mTORC1 Inactivation Promotes Colitis-Induced Colorectal Cancer but Protects from APC Loss-Dependent Tumorigenesis

Targeting Grancalcin Accelerates Wound Healing by Improving Angiogenesis in Diabetes

Chronic diabetic wounds are a serious complication of diabetes and often result in limb amputations and confer high mortality rates. The proinflammatory secretome in the wound perpetuates defective neovascularization and contributes to dysregulated tissue repair. This study aims to design a gelatin methacrylamide (GelMA) hydrogel to sustained the release of grancalcin-neutralizing antibody (GCA-NAb) and evaluate it as a potential scaffold to promote diabetic wound healing. Results show that the expression of grancalcin(GCA), a protein secreted by bone marrow-derived immune cells, is elevated in the wound sites of individuals and animals with diabetic ulcers. Genetic inhibition of grancalcin expression accelerates vascularization and healing in an animal model. Mechanistic studies show that grancalcin binds to transient receptor potential melastatin 8(TRPM8) and partially inactivates its downstream signaling pathways, thereby impairing angiogenesis in vitro and ex vivo. Systemic or topical administration of a GCA-NAb accelerate wound repair in mice with diabetes. The data suggest that GCA is a potential therapeutic target for the treatment of diabetic ulcers.

mTORC2-AKT signaling to PFKFB2 activates glycolysis that enhances stemness and tumorigenicity of intestinal epithelial cells

Although elevated glycolysis has been widely recognized as a hallmark for highly proliferating cells like stem cells and cancer, its regulatory mechanisms are still being updated. Here, we found a previously unappreciated mechanism of mammalian target of rapamycin complex 2 (mTORC2) in regulating glycolysis in intestinal stem cell maintenance and cancer progression. mTORC2 key subunits expression levels and its kinase activity were specifically upregulated in intestinal stem cells, mouse intestinal tumors, and human colorectal cancer (CRC) tissues. Genetic ablation of its key scaffolding protein Rictor in both mouse models and cell lines revealed that mTORC2 played an important role in promoting intestinal stem cell proliferation and self-renewal. Moreover, utilizing mouse models and organoid culture, mTORC2 loss of function was shown to impair growth of gut adenoma and tumor organoids. Based on these findings, we performed RNA-seq and noticed significant metabolic reprogramming in Rictor conditional knockout mice. Among all the pathways, carbohydrate metabolism was most profoundly altered, and further studies demonstrated that mTORC2 promoted glycolysis in intestinal epithelial cells. Most importantly, we showed that a rate-limiting enzyme in regulating glycolysis, 6-phosphofructo-2-kinase (PFKFB2), was a direct target for the mTORC2-AKT signaling. PFKFB2 was phosphorylated upon mTORC2 activation, but not mTORC1, and this process was AKT-dependent. Together, this study has identified a novel mechanism underlying mTORC2 activated glycolysis, offering potential therapeutic targets for treating CRC.

TRAF4-Mediated LAMTOR1 Ubiquitination Promotes mTORC1 Activation and Inhibits the Inflammation-Induced Colorectal Cancer Progression

Mechanistic target of rapamycin complex 1 (mTORC1) is a conserved serine/threonine kinase that integrates various environmental signals to regulate cell growth and metabolism. mTORC1 activation requires tethering to lysosomes by the Ragulator-Rag complex. However, the dynamic regulation of the interaction between Ragulator and Rag guanosine triphosphatase (GTPase) remains unclear. In this study, that LAMTOR1, an essential component of Ragulator, is dynamically ubiquitinated depending on amino acid abundance is reported. It is found that the E3 ligase TRAF4 directly interacts with LAMTOR1 and catalyzes the K63-linked polyubiquitination of LAMTOR1 at K151. Ubiquitination of LAMTOR1 by TRAF4 promoted its binding to Rag GTPases and enhanced mTORC1 activation, K151R knock-in or TRAF4 knock-out blocks amino acid-induced mTORC1 activation and accelerates the development of inflammation-induced colon cancer. This study revealed that TRAF4-mediated LAMTOR1 ubiquitination is a regulatory mechanism for mTORC1 activation and provides a therapeutic target for diseases involving mTORC1 dysregulation.

Deficiency of BCAT2-mediated branched-chain amino acid catabolism promotes colorectal cancer development

OBJECTIVE

Branched-chain amino acid (BCAA) metabolism is involved in the development of colorectal cancer (CRC); however, the underlying mechanism remains unclear. Therefore, this study investigates the role of BCAA metabolism in CRC progression.

METHODS

Dietary BCAA was administered to both azoxymethane-induced and azoxymethane/dextran sodium sulfate-induced CRC mouse models. The expression of genes related to BCAA metabolism was determined using RNA sequencing. Adjacent tissue samples, obtained from 58 patients with CRC, were subjected to quantitative real-time PCR and immunohistochemical analysis. Moreover, the suppressive role of branched-chain aminotransferase 2 (BCAT2) in cell proliferation, apoptosis, and xenograft mouse models was investigated. Alterations in BCAAs and activation of downstream pathways were also assessed using metabolic analysis and western blotting.

RESULTS

High levels of dietary BCAA intake promoted CRC tumorigenesis in chemical-induced CRC and xenograft mouse models. Both the mRNA and protein levels of BCAT2 were decreased in tumor tissues of patients with CRC compared to those in normal tissues. Proliferation assays and xenograft models confirmed the suppressive role of BCAT2 in CRC progression. Furthermore, the accumulation of BCAAs caused by BCAT2 deficiency facilitated the chronic activation of mTORC1, thereby mediating the oncogenic effect of BCAAs.

CONCLUSION

BCAT2 deficiency promotes CRC progression through inhibition of BCAAs metabolism and chronic activation of mTORC1.

Traces of Canine Inflammatory Bowel Disease Reflected by Intestinal Organoids

Inflammatory bowel disease (IBD) is a chronic inflammatory condition that affects humans and several domestic animal species, including cats and dogs. In this study, we have analyzed duodenal organoids derived from canine IBD patients using quantitative proteomics. Our objective was to investigate whether these organoids show phenotypic traits of the disease compared with control organoids obtained from healthy donors. To this aim, IBD and control organoids were subjected to quantitative proteomics analysis via liquid chromatography-mass spectrometry. The obtained data revealed notable differences between the two groups. The IBD organoids exhibited several alterations at the levels of multiple proteins that are consistent with some known IBD alterations. The observed phenotype in the IBD organoids to some degree mirrors the corresponding intestinal condition, rendering them a compelling approach for investigating the disease and advancing drug exploration. Additionally, our study revealed similarities to some human IBD biomarkers, further emphasizing the translational and comparative value of dogs for future investigations related to the causes and treatment of IBD. Relevant proteins such as CALU, FLNA, MSN and HMGA2, which are related to intestinal diseases, were all upregulated in the IBD duodenal organoids. At the same time, other proteins such as intestinal keratins and the mucosal immunity PIGR were depleted in these IBD organoids. Based on these findings, we propose that these organoids could serve as a valuable tool for evaluating the efficacy of therapeutic interventions against canine IBD.

When You Come to a Fork in the Road, Take It: Wnt Signaling Activates Multiple Pathways through the APC/Axin/GSK-3 Complex

The Wnt signaling pathway is a highly conserved regulator of metazoan development and stem cell maintenance. Activation of Wnt signaling is an early step in diverse malignancies. Work over the past four decades has defined a "canonical" Wnt pathway that is initiated by Wnt proteins, secreted glycoproteins that bind to a surface receptor complex and activate intracellular signal transduction by inhibiting a catalytic complex composed of the classical tumor suppressor Adenomatous Polyposis Coli (APC), Axin, and Glycogen Synthase Kinase-3 (GSK-3). The best characterized effector of this complex is β-catenin, which is stabilized by inhibition of GSK-3, allowing β-catenin entrance to the nucleus and activation of Wnt target gene transcription, leading to multiple cancers when inappropriately activated. However, canonical Wnt signaling through the APC/Axin/GSK-3 complex impinges on other effectors, independently of β-catenin, including the mechanistic Target of Rapamycin (mTOR), regulators of protein stability, mitotic spindle orientation, and Hippo signaling. This review focuses on these alternative effectors of the canonical Wnt pathway and how they may contribute to cancers.

The molecular characteristics and functional roles of microspherule protein 1 (MCRS1) in gene expression, cell proliferation, and organismic development

Accurate spatial and temporal regulation of cell cycle progression is essential for cell proliferation and organismic development. This review demonstrates the role of microspherule protein 58kD, commonly known as MCRS1, as a key cell cycle regulator of higher eukaryotic organisms. We discuss the isoforms and functional domains of MCRS1 as well as their subcellular localization at specific stages of the cell cycle. These molecular characteristics reveal MCRS1's dynamic regulatory role in gene expression, genome stability, cell proliferation, and organismic development. Furthermore, we discuss the molecular details of its seemingly opposite, tumor-suppressive or tumor-promoting, role in different types of cancer.

Is liver regeneration key in hepatocellular carcinoma development?

The liver is the largest organ of the mammalian body and has the remarkable ability to fully regenerate in order to maintain tissue homeostasis. The adult liver consists of hexagonal lobules, each with a central vein surrounded by six portal triads localized in the lobule border containing distinct parenchymal and nonparenchymal cells. Because the liver is continuously exposed to diverse stress signals, several sophisticated regenerative processes exist to restore its functional status following impairment. However, these stress signals can affect the liver's capacity to regenerate and may lead to the development of hepatocellular carcinoma (HCC), one of the most aggressive liver cancers. Here, we review the mechanisms of hepatic regeneration and their potential to influence HCC development.

Transit-amplifying cells control R-spondins in the mouse crypt to modulate intestinal stem cell proliferation

Intestinal epithelium regenerates rapidly through proliferation of intestinal stem cells (ISCs), orchestrated by potent mitogens secreted within the crypt niche. However, mechanisms regulating these mitogenic factors remain largely unknown. Here, we demonstrate that transit-amplifying (TA) cells, marked by unconventional prefoldin RPB5 interactor (URI), control R-spondin production to guide ISC proliferation. Genetic intestinal URI ablation in mice injures TA cells, reducing their survival capacity, leading to an inflamed tissue and subsequently decreasing R-spondin levels, thereby causing ISC quiescence and disruption of intestinal structure. R-spondin supplementation or restoration of R-spondin levels via cell death inhibition by c-MYC elimination or the suppression of inflammation reinstates ISC proliferation in URI-depleted mice. However, selective c-MYC and p53 suppression are required to fully restore TA cell survival and differentiation capacity and preserve complete intestinal architecture. Our data reveal an unexpected role of TA cells, which represent a signaling platform instrumental for controlling inflammatory cues and R-spondin production, essential for maintaining ISC proliferation and tissue regeneration.

Dysregulation of miR-1-3p: An Early Event in Colitis-Associated Dysplasia

Detection of colorectal dysplasia during surveillance colonoscopy remains the best method of determining risk for colitis-associated colorectal cancer (CAC). miRNAs (miRs) show great promise as tissue-specific biomarkers of neoplasia. The goal of this study was to explore the miR expression profile of precancerous dysplastic lesions in the AOM/DSS mouse model and identify early molecular changes associated with CAC. Epithelial cells were laser-microdissected from the colonic mucosa (inflamed versus dysplastic) of mice with AOM/DSS-induced colitis. A miR signature that can distinguish inflamed non-neoplastic mucosa from dysplasia was identified. Bioinformatic analyses led to the discovery of associated miR gene targets and enriched pathways and supported the construction of a network interaction map. miR-1a-3p was one of the miRs with the highest number of predicted targets, including Cdk6. Interestingly, miR-1a-3p and Cdk6 were down- and up-regulated in dysplastic lesions, respectively. Transfection of HCT116 and RKO cells with miR-1a-3p mimics induced apoptosis and cell cycle arrest in G1, suggesting its biological function. A slight reduction in the level of CDK6 transcripts was also observed in cells transfected with miR-1. These data provide novel insight into the early molecular alterations that accompany the development of CAC and identify a miR signature that represents a promising biomarker for the early detection of colitis-associated dysplasia.

Metalloprotease ADAM9 cleaves ephrin-B ligands and differentially regulates Wnt and mTOR signaling downstream of Akt kinase in colorectal cancer cells

Ephrin-B signaling has been implicated in many normal and pathological processes, including neural crest development and tumor metastasis. We showed previously that proteolysis of ephrin-B ligands by the disintegrin metalloprotease ADAM13 is necessary for canonical Wnt signal activation and neural crest induction in Xenopus, but it was unclear if these mechanisms are conserved in mammals. Here, we report that mammalian ADAM9 cleaves ephrin-B1 and ephrin-B2 and can substitute for Xenopus ADAM13 to induce the neural crest. We found that ADAM9 expression is elevated in human colorectal cancer (CRC) tissues and that knockdown (KD) of ADAM9 inhibits the migration and invasion of SW620 and HCT116 CRC cells by reducing the activity of Akt kinase, which is antagonized by ephrin-Bs. Akt is a signaling node that activates multiple downstream pathways, including the Wnt and mTOR pathways, both of which can promote CRC cell migration/invasion. Surprisingly, we also found that KD of ADAM9 downregulates Wnt signaling but has negligible effects on mTOR signaling in SW620 cells; in contrast, mTOR activity is suppressed while Wnt signaling remains unaffected by ADAM9 KD in HCT116 cells. These results suggest that mammalian ADAM9 cleaves ephrin-Bs to derepress Akt and promote CRC migration and invasion; however, the signaling pathways downstream of Akt are differentially regulated by ADAM9 in different CRC cell lines, reflecting the heterogeneity of CRC cells in responding to manipulations of upstream Akt regulators.

MCRS1 Expression Regulates Tumor Activity and Affects Survival Probability of Patients with Gastric Cancer

Gastric cancer is the fifth most common cancer worldwide and the third most common cause of cancer-related deaths. Surgery remains the first-choice treatment. Chemotherapy is considered in the middle and advanced stages, but has limited success. Microspherule protein 1 (MCRS1, also known as MSP58) is a protein originally identified in the nucleus and cytoplasm that is involved in the cell cycle. High expression of MCRS1 increases tumor growth, invasiveness, and metastasis. The mechanistic relationships between MCSR1 and proliferation, apoptosis, angiogenesis, and epithelial–mesenchymal transition (EMT) remain to be elucidated. We clarified these relationships using immunostaining of tumor tissues and normal tissues from patients with gastric cancer. High MCRS1 expression in gastric cancer positively correlated with Ki-67, Caspase3, CD31, Fibronectin, pAKT, and pAMPK. The hazard ratio of high MCRS1 expression was 2.44 times that of low MCRS1 expression, negatively impacting patient survival.

Lauric acid alleviates deoxynivalenol-induced intestinal stem cell damage by potentiating the Akt/mTORC1/S6K1 signaling axis

Intestinal stem cell (ISC)-driven intestinal homeostasis is subjected to dual regulation by dietary nutrients and toxins. Our study investigated the use of lauric acid (LA) to alleviate deoxynivalenol (DON)-induced intestinal epithelial damage. C57BL/6 mice in the control, LA, DON, and LA + DON groups were orally administered PBS, 10 mg/kg BW LA, 2 mg/kg BW DON, and 10 mg/kg BW LA + 2 mg/kg BW DON for 10 days. The results showed that LA increased the average daily gain and average daily feed intake of the mice exposed to DON. Moreover, the DON-triggered impairment of jejunal morphology and barrier function was significantly improved after LA supplementation. Moreover, LA rescued ISC proliferation, inhibited intestinal cell apoptosis, and promoted ISC differentiation into absorptive cells, goblet cells, and Paneth cells. The jejunum crypt cells from the mice in the LA group expanded into enteroids, resulting in a significantly greater enteroid area than that in the DON group. Furthermore, LA reversed the DON-mediated inhibition of the Akt/mTORC1/S6K1 signaling axis in the jejunum. Our results indicated that LA accelerates ISC regeneration to repair intestinal epithelial damage after DON insult by reactivating the Akt/mTORC1/S6K1 signaling pathway, which provides new implications for the function of LA in ISCs.

Control of the eIF4E activity: structural insights and pharmacological implications

The central role of eukaryotic translation initiation factor 4E (eIF4E) in controlling mRNA translation has been clearly assessed in the last decades. eIF4E function is essential for numerous physiological processes, such as protein synthesis, cellular growth and differentiation; dysregulation of its activity has been linked to ageing, cancer onset and progression and neurodevelopmental disorders, such as autism spectrum disorder (ASD) and Fragile X Syndrome (FXS). The interaction between eIF4E and the eukaryotic initiation factor 4G (eIF4G) is crucial for the assembly of the translational machinery, the initial step of mRNA translation. A well-characterized group of proteins, named 4E-binding proteins (4E-BPs), inhibits the eIF4E–eIF4G interaction by competing for the same binding site on the eIF4E surface. 4E-BPs and eIF4G share a single canonical motif for the interaction with a conserved hydrophobic patch of eIF4E. However, a second non-canonical and not conserved binding motif was recently detected for eIF4G and several 4E-BPs. Here, we review the structural features of the interaction between eIF4E and its molecular partners eIF4G and 4E-BPs, focusing on the implications of the recent structural and biochemical evidence for the development of new therapeutic strategies. The design of novel eIF4E-targeting molecules that inhibit translation might provide new avenues for the treatment of several conditions.

The HSP90/R2TP assembly chaperone promotes cell proliferation in the intestinal epithelium

The R2TP chaperone cooperates with HSP90 to integrate newly synthesized proteins into multi-subunit complexes, yet its role in tissue homeostasis is unknown. Here, we generated conditional, inducible knock-out mice for Rpap3 to inactivate this core component of R2TP in the intestinal epithelium. In adult mice, Rpap3 invalidation caused destruction of the small intestinal epithelium and death within 10 days. Levels of R2TP substrates decreased, with strong effects on mTOR, ATM and ATR. Proliferative stem cells and progenitors deficient for Rpap3 failed to import RNA polymerase II into the nucleus and they induced p53, cell cycle arrest and apoptosis. Post-mitotic, differentiated cells did not display these alterations, suggesting that R2TP clients are preferentially built in actively proliferating cells. In addition, high RPAP3 levels in colorectal tumors from patients correlate with bad prognosis. Here, we show that, in the intestine, the R2TP chaperone plays essential roles in normal and tumoral proliferation.

Detection of chromosome instability by interphase FISH in mouse and human tissues

Chromosomal instability (CIN), a type of genomic instability, favors changes in chromosome number and structure and it is associated with the progression and initiation of multiple diseases, including cancer. Therefore, CIN identification and analysis represents a useful tool for cancer diagnosis and treatment. Here, we report an optimized molecular cytogenetic protocol to detect CIN in formalin-fixed, paraffin-embedded mouse and human tissues, using fluorescent in situ hybridization to visualize and quantify chromosomal alterations such as amplifications, deletions, and translocations.

For complete information on the generation and use of this protocol, please refer to Brandt et al. (2018).

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A protocol for single-cell CIN analysis in paraffin-embedded tissues

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Design of FISH probes for CIN detection

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Identification, visualization, and quantification of CIN by FISH

When dormancy fuels tumour relapse

Tumour recurrence is a serious impediment to cancer treatment, but the mechanisms involved are poorly understood. The most frequently used anti-tumour therapies-chemotherapy and radiotherapy-target highly proliferative cancer cells. However non- or slow-proliferative dormant cancer cells can persist after treatment, eventually causing tumour relapse. Whereas the reversible growth arrest mechanism allows quiescent cells to re-enter the cell cycle, senescent cells are largely thought to be irreversibly arrested, and may instead contribute to tumour growth and relapse through paracrine signalling mechanisms. Thus, due to the differences in their growth arrest mechanism, metabolic features, plasticity and adaptation to their respective tumour microenvironment, dormant-senescent and -quiescent cancer cells could have different but complementary roles in fuelling tumour growth. In this review article, we discuss the implication of dormant cancer cells in tumour relapse and the need to understand how quiescent and senescent cells, respectively, may play a part in this process.

Inhibition of the IL-17A axis in adipocytes suppresses diet-induced obesity and metabolic disorders in mice

Overnutrition causes obesity, a global health problem without any effective therapy. Obesity is characterized by low-grade inflammation, which predisposes individuals to metabolic syndrome via unknown mechanisms. Here, we demonstrate that abolishing the interleukin-17A (IL-17A) axis in mice by inhibition of RORγt-mediated IL-17A production by digoxin, or by ubiquitous deletion of IL-17 receptor A (Il17ra), suppresses diet-induced obesity (DIO) and metabolic disorders, and promotes adipose-tissue browning, thermogenesis and energy expenditure. Genetic ablation of Il17ra specifically in adipocytes is sufficient to completely prevent DIO and metabolic dysfunction in mice. IL-17A produced in response to DIO induces PPARγ phosphorylation at Ser273 in adipocytes in a CDK5-dependent manner, thereby modifying expression of diabetogenic and obesity genes, which correlates with IL-17A signalling in white adipose tissues of individuals with morbid obesity. These findings reveal an unanticipated role for IL-17A in adipocyte biology, in which its direct action pathogenically reprograms adipocytes, promoting DIO and metabolic syndrome. Targeting the IL-17A axis could be an efficient antiobesity strategy.

Role of adenomatous polyposis coli in proliferation and differentiation of colon epithelial cells in organoid culture

Adenomatous polyposis coli (APC) is a tumor-suppressing protein whose inactivation triggers the formation of colorectal polyps. Numerous studies using cell lines or genetically engineered mice have revealed its role in suppressing Wnt/β-catenin signaling pathway and regulating cell proliferation and differentiation. Here, we performed genetic analyses of APC using a three-dimensional organoid culture of mouse colon epithelia, which enables the detailed examination of epithelial properties. Analyses of Apc-knockout colon organoids not only confirmed the importance of APC in suppressing Wnt/β-catenin signaling and regulating cell differentiation, but also revealed several novel features: a significant decrease in proliferating speed and an increase in cross-sectional area of cells. Moreover, we found a significant number of lysozyme-positive Paneth-like cells, which were never observed in wild-type colon tissues or organoids, but have been reported to emerge in colon cancers. Therefore, APC autonomously suppresses ectopic differentiation into lysozyme-positive cells, specifically in the colon epithelia. Colon organoids would be an ideal material to investigate the molecular mechanism and biological importance of the ectopic differentiation associated with cancer development.

Controversies around the function of LARP1

The RNA-binding protein LARP1 has generated interest in recent years for its role in the mTOR signalling cascade and its regulation of terminal oligopyrimidine (TOP) mRNA translation. Paradoxically, some scientists have shown that LARP1 represses TOP translation while others that LARP1 activates it. Here, we present opinions from four leading scientists in the field to discuss these and other contradictory findings.

Metabolic and immunologic control of intestinal cell function by mTOR

The intestinal epithelium is one of the most quickly dividing tissues in our body, combining the absorptive advantages of a single layer with the protection of a constantly renewing barrier. It is continuously exposed to nutrients and commensal bacteria as well as microbial and host-derived metabolites, but also to hazards such as pathogenic bacteria and toxins. These environmental cues are sensed by the mucosa and a vast repertory of immune cells, especially macrophages. A disruption of intestinal homeostasis in terms of barrier interruption can lead to inflammatory bowel diseases and colorectal cancer, and macrophages have an important role in restoring epithelial function following injury. The mammalian/mechanistic target of rapamycin (mTOR) signalling pathway senses environmental cues and integrates metabolic responses. It has emerged as an important regulator of intestinal functions in homeostasis and disease. In this review, we are going to discuss intestinal mTOR signalling and metabolic regulation in different intestinal cell populations with a special focus on immune cells and their actions on intestinal function.

Berberine Administration in Treatment of Colitis: A Review

Berberine (Brb) is one of the well-known naturally occurring compounds exclusively found in Berberis vulgaris and other members of this family, such as Berberis aristata, Berberis aroatica, and Berberis aquifolium. This plant-derived natural compound has a variety of therapeutic impacts, including anti-oxidant, anti-inflammatory, anti-diabetic, and anti-tumor. Multiple studies have demonstrated that Brb has great anti-inflammatory activity and is capable of reducing the levels of proinflammatory cytokines, while it enhances the concentrations of anti-inflammatory cytokines, making it suitable for the treatment of inflammatory disorders. Colitis is an inflammatory bowel disease with chronic nature. Several factors are involved in the development of colitis and it appears that inflammation and oxidative stress are the most important ones. With respect to the anti-inflammatory and antioxidant effects of Brb, its administration seems to be beneficial in the treatment of colitis. In the present review, the protective effects of Brb in colitis treatment and its impact on molecular pathways are discussed.

Emerging roles for HMGA2 in colorectal cancer

HMGA2 (High Mobility Group AT-hook 2) has been reported to promote colorectal cancer (CRC) development by regulating the transcription of target genes. It participates in nearly all aspects of cellular processes, including cell transformation, proliferation, apoptosis, senescence, metastasis, epithelial-to-mesenchymal transition (EMT), DNA repair and stem cell self-renewal. In the past decades, a group of downstream targets and binding partners have been identified in a wide range of cancers. Our findings of HMGA2 as a key factor in the MDM2/p53, IL11/STAT3 and Wnt/β-catenin signaling pathways prompt us to summarize current advances in the functional and molecular basis of HMGA2 in CRC. In this review, we address the roles of HMGA2 in the oncogenic networks of CRC based on recent advances. We review its aberrant expression, explore underlying mechanisms, discuss its pro-tumorigenic effects, and highlight promising small-molecule inhibitors based on targeting HMGA2 here. However, the understanding of HMGA2 in CRC progression is still elusive, thus we also discuss the future perspectives in this review. Collectively, this review provides novel insights into the oncogenic properties of HMGA2, which has potential implications in the diagnosis and treatment of CRC.

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HMGA2 promotes colorectal cancer (CRC) development by regulating the transcriptions of target genes.

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Circulating cell-free HMGA2 mRNA has been identified as a potential screening marker in CRC.

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HMGA2 appears to be a key factor in the networks of MDM2/p53, IL11/STAT3 and Wnt/β-catenin signaling pathways in CRC.

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Many agents and siRNAs serve as potential therapeutic approaches by targeting HMGA2 for the treatment of CRC.

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Deciphering HMGA2-mediated machinery helps to conceive effective therapy strategies and develop novel inhibitors in CRC.

WHSC1 Promotes Cell Proliferation, Migration, and Invasion in Hepatocellular Carcinoma by Activating mTORC1 Signaling

Background

Wolf-Hirschhorn syndrome candidate gene-1 (WHSC1) plays key regulatory roles in cancer development and progression. However, its specific functions and potential mechanisms of action remain to be described in hepatocellular carcinoma (HCC).

Materials and Methods

WHSC1 expression in HCC was evaluated using The Cancer Genome Atlas and verified in HCC tissues and cell lines using qRT-PCR, Western blotting, and immunohistochemistry. Functional assays were performed to explore the role of WHSC1 in HCC progression. Immunoprecipitation-mass spectrometry, co-immunoprecipitation, immunofluorescence, and immunohistochemistry were conducted to evaluate the interaction between WHSC1 and prolyl 4-hydroxylase subunit beta (P4HB). Pathway enrichment was performed using gene set enrichment analysis.

Results

WHSC1 was markedly overexpressed in HCC tissues and cell lines. The level of expression was strongly associated with adverse clinicopathological characteristics. Survival analyses revealed that WHSC1 upregulation predicted poor overall survival and higher recurrence rates in patients with HCC. Functional studies revealed that WHSC1 significantly stimulated HCC proliferation, migration, and invasion in vitro and in vivo. WHSC1 was shown to interact with P4HB to stimulate P4HB expression and subsequently activate mTOR1 signaling.

Conclusion

We determined the oncogenic role of WHSC1 in HCC, via P4HB interaction, which activates mTOR1 signaling, and identified WHSC1 as a promising therapeutic target for HCC.

Are Wnt/β-Catenin and PI3K/AKT/mTORC1 Distinct Pathways in Colorectal Cancer?

Wnt/β-catenin and phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin complex 1 (PI3K/AKT/mTORC1) pathways both are critically involved in colorectal cancer (CRC) development, although they are implicated in the modulation of distinct oncogenic mechanisms. In homeostatic and pathologic conditions, these pathways show a fine regulation based mainly on feedback mechanisms, and are connected at multiple levels involving both upstream and downstream common effectors. The ability of the Wnt/β-catenin and PI3K/AKT/mTORC1 pathways to reciprocally control themselves represents one of the main resistance mechanisms to selective inhibitors in CRC, leading to the hypothesis that in specific settings, particularly in cancer driven by genetic alterations in Wnt/β-catenin signaling, the relationship between Wnt/β-catenin and PI3K/AKT/mTORC1 pathways could be so close that they should be considered as a unique therapeutic target. This review provides an update on the Wnt/β-catenin and PI3K/AKT/mTORC1 pathway interconnections in CRC, describing the main molecular players and the potential implications of combined inhibitors as an approach for CRC chemoprevention and treatment.

RAPTOR promotes colorectal cancer proliferation by inducing mTORC1 and upregulating ribosome assembly factor URB1

Mammalian target of rapamycin complex 1 (mTORC1) is evolutionally conserved and frequently activated in various tumors, including colorectal cancer (CRC). It has been reported that the ribosome assembly factor Urb1 acts downstream of mTORC1/raptor signaling and contributes to digestive organ development in zebrafish. Previously, we highlighted that URB1 was overexpressed in CRC. Here, we assessed the mTORC1/regulatory associated protein with mTOR (RAPTOR)-URB1 axis in CRC tumorigenesis. We found that RAPTOR was overexpressed in CRC tissues and cell lines, was a favorable predictor in patients with CRC, and positively correlated with URB1. Silencing of RAPTOR suppressed CRC cell proliferation and migration and induced cell cycle arrest and apoptosis in vitro and inhibited xenograft growth in vivo. Moreover, ectopic overexpression of RAPTOR exerted an inverse biological phenotype. Knockdown of RAPTOR quenched mTORC1 activity and reduced the expression of URB1 and cyclinA2 (CCNA2). In contrast, overexpression of RAPTOR activated mTORC1 and upregulated URB1 and CCNA2. Furthermore, URB1 and CCNA2 expression were also impeded by rapamycin, which is a specific inhibitor of mTORC1. Thus, RAPTOR promoted CRC proliferation, migration, and cell cycle progression by inducing mTORC1 signaling and transcriptional activation of both URB1 and CCNA2. Taken together, we concluded that RAPTOR has the potential to serve as a novel biomarker and therapeutic target for CRC.

URI is required to maintain intestinal architecture during ionizing radiation

Ionizing radiation (IR) can cause gastrointestinal syndrome (GIS), a lethal disorder, by means of unknown mechanisms. We show that high-dose irradiation increases unconventional prefoldin RPB5 interactor (URI) levels in mouse intestinal crypt, but organ regeneration correlates with URI reductions. URI overexpression in intestine protects mice from radiation-induced GIS, whereas halving URI expression sensitizes mice to IR. URI specifically inhibits β-catenin in stem cell-like label-retaining (LR) cells, which are essential for organ regeneration after IR. URI reduction activates β-catenin-induced c-MYC expression, causing proliferation of and DNA damage to LR cells, rendering them radiosensitive. Therefore, URI labels LR cells which promote tissue regeneration in response to high-dose irradiation, and c-MYC inhibitors could be countermeasures for humans at risk of developing GIS.

Diet, Microbiota, and Colorectal Cancer

The intestinal epithelium is a very dynamic tissue under a high regenerative pressure, which makes it susceptible to malignant transformation. Proper integration of various cell signaling pathways and a balanced cross talk between different cell types composing the organ are required to maintain intestinal homeostasis. Dysregulation of this balance can lead to colorectal cancer (CRC). Here, we review important insights into molecular and cellular mechanisms of CRC. We discuss how perturbation in complex regulatory networks, including the Wnt, Notch, BMP, and Hedgehog pathways; and how variations in inflammatory signaling, nutrients, and microbiota can affect intestinal homeostasis contributing to the malignant transformation of intestinal cells.

Berberine Protects Mice Against Dextran Sulfate Sodium-Induced Colitis by Activating mTORC1 Pathway

Berberine is a plant alkaloid that can be extracted from many Chinese herbs. It has been reported that berberine could protect mice from ulcerative colitis, but the mechanism remains unclear. The current study’s aim was to determine the potential mechanism by which berberine exhibits its anti-inflammatory function. Mice with colitis induced by dextran sulfate sodium (DSS) were administered with berberine at 50 mg/kg by gavage. Berberine significantly increased the proportion of regulatory T cells (Treg cells). The targeted metabolomics analysis was then performed to find that glutamine and glutamate metabolism played an important role in the process of regulating immune response. mTORC1 pathway was reported to closely relate with glutamine metabolism. As a result, the relative expression levels of downstream effector genes of mTORC were further determined, and data obtained showed that berberine could significantly increase the relative expression levels of S6K1 and 4EBP1. In addition, rapamycin was used to inhibit mTORC1 signaling, and it was found that colon length, disease associated index (DAI), and proportion of Treg cells of mice in the rapamycin-DSS group were not different from those of mice in the rapamycin/berberine-DSS group. Together, these results suggest that berberine exhibits significant protective effects against DSS colitis by activating the mTORC1 pathway to increase the proportion of Treg cells.

Myeloid p38α signaling promotes intestinal IGF-1 production and inflammation-associated tumorigenesis

The protein kinase p38α plays a key role in cell homeostasis, and p38α signaling in intestinal epithelial cells protects against colitis-induced tumorigenesis. However, little is known on the contribution of p38α signaling in intestinal stromal cells. Here, we show that myeloid cell-specific downregulation of p38α protects mice against inflammation-associated colon tumorigenesis. The reduced tumorigenesis correlates with impaired detection in the colon of crucial chemokines for immune cell recruitment. We identify insulin-like growth factor-1 (IGF-1) as a novel mediator of the p38α pathway in macrophages. Moreover, using genetic and pharmacological approaches, we confirm the implication of IGF-1 produced by myeloid cells in colon inflammation and tumorigenesis. We also show a correlation between IGF-1 pathway activation and the infiltration of myeloid cells with active p38α in colon samples from patients with ulcerative colitis or colon cancer. Altogether, our results uncover an important role for myeloid IGF-1 downstream of p38α in colitis-associated tumorigenesis and suggest the interest in evaluating IGF-1 therapies for inflammation-associated intestinal diseases, taking into consideration IGF-1 signaling and immune cell infiltration in patient biopsies.

Regnase-1 controls colon epithelial regeneration via regulation of mTOR and purine metabolism

Idiopathic inflammatory bowel disease (IBD) is associated with the gut microbiota and immune system of the host; however, the precise pathogenesis of IBD is poorly defined. We show that specific deletion of the endoribonuclease Regnase-1 in intestinal epithelial cells relieves the symptoms of experimental colitis during acute inflammation. Regnase-1 deficiency potentiates mTOR signaling and purine metabolism in the colon epithelium. These data provide insight into the role of epithelial Regnase-1 in IBD.

Damage to intestinal epithelial cell (IEC) layers during intestinal inflammation is associated with inflammatory bowel disease. Here we show that the endoribonuclease Regnase-1 controls colon epithelial regeneration by regulating protein kinase mTOR (the mechanistic target of rapamycin kinase) and purine metabolism. During dextran sulfate sodium-induced intestinal epithelial injury and acute colitis, Regnase-1^∆IEC mice, which lack Regnase-1 specifically in the intestinal epithelium, were resistant to body weight loss, maintained an intact intestinal barrier, and showed increased cell proliferation and decreased epithelial apoptosis. Chronic colitis and tumor progression were also attenuated in Regnase-1^∆IEC mice. Regnase-1 predominantly regulates mTORC1 signaling. Metabolic analysis revealed that Regnase-1 participates in purine metabolism and energy metabolism during inflammation. Furthermore, increased expression of ectonucleotidases contributed to the resolution of acute inflammation in Regnase-1^∆IEC mice. These findings provide evidence that Regnase-1 deficiency has beneficial effects on the prevention and/or blocking of intestinal inflammatory disorders.

mTORC1 signaling suppresses Wnt/β-catenin signaling through DVL-dependent regulation of Wnt receptor FZD level

Wnt/β-catenin signaling plays pivotal roles in cell proliferation and tissue homeostasis by maintaining somatic stem cell functions. The mammalian target of rapamycin (mTOR) signaling functions as an integrative rheostat that orchestrates various cellular and metabolic activities that shape tissue homeostasis. Whether these two fundamental signaling pathways couple to exert physiological functions still remains mysterious. Using a genome-wide CRISPR-Cas9 screening, we discover that mTOR complex 1 (mTORC1) signaling suppresses canonical Wnt/β-catenin signaling. Deficiency in tuberous sclerosis complex 1/2 (TSC1/2), core negative regulators of mTORC1 activity, represses Wnt/β-catenin target gene expression, which can be rescued by RAD001. Mechanistically, mTORC1 signaling regulates the cell surface level of Wnt receptor Frizzled (FZD) in a Dishevelled (DVL)-dependent manner by influencing the association of DVL and clathrin AP-2 adaptor. Sustained mTORC1 activation impairs Wnt/β-catenin signaling and causes loss of stemness in intestinal organoids ex vivo and primitive intestinal progenitors in vivo. Wnt/β-catenin-dependent liver metabolic zonation gene expression program is also down-regulated by mTORC1 activation. Our study provides a paradigm that mTORC1 signaling cell autonomously regulates Wnt/β-catenin pathway to influence stem cell maintenance.

mTORC1 Prevents Epithelial Damage During Inflammation and Inhibits Colitis-Associated Colorectal Cancer Development

Epithelial cells lining the intestinal mucosa constitute a selective-semipermeable barrier acting as first line of defense in the organism. The number of those cells remains constant during physiological conditions, but disruption of epithelial cell homeostasis has been observed in several pathologies. During colitis, epithelial cell proliferation decreases and cell death augments. The mechanism responsible for these changes remains unknown. Here, we show that the pro-inflammatory cytokine IFNγ contributes to the inhibition of epithelial cell proliferation in intestinal epithelial cells (IECs) by inducing the activation of mTORC1. Activation of mTORC1 in response to IFNγ was detected in IECs present along the crypt axis and in colonic macrophages. mTORC1 inhibition enhances cell proliferation, increases DNA damage in IEC. In macrophages, mTORC1 inhibition strongly reduces the expression of pro-inflammatory markers. As a consequence, mTORC1 inhibition exacerbated disease activity, increased mucosal damage, enhanced ulceration, augmented cell infiltration, decreased survival and stimulated tumor formation in a model of colorectal cancer CRC associated to colitis. Thus, our findings suggest that mTORC1 signaling downstream of IFNγ prevents epithelial DNA damage and cancer development during colitis.