RNF43 and ZNRF3 are commonly altered in serrated pathway colorectal tumorigenesis

Small-molecule inhibitors of WNT signalling in cancer therapy and their links to autophagy and apoptosis

Cancer represents an intricate and heterogeneous ailment that evolves from a multitude of epigenetic and genetic variations that disrupt normal cellular function. The WNT/β-catenin pathway is essential in maintaining the balance between cell renewal and differentiation in various tissues. Abnormal activation of this pathway can lead to uncontrolled cell growth and initiate cancer across a variety of tissues such as the colon, skin, liver, and ovary. It enhances characteristics that lead to cancer progression, including angiogenesis, invasion and metastasis. Processes like autophagy and apoptosis which regulate cell death and play a crucial role in maintaining cellular equilibrium are also intimately linked with WNT/ β-catenin pathway. Thus, targeting WNT pathway has become a key strategy in developing antitumor therapies. Employing small molecule inhibitors has emerged as a targeted therapy to improve the clinical outcome compared to conventional cancer treatments. Many strategies using small molecule inhibitors for modulating the WNT/β-catenin pathway, such as hindering WNT ligands' secretion or interaction, disrupting receptor complex, and blocking the nuclear translocation of β-catenin have been investigated. These interventions have shown promise in both preclinical and clinical settings. This review provides a comprehensive understanding of the role of WNT/β-catenin signalling pathway's role in cancer, emphasizing its regulation of autophagy and apoptosis. Our goal is to highlight the potential of specific small molecule inhibitors targeting this pathway, fostering the development of novel, tailored cancer treatments.

Zinc and its binding proteins: essential roles and therapeutic potential

Zinc is an essential micronutrient that participates in a multitude of cellular and biochemical processes. It is indispensable for normal growth and the maintenance of physiological functions. As one of the most significant trace elements in the body, zinc fulfills three primary biological roles: catalytic, structural, and regulatory. It serves as a cofactor in over 300 enzymes, and more than 3000 proteins require zinc, underscoring its crucial role in numerous physiological processes such as cell division and growth, immune function, tissue maintenance, as well as synthesis protein and collagen synthesis. Zinc deficiency has been linked to increased oxidative stress and inflammation, which may contribute to the pathogenesis of a multitude of diseases, like neurological disorders and cancer. In addition, zinc is a key constituent of zinc-binding proteins, which play a pivotal role in maintaining cellular zinc homeostasis. This review aims to update and expand upon the understanding of zinc biology, highlighting the fundamental roles of zinc in biological processes and the health implications of zinc deficiency. This work also explores the diverse functions of zinc in immune regulation, cellular growth, and neurological health, emphasizing the need for further research to fully elucidate the therapeutic potential of zinc supplementation in disease prevention and management.

Loss of ZNRF3/RNF43 Unleashes EGFR in Cancer

ZNRF3 and RNF43 are closely related transmembrane E3 ubiquitin ligases with significant roles in development and cancer. Conventionally, their biological functions have been associated with regulating WNT signaling receptor ubiquitination and degradation. However, our proteogenomic studies have revealed EGFR as the protein most negatively correlated with ZNRF3/RNF43 mRNA levels in multiple human cancers. Through biochemical investigations, we demonstrate that ZNRF3/RNF43 interact with EGFR via their extracellular domains, leading to EGFR ubiquitination and subsequent degradation facilitated by the E3 ligase RING domain. Overexpression of ZNRF3 reduces EGFR levels and suppresses cancer cell growth in vitro and in vivo, whereas knockout of ZNRF3/RNF43 stimulates cell growth and tumorigenesis through upregulated EGFR signaling. Together, these data highlight ZNRF3 and RNF43 as novel E3 ubiquitin ligases of EGFR and establish the inactivation of ZNRF3/RNF43 as a driver of increased EGFR signaling, ultimately promoting cancer progression. This discovery establishes a connection between two fundamental signaling pathways, EGFR and WNT, at the level of cytoplasmic membrane receptors, uncovering a novel mechanism underlying the frequent co-activation of EGFR and WNT signaling in development and cancer.

Tenascin-C potentiates Wnt signaling in thyroid cancer

Tenascin-C (TNC) is a secreted extracellular matrix protein that is highly expressed during embryonic development and re-expressed during wound healing, inflammation, and neoplasia. Studies in developmental models suggest that TNC may regulate the Wnt signaling pathway. Our lab has shown high levels of Wnt signaling and TNC expression in anaplastic thyroid cancer (ATC), a highly lethal cancer with an abysmal ∼3-5 month median survival. Here, we investigated the role of TNC in facilitating ligand-dependent Wnt signaling in thyroid cancer. We utilized bulk RNA-sequencing from three independent multi-institutional thyroid cancer patient cohorts. TNC expression was spatially localized in patient tumors with RNA in situ hybridization. The role of TNC was investigated in vitro using Wnt reporter assays and in vivo with a NOD.PrkdcscidIl2rg-/- mouse ATC xenograft tumor model. TNC expression was associated with aggressive thyroid cancer behavior, including anaplastic histology, extrathyroidal extension, and metastasis. Spatial localization of TNC in patient tissue demonstrated a dramatic increase in expression within cancer cells along the invasive edge, adjacent to Wnt ligand-producing fibroblasts. TNC expression was also increased in areas of intravascular invasion. In vitro, TNC bound Wnt ligands and potentiated Wnt signaling. Finally, in an ATC mouse model, TNC increased Wnt signaling, tumor burden, invasion, and metastasis. Altogether, TNC potentiated ligand driven Wnt signaling and promotes cancer cell invasion and metastasis in a mouse model of thyroid cancer. Understanding the role of TNC and its interaction with Wnt ligands could lead to the development of novel biomarkers and targeted therapeutics for thyroid cancer.

RNF43 and ZNRF3: Versatile regulators at the membrane and their role in cancer

RNF43 and ZNRF3 are recognized as important regulators of Wnt/β-catenin signaling by maintaining Wnt-receptors at minimal essential levels. In various cancer types, particularly gastrointestinal tumors, mutations in these genes lead to abnormal Wnt-dependent activation of β-catenin signaling. However, recent findings implicate RNF43/ZNRF3 also in the regulation of other tumor-related proteins, including EGFR, BRAF, and the BMP-signaling pathway, which may have important implications for tumor biology. Additionally, we describe in detail how phosphorylation and ubiquitination may finetune RNF43 and ZNRF3 activity. We also address the variety of mutations observed in cancers and the mechanism through which they support tumor growth, and challenge the prevailing view that specific missense mutations in the R-spondin and RING domains may possess dominant-negative activity in contributing to tumor formation.

Correcting for Observation Bias in Cancer Progression Modeling

Tumor progression is driven by the accumulation of genetic alterations, including both point mutations and copy number changes. Understanding the temporal sequence of these events is crucial for comprehending the disease but is not directly discernible from cross-sectional genomic data. Cancer progression models, including Mutual Hazard Networks (MHNs), aim to reconstruct the dynamics of tumor progression by learning the causal interactions between genetic events based on their co-occurrence patterns in cross-sectional data. Here, we highlight a commonly overlooked bias in cross-sectional datasets that can distort progression modeling. Tumors become clinically detectable when they cause symptoms or are identified through imaging or tests. Detection factors, such as size, inflammation (fever, fatigue), and elevated biochemical markers, are influenced by genomic alterations. Ignoring these effects leads to "conditioning on a collider" bias, where events making the tumor more observable appear anticorrelated, creating false suppressive effects or masking promoting effects among genetic events. We enhance MHNs by incorporating the effects of genetic progression events on the inclusion of a tumor in a dataset, thus correcting for collider bias. We derive an efficient tensor formula for the likelihood function and apply it to two datasets from the MSK-IMPACT study. In colon adenocarcinoma, we observe a significantly higher rate of clinical detection for TP53-positive tumors, while in lung adenocarcinoma, the same is true for EGFR-positive tumors. Compared to classical MHNs, this approach eliminates several spurious suppressive interactions and uncovers multiple promoting effects.

Deleterious ZNRF3 germline variants cause neurodevelopmental disorders with mirror brain phenotypes via domain-specific effects on Wnt/β-catenin signaling

Zinc and RING finger 3 (ZNRF3) is a negative-feedback regulator of Wnt/β-catenin signaling, which plays an important role in human brain development. Although somatically frequently mutated in cancer, germline variants in ZNRF3 have not been established as causative for neurodevelopmental disorders (NDDs). We identified 12 individuals with ZNRF3 variants and various phenotypes via GeneMatcher/Decipher and evaluated genotype-phenotype correlation. We performed structural modeling and representative deleterious and control variants were assessed using in vitro transcriptional reporter assays with and without Wnt-ligand Wnt3a and/or Wnt-potentiator R-spondin (RSPO). Eight individuals harbored de novo missense variants and presented with NDD. We found missense variants associated with macrocephalic NDD to cluster in the RING ligase domain. Structural modeling predicted disruption of the ubiquitin ligase function likely compromising Wnt receptor turnover. Accordingly, the functional assays showed enhanced Wnt/β-catenin signaling for these variants in a dominant negative manner. Contrarily, an individual with microcephalic NDD harbored a missense variant in the RSPO-binding domain predicted to disrupt binding affinity to RSPO and showed attenuated Wnt/β-catenin signaling in the same assays. Additionally, four individuals harbored de novo truncating or de novo or inherited large in-frame deletion variants with non-NDD phenotypes, including heart, adrenal, or nephrotic problems. In contrast to NDD-associated missense variants, the effects on Wnt/β-catenin signaling were comparable between the truncating variant and the empty vector and between benign variants and the wild type. In summary, we provide evidence for mirror brain size phenotypes caused by distinct pathomechanisms in Wnt/β-catenin signaling through protein domain-specific deleterious ZNRF3 germline missense variants.

RNF43 in cancer: Molecular understanding and clinical significance in immunotherapy

Identifying biomarkers to predict immune checkpoint inhibitor (ICI) efficacy is warranted. Considering that somatic mutation-derived neoantigens induce strong immune responses, patients with a high tumor mutational burden reportedly tend to respond to ICIs. Therefore, the original function of neoantigenic mutations and their impact on the tumor microenvironment (TME) require attention. RNF43 is a type of RING E3 ubiquitin ligase, and long-term survivors in most cancers had conserved patterns of mutations of RNF43. Also, high microsatellite instability patients had a higher RNF43 mutation rate compared with microsatellite stability tumor patients, who were more sensitive to ICI treatment. Therefore, RNF43 has become a promising biomarker of immunotherapy in a wide range of cancers. This review focuses on the up-to-date knowledge of RNF43 mutation in cancer. We summarize the cancer hallmarks involving activities regulated by RNF43 and highlight its extremely sophisticated regulation of WNT signaling and tumor microenvironment. The key genes interacting with RNF43 have also been summarized and discussed. Additionally, we highlight and propose new strategies of targeting RNF43 and RNF43-based combinations with established immunotherapy and combination therapy. These efforts may provide new perspectives for RNF43-based target therapy in cancer.

New insights in ubiquitin-dependent Wnt receptor regulation in tumorigenesis

Wnt signaling plays a crucial role in embryonic development and homeostasis maintenance. Delicate and sensitive fine-tuning of Wnt signaling based on the proper timings and positions is required to balance cell proliferation and differentiation and maintain individual health. Therefore, homeostasis is broken by tissue hypoplasia or tumor formation once Wnt signal dysregulation disturbs the balance of cell proliferation. The well-known regulatory mechanism of Wnt signaling is the molecular reaction associated with the cytoplasmic accumulation of effector β-catenin. In addition to β-catenin, most Wnt effector proteins are also regulated by ubiquitin-dependent modification, both qualitatively and quantitatively. This review will explain the regulation of the whole Wnt signal in four regulatory phases, as well as the different ubiquitin ligases and the function of deubiquitinating enzymes in each phase. Along with the recent results, the mechanism by which RNF43 negatively regulates the surface expression of Wnt receptors, which has recently been well understood, will be detailed. Many RNF43 mutations have been identified in pancreatic and gastrointestinal cancers and examined for their functional alteration in Wnt signaling. Several mutations facilitate or activate the Wnt signal, reversing the RNF43 tumor suppressor function into an oncogene. RNF43 may simultaneously play different roles in classical multistep tumorigenesis, as both wild-type and mutant RNF43 suppress the p53 pathway. We hope that the knowledge obtained from further research in RNF43 will be applied to cancer treatment in the future despite the fully unclear function of RNF43.

Combinatorial in vivo genome editing identifies widespread epistasis during lung tumorigenesis

Lung adenocarcinoma, the most common subtype of lung cancer, is genomically complex, with tumors containing tens to hundreds of non-synonymous mutations. However, little is understood about how genes interact with each other to enable tumorigenesis in vivo , largely due to a lack of methods for investigating genetic interactions in a high-throughput and multiplexed manner. Here, we employed a novel platform to generate tumors with all pairwise inactivation of ten tumor suppressor genes within an autochthonous mouse model of oncogenic KRAS-driven lung cancer. By quantifying the fitness of tumors with every single and double mutant genotype, we show that most tumor suppressor genetic interactions exhibited negative epistasis, with diminishing returns on tumor fitness. In contrast, Apc inactivation showed positive epistasis with the inactivation of several other genes, including dramatically synergistic effects on tumor fitness in combination with Lkb1 or Nf1 inactivation. This approach has the potential to expand the scope of genetic interactions that may be functionally characterized in vivo , which could lead to a better understanding of how complex tumor genotypes impact each step of carcinogenesis.

Aberrant PRDM2 methylation as an early event in serrated lesions destined to evolve into microsatellite-instable colorectal cancers

Up to 30% of colorectal cancers (CRCs) develop from sessile serrated lesions (SSLs). Within the serrated neoplasia pathway, at least two principally distinct oncogenetic routes exist generating microsatellite-stable and microsatellite-instable CRCs, respectively. Aberrant DNA methylation (DNAm) is found early in the serrated pathway and might play a role in both oncogenetic routes. We studied a cohort of 23 SSLs with a small focus (<10 mm) of dysplasia or cancer, 10 of which were MLH1 deficient and 13 MLH1 proficient. By comparing, for each SSL, the methylation status of (1) the region of dysplasia or cancer (SSL-D), (2) the nondysplastic SSL (SSL), and (3) adjacent normal mucosa, differentially methylated probes (DMPs) and regions (DMRs) were assessed both genome-wide as well as in a tumor-suppressor gene-focused approach. By comparing DNAm of MLH1-deficient SSL-Ds with their corresponding SSLs, we identified five DMRs, including those annotating for PRDM2 and, not unexpectedly, MLH1. PRDM2 gene promotor methylation was associated with MLH1 expression status, as it was largely hypermethylated in MLH1-deficient SSL-Ds and hypomethylated in MLH1-proficient SSL-Ds. Significantly increased DNAm levels of PRDM2 and MLH1, in particular at 'critical' MLH1 probe sites, were to some extent already visible in SSLs as compared to normal mucosa (p = 0.02, p = 0.01, p < 0.0001, respectively). No DMRs, nor DMPs, were identified for SSLs destined to evolve into MLH1-proficient SSL-Ds. Our data indicate that, within both arms of the serrated CRC pathway, the majority of the epigenetic alterations are introduced early during SSL formation. Promoter hypermethylation of PRDM2 and MLH1 on the other hand specifically initiates in SSLs destined to transform into MLH1-deficient CRCs suggesting that the fate of SSLs may not necessarily result from a stochastic process but possibly is already imprinted and predisposed.

Inherited BRCA1 and RNF43 pathogenic variants in a familial colorectal cancer type X family

Genetic susceptibility to familial colorectal cancer (CRC), including for individuals classified as Familial Colorectal Cancer Type X (FCCTX), remains poorly understood. We describe a multi-generation CRC-affected family segregating pathogenic variants in both BRCA1, a gene associated with breast and ovarian cancer and RNF43, a gene associated with Serrated Polyposis Syndrome (SPS). A single family out of 105 families meeting the criteria for FCCTX (Amsterdam I family history criteria with mismatch repair (MMR)-proficient CRCs) recruited to the Australasian Colorectal Cancer Family Registry (ACCFR; 1998-2008) that underwent whole exome sequencing (WES), was selected for further testing. CRC and polyp tissue from four carriers were molecularly characterized including a single CRC that underwent WES to determine tumor mutational signatures and loss of heterozygosity (LOH) events. Ten carriers of a germline pathogenic variant BRCA1:c.2681_2682delAA p.Lys894ThrfsTer8 and eight carriers of a germline pathogenic variant RNF43:c.988 C > T p.Arg330Ter were identified in this family. Seven members carried both variants, four of which developed CRC. A single carrier of the RNF43 variant met the 2019 World Health Organization (WHO2019) criteria for SPS, developing a BRAF p.V600 wildtype CRC. Loss of the wildtype allele for both BRCA1 and RNF43 variants was observed in three CRC tumors while a LOH event across chromosome 17q encompassing both genes was observed in a CRC. Tumor mutational signature analysis identified the homologous recombination deficiency (HRD)-associated COSMIC signatures SBS3 and ID6 in a CRC for a carrier of both variants. Our findings show digenic inheritance of pathogenic variants in BRCA1 and RNF43 segregating with CRC in a FCCTX family. LOH and evidence of BRCA1-associated HRD supports the importance of both these tumor suppressor genes in CRC tumorigenesis.

Wnt Signaling and Therapeutic Resistance in Castration-Resistant Prostate Cancer

Purpose of Review

Castration-resistant prostate cancer (CRPC) is a lethal form of prostate cancer (PCa) due to the development of resistance to androgen deprivation therapy and anti-androgens. Here, we review the emerging role of Wnt signaling in therapeutic resistance of CRPC.

Recent Findings

Convincing evidence have accumulated that Wnt signaling is aberrantly activated through genomic alterations and autocrine and paracrine augmentations. Wnt signaling plays a critical role in a subset of CRPC and in resistance to anti-androgen therapies. Wnt signaling navigates CRPC through PCa heterogeneity, neuroendocrine differentiation, DNA repair, PCa stem cell maintenance, epithelial-mesenchymal-transition and metastasis, and immune evasion.

Summary

Components of Wnt signaling can be harnessed for inhibiting PCa growth and metastasis and for developing novel therapeutic strategies to manage metastatic CRPC. There are many Wnt pathway-based potential drugs in different stages of pre-clinical development and clinical trials but so far, no Wnt signaling-specific drug has been approved by FDA for clinical use in CRPC.

Phosphorylation of PPDPF via IL6-JAK2 activates the Wnt/β-catenin pathway in colorectal cancer

Inflammation plays an important role in the initiation and progression of colorectal cancer (CRC) and leads to β-catenin accumulation in colitis-related CRC. However, the mechanism remains largely unknown. Here, pancreatic progenitor cell differentiation and proliferation factor (PPDPF) is found to be upregulated in CRC and significantly correlated with tumor-node-metastasis (TNM) stages and survival time. Knockout of PPDPF in the intestinal epithelium shortens crypts, decreases the number of stem cells, and inhibits the growth of organoids and the occurrence of azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced CRC. Mechanistically, PPDPF is found to interact with Casein kinase 1α (CK1α), thereby disrupting its binding to Axin, disassociating the β-catenin destruction complex, decreasing the phosphorylation of β-catenin, and activating the Wnt/β-catenin pathway. Furthermore, interleukin 6 (IL6)/Janus kinase 2 (JAK2)-mediated inflammatory signals lead to phosphorylation of PPDPF at Tyr16 and Tyr17, stabilizing the protein. In summary, this study demonstrates that PPDPF is a key molecule in CRC carcinogenesis and progression that connects inflammatory signals to the Wnt/β-catenin signaling pathway, providing a potential novel therapeutic target.

A Phase Ib/II Study of WNT974 + Encorafenib + Cetuximab in Patients With BRAF V600E-Mutant KRAS Wild-Type Metastatic Colorectal Cancer

BACKGROUND

WNT974 is a small molecule inhibitor of Wnt signaling that specifically inhibits porcupine O-acyltransferase. This phase Ib dose--escalation study evaluated the maximum tolerated dose of WNT974 in combination with encorafenib and cetuximab in patients with BRAF V600E-mutant metastatic colorectal cancer with RNF43 mutations or RSPO fusions.

PATIENTS AND METHODS

Patients received once-daily encorafenib and weekly cetuximab, in addition to once-daily WNT974, in sequential dosing cohorts. In the first cohort, patients received 10-mg WNT974 (COMBO10), which was reduced in subsequent cohorts to 7.5-mg (COMBO7.5) or 5-mg (COMBO5) after dose-limiting toxicities (DLTs) were observed. Primary endpoints were incidence of DLTs and exposure to WNT974 and encorafenib. Secondary endpoints were anti-tumor activity and safety.

RESULTS

Twenty patients were enrolled (COMBO10, n = 4; COMBO7.5, n = 6; COMBO5, n = 10). DLTs were observed in 4 patients, including grade 3 hypercalcemia (COMBO10, n = 1; COMBO7.5, n = 1), grade 2 dysgeusia (COMBO10, n = 1), and lipase increased (COMBO10, n = 1). A high incidence of bone toxicities (n = 9) was reported, including rib fracture, spinal compression fracture, pathological fracture, foot fracture, hip fracture, and lumbar vertebral fracture. Serious adverse events were reported in 15 patients, most frequently bone fracture, hypercalcemia, and pleural effusion. The overall response rate was 10% and disease control rate 85%; most patients achieved stable disease as their best response.

CONCLUSION

Concerns surrounding the safety and lack of preliminary evidence of improved anti-tumor activity of WNT974 + encorafenib + cetuximab, compared with previous encorafenib + cetuximab data, ultimately led to study discontinuation. Phase II was not initiated.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02278133.

Whole genome sequencing of Malaysian colorectal cancer patients reveals specific druggable somatic mutations

The incidences of colorectal cancer (CRC) are continuously increasing in some areas of the world, including Malaysia. In this study, we aimed to characterize the landscape of somatic mutations using the whole-genome sequencing approach and identify druggable somatic mutations specific to Malaysian patients. Whole-genome sequencing was performed on the genomic DNA obtained from 50 Malaysian CRC patients' tissues. We discovered the top significantly mutated genes were APC, TP53, KRAS, TCF7L2 and ACVR2A. Four novel, non-synonymous variants were identified in three genes, which were KDM4E, MUC16 and POTED. At least one druggable somatic alteration was identified in 88% of our patients. Among them were two frameshift mutations in RNF43 (G156fs and P192fs) predicted to have responsive effects against the Wnt pathway inhibitor. We found that the exogenous expression of this RNF43 mutation in CRC cells resulted in increased cell proliferation and sensitivity against LGK974 drug treatment and G1 cell cycle arrest. In conclusion, this study uncovered our local CRC patients' genomic landscape and druggable alterations. It also highlighted the role of specific RNF43 frameshift mutations, which unveil the potential of an alternative treatment targeting the Wnt/β-Catenin signalling pathway and could be beneficial, especially to Malaysian CRC patients.

Clinicopathological and molecular characterization of deficient mismatch repair colorectal cancer

Tumors demonstrating deficient mismatch repair (dMMR) account for 12%-15% of colorectal cancers (CRCs), but their characteristics have not been fully elucidated. The aim of this study was to characterize dMMR CRCs in terms of clinicopathological findings and molecular alterations. Immunostaining for mismatch repair (MMR) proteins was performed to determine MMR status, and then MLH1 promoter methylation and genetic variants of 25 genes involved in colorectal carcinogenesis were analyzed by next-generation sequencing in dMMR tumors. Coexistence of precancerous lesions was histologically evaluated to characterize the type of precursors. Immunohistochemistry revealed 34 dMMR tumors in 492 CRCs. Among dMMR CRCs, there were 25 MLH1 methylation-positive, 16 BRAF V600E variant-positive, and 7 KRAS variant-positive tumors. Positive MLH1 methylation was associated with BRAF V600E, older age, and right-side tumor location. MLH1 methylated BRAF/KRAS wild-type tumors were distinct in that all 5 tumors possessed variants in ligand-independent WNT signaling genes including APC, AXIN2, and CTNNB1. Among 10 dMMR CRCs that presented with precancerous lesions, 4 BRAF variant-positive, 1 KRAS variant-positive, and 2 BRAF/KRAS wild-type MLH1 methylated tumors coexisted with serrated lesions, whereas 1 MLH1 methylated BRAF/KRAS wild-type tumor and 2 MLH1 unmethylated tumors accompanied conventional adenomas. The present study characterized distinct subgroups of dMMR CRCs based on molecular alterations including MLH1 methylation and variants in BRAF, KRAS, and ligand-independent WNT signaling genes. The existence of distinct precursor lesions including serrated lesion and conventional adenoma further illustrates the involvement of heterogeneous carcinogenetic pathways in the development of dMMR CRCs.

Clone wars: From molecules to cell competition in intestinal stem cell homeostasis and disease

The small intestine is among the fastest self-renewing tissues in adult mammals. This rapid turnover is fueled by the intestinal stem cells residing in the intestinal crypt. Wnt signaling plays a pivotal role in regulating intestinal stem cell renewal and differentiation, and the dysregulation of this pathway leads to cancer formation. Several studies demonstrate that intestinal stem cells follow neutral drift dynamics, as they divide symmetrically to generate other equipotent stem cells. Competition for niche space and extrinsic signals in the intestinal crypt is the governing mechanism that regulates stemness versus cell differentiation, but the underlying molecular mechanisms are still poorly understood, and it is not yet clear how this process changes during disease. In this review, we highlight the mechanisms that regulate stem cell homeostasis in the small intestine, focusing on Wnt signaling and its regulation by RNF43 and ZNRF3, key inhibitors of the Wnt pathway. Furthermore, we summarize the evidence supporting the current model of intestinal stem cell regulation, highlighting the principles of neutral drift at the basis of intestinal stem cell homeostasis. Finally, we discuss recent studies showing how cancer cells bypass this mechanism to gain a competitive advantage against neighboring normal cells.

Stem cells in the gut rapidly renew themselves through processes that cancer cells co-opt to trigger tumor development. Gabriele Colozza from the Institute of Molecular Biotechnology in Vienna, Austria, and colleagues review how a network of critical molecular signals and competition for limited space help to regulate the dynamics of stem cells in the intestines. The correct balance between self-renewal and differentiation is tightly controlled by the so-called Wnt signaling pathway and its inhibitors. Competition between dividing cells in the intestinal crypts, the locations between finger-like protrusions in the gut where stem cells are found, provides another protective mechanism against runaway stem cell growth. However, intestinal cancer cells, thanks to their activating mutations, bypass these safeguards to gain a survival advantage. Drugs that target these ‘super-competitive’ behaviors could therefore help combat tumor proliferation.

Genetic and epigenetic dependencies in colorectal cancer development

Recent studies have mapped key genetic changes in colorectal cancer (CRC) that impact important pathways contributing to the multistep models for CRC initiation and development. In parallel with genetic changes, normal and cancer tissues harbor epigenetic alterations impacting regulation of critical genes that have been shown to play profound roles in the tumor initiation. Cumulatively, these molecular changes are only loosely associated with heterogenous transcriptional programs, reflecting the heterogeneity in the various CRC molecular subtypes and the paths to CRC development. Studies from mapping molecular alterations in early CRC lesions and use of experimental models suggest that the intricate dependencies of various genetic and epigenetic hits shape the early development of CRC via different pathways and its manifestation into various CRC subtypes. We highlight the dependency of epigenetic and genetic changes in driving CRC development and discuss factors affecting epigenetic alterations over time and, by extension, risk for cancer.

Exome sequencing revealed comparable frequencies of RNF43 and BRAF mutations in Middle Eastern colorectal cancer

Mutation-induced activation of Wnt-β Catenin signaling pathway is frequent in CRC. The E3 ubiquitin ligase, RNF43, has been reported to negatively regulate the Wnt signaling pathway and RNF43 mutations are frequently seen in CRC. However, its role in Middle Eastern CRC remains unclear. Therefore, we employed Exome and Sanger sequencing technology to assess the frequency of RNF43 mutations and its association with other clinico-pathological features in Middle Eastern CRC. RNF43 mutations were found in 5.9% (13/220) of CRC cases and was inversely correlated to APC and TP53 mutations. A strong association of RNF43 mutations with right sided and sporadic microsatellite instable (MSI) CRC was observed. No association was identified between RNF43 mutation and other clinico-pathological features including BRAF mutation, age, tumor histological subtype, tumor grade or patients’ prognosis. Multivariate logistic regression analysis revealed that MSI status and wild type APC were independent predictor of RNF43 mutation. We conclude that RNF43 mutations occur in Middle Eastern CRC at comparable frequencies with BRAF mutations and represent a distinct molecular subtype which further enhances our understanding of how different mutational subsets of Wnt tumor suppressor genes link to distinct tumor characteristics, which might be considered for treatment strategies for CRC patients.

Serrated Colorectal Lesions: An Up-to-Date Review from Histological Pattern to Molecular Pathogenesis

Until 2010, colorectal serrated lesions were generally considered as harmless lesions and reported as hyperplastic polyps (HPs) by pathologists and gastroenterologists. However, recent evidence showed that they may bear the potential to develop into colorectal carcinoma (CRC). Therefore, the World Health Organization (WHO) classification has identified four categories of serrated lesions: hyperplastic polyps (HPs), sessile serrated lesions (SSLs), traditional serrated adenoma (TSAs) and unclassified serrated adenomas. SSLs with dysplasia and TSAs are the most common precursors of CRC. CRCs arising from serrated lesions originate via two different molecular pathways, namely sporadic microsatellite instability (MSI) and the CpG island methylator phenotype (CIMP), the latter being considered as the major mechanism that drives the serrated pathway towards CRC. Unlike CRCs arising through the adenoma-carcinoma pathway, APC-inactivating mutations are rarely shown in the serrated neoplasia pathway.

The earliest events in BRAF-mutant colorectal cancer: exome sequencing of sessile serrated lesions with a tiny focus dysplasia or cancer reveals recurring mutations in two distinct progression pathways

Around 15–30% of colorectal cancers (CRC) develop from sessile serrated lesions (SSLs). After many years of indolent growth, SSLs can develop dysplasia and rapidly progress to CRC through events that are only partially understood. We studied molecular events at the very early stages of progression of SSLs via the MLH1‐proficient and deficient pathways to CRC. We collected a cohort of rare SSLs with a small focus (<10 mm) of dysplasia or cancer from the pathology archives of three hospitals. Whole‐exome sequencing was performed on DNA from nonprogressed and progressed components of each SSL. Putative somatic driver mutations were identified in known cancer genes that were differentially mutated in the progressed component. All analyses were stratified by MLH1 proficiency. Forty‐five lesions with a focus dysplasia or cancer were included, of which 22 (49%) were MLH1‐deficient. Lesions had a median diameter of 10 mm (interquartile range [IQR] 8–15), while the progressed component had a median diameter of 3.5 mm (IQR 1.75–4.75). Tumor mutational burden (TMB) was high in MLH1‐deficient lesions (23.9 mutations per MB) as compared to MLH1‐proficient lesions (6.3 mutations per MB). We identified 34 recurrently mutated genes in MLH1‐deficient lesions. Most prominently, ACVR2A and RNF43 were affected in 18/22 lesions, with mutations clustered in three hotspots. Most lesions with RNF43 mutations had concurrent mutations in ZNRF3. In MLH1‐proficient lesions APC (10/23 lesions) and TP53 (6/23 lesions) were recurrently mutated. Our results show that the mutational burden is exceptionally high even in the earliest MLH1‐deficient lesions. We demonstrate that hotspot mutations in ACVR2A and in the RNF43/ZNRF3 complex are extremely common in the early progression of SSLs along the MLH1‐deficient serrated pathway, while APC and TP53 mutations are early events in the the MLH1‐proficient pathway. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Characterization of RNF43 frameshift mutations that drive Wnt ligand- and R-spondin-dependent colon cancer

Loss‐of‐function mutations in RNF43 induce activation of Wnt ligand‐dependent Wnt/β‐catenin signaling through stabilization of the Frizzled receptor, which is often found in microsatellite instability (MSI)‐type colorectal cancer (CRC) that develops from sessile serrated adenomas. However, the mechanism underlying how RNF43 mutations promote tumorigenesis remains poorly understood. In this study, we established nine human CRC‐derived organoids and found that three organoid lines carried RNF43 frameshift mutations associated with MSI‐high and BRAF^V600E mutations, suggesting that these CRCs developed through the serrated pathway. RNF43 frameshift mutant organoids required both Wnt ligands and R‐spondin for proliferation, indicating that suppression of ZNRF3 and retained RNF43 function by R‐spondin are required to achieve an indispensable level of Wnt activation for tumorigenesis. However, active β‐catenin levels in RNF43‐mutant organoids were lower than those in APC two‐hit mutant CRC, suggesting a lower threshold for Wnt activation in CRC that developed through the serrated pathway. Interestingly, transplantation of RNF43‐mutant organoids with intestinal myofibroblasts accelerated the β‐catenin nuclear accumulation and proliferation of xenograft tumors, indicating a key role of stromal cells in the promotion of the malignant phenotype of RNF43‐mutant CRC cells. Sequencing of subcloned organoid cell‐expressed transcripts revealed that two organoid lines carried monoallelic RNF43 cis‐mutations, with two RNF43 frameshift mutations introduced in the same allele and the wild‐type RNF43 allele remaining, while the other organoid line carried two‐hit biallelic RNF43 trans‐mutations. These results suggest that heterozygous RNF43 frameshift mutations contribute to CRC development via the serrated pathway; however, a second‐hit RNF43 mutation may be advantageous in tumorigenesis compared with a single‐hit mutation through further activation of Wnt signaling. Finally, treatment with the PORCN inhibitor significantly suppressed RNF43‐mutant cell‐derived PDX tumor development. These results suggest a novel mechanism underlying RNF43 mutation‐associated CRC development and the therapeutic potential of Wnt ligand inhibition against RNF43‐mutant CRC. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

RNF43 inhibits WNT5A-driven signaling and suppresses melanoma invasion and resistance to the targeted therapy

RNF43 is an E3 ubiquitin ligase and known negative regulator of WNT/β-catenin signaling. We demonstrate that RNF43 is also a regulator of noncanonical WNT5A-induced signaling in human cells. Analysis of the RNF43 interactome using BioID and immunoprecipitation showed that RNF43 can interact with the core receptor complex components dedicated to the noncanonical Wnt pathway such as ROR1, ROR2, VANGL1, and VANGL2. RNF43 triggers VANGL2 ubiquitination and proteasomal degradation and clathrin-dependent internalization of ROR1 receptor and inhibits ROR2 activation. These activities of RNF43 are physiologically relevant and block pro-metastatic WNT5A signaling in melanoma. RNF43 inhibits responses to WNT5A, which results in the suppression of invasive properties of melanoma cells. Furthermore, RNF43 prevented WNT5A-assisted development of resistance to BRAF V600E and MEK inhibitors. Next, RNF43 acted as melanoma suppressor and improved response to targeted therapies in vivo. In line with these findings, RNF43 expression decreases during melanoma progression and RNF43-low patients have a worse prognosis. We conclude that RNF43 is a newly discovered negative regulator of WNT5A-mediated biological responses that desensitizes cells to WNT5A.

RNF43 pathogenic Germline variant in a family with colorectal cancer

The role of RNF43 as a cause of an inherited predisposition to colorectal cancer (CRC) is yet to be fully explored. This report presents our findings of two individuals with CRC from a single family carrying a likely-pathogenic inherited germline variant in RNF43. The proband (III:1) and the proband's mother (II:2) were diagnosed with mismatch repair proficient CRCs at the age of 50 years and 65 years, respectively. Both patients had BRAF^V600E mutated colon tumours, indicating that the CRCs arose in sessile serrated lesions. The germline variant RNF43:c.375+1G>A was identified in both patients. RNA studies showed that this variant resulted in an aberrantly spliced transcript, which was predicted to encode RNF43:p.Ala126Ilefs*50 resulting in premature termination of protein synthesis and was classified as a likely-pathogenic variant. Our report adds further evidence to the hereditary role of RNF43 as a tumour suppressor gene in colorectal tumorigenesis and supports the inclusion of RNF43 as a gene of interest in the investigation of CRC predispositions outside the setting of serrated polyposis.

WNT as a Driver and Dependency in Cancer

The WNT signaling pathway is a critical regulator of development and adult tissue homeostasis and becomes dysregulated in many cancer types. Although hyperactivation of WNT signaling is common, the type and frequency of genetic WNT pathway alterations can vary dramatically between different cancers, highlighting possible cancer-specific mechanisms for WNT-driven disease. In this review, we discuss how WNT pathway disruption contributes to tumorigenesis in different organs and how WNT affects the tumor cell and immune microenvironment. Finally, we describe recent and ongoing efforts to target oncogenic WNT signaling as a therapeutic strategy. SIGNIFICANCE: WNT signaling is a fundamental regulator of tissue homeostasis and oncogenic driver in many cancer types. In this review, we highlight recent advances in our understanding of WNT signaling in cancer, particularly the complexities of WNT activation in distinct cancer types, its role in immune evasion, and the challenge of targeting the WNT pathway as a therapeutic strategy.

How to Differentiate Benign from Malignant Adrenocortical Tumors?

Simple Summary

Adrenocortical carcinoma is a rare cancer with a poor prognosis. Adrenal tumors are, however, commonly identified in clinical practice. Discrimination between benign and malignant adrenal tumors is of great importance to determine the appropriate treatment and follow-up strategy. This review summarizes the current diagnostic strategies and challenges to distinguish benign from malignant adrenal lesions. We will focus both on radiological and biochemical assessments, enabling diagnosis of the adrenal lesion preoperatively, and on histopathological and a wide variety of molecular assessments that can be done after surgical removal of the adrenal lesion. Furthermore, new non-invasive strategies such as liquid biopsies, in which blood samples are used to study circulating tumor cells, tumor DNA and microRNA, will be addressed in this review.

Abstract

Adrenocortical carcinoma (ACC) is a rare cancer with a poor prognosis. Adrenal incidentalomas are, however, commonly identified in clinical practice. Discrimination between benign and malignant adrenal tumors is of great importance considering the large differences in clinical behavior requiring different strategies. Diagnosis of ACC starts with a thorough physical examination, biochemical evaluation, and imaging. Computed tomography is the first-level imaging modality in adrenal tumors, with tumor size and Hounsfield units being important features for determining malignancy. New developments include the use of urine metabolomics, also enabling discrimination of ACC from adenomas preoperatively. Postoperatively, the Weiss score is used for diagnosis of ACC, consisting of nine histopathological criteria. Due to known limitations as interobserver variability and lack of accuracy in borderline cases, much effort has been put into new tools to diagnose ACC. Novel developments vary from immunohistochemical markers and pathological scores, to markers at the level of DNA, methylome, chromosome, or microRNA. Molecular studies have provided insights into the most promising and most frequent alterations in ACC. The use of liquid biopsies for diagnosis of ACC is studied, although in a small number of patients, requiring further investigation. In this review, current diagnostic modalities and challenges in ACC will be addressed.

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.

Genetic and Epigenetic Characteristics of Inflammatory Bowel Disease-Associated Colorectal Cancer

BACKGROUND & AIMS

Inflammatory bowel disease (IBD) is a chronic, relapsing inflammatory disorder associated with an elevated risk of colorectal cancer (CRC). IBD-associated CRC (IBD-CRC) may represent a distinct pathway of tumorigenesis compared to sporadic CRC (sCRC). Our aim was to comprehensively characterize IBD-associated tumorigenesis integrating multiple high-throughput approaches, and to compare the results with in-house data sets from sCRCs.

METHODS

Whole-genome sequencing, single nucleotide polymorphism arrays, RNA sequencing, genome-wide methylation analysis, and immunohistochemistry were performed using fresh-frozen and formalin-fixed tissue samples of tumor and corresponding normal tissues from 31 patients with IBD-CRC.

RESULTS

Transcriptome-based tumor subtyping revealed the complete absence of canonical epithelial tumor subtype associated with WNT signaling in IBD-CRCs, dominated instead by mesenchymal stroma-rich subtype. Negative WNT regulators AXIN2 and RNF43 were strongly down-regulated in IBD-CRCs and chromosomal gains at HNF4A, a negative regulator of WNT-induced epithelial-mesenchymal transition (EMT), were less frequent compared to sCRCs. Enrichment of hypomethylation at HNF4α binding sites was detected solely in sCRC genomes. PIGR and OSMR involved in mucosal immunity were dysregulated via epigenetic modifications in IBD-CRCs. Genome-wide analysis showed significant enrichment of noncoding mutations to 5'untranslated region of TP53 in IBD-CRCs. As reported previously, somatic mutations in APC and KRAS were less frequent in IBD-CRCs compared to sCRCs.

CONCLUSIONS

Distinct mechanisms of WNT pathway dysregulation skew IBD-CRCs toward mesenchymal tumor subtype, which may affect prognosis and treatment options. Increased OSMR signaling may favor the establishment of mesenchymal tumors in patients with IBD.

Cancer Genomic Profiling in Colorectal Cancer: Current Challenges in Subtyping Colorectal Cancers Based on Somatic and Germline Variants

Colorectal cancer (CRC) is a heterogeneous disease caused by the accumulation of multistep genetic alterations under the influence of genomic instability. Different backgrounds of genomic instability, such as chromosomal instability, microsatellite instability, hypermutated-single nucleotide variants, and genome stable-induced transformation in the colonic epithelium, can result in adenomas, adenocarcinomas, and metastatic tumors. Characterization of molecular subtypes and establishment of treatment policies based on each subtype will lead to better treatment outcomes and an improved selection of molecularly targeted agents. In Japan, cancer precision medicine has been introduced in the National Health Insurance program through the addition of the cancer genomic profiling (CGP) examination. It has also become possible to access a large amount of genomic information, including information on pathogenic somatic and germline variants, incomparable to conventional diagnostic tests. This information enables us to apply research data to clinical decision-making, benefiting patients and their healthy family members. In this article, we discuss the important molecules and signaling pathways presumed to be the driver genes of CRC progression and the signal transduction system in which they are involved. Molecular subtypes of CRC based on CGP examinations and gene expression profiles have been established in The Cancer Genome Atlas Network with the advent of next-generation sequencing technology. We will also discuss the recommended management of secondary/germline findings, pathogenic germline variants, and presumed germline pathogenic variants obtained from CGP examination and review the current challenges to better understand these data in a new era of cancer genomic medicine.

Phase 1 study of single-agent WNT974, a first-in-class Porcupine inhibitor, in patients with advanced solid tumours

BACKGROUND

This Phase 1 study assessed the safety and efficacy of the Porcupine inhibitor, WNT974, in patients with advanced solid tumours.

METHODS

Patients (n = 94) received oral WNT974 at doses of 5-30 mg once-daily, plus additional dosing schedules.

RESULTS

The maximum tolerated dose was not established; the recommended dose for expansion was 10 mg once-daily. Dysgeusia was the most common adverse event (50% of patients), likely resulting from on-target Wnt pathway inhibition. No responses were seen by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1; 16% of patients had stable disease (median duration 19.9 weeks). AXIN2 expression by RT-PCR was reduced in 94% of paired skin biopsies (n = 52) and 74% of paired tumour biopsies (n = 35), confirming inhibition of the Wnt pathway. In an exploratory analysis, an inverse association was observed between AXIN2 change and immune signature change in paired tumour samples (n = 8).

CONCLUSIONS

Single-agent WNT974 treatment was generally well tolerated. Biomarker analyses suggest that WNT974 may influence immune cell recruitment to tumours, and may enhance checkpoint inhibitor activity.

CLINICAL TRIAL REGISTRATION

NCT01351103.

Exploring clinical and gene expression markers of benefit from FOLFOXIRI/bevacizumab in patients with BRAF-mutated metastatic colorectal cancer: Subgroup analyses of the TRIBE2 study

BACKGROUND

Recent data from the TRIBE2 study have failed to suggest a higher magnitude of benefit from upfront FOLFOXIRI/bevacizumab in patients with BRAF-mutant metastatic colorectal cancer (mCRC) as previously reported in the TRIBE study.

PATIENTS AND METHODS

Clinical characteristics and gene expression signatures of patients with BRAF-mutant mCRC enrolled in the TRIBE2 study were evaluated with the aim of understanding that patients may derive benefit from the intensification of the upfront chemotherapy.

RESULTS

Of 46 BRAF-mutant tumour samples analysed, 24 (52%) and 22 (48%) were classified as BM1 and BM2, respectively, and 27 (59%) and 19 (41%) were assigned to ligand-independent (LI) and ligand-dependent (LD) Wnt pathway subgroups, respectively. No prognostic impact was shown for both BM1/BM2 and LI/LD subtypes. No interaction was evident between BM1/BM2 or LI/LD signatures and the benefit provided by FOLFOXIRI/bevacizumab. Significant interaction effect was evident in terms of progression-free survival between treatment arm and primary tumour sidedness (P = 0.05) and Eastern Cooperative Oncology Group performance status (ECOG-PS; P < 0.001).

CONCLUSIONS

Gene expression analysis failed to identify patients with BRAF-mutant mCRC candidate to upfront FOLFOXIRI/bevacizumab. ECOG-PS >0 and left-sidedness seem associated with no benefit from the intensified treatment.

Annexin A10 and HES-1 Immunohistochemistry in Right-sided Traditional Serrated Adenomas Suggests an Origin From Sessile Serrated Adenoma

There is increasing body of evidence to suggest that some colonic serrated polyps do not fit morphologically with any of the proposed categories for serrated polyps recommended by the World Health Organization. Most of these polyps have morphologic features of traditional serrated adenoma (TSA) admixed with areas resembling sessile serrated adenoma (SSA) or hyperplastic polyp (HP). Based on these findings it has been suggested that at least some TSAs may arise in association with precursor HP or SSA lesions, particularly those that develop in right colon. To further evaluate this hypothesis, 39 serrated polyps from right side of the colon (cecum, ascending, and transverse colon) with mixed features of TSA and SSA were evaluated by 2 immunostains previously shown to represent markers of SSA. One is Annexin A10 which shows upregulated expression in SSA and the other is Hes-1 which is shown to be down regulated in SSA. The expression patterns of these markers were evaluated in SSA and TSA components of hybrid polyps and compared with control groups (pure SSAs and TSAs of right colon). SSA component in hybrid polyps did not show any significant difference in staining pattern compared with that seen in TSA component of hybrid polyps or in pure TSA polyps. These findings further support the hypothesis that recognizes SSA as a precursor lesion for TSA in the right colon.

USP42 protects ZNRF3/RNF43 from R-spondin-dependent clearance and inhibits Wnt signalling

The tumour suppressors RNF43 and ZNRF3 play a central role in development and tissue homeostasis by promoting the turnover of the Wnt receptors LRP6 and Frizzled (FZD). The stem cell growth factor R‐spondin induces auto‐ubiquitination and membrane clearance of ZNRF3/RNF43 to promote Wnt signalling. However, the deubiquitinase stabilising ZNRF3/RNF43 at the plasma membrane remains unknown. Here, we show that the USP42 antagonises R‐spondin by protecting ZNRF3/RNF43 from ubiquitin‐dependent clearance. USP42 binds to the Dishevelled interacting region (DIR) of ZNRF3 and stalls the R‐spondin‐LGR4‐ZNRF3 ternary complex by deubiquitinating ZNRF3. Accordingly, USP42 increases the turnover of LRP6 and Frizzled (FZD) receptors and inhibits Wnt signalling. Furthermore, we show that USP42 functions as a roadblock for paracrine Wnt signalling in colon cancer cells and mouse small intestinal organoids. We provide new mechanistic insights into the regulation R‐spondin and conclude that USP42 is crucial for ZNRF3/RNF43 stabilisation at the cell surface.

Post-translational Wnt receptor regulation: Is the fog slowly clearing?: The molecular mechanism of RNF43/ZNRF3 ubiquitin ligases is not yet fully elucidated and still controversial

Wnt signaling plays pivotal roles during our entire lives, from conception to death, through the regulation of morphogenesis in developing embryos and the maintenance of tissue homeostasis in adults. The regulation of Wnt signaling occurs on several levels: at the receptor level on the plasma membrane, at the β-catenin protein level in the cytoplasm, and through transcriptional regulation in the nucleus. Several recent studies have focused on the mechanisms of Wnt receptor regulation, following the discovery that the Wnt receptor frizzled (Fzd) is a target of the ubiquitin ligases, RNF43 and ZNRF3. RNF43 and ZNRF3 are homologous genes that are mutated in several cancers. The details underlying their mechanism of action continue to unfold, while at the same time raising many new questions. In this review, we discuss advances and controversies in our understanding of Wnt receptor regulation.

Low Protein Expression of both ATRX and ZNRF3 as Novel Negative Prognostic Markers of Adult Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) is a rare malignancy that is associated with a dismal prognosis. Pan-genomic studies have demonstrated the involvement of ATRX and ZNRF3 genes in adrenocortical tumorigenesis. Our aims were to evaluate the protein expression of ATRX and ZNRF3 in a cohort of 82 adults with ACC and to establish their prognostic value. Two pathologists analyzed immuno-stained slides of a tissue microarray. The low protein expression of ATRX and ZNRF3 was associated with a decrease in overall survival (OS) (p = 0.045, p = 0.012, respectively). The Cox regression for ATRX protein expression of >1.5 showed a hazard ratio (HR) for OS of 0.521 (95% CI 0.273-0.997; p = 0.049) when compared with ≤1.5; for ZNRF3 expression >2, the HR for OS was 0.441 (95% CI, 0.229-0.852; p = 0.015) when compared with ≤2. High ATRX and ZNRF3 protein expressions were associated with optimistic recurrence-free survival (RFS) (p = 0.027 and p = 0.005, respectively). The Cox regression of RFS showed an HR of 0.332 (95%CI, 0.111-0.932) for ATRX expression >2.7 (p = 0.037), and an HR of 0.333 (95%CI, 0.140-0.790) for ZNRF3 expression >2 (p = 0.013). In conclusion, low protein expression of ATRX and ZNRF3 are negative prognostic markers of ACC; however, different cohorts should be evaluated to validate these findings.

Molecular Features of the Serrated Pathway to Colorectal Cancer: Current Knowledge and Future Directions

Serrated lesions are the precursor lesions of a new model of colorectal carcinogenesis. From a molecular standpoint, the serrated pathway is thought to be responsible for up to 30% of all colorectal cancer cases. The three major processes of this molecular mechanism are alterations in the mitogen-activated protein kinase pathway, production of the CpG island methylation phenotype, and generation of microsatellite instability. Other contributing processes are activation of WNT, alterations in the regulation of tumor suppressor genes, and alterations in microRNAs or in MUC5AC hypomethylation. Although alterations in the serrated pathway also contribute, their precise roles remain obscure because of the various methodologies and definitions used by different research groups. This knowledge gap affects clinical assessment of precursor lesions for their carcinogenic risk. The present review describes the current literature reporting the molecular mechanisms underlying each type of serrated lesion and each phenotype of serrated pathway colorectal cancer, identifying those areas that merit additional research. We also propose a unified serrated carcinogenesis pathway combining molecular alterations and types of serrated lesions, which ends in different serrated pathway colorectal cancer phenotypes depending on the route followed. Finally, we describe some key issues that need to be addressed in order to incorporate the newest technologies in serrated pathway research and to improve overall knowledge for developing specific prevention strategies and new therapeutic targets.

Mutations and mechanisms of WNT pathway tumour suppressors in cancer

Mutation-induced activation of WNT-β-catenin signalling is a frequent driver event in human cancer. Sustained WNT-β-catenin pathway activation endows cancer cells with sustained self-renewing growth properties and is associated with therapy resistance. In healthy adult stem cells, WNT pathway activity is carefully controlled by core pathway tumour suppressors as well as negative feedback regulators. Gene inactivation experiments in mouse models unequivocally demonstrated the relevance of WNT tumour suppressor loss-of-function mutations for cancer growth. However, in human cancer, a far more complex picture has emerged in which missense or truncating mutations mediate stable expression of mutant proteins, with distinct functional and phenotypic ramifications. Herein, we review recent advances and challenges in our understanding of how different mutational subsets of WNT tumour suppressor genes link to distinct cancer types, clinical outcomes and treatment strategies.

The Functional Landscape of Patient-Derived RNF43 Mutations Predicts Sensitivity to Wnt Inhibition

A subset of Wnt-addicted cancers are sensitive to targeted therapies that block Wnt secretion or receptor engagement. RNF43 loss-of-function (LOF) mutations that increase cell surface Wnt receptor abundance cause sensitivity to Wnt inhibitors. However, it is not clear which of the clinically identified RNF43 mutations affect its function in vivo. We assayed 119 missense and 45 truncating RNF43 mutations found in human cancers using a combination of cell-based reporter assays, genome editing, flow cytometry, and immunofluorescence microscopy. Five common germline variants of RNF43 exhibited wild-type activity. Cancer-associated missense mutations in the RING ubiquitin ligase domain and a subset of mutations in the extracellular domain hyperactivate Wnt/β-catenin signaling through formation of inactive dimers with endogenous RNF43 or ZNRF3. RNF43 C-terminal truncation mutants, including the common G659fs mutant are LOF specifically when endogenous mutations are examined, unlike their behavior in transient transfection assays. Patient-derived xenografts and cell lines with C-terminal truncations showed increased cell surface Frizzled and Wnt/β-catenin signaling and were responsive to porcupine (PORCN) inhibition in vivo, providing clear evidence of RNF43 impairment. Our study provides potential guidelines for patient assignment, as virtually all RNF43 nonsense and frameshift mutations, including those in the C-terminal domain and a large number of patient-associated missense mutations in the RING domain and N-terminal region compromise its activity, and therefore predict response to upstream Wnt inhibitors in cancers without microsatellite instability. This study expands the landscape of actionable RNF43 mutations, extending the benefit of these therapies to additional patients. SIGNIFICANCE: Systematic examination of patient-derived RNF43 mutations identifies rules to guide patient selection, including that truncation or point mutations in well-defined functional domains sensitize cancers to PORCN inhibitors.

A phospho-switch controls RNF43-mediated degradation of Wnt receptors to suppress tumorigenesis

Frequent mutation of the tumour suppressor RNF43 is observed in many cancers, particularly colon malignancies. RNF43, an E3 ubiquitin ligase, negatively regulates Wnt signalling by inducing degradation of the Wnt receptor Frizzled. In this study, we discover that RNF43 activity requires phosphorylation at a triplet of conserved serines. This phospho-regulation of RNF43 is required for zebrafish development and growth of mouse intestinal organoids. Cancer-associated mutations that abrogate RNF43 phosphorylation cooperate with active Ras to promote tumorigenesis by abolishing the inhibitory function of RNF43 in Wnt signalling while maintaining its inhibitory function in p53 signalling. Our data suggest that RNF43 mutations cooperate with KRAS mutations to promote multi-step tumorigenesis via the Wnt-Ras-p53 axis in human colon cancers. Lastly, phosphomimetic substitutions of the serine trio restored the tumour suppressive activity of extracellular oncogenic mutants. Therefore, harnessing phospho-regulation of RNF43 might be a potential therapeutic strategy for tumours with RNF43 mutations.

Casein Kinase 1α as a Regulator of Wnt-Driven Cancer

Wnt signaling regulates numerous cellular processes during embryonic development and adult tissue homeostasis. Underscoring this physiological importance, deregulation of the Wnt signaling pathway is associated with many disease states, including cancer. Here, we review pivotal regulatory events in the Wnt signaling pathway that drive cancer growth. We then discuss the roles of the established negative Wnt regulator, casein kinase 1α (CK1α), in Wnt signaling. Although the study of CK1α has been ongoing for several decades, the bulk of such research has focused on how it phosphorylates and regulates its various substrates. We focus here on what is known about the mechanisms controlling CK1α, including its putative regulatory proteins and alternative splicing variants. Finally, we describe the discovery and validation of a family of pharmacological CK1α activators capable of inhibiting Wnt pathway activity. One of the important advantages of CK1α activators, relative to other classes of Wnt inhibitors, is their reduced on-target toxicity, overcoming one of the major impediments to developing a clinically relevant Wnt inhibitor. Therefore, we also discuss mechanisms that regulate CK1α steady-state homeostasis, which may contribute to the deregulation of Wnt pathway activity in cancer and underlie the enhanced therapeutic index of CK1α activators.

Diverse LEF/TCF Expression in Human Colorectal Cancer Correlates with Altered Wnt-Regulated Transcriptome in a Meta-Analysis of Patient Biopsies

Aberrantly activated Wnt signaling causes cellular transformation that can lead to human colorectal cancer. Wnt signaling is mediated by Lymphoid Enhancer Factor/T-Cell Factor (LEF/TCF) DNA-binding factors. Here we investigate whether altered LEF/TCF expression is conserved in human colorectal tumor sample and may potentially be correlated with indicators of cancer progression. We carried out a meta-analysis of carefully selected publicly available gene expression data sets with paired tumor biopsy and adjacent matched normal tissues from colorectal cancer patients. Our meta-analysis confirms that among the four human LEF/TCF genes, LEF1 and TCF7 are preferentially expressed in tumor biopsies, while TCF7L2 and TCF7L1 in normal control tissue. We also confirm positive correlation of LEF1 and TCF7 expression with hallmarks of active Wnt signaling (i.e., AXIN2 and LGR5). We are able to correlate differential LEF/TCF gene expression with distinct transcriptomes associated with cell adhesion, extracellular matrix organization, and Wnt receptor feedback regulation. We demonstrate here in human colorectal tumor sample correlation of altered LEF/TCF gene expression with quantitatively and qualitatively different transcriptomes, suggesting LEF/TCF-specific transcriptional regulation of Wnt target genes relevant for cancer progression and survival. This bioinformatics analysis provides a foundation for future more detailed, functional, and molecular analyses aimed at dissecting such functional differences.

APC Mutation Marks an Aggressive Subtype of BRAF Mutant Colorectal Cancers

BACKGROUND

WNT activation is a hallmark of colorectal cancer. BRAF mutation is present in 15% of colorectal cancers, and the role of mutations in WNT signaling regulators in this context is unclear. Here, we evaluate the mutational landscape of WNT signaling regulators in BRAF mutant cancers.

METHODS

we performed exome-sequencing on 24 BRAF mutant colorectal cancers and analyzed these data in combination with 175 publicly available BRAF mutant colorectal cancer exomes. We assessed the somatic mutational landscape of WNT signaling regulators, and performed hotspot and driver mutation analyses to identify potential drivers of WNT signaling. The effects of Apc and Braf mutation were modelled, in vivo, using the Apcmin/+ and BrafV637/Villin-CreERT2/+ mouse, respectively.

RESULTS

RNF43 was the most frequently mutated WNT signaling regulator (41%). Mutations in the beta-catenin destruction complex occurred in 48% of cancers. Hotspot analyses identified potential cancer driver genes in the WNT signaling cascade, including MEN1, GNG12 and WNT16. Truncating APC mutation was identified in 20.8% of cancers. Truncating APC mutation was associated with early age at diagnosis (p < 2 × 10-5), advanced stage (p < 0.01), and poor survival (p = 0.026). Apcmin/+/BrafV637 animals had more numerous and larger SI and colonic lesions (p < 0.0001 and p < 0.05, respectively), and a markedly reduced survival (median survival: 3.2 months, p = 8.8 × 10-21), compared to animals with Apc or Braf mutation alone.

CONCLUSIONS

the WNT signaling axis is frequently mutated in BRAF mutant colorectal cancers. WNT16 and MEN1 may be novel drivers of aberrant WNT signaling in colorectal cancer. Co-mutation of BRAF and APC generates an extremely aggressive neoplastic phenotype that is associated with poor patient outcome.

Actionable Potentials of Less Frequently Mutated Genes in Colorectal Cancer and Their Roles in Precision Medicine

Global statistics have placed colorectal cancer (CRC) as the third most frequently diagnosed cancer and the fourth principal cause of cancer-related deaths worldwide. Improving survival for CRC is as important as early detection. Personalized medicine is important in maximizing an individual's treatment success and minimizing the risk of adverse reactions. Approaches in achieving personalized therapy in CRC have included analyses of specific genes with its clinical implications. Tumour genotyping via next-generation sequencing has become a standard practice to guide clinicians into predicting tumor behaviour, disease prognosis, and treatment response. Nevertheless, better prognostic markers are necessary to further stratify patients for personalized treatment plans. The discovery of new markers remains indispensable in providing the most effective chemotherapy in order to improve the outcomes of treatment and survival in CRC patients. This review aims to compile and discuss newly discovered, less frequently mutated genes in CRC. We also discuss how these mutations are being used to assist therapeutic decisions and their potential prospective clinical utilities. In addition, we will summarize the importance of profiling the large genomic rearrangements, gene amplification, and large deletions and how these alterations may assist in determining the best treatment option for CRC patients.

WNT and β-Catenin in Cancer: Genes and Therapy

The WNT pathway is a pleiotropic signaling pathway that controls developmental processes, tissue homeostasis, and cancer. The WNT pathway is commonly mutated in many cancers, leading to widespread research into the role of WNT signaling in carcinogenesis. Understanding which cancers are reliant upon WNT activation and which components of the WNT signaling pathway are mutated is paramount to advancing therapeutic strategies. In addition, building holistic insights into the role of WNT signaling in not only tumor cells but also the tumor microenvironment is a vital area of research and may be a promising therapeutic strategy in multiple immunologically inert cancers. Novel compounds aimed at modulating the WNT signaling pathway using diverse mechanisms are currently under investigation in preclinical/early clinical studies. Here, we review how the WNT pathway is activated in multiple cancers and discuss current strategies to target aberrant WNT signaling.

Sessile Serrated Polyposis: Not an Inherited Syndrome?

BACKGROUND

Researchers are searching in vain for a coherent genetic explanation for serrated polyposis. We hypothesize that there is no consistent monogenetic inheritance.

OBJECTIVE

The purpose of this study was to describe the serrated polyposis phenotype, assessing features of mendelian inheritance, and to compare these features with patients with a solitary sessile serrated lesion.

DESIGN

This was a retrospective review of a prospectively maintained database comparing patients with serrated polyposis versus solitary sessile serrated lesions.

SETTINGS

The study was conducted at a single-institution tertiary referral center.

PATIENTS

Patients with serrated polyposis meeting World Health Organization criteria type I (≥5 serrated polyps proximal to the sigmoid, ≥2 of which are ≥10 mm in diameter) and isolated sessile serrated lesions were included MAIN OUTCOME MEASURES:: Disease phenotype was the main outcome measured.

RESULTS

A total of 46 serrated polyposis patients were identified. Median age of first sessile serrated lesion was 66 years (interquartile range, 42-70 y). A total of 60.3% were current or past smokers (mean = 38.6 packs per year). Serrated polyposis patients had a higher number of all types of polyps (26.3 vs 4.4) and a higher rate of high-grade dysplasia (19.6% vs 3.7%) compared with patients with a solitary sessile serrated lesion. A total of 36.2% of patients had personal history of noncolorectal cancers, including skin, prostate, breast, thyroid, and renal cell cancers and leukemia. In addition, 32.6% had a family history of colorectal cancer in first- or second-degree relatives; these cancers were not young age of onset. Breast and prostate cancers were also common (family history of any cancer, 83.0%). Ten patients underwent genetic testing: 4 had negative panels, 1 had a pathogenic variant in MSH2, 1 an IVS7 deletion in PTEN, 2 negative APC sequencing (1 negative MYH), and 1 a pathogenic variant in Chek2.

LIMITATIONS

RNF4 was not sequenced. Genetic analysis was performed on a subset of patients.

CONCLUSIONS

The rate of associated cancers suggests an underlying genetic predisposition to disordered growth, but serrated polyposis does not have typical features of dominant inheritance. The association with smoking suggests that familial/environmental factors play a role. See Video Abstract at http://links.lww.com/DCR/B84. POLIPOSIS SERRADA SÉSIL: ¿NO ES UN SÍNDROME HEREDITARIO?: Los investigadores están buscando en vano una explicación genética coherente para la póliposis serrados. Suponemos que no existe una herencia monogenética consistente.1) Describir el fenotipo de póliposis serrada, evaluando las características de la herencia mendeliana, 2) comparar estas características con pacientes con una lesión serrada sésil solitaria.Revisión retrospectiva de una base de datos mantenida prospectivamente que compara pacientes con póliposis serrada versus lesiones serradas sésiles solitarias.Institución única, centro de referencia terciario.Pacientes con póliposis serrada que cumplen con los Criterios de la Organización Mundial de la Salud Tipo I (≥ 5 pólipos serrados proximales al sigmoideo, ≥2 de los cuales tienen ≥10 mm de diámetro) y lesiones serradas sésiles aisladas.Fenotipo de la enfermedad.Se identificaron un total de 46 pacientes con póliposis serrada. La edad mediana de la primera lesión serrada sésil fue de 66 años (RIC: 42-70 años). El 60.3% eran fumadores actuales o pasados (medio 38.6 paquetes / año). Los pacientes con póliposis serrada tuvieron un mayor número de todos los tipos de pólipos (26.3 versus 4.4) y una mayor tasa de displasia de alto grado (19.6% versus 3.7%) en comparación con los pacientes con una lesión serrada sésil solitaria. El 36.2% de los pacientes tenían antecedentes personales de cánceres no colorectales, incluyendo los cánceres de piel, próstata, mama, tiroides, células renales y leucemia. El 32.6% tenía antecedentes familiares de cáncer colorectal en familiares de primer o segundo grado; estos cánceres no eran de inicio de edad temprana. El cáncer de mama y próstata también fue frecuente (antecedentes familiares de cualquier tipo de cáncer: 83.0%). 10 pacientes se sometieron a pruebas genéticas: 4 tenían paneles negativos, 1 tenía una variante patogénica en MSH2, 1 una eliminación IVS7 en PTEN, 2 secuenciación APC negativa (1 MYH negativa) y 1 variante patogénica en Chek2.RNF4 no fue secuenciado. El análisis genético se realizó en un subconjunto de pacientes.La tasa de cánceres asociados sugiere una predisposición genética subyacente al crecimiento desordenado, pero la póliposis serrada no tiene características típicas de herencia dominante. La asociación con el tabaquismo sugiere que los factores familiares / ambientales juegan un papel. Consulte Video Resumen en http://links.lww.com/DCR/B84. (Traducción-Dr. Yesenia Rojas-Khalil).

Alterations in signaling pathways that accompany spontaneous transition to malignancy in a mouse model of BRAF mutant microsatellite stable colorectal cancer

The serrated neoplasia pathway gives rise to a distinct subgroup of colorectal cancers distinguished by the presence of mutant BRAF^V600E and the CpG Island Methylator Phenotype (CIMP). BRAF mutant CRC are commonly associated with microsatellite instability, which have an excellent clinical outcome. However, a proportion of BRAF mutant CRC retain microsatellite stability and have a dismal prognosis. The molecular drivers responsible for the development of this cancer subgroup are unknown. To address this, we established a murine model of BRAF^V600E mutant microsatellite stable CRC and comprehensively investigated the exome and transcriptome to identify molecular alterations in signaling pathways that drive malignancy. Exome sequencing of murine serrated lesions (mSL) and carcinomas identified frequent hot spot mutations within the gene encoding β-catenin (Ctnnb1). Immunohistochemical staining of β-catenin indicated that these mutations led to an increase in the presence of aberrant nuclear β-catenin that resulted in gene expression changes in targets of β-catenin transcription. Gene expression profiling identified a significant enrichment for transforming growth factor-β (TGF-β) signaling that was present in mSL and carcinomas. Early activation of TGF-β suggests that this pathway may be an early cue directing mSL to microsatellite stable carcinoma. These findings in the mouse model support the importance of alterations in WNT and TGF-β signaling during the transition of human sessile serrated lesions to malignancy.

Quantifying gene selection in cancer through protein functional alteration bias

Compiling the catalogue of genes actively involved in cancer is an ongoing endeavor, with profound implications to the understanding and treatment of the disease. An abundance of computational methods have been developed to screening the genome for candidate driver genes based on genomic data of somatic mutations in tumors. Existing methods make many implicit and explicit assumptions about the distribution of random mutations. We present FABRIC, a new framework for quantifying the selection of genes in cancer by assessing the effects of de-novo somatic mutations on protein-coding genes. Using a machine-learning model, we quantified the functional effects of ∼3M somatic mutations extracted from over 10 000 human cancerous samples, and compared them against the effects of all possible single-nucleotide mutations in the coding human genome. We detected 593 protein-coding genes showing statistically significant bias towards harmful mutations. These genes, discovered without any prior knowledge, show an overwhelming overlap with known cancer genes, but also include many overlooked genes. FABRIC is designed to avoid false discoveries by comparing each gene to its own background model using rigorous statistics, making minimal assumptions about the distribution of random somatic mutations. The framework is an open-source project with a simple command-line interface.

Pathways of Colorectal Carcinogenesis

Colorectal cancer is a heterogeneous disease that develops via stepwise accumulation of well-characterized genetic and epigenetic alterations. We review the genetic changes associated with the development of precancerous colorectal adenomas and their progression to tumors, as well as the effects of defective DNA repair, chromosome instability, microsatellite instability, and alterations in the serrated pathway and DNA methylation. We provide insights into the different molecular subgroups of colorectal tumors that develop via each of these different mechanisms and their associations with patient outcomes.

The most common RNF43 mutant G659Vfs*41 is fully functional in inhibiting Wnt signaling and unlikely to play a role in tumorigenesis

RNF43 is an E3 ligase that inhibits Wnt signaling by ubiquitinating Wnt receptors for degradation. It is mutated in various cancer types with the most recurrent mutation being the frameshift G659Vfs*41 with frequencies of ~5-8% in colon, stomach and endometrial cancers. This mutation, a deletion of G in a 7-G repeat, has been assumed to encode an inactive enzyme that would lead to increased Wnt signaling and drive tumorigenesis, yet no functional characterization has been reported. We analyzed the distribution of G659Vfs*41 and its association with other cancer gene mutations, and found that the mutation occurred nearly exclusively in tumors with low expression of the DNA mismatch repair gene MLH1. Mutant RNF43-G659Vfs*41 was no different from wild type RNF43 in expression, stability, localization, R-spondin binding, and inhibition of Wnt signaling. No dominant negative activity of the mutant was observed. Colon tumors with RNF43-G659Vfs*41 had low Wnt/β-catenin signaling and were frequently mutated in BRAF. A colon cancer cell line with RNF43-G659Vfs*41 and BRAF-V600E mutations was sensitive to activation of Wnt/β-catenin signaling. These findings suggest that the frequent occurrence of RNF43-G659Vfs*41 may result from error-prone replication of the 7-G repeat in MLH1-deficient tumors and that the mutation itself does not inactivate enzyme.