Analysis of Tumor-Associated AXIN1 Missense Mutations Identifies Variants That Activate ß-Catenin Signaling.

AXIN1 is a major component of the ß-catenin destruction complex and is frequently mutated in various cancer types, particularly liver cancers. Truncating AXIN1 mutations are recognized to encode a defective protein that leads to ß-catenin stabilization, but the functional consequences of missense mutations are not well characterized. Here, we first identified the GSK3ß, ß-catenin, and RGS/APC interaction domains of AXIN1 that are the most critical for proper ß-catenin regulation. Analysis of 80 tumor-associated variants in these domains identified 18 that significantly affected ß-catenin signaling. Coimmunoprecipitation experiments revealed that most of them lost binding to the binding partner corresponding to the mutated domain. A comprehensive protein structure analysis predicted the consequences of these mutations, which largely overlapped with the observed effects on ß-catenin signaling in functional experiments. The structure analysis also predicted that loss-of-function mutations within the RGS/APC interaction domain either directly affected the interface for APC binding or were located within the hydrophobic core and destabilized the entire structure. In addition, truncated AXIN1 length inversely correlated with the ß-catenin regulatory function, with longer proteins retaining more functionality. These analyses suggest that all AXIN1-truncating mutations at least partially affect ß-catenin regulation, whereas this is only the case for a subset of missense mutations. Consistently, most colorectal and liver cancers carrying missense variants acquire mutations in other ß-catenin regulatory genes such as APC and CTNNB1. These results will aid the functional annotation of AXIN1 mutations identified in large-scale sequencing efforts or in individual patients. SIGNIFICANCE: Characterization of 80 tumor-associated missense variants of AXIN1 reveals a subset of 18 mutations that disrupt its ß-catenin regulatory function, whereas the majority are passenger mutations.

Wnt/ß-Catenin Signaling Pathway Is Necessary for the Specification but Not the Maintenance of the Mouse Retinal Pigment Epithelium.

ß-Catenin (Ctnnb1) has been shown to play critical roles in the development and maintenance of epithelial cells, including the retinal pigment epithelium (RPE). Ctnnb1 is not only a component of intercellular junctions in the epithelium, it also functions as a transcriptional regulator in the Wnt signaling pathway. To identify which of its functional modalities is critically involved in mouse RPE development and maintenance, we varied Ctnnb1 gene content and activity in mouse RPE lineage cells and tested their impacts on mouse eye development. We found that a Ctnnb1 double mutant (Ctnnb1dm), which exhibits impaired transcriptional activity, could not replace Ctnnb1 in the RPE, whereas Ctnnb1Y654E, which has reduced affinity for the junctions, could do so. Expression of the constitutively active Ctnnb1∆ex3 mutant also suppressed the development of RPE, instead facilitating a ciliary cell fate. However, the post-mitotic or mature RPE was insensitive to the loss, inactivation, or constitutive activation of Ctnnb1. Collectively, our results suggest that Ctnnb1 should be maintained within an optimal range to specify RPE through transcriptional regulation of Wnt target genes in the optic neuroepithelium.

Issues with RNF43 antibodies to reliably detect intracellular location.

RNF43 is an important negative regulator of ß-catenin signaling by removing Wnt-receptors from the membrane. It is often mutated in cancers, leading to aberrant Wnt-dependent nuclear translocation of ß-catenin. RNF43 has also been suggested to regulate ß-catenin signaling directly within the nucleus, among other proposed nuclear functions. Given the importance of RNF43 in regulating Wnt/ß-catenin signaling and its potential therapeutic relevance, a proper understanding of RNF43 biology is required. However, the presumed nuclear location is mainly based on available antibodies. These same antibodies have also been used extensively for immunoblotting or immunohistochemical purposes. However, a proper evaluation of their quality to reliably detect endogenous RNF43 has not been performed. Here, using genome editing we have generated a cell line that entirely misses RNF43 exons 8 and 9, encoding the epitopes of commonly used RNF43 antibodies. Using this clone in addition to various other cell line tools, we show that four RNF43 antibodies only yield non-specific signals when applied in immunoblotting, immunofluorescence and immunohistochemical experiments. In other words, they cannot reliably detect endogenous RNF43. Our results suggest that the nuclear staining patterns are an antibody artifact and that RNF43 is unlikely to localize within the nucleus. More generally, reports using RNF43 antibodies should be interpreted with caution, at least for the RNF43 protein aspects described in these papers.

RNF43 mutations predict response to anti-BRAF/EGFR combinatory therapies in BRAFV600E metastatic colorectal cancer.

Anti-BRAF/EGFR therapy was recently approved for the treatment of metastatic BRAFV600E colorectal cancer (mCRCBRAF-V600E). However, a large fraction of patients do not respond, underscoring the need to identify molecular determinants of treatment response. Using whole-exome sequencing in a discovery cohort of patients with mCRCBRAF-V600E treated with anti-BRAF/EGFR therapy, we found that inactivating mutations in RNF43, a negative regulator of WNT, predict improved response rates and survival outcomes in patients with microsatellite-stable (MSS) tumors. Analysis of an independent validation cohort confirmed the relevance of RNF43 mutations to predicting clinical benefit (72.7% versus 30.8%; P = 0.03), as well as longer progression-free survival (hazard ratio (HR), 0.30; 95% confidence interval (CI), 0.12-0.75; P = 0.01) and overall survival (HR, 0.26; 95% CI, 0.10-0.71; P = 0.008), in patients with MSS-RNF43mutated versus MSS-RNF43wild-type tumors. Microsatellite-instable tumors invariably carried a wild-type-like RNF43 genotype encoding p.G659fs and presented an intermediate response profile. We found no association of RNF43 mutations with patient outcomes in a control cohort of patients with MSS-mCRCBRAF-V600E tumors not exposed to anti-BRAF targeted therapies. Overall, our findings suggest a cross-talk between the MAPK and WNT pathways that may modulate the antitumor activity of anti-BRAF/EGFR therapy and uncover predictive biomarkers to optimize the clinical management of these patients.

Human branching cholangiocyte organoids recapitulate functional bile duct formation.

Human cholangiocyte organoids show great promise for regenerative therapies and in vitro modeling of bile duct development and diseases. However, the cystic organoids lack the branching morphology of intrahepatic bile ducts (IHBDs). Here, we report establishing human branching cholangiocyte organoid (BRCO) cultures. BRCOs self-organize into complex tubular structures resembling the IHBD architecture. Single-cell transcriptomics and functional analysis showed high similarity to primary cholangiocytes, and importantly, the branching growth mimics aspects of tubular development and is dependent on JAG1/NOTCH2 signaling. When applied to cholangiocarcinoma tumor organoids, the morphology changes to an in vitro morphology like primary tumors. Moreover, these branching cholangiocarcinoma organoids (BRCCAOs) better match the transcriptomic profile of primary tumors and showed increased chemoresistance to gemcitabine and cisplatin. In conclusion, BRCOs recapitulate a complex process of branching morphogenesis in vitro. This provides an improved model to study tubular formation, bile duct functionality, and associated biliary diseases.

HOXA13 in etiology and oncogenic potential of Barrett's esophagus.

Barrett's esophagus in gastrointestinal reflux patients constitutes a columnar epithelium with distal characteristics, prone to progress to esophageal adenocarcinoma. HOX genes are known mediators of position-dependent morphology. Here we show HOX collinearity in the adult gut while Barrett's esophagus shows high HOXA13 expression in stem cells and their progeny. HOXA13 overexpression appears sufficient to explain both the phenotype (through downregulation of the epidermal differentiation complex) and the oncogenic potential of Barrett's esophagus. Intriguingly, employing a mouse model that contains a reporter coupled to the HOXA13 promotor we identify single HOXA13-positive cells distally from the physiological esophagus, which is mirrored in human physiology, but increased in Barrett's esophagus. Additionally, we observe that HOXA13 expression confers a competitive advantage to cells. We thus propose that Barrett's esophagus and associated esophageal adenocarcinoma is the consequence of expansion of this gastro-esophageal HOXA13-expressing compartment following epithelial injury.

Evaluation of AXIN1 and AXIN2 as targets of tankyrase inhibition in hepatocellular carcinoma cell lines.

AXIN1 mutations are observed in 8-10% of hepatocellular carcinomas (HCCs) and originally were considered to support tumor growth by aberrantly enhancing ß-catenin signaling. This view has however been challenged by reports showing neither a clear nuclear ß-catenin accumulation nor clearly enhanced expression of ß-catenin target genes. Here, using nine HCC lines, we show that AXIN1 mutation or siRNA mediated knockdown contributes to enhanced ß-catenin signaling in all AXIN1-mutant and non-mutant lines, also confirmed by reduced signaling in AXIN1-repaired SNU449 cells. Both AXIN1 and AXIN2 work synergistically to control ß-catenin signaling. While in the AXIN1-mutant lines, AXIN2 is solely responsible for keeping signaling in check, in the non-mutant lines both AXIN proteins contribute to ß-catenin regulation to varying levels. The AXIN proteins have gained substantial interest in cancer research for a second reason. Their activity in the ß-catenin destruction complex can be increased by tankyrase inhibitors, which thus may serve as a therapeutic option to reduce the growth of ß-catenin-dependent cancers. At concentrations that inhibit tankyrase activity, some lines (e.g. HepG2, SNU398) were clearly affected in colony formation, but in most cases apparently independent from effects on ß-catenin signaling. Overall, our analyses show that AXIN1 inactivation leads to enhanced ß-catenin signaling in HCC cell lines, questioning the strong statements that have been made in this regard. Enhancing AXIN activity by tankyrase monotherapy provides however no effective treatment to affect their growth exclusively through reducing ß-catenin signaling.

Cancer-Associated Fibroblasts Provide a Stromal Niche for Liver Cancer Organoids That Confers Trophic Effects and Therapy Resistance.

BACKGROUND & AIMS: Cancer-associated fibroblasts (CAFs) play a key role in the cancer process, but the research progress is hampered by the paucity of preclinical models that are essential for mechanistic dissection of cancer cell-CAF interactions. Here, we aimed to establish 3-dimensional (3D) organotypic co-cultures of primary liver tumor-derived organoids with CAFs, and to understand their interactions and the response to treatment. METHODS: Liver tumor organoids and CAFs were cultured from murine and human primary liver tumors. 3D co-culture models of tumor organoids with CAFs and Transwell culture systems were established in vitro. A xenograft model was used to investigate the cell-cell interactions in vivo. Gene expression analysis of CAF markers in our hepatocellular carcinoma cohort and an online liver cancer database indicated the clinical relevance of CAFs. RESULTS: To functionally investigate the interactions of liver cancer cells with CAFs, we successfully established murine and human 3D co-culture models of liver tumor organoids with CAFs. CAFs promoted tumor organoid growth in co-culture with direct cell-cell contact and in a Transwell system via paracrine signaling. Vice versa, cancer cells secrete paracrine factors regulating CAF physiology. Co-transplantation of CAFs with liver tumor organoids of mouse or human origin promoted tumor growth in xenograft models. Moreover, tumor organoids conferred resistance to clinically used anticancer drugs including sorafenib, regorafenib, and 5-fluorouracil in the presence of CAFs, or the conditioned medium of CAFs. CONCLUSIONS: We successfully established murine and human 3D co-culture models and have shown robust effects of CAFs in liver cancer nurturing and treatment resistance.

The biological process of lysine-tRNA charging is therapeutically targetable in liver cancer.

BACKGROUND & AIMS: Mature transfer RNAs (tRNA) charged with amino acids decode mRNA to synthesize proteins. Dysregulation of translational machineries has a fundamental impact on cancer biology. This study aims to map the tRNAome landscape in liver cancer patients and to explore potential therapeutic targets at the interface of charging amino acid with tRNA. METHODS: Resected tumour and paired tumour-free (TFL) tissues from hepatocellular carcinoma (HCC) patients (n = 69), and healthy liver tissues from organ transplant donors (n = 21), HCC cell lines, and cholangiocarcinoma (CC) patient-derived tumour organoids were used. RESULTS: The expression levels of different mature tRNAs were highly correlated and closely clustered within individual tissues, suggesting that different members of the tRNAome function cooperatively in protein translation. Interestingly, high expression of tRNA-Lys-CUU in HCC tumours was associated with more tumour recurrence (HR 1.1; P = .022) and worse patient survival (HR 1.1; P = .0037). The expression of Lysyl-tRNA Synthetase (KARS), the enzyme catalysing the charge of lysine to tRNA-Lys-CUU, was significantly upregulated in HCC tumour tissues compared to tumour-free liver tissues. In HCC cell lines, lysine deprivation, KARS knockdown or treatment with the KARS inhibitor cladosporin effectively inhibited overall cell growth, single cell-based colony formation and cell migration. This was mechanistically mediated by cell cycling arrest and induction of apoptosis. Finally, these inhibitory effects were confirmed in 3D cultured patient-derived CC organoids. CONCLUSIONS: The biological process of charging tRNA-Lys-CUU with lysine sustains liver cancer cell growth and migration, and is clinically relevant in HCC patients. This process can be therapeutically targeted and represents an unexplored territory for developing novel treatment strategies against liver cancer.

Differentially Methylated Regions in Desmoid-Type Fibromatosis: A Comparison Between CTNNB1 S45F and T41A Tumors.

INTRODUCTION: The majority of desmoid-type fibromatosis (DTF) tumors harbor a ß-catenin mutation, affecting specific codons in CTNNB1 exon 3. S45F tumors are reported to have a higher chance of recurrence after surgery and more resistance to systemic treatments compared to wild-type (WT) and T41A tumors. The aim of this pilot study was to examine the genome-wide DNA methylation profiles of S45F and T41A mutated DTF, to explain the observed differences in clinical behavior between these DTF subtypes. MATERIAL AND METHODS: Genome-wide analysis of DNA methylation was performed using MeD-seq on formalin-fixed, paraffin-embedded primary DTF samples harboring a S45F (n = 14) or a T41A (n = 15) mutation. Differentially methylated regions (DMRs) between S45F and T41A DTF were identified and used for a supervised hierarchical cluster analysis. DMRs with a fold-change ≥1.5 were considered to be differentially methylated and differences between S45F and T41A tumors were quantitatively assessed. The effect of DMRs on the expression of associated genes was assessed using an independent mRNA expression dataset. Protein-protein interactions between WT ß-catenin and mutant variants and DNA methyltransferase 1 (DNMT1) were examined by immunoprecipitation experiments. RESULTS: MeD-seq analyses indicated 354 regions that displayed differential methylation. Cluster analysis yielded no distinct clusters based on mutation, sex, tumor site or tumor size. A supervised clustering based on DMRs between small (≤34 mm) and large (>87 mm) DTF distinguished the two groups. Only ten DMRs displayed a fold change of ≥1.5 and six of them were found associated with the following genes: NLRP4, FOXK2, PERM1, CCDC6, NOC4L, and DUX4L6. The effects of DMRs on gene expression yielded a significant difference (p < 0.05) in the expression between S45F and T41A for CCDC6 and FOXK2 but not for all Affymetrix probe-sets used to detect these genes. Immunoprecipitations did not reveal an association of WT ß-catenin or mutant variants with DNMT1. CONCLUSION: This study demonstrated that S45F and T41A DTF tumors did not exhibit gross differences in DNA methylation patterns. This implies that distinct DNA methylation profiles are not the sole determinant for the divergent clinical behavior of these different DTF mutant subtypes.

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/ß-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/ß-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.

Smooth-muscle-derived WNT5A augments allergen-induced airway remodelling and Th2 type inflammation.

Asthma is a heterogeneous disease characterized by chronic inflammation and structural changes in the airways. The airway smooth muscle (ASM) is responsible for airway narrowing and an important source of inflammatory mediators. We and others have previously shown that WNT5A mRNA and protein expression is higher in the ASM of asthmatics compared to healthy controls. Here, we aimed to characterize the functional role of (smooth muscle-derived) WNT5A in asthma. We generated a tet-ON smooth-muscle-specific WNT5A transgenic mouse model, enabling in vivo characterization of smooth-muscle-derived WNT5A in response to ovalbumin. Smooth muscle specific WNT5A overexpression showed a clear trend towards enhanced actin (α-SMA) expression in the ASM in ovalbumin challenged animals, but had no effect on collagen content. WNT5A overexpression in ASM also significantly enhanced the production of the Th2-cytokines IL4 and IL5 in lung tissue after ovalbumin exposure. In line with this, WNT5A increased mucus production, and enhanced eosinophilic infiltration and serum IgE production in ovalbumin-treated animals. In addition, CD4+ T cells of asthma patients and healthy controls were stimulated with WNT5A and changes in gene transcription assessed by RNA-seq. WNT5A promoted expression of 234 genes in human CD4+ T cells, among which the Th2 cytokine IL31 was among the top 5 upregulated genes. IL31 was also upregulated in response to smooth muscle-specific WNT5A overexpression in the mouse. In conclusion, smooth-muscle derived WNT5A augments Th2 type inflammation and remodelling. Our findings imply a pro-inflammatory role for smooth muscle-derived WNT5A in asthma, resulting in increased airway wall inflammation and remodelling.

LGR5 marks targetable tumor-initiating cells in mouse liver cancer.

Cancer stem cells (CSCs) or tumor-initiating cells (TICs) are thought to be the main drivers for disease progression and treatment resistance across various cancer types. Identifying and targeting these rare cancer cells, however, remains challenging with respect to therapeutic benefit. Here, we report the enrichment of LGR5 expressing cells, a well-recognized stem cell marker, in mouse liver tumors, and the upregulation of LGR5 expression in human hepatocellular carcinoma. Isolated LGR5 expressing cells from mouse liver tumors are superior in initiating organoids and forming tumors upon engraftment, featuring candidate TICs. These cells are resistant to conventional treatment including sorafenib and 5-FU. Importantly, LGR5 lineage ablation significantly inhibits organoid initiation and tumor growth. The combination of LGR5 ablation with 5-FU, but not sorafenib, further augments the therapeutic efficacy in vivo. Thus, we have identified the LGR5+ compartment as an important TIC population, representing a viable therapeutic target for combating liver cancer.

Commonly observed RNF43 mutations retain functionality in attenuating Wnt/ß-catenin signaling and unlikely confer Wnt-dependency onto colorectal cancers.

Cancer-associated RNF43 mutations lead to activation of ß-catenin signaling through aberrantly increasing Wnt-receptor levels at the membrane. Importantly, inactivating RNF43 mutations have been suggested to render cancer cells sensitive to Wnt-based therapeutics. However, the extent to which RNF43 mutations lead to impaired regulation of Wnt/ß-catenin signaling has been poorly investigated. Here, we observed that tumors with a functional mismatch repair system show a predominant 5'-location of truncating RNF43 mutations, suggesting C-terminal truncations such as the most commonly reported p.G659fs mutation, do not affect ß-catenin signaling. In accordance, expressing C-terminal truncation mutants and wild-type RNF43, showed equal effects on ß-catenin signaling, Wnt-receptor turnover, and DVL-binding. We confirmed these observations at endogenous levels by CRISPR-Cas9-mediated knockout of G659fs RNF43 expression in KM12 cells and generating comparable mutations in HEK293T cells. We could not confirm previous reports linking RNF43 to p53 and E-cadherin breakdown. Our data also suggest that only colorectal cancer cells harboring N-terminal mutations of RNF43 convey Wnt-dependency onto the tumor cells. Results of this study have potentially important clinical implications indicating that Wnt-based therapeutics should be applied cautiously in cancer patients harboring RNF43 mutations.

Oncogenic Mutations in Armadillo Repeats 5 and 6 of ß-Catenin Reduce Binding to APC, Increasing Signaling and Transcription of Target Genes.

BACKGROUND & AIMS: The ß-catenin signaling pathway is one of the most commonly deregulated pathways in cancer cells. Amino acid substitutions within armadillo repeats 5 and 6 (K335, W383, and N387) of ß-catenin are found in several tumor types, including liver tumors. We investigated the mechanisms by which these substitutions increase signaling and the effects on liver carcinogenesis in mice. METHODS: Plasmids encoding tagged full-length ß-catenin (CTNNB1) or ß-catenin with the K335I or N387K substitutions, along with MET, were injected into tails of FVB/N mice. Tumor growth was monitored, and livers were collected and analyzed by histology, immunohistochemistry, and quantitative reverse-transcription polymerase chain reaction. Tagged full-length and mutant forms of ß-catenin were expressed in HEK293, HCT116, and SNU449 cells, which were analyzed by immunoblots and immunoprecipitation. A panel of ß-catenin variants and cell lines with knock-in mutations were analyzed for differences in N-terminal phosphorylation, half-life, and association with other proteins in the signaling pathway. RESULTS: Mice injected with plasmids encoding K335I or N387K ß-catenin and MET developed larger, more advanced tumors than mice injected with plasmids encoding WT ß-catenin and MET. K335I and N387K ß-catenin bound APC with lower affinity than WT ß-catenin but still interacted with scaffold protein AXIN1 and in the nucleus with TCF7L2. This interaction resulted in increased transcription of genes regulated by ß-catenin. Studies of protein structures supported the observed changes in relative binding affinities. CONCLUSION: Expression of ß-catenin with mutations in armadillo repeats 5 and 6, along with MET, promotes formation of liver tumors in mice. In contrast to N-terminal mutations in ß-catenin that directly impair its phosphorylation by GSK3 or binding to BTRC, the K335I or N387K substitutions increase signaling via reduced binding to APC. However, these mutant forms of ß-catenin still interact with the TCF family of transcription factors in the nucleus. These findings show how these amino acid substitutions increase ß-catenin signaling in cancer cells.

Wnt/ß-Catenin Signaling in Liver Cancers.

Liver cancer is among the leading global healthcare issues associated with high morbidity and mortality. Liver cancer consists of hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), hepatoblastoma (HB), and several other rare tumors. Progression has been witnessed in understanding the interactions between etiological as well as environmental factors and the host in the development of liver cancers. However, the pathogenesis remains poorly understood, hampering the design of rational strategies aiding in preventing liver cancers. Accumulating evidence demonstrates that aberrant activation of the Wnt/ß-catenin signaling pathway plays an important role in the initiation and progression of HCC, CCA, and HB. Targeting Wnt/ß-catenin signaling potentiates a novel avenue for liver cancer treatment, which may benefit from the development of numerous small-molecule inhibitors and biologic agents in this field. In this review, we discuss the interaction between various etiological factors and components of Wnt/ß-catenin signaling early in the precancerous lesion and the acquired mechanisms to further enhance Wnt/ß-catenin signaling to promote robust cancer formation at later stages. Additionally, we shed light on current relevant inhibitors tested in liver cancers and provide future perspectives for preclinical and clinical liver cancer studies.

Bacterial biofilms as a potential contributor to mucinous colorectal cancer formation.

A prominent mucinous phenotype is observed in 10-15% of all colorectal cancers (CRCs). They are associated with a proximal location, and more commonly observed among tumors with mismatch repair defects and a promoter CpG methylator phenotype. However, none of these features has been clearly linked mechanistically to this mucinous subtype. Here, we propose that bacterial biofilms could represent a currently unappreciated contributor to mucinous CRC formation. The colonic microbiome and biofilms in particular, are emerging as important factors in tumor initiation and progression. Intriguingly, biofilms preferentially accompany proximal tumors, suggesting that there may be a direct mechanistic link with mucinous CRCs.

Activated Signaling Pathways and Targeted Therapies in Desmoid-Type Fibromatosis: A Literature Review.

Desmoid-type fibromatosis (DTF) is a rare, soft tissue tumor of mesenchymal origin which is characterized by local infiltrative growth behavior. Besides "wait and see," surgery and radiotherapy, several systemic treatments are available for symptomatic patients. Recently, targeted therapies are being explored in DTF. Unfortunately, effective treatment is still hampered by the limited knowledge of the molecular mechanisms that prompt DTF tumorigenesis. Many studies focus on Wnt/ß-catenin signaling, since the vast majority of DTF tumors harbor a mutation in the CTNNB1 gene or the APC gene. The established role of the Wnt/ß-catenin pathway in DTF forms an attractive therapeutic target, however, drugs targeting this pathway are still in an experimental stage and not yet available in the clinic. Only few studies address other signaling pathways which can drive uncontrolled growth in DTF such as: JAK/STAT, Notch, PI3 kinase/AKT, mTOR, Hedgehog, and the estrogen growth regulatory pathways. Evidence for involvement of these pathways in DTF tumorigenesis is limited and predominantly based on the expression levels of key pathway genes, or on observed clinical responses after targeted treatment. No clear driver role for these pathways in DTF has been identified, and a rationale for clinical studies is often lacking. In this review, we highlight common signaling pathways active in DTF and provide an up-to-date overview of their therapeutic potential.

HOXA9 mediates and marks premalignant compartment size expansion in colonic adenomas.

The transformation of normal colonic epithelium to colorectal cancer (CRC) involves a relatively ordered progression, and understanding the molecular alterations involved may aid rational design of strategies aimed at preventing or counteracting disease. Homeobox A9 (HOXA9) is an oncogene in leukemia and has been implicated in CRC pathology, although its role in disease etiology remains obscure at best. We observe that HOXA9 expression is increased in colonic adenomas compared with location-matched healthy colon epithelium. Its forced expression results in dramatic genetic and signaling changes, with increased expression of growth factors IGF1 and FLT3, super-activity of the AKT survival pathway and a concomitant increase in compartment size. Furthermore, a reduced mRNA expression of the epithelial to mesenchymal transition marker N-cadherin as well as reduced activity of the actin cytoskeletal mediator PAK was seen, which is in apparent agreement with an observed reduced migratory response in HOXA9-overexpressing cells. Thus, HOXA9 appears closely linked with adenoma growth while impairing migration and metastasis and hence is both a marker and driver of premalignant polyp growth. Colonic polyps grow but remain premalignant for up to decades. Here, we show that HOXA9 drives growth in premalignant polyps, but simultaneously prevents further transformation.