 3 (GSK3) that normally destroy β-catenin. In Xenopus, the Wnt-like activity of GSK3 inhibitors and of Hwa mRNA can be blocked by brief treatment with inhibitors of membrane trafficking or lysosomes at the 32-cell stage. In dorsal blastomeres, lysosomal cathepsin is activated and intriguing MVBs surrounded by electron dense vesicles are formed at the 64-cell stage. We conclude that membrane trafficking and lysosomal activity are critically important for the earliest asymmetries in vertebrate embryonic development.

Head organizer: Cerberus and IGF cooperate in brain induction in Xenopus embryos

Neural induction by cell-cell signaling was discovered a century ago by the organizer transplantations of Spemann and Mangold in amphibians. Spemann later found that early dorsal blastopore lips induced heads and late organizers trunk-tail structures. Identifying region-specific organizer signals has been a driving force in the progress of animal biology. Head induction in the absence of trunk is designated archencephalic differentiation. Two specific head inducers, Cerberus and Insulin-like growth factors (IGFs), that induce archencephalic brain but not trunk-tail structures have been described previously. However, whether these two signals interact with each other had not been studied to date and was the purpose of the present investigation. It was found that Cerberus, a multivalent growth factor antagonist that inhibits Nodal, BMP and Wnt signals, strongly cooperated with IGF2, a growth factor that provides a positive signal through tyrosine kinase IGF receptors that activate MAPK and other pathways. The ectopic archencephalic structures induced by the combination of Cerberus and IGF2 are of higher frequency and larger than either one alone. They contain brain, a cyclopic eye and multiple olfactory placodes, without trace of trunk structures such as notochord or somites. A dominant-negative secreted IGF receptor 1 blocked Cerberus activity, indicating that endogenous IGF signals are required for ectopic brain formation. In a sensitized embryonic system, in which embryos were depleted of β-catenin, IGF2 did not by itself induce neural tissue while in combination with Cerberus it greatly enhanced formation of circular brain structures expressing the anterior markers Otx2 and Rx2a, but not spinal cord or notochord markers. The main conclusion of this work is that IGF provides a positive signal initially uniformly expressed throughout the embryo that potentiates the effect of an organizer-specific negative signal mediated by Cerberus. The results are discussed in the context of the history of neural induction.

The PMA phorbol ester tumor promoter increases canonical Wnt signaling via macropinocytosis

Activation of the Wnt pathway lies at the core of many human cancers. Wnt and macropinocytosis are often active in the same processes, and understanding how Wnt signaling and membrane trafficking cooperate should improve our understanding of embryonic development and cancer. Here, we show that a macropinocytosis activator, the tumor promoter phorbol 12-myristate 13-acetate (PMA), enhances Wnt signaling. Experiments using the Xenopus embryo as an in vivo model showed marked cooperation between the PMA phorbol ester and Wnt signaling, which was blocked by inhibitors of macropinocytosis, Rac1 activity, and lysosome acidification. Human colorectal cancer tissue arrays and xenografts in mice showed a correlation of cancer progression with increased macropinocytosis/multivesicular body/lysosome markers and decreased GSK3 levels. The crosstalk between canonical Wnt, focal adhesions, lysosomes, and macropinocytosis suggests possible therapeutic targets for cancer progression in Wnt-driven cancers.

Addition of exogenous diacylglycerol enhances Wnt/β-catenin signaling through stimulation of macropinocytosis

Activation of Wnt signaling triggers macropinocytosis and drives many tumors. We now report that the exogenous addition of the second messenger lipid sn-1,2 DAG to the culture medium rapidly induces macropinocytosis. This is accompanied by potentiation of the effects of added Wnt3a recombinant protein or the glycogen synthase kinase 3 (GSK3) inhibitor lithium chloride (LiCl, which mimics Wnt signaling) in luciferase transcriptional reporter assays. In a colorectal carcinoma cell line in which mutation of adenomatous polyposis coli (APC) causes constitutive Wnt signaling, DAG addition increased levels of nuclear β-catenin, and this increase was partially inhibited by an inhibitor of macropinocytosis. DAG also expanded multivesicular bodies marked by the tetraspan protein CD63. In an in vivo situation, microinjection of DAG induced Wnt-like twinned body axes when co-injected with small amounts of LiCl into Xenopus embryos. These results suggest that the DAG second messenger plays a role in Wnt-driven cancer progression.

The PMA Phorbol Ester Tumor Promoter Increases Canonical Wnt Signaling Via Macropinocytosis

Activation of the Wnt pathway lies at the core of many human cancers. Wnt and macropinocytosis are often active in the same processes, and understanding how Wnt signaling and membrane trafficking cooperate should improve our understanding of embryonic development and cancer. Here we show that a macropinocytosis activator, the tumor promoter Phorbol 12-myristate 13-acetate (PMA), enhances Wnt signaling. Experiments using the Xenopus embryo as an in vivo model showed marked cooperation between the PMA phorbol ester and Wnt signaling, which was blocked by inhibitors of macropinocytosis, Rac1 activity, and lysosome acidification. Human colorectal cancer tissue arrays and xenografts in mice showed a correlation of cancer progression with increased macropinocytosis/multivesicular body/lysosome markers and decreased GSK3 levels. The crosstalk between canonical Wnt, focal adhesions, lysosomes, and macropinocytosis suggests possible therapeutic targets for cancer progression in Wnt-driven cancers.

The complete dorsal structure is formed from only the blastocoel roof of Xenopus blastula: insight into the gastrulation movement evolutionarily conserved among chordates

Gastrulation is a critical event whose molecular mechanisms are thought to be conserved among vertebrates. However, the morphological movement during gastrulation appears to be divergent across species, making it difficult to discuss the evolution of the process. Previously, we proposed a novel amphibian gastrulation model, the "subduction and zippering (S&Z) model". In this model, the organizer and the prospective neuroectoderm are originally localized in the blastula's blastocoel roof, and these embryonic regions move downward to make physical contact of their inner surfaces with each other at the dorsal marginal zone. The developmental stage when contact between the head organizer and the anterior-most neuroectoderm is established is called "anterior contact establishment (ACE)." After ACE, the A-P body axis elongates posteriorly. According to this model, the body axis is derived from limited regions of the dorsal marginal zone at ACE. To investigate this possibility, we conducted stepwise tissue deletions using Xenopus laevis embryos and revealed that the dorsal one-third of the marginal zone had the ability to form the complete dorsal structure by itself. Furthermore, a blastocoel roof explant of the blastula, which should contain the organizer and the prospective neuroectoderm in the S&Z model, autonomously underwent gastrulation and formed the complete dorsal structure. Collectively, these results are consistent with the S&Z gastrulation model and identify the embryonic region sufficient for construction of the complete dorsal structure. Finally, by comparing amphibian gastrulation to gastrulation of protochordates and amniotes, we discuss the gastrulation movement evolutionarily conserved among chordates.

Protocol for culturing and imaging of ectodermal cells from Xenopus

The Xenopus embryo provides an advantageous model system where genes can be readily transplanted as DNA or mRNA or depleted with antisense techniques. Here, we present a protocol to culture and image the cell biological properties of explanted Xenopus cap cells in tissue culture. We illustrate how this protocol can be applied to visualize lysosomes, macropinocytosis, focal adhesions, Wnt signaling, and cell migration. For complete details on the use and execution of this protocol, please refer to Tejeda-Muñoz et al. (2022).

Targeting Membrane Trafficking as a Strategy for Cancer Treatment

Membrane trafficking is emerging as an attractive therapeutic strategy for cancer. Recent reports have found a connection between Wnt signaling, receptor-mediated endocytosis, V-ATPase, lysosomal activity, and macropinocytosis through the canonical Wnt pathway. In macropinocytic cells, a massive internalization of the plasma membrane can lead to the loss of cell-surface cadherins, integrins, and other antigens that mediate cell–cell adhesion, favoring an invasive phenotype. V-ATPase is a key regulator in maintaining proper membrane trafficking, homeostasis, and the earliest developmental decisions in the Xenopus vertebrate development model system. Here, we review how the interference of membrane trafficking with membrane trafficking inhibitors might be clinically relevant in humans.