The role of Evi/Wntless in exporting Wnt proteins

Recent advances in understanding the role of Wnt5a in prostate cancer and bone metastasis

Prostate cancer (PCa) is a leading cause of cancer-related mortality in men, with a high propensity for bone metastasis that significantly impairs patient quality of life. The Wnt5a signaling pathway plays a pivotal role in the progression and metastasis of PCa. Wnt5a can act as both an oncogene and a tumor suppressor, highlighting its complex and context-dependent functions. In PCa, Wnt5a promotes tumor progression through mechanisms such as epithelial-mesenchymal transition (EMT) and interaction with androgen receptor (AR) signaling. Conversely, Wnt5a can induce dormancy in bone-metastatic PCa cells via the ROR2/SIAH2 axis, inhibiting the Wnt/β-catenin pathway. Understanding the dual roles of Wnt5a in PCa and bone metastasis is crucial for elucidating the underlying mechanisms of disease progression and identifying potential therapeutic targets. This review focuses on the current understanding of Wnt5a's role in PCa and bone metastasis, emphasizing its significance in tumor biology and clinical management.

Mechanistic insights into Wnt-β-catenin pathway activation and signal transduction

In multicellular organisms, Wnt proteins govern stem and progenitor cell renewal and differentiation to regulate embryonic development, adult tissue homeostasis and tissue regeneration. Defects in canonical Wnt signalling, which is transduced intracellularly by β-catenin, have been associated with developmental disorders, degenerative diseases and cancers. Although a simple model describing Wnt-β-catenin signalling is widely used to introduce this pathway and has largely remained unchanged over the past 30 years, in this Review we discuss recent studies that have provided important new insights into the mechanisms of Wnt production, receptor activation and intracellular signalling that advance our understanding of the molecular mechanisms that underlie this important cell-cell communication system. In addition, we review the recent development of molecules capable of activating the Wnt-β-catenin pathway with selectivity in vitro and in vivo that is enabling new lines of study to pave the way for the development of Wnt therapies for the treatment of human diseases.

WNT5a export onto extracellular vesicles studied at single-molecule and single-vesicle resolution

WNT signaling governs development, homeostasis, and aging of cells and tissues, and is frequently dysregulated in pathophysiological processes such as cancer. WNT proteins are hydrophobic and traverse the intercellular space between the secreting and receiving cells on various carriers, including extracellular vesicles (EVs). Here, we address the relevance of different EV fractions and other vehicles for WNT5a protein, a non-canonical WNT ligand that signals independently of beta-catenin. Its highly context-dependent roles in cancer (either tumor-suppressive or tumor-promoting) have been attributed to two distinct isoforms, WNT5a Short (WNT5aS) and WNT5a Long (WNT5aL), resulting from different signal peptide cleavage sites. To explore possible differences in secretion and extracellular transport, we developed fusion constructs with the fluorescent proteins (FPs) mScarlet and mOxNeonGreen. Functional reporter assays revealed that both WNT5a isoforms inhibit canonical WNT signaling, and EVs produced by WNT5a-bearing tumor cells, carrying either of the WNT5a isoforms, induced invasiveness of the luminal A breast cancer cell line MCF7. We used fluorescence intensity distribution analysis (FIDA) and fluorescence correlation spectroscopy (FCS) to characterize at single-molecule sensitivity WNT5aL-bearing entities secreted by HEK293T cells. Importantly, we found that most WNT5aL proteins remained monomeric in the supernatant after ultracentrifugation; only a minor fraction was EV-bound. We further determined the average sizes of the EV fractions and the average number of WNT5aL proteins per EV. Our detailed biophysical analysis of the physical nature of the EV populations is an important step toward understanding context-dependent WNT cargo loading and signaling in future studies.

Ehbp1 orchestrates orderly sorting of Wnt/Wingless to the basolateral and apical cell membranes

Wingless (Wg)/Wnt signaling plays a critical role in both development and adult tissue homeostasis. In the Drosophila larval wing disc epithelium, the orderly delivery of Wg/Wnt to the apical and basal cell surfaces is essential for wing development. Here, we identified Ehbp1 as the switch that dictates the direction of Wg/Wnt polarized intracellular transport: the Adaptor Protein complex 1 (AP-1) delivers Wg/Wnt to the basolateral cell surface, and its sequestration by Ehbp1 redirects Wg/Wnt for apical delivery. Genetic analyses showed that Ehbp1 specifically regulates the polarized distribution of Wg/Wnt, a process that depends on the dedicated Wg/Wnt cargo receptor Wntless. Mechanistically, Ehbp1 competes with Wntless for AP-1 binding, thereby preventing the unregulated basolateral Wg/Wnt transport. Reducing Ehbp1 expression, or removing the coiled-coil motifs within its bMERB domain, leads to basolateral Wg/Wnt accumulation. Importantly, the regulation of polarized Wnt delivery by EHBP1 is conserved in vertebrates. The generality of this switch mechanism for regulating intracellular transport remains to be determined in future studies.

The Wnt signaling pathway in hepatocellular carcinoma: Regulatory mechanisms and therapeutic prospects

Hepatocellular carcinoma (HCC) is a malignant tumor that arises from hepatocytes. Multiple signaling pathways play a regulatory role in the occurrence and development of HCC, with the Wnt signaling pathway being one of the primary regulatory pathways. In normal hepatocytes, the Wnt signaling pathway maintains cell regeneration and organ development. However, when aberrant activated, the Wnt pathway is closely associated with invasion, cancer stem cells(CSCs), drug resistance, and immune evasion in HCC. Among these factors, the development of drug resistance is one of the most important factors affecting the efficacy of HCC treatment. These mechanisms form the basis for tumor cell adaptation and evolution within the body, enabling continuous changes in tumor cells, resistance to drugs and immune system attacks, leading to metastasis and recurrence. In recent years, there have been numerous new discoveries regarding these mechanisms. An increasing number of drugs targeting the Wnt signaling pathway have been developed, with some already entering clinical trials. Therefore, this review encompasses the latest research on the role of the Wnt signaling pathway in the onset and progression of HCC, as well as advancements in its therapeutic strategies.

Engineered extracellular vesicles enable high-efficient delivery of intracellular therapeutic proteins

Developing an intracellular delivery system is of key importance in the expansion of protein-based therapeutics acting on cytosolic or nuclear targets. Recently, extracellular vesicles (EVs) have been exploited as next-generation delivery modalities due to their natural role in intercellular communication and biocompatibility. However, fusion of protein of interest to a scaffold represents a widely used strategy for cargo enrichment in EVs, which could compromise the stability and functionality of cargo. Herein, we report intracellular delivery via EV-based approach (IDEA) that efficiently packages and delivers native proteins both in vitro and in vivo without the use of a scaffold. As a proof-of-concept, we applied the IDEA to deliver cyclic GMP-AMP synthase (cGAS), an innate immune sensor. The results showed that cGAS-carrying EVs activated interferon signaling and elicited enhanced antitumor immunity in multiple syngeneic tumor models. Combining cGAS EVs with immune checkpoint inhibition further synergistically boosted antitumor efficacy in vivo. Mechanistically, scRNA-seq demonstrated that cGAS EVs mediated significant remodeling of intratumoral microenvironment, revealing a pivotal role of infiltrating neutrophils in the antitumor immune milieu. Collectively, IDEA, as a universal and facile strategy, can be applied to expand and advance the development of protein-based therapeutics.

Dissociation of Drosophila Evi-Wg Complex Occurs Post Apical Internalization in the Maturing Acidic Endosomes

Signaling pathways activated by secreted Wnt ligands play an essential role in tissue development and the progression of diseases, like cancer. Secretion of the lipid-modified Wnt proteins is tightly regulated by a repertoire of intracellular factors. For instance, a membrane protein, Evi, interacts with the Wnt ligand in the ER, and it is essential for its further trafficking and release in the extracellular space. After dissociating from the Wnt, the Wnt-unbound Evi is recycled back to the ER via Golgi. However, where in this trafficking path Wnt proteins dissociate from Evi remains unclear. Here, we have used the Drosophila wing epithelium to trace the route of the Evi-Wg (Wnt homolog) complex leading up to their separation. In these polarized cells, Wg is first trafficked to the apical surface; however, the secretion of Wg is believed to occurs post-internalization via recycling. Our results show that the Evi-Wg complex is internalized from the apical surface and transported to the retromer-positive endosomes. Furthermore, using antibodies that specifically label the Wnt-unbound Evi, we show that Evi and Wg separation occurs post-internalization in the acidic endosomes. These results refine our understanding of the polarized trafficking of Wg and highlight the importance of Wg endocytosis in its secondary secretion.

The origin and evolution of Wnt signalling

The Wnt signal transduction pathway has essential roles in the formation of the primary body axis during development, cellular differentiation and tissue homeostasis. This animal-specific pathway has been studied extensively in contexts ranging from developmental biology to medicine for more than 40 years. Despite its physiological importance, an understanding of the evolutionary origin and primary function of Wnt signalling has begun to emerge only recently. Recent studies on very basal metazoan species have shown high levels of conservation of components of both canonical and non-canonical Wnt signalling pathways. Furthermore, some pathway proteins have been described also in non-animal species, suggesting that recruitment and functional adaptation of these factors has occurred in metazoans. In this Review, we summarize the current state of research regarding the evolutionary origin of Wnt signalling, its ancestral function and the characteristics of the primal Wnt ligand, with emphasis on the importance of genomic studies in various pre-metazoan and basal metazoan species.