CIC is a critical regulator of neuronal differentiation

Investigation of the correlation between AGRN expression and perineural invasion in colon cancer

Background and Purpose

Colon cancer is one of the most common gastrointestinal malignancies. According to the traditional view, the primary modes of transmission include direct dissemination, hematogenous metastasis, and lymph node metastasis. In recent years, the role of perineural invasion (PNI) in the spread and metastasis of tumors has received immense attention. However, there are still relatively few reports on the potential mechanisms and biomarkers of PNI occurrence and development in colon cancer.

Method

We identified genes linked to the onset and progression of PNI in colon cancer using bioinformatics tools and extensive databases. Gene function enrichment analysis was used to explore the potential roles of these genes in tumor proliferation, invasion, and PNI. A collection of postoperative pathological specimens from colon cancer patients who underwent surgery, related clinicopathological data, and immunohistochemistry were used to validate AGRN expression in PNI tissues.

Results

Bioinformatics analysis revealed that AGRN is overexpressed in colon cancer tissues and correlates with poor patient prognosis. The findings from gene association and enrichment studies indicate that AGRN and its associated genes may play a role in PNI development and progression in colon cancer by simultaneously enhancing tumor cell invasion and neural cell growth. Immunohistochemical analysis of clinical samples confirmed that AGRN expression is elevated in colon cancer tissues with PNI.

Conclusion

We found that AGRN is significantly overexpressed in colon cancer tissues exhibiting PNI and is linked to poor patient survival. AGRN and its related genes may contribute to PNI by promoting tumor cell invasion and neural cell growth. Hence, AGRN may play a crucial role in the initiation and progression of PNI in colon cancer.

O-GlcNAc transferase congenital disorder of glycosylation (OGT-CDG): Potential mechanistic targets revealed by evaluating the OGT interactome

O-GlcNAc transferase (OGT) is the sole enzyme responsible for the post-translational modification of O-GlcNAc on thousands of target nucleocytoplasmic proteins. To date, nine variants of OGT that segregate with OGT Congenital Disorder of Glycosylation (OGT-CDG) have been reported and characterized. Numerous additional variants have been associated with OGT-CDG, some of which are currently undergoing investigation. This disorder primarily presents with global developmental delay and intellectual disability (ID), alongside other variable neurological features and subtle facial dysmorphisms in patients. Several hypotheses aim to explain the etiology of OGT-CDG, with a prominent hypothesis attributing the pathophysiology of OGT-CDG to mutations segregating with this disorder disrupting the OGT interactome. The OGT interactome consists of thousands of proteins, including substrates as well as interactors that require noncatalytic functions of OGT. A key aim in the field is to identify which interactors and substrates contribute to the primarily neural-specific phenotype of OGT-CDG. In this review, we will discuss the heterogenous phenotypic features of OGT-CDG seen clinically, the variable biochemical effects of mutations associated with OGT-CDG, and the use of animal models to understand this disorder. Furthermore, we will discuss how previously identified OGT interactors causal for ID provide mechanistic targets for investigation that could explain the dysregulated gene expression seen in OGT-CDG models. Identifying shared or unique altered pathways impacted in OGT-CDG patients will provide a better understanding of the disorder as well as potential therapeutic targets.

Molecular and therapeutic advancements in Capicua (CIC)-rearranged sarcoma

Capicua (CIC)-rearranged sarcomas are an aggressive subset of undifferentiated round cell sarcomas. CIC::DUX4, the proto-typical CIC fusion oncoprotein is associated with rapid clinical progression and chemotherapy resistance leading to poor clinical outcomes. Recent studies have identified additional CIC fusions (CIC::NUTM1, CIC::FOXO4, and CIC::LEUTX) that largely retain CIC-binding specificity but leverage C-terminal binding partners (NUTM1, FOXO4, and LEUTX) to potentially activate transcriptional programs that drive oncogenesis. Moreover, the recent development of preclinical models to study CIC::DUX4 sarcoma have advanced our understanding of the underlying biological mechanisms and uncovered key dependencies that can be translated into rational therapies. In this review, we will highlight these recent advancements in CIC-rearranged sarcoma biology with a vision for clinical translation to improve patient outcomes.

The upregulation of VGF enhances the progression of oral squamous carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a prevalent neoplasm worldwide, necessitating a deeper understanding of its pathogenesis. VGF nerve growth factor inducible (VGF), a neuropeptide, plays critical roles in nerve and endocrine cell regulation.

METHODS

In this study, the TCGA datasets were initially screened, identifying the upregulation of VGF in various malignancies. We focused on OSCC cell lines, identifying the suppressor mRNA miR-432-5p as a negative regulator of VGF. Additionally, we examined the prognostic value of VGF expression in OSCC tumors and its impact on cellular functions.

RESULTS

VGF expression was found to be an independent prognostic predictor in OSCC tumors. Cells expressing VGF exhibited increased oncogenicity, influencing the proliferation and migration of oral mucosal fibroblast. Transcriptome analysis revealed associations between VGF and various pathological processes, including malignancies, exosome release, fibrosis, cell cycle disruption, and tumor immune suppression. Moreover, IL23R expression, a favorable OSCC prognostic factor, was inversely correlated with VGF expression. Exogenous IL23R expression was found to suppress VGF-associated mobility phenotypes.

CONCLUSIONS

This study highlights the multifaceted role of VGF in OSCC pathogenesis and introduces the miR-432-5p-VGF-IL23R regulatory axis as a critical mediator. The combined expression of VGF and IL23R emerges as a potent predictor of survival in oral carcinoma cases, suggesting potential implications for future therapeutic strategies.

Longitudinal single-cell transcriptional dynamics throughout neurodegeneration in SCA1

Neurodegeneration is a protracted process involving progressive changes in myriad cell types that ultimately results in the death of vulnerable neuronal populations. To dissect how individual cell types within a heterogeneous tissue contribute to the pathogenesis and progression of a neurodegenerative disorder, we performed longitudinal single-nucleus RNA sequencing of mouse and human spinocerebellar ataxia type 1 (SCA1) cerebellar tissue, establishing continuous dynamic trajectories of each cell population. Importantly, we defined the precise transcriptional changes that precede loss of Purkinje cells and, for the first time, identified robust early transcriptional dysregulation in unipolar brush cells and oligodendroglia. Finally, we applied a deep learning method to predict disease state accurately and identified specific features that enable accurate distinction of wild-type and SCA1 cells. Together, this work reveals new roles for diverse cerebellar cell types in SCA1 and provides a generalizable analysis framework for studying neurodegeneration.

PRMT5 inhibition drives therapeutic vulnerability to combination treatment with BCL-2 inhibition in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an incurable B-cell malignancy that comprises up to 6% of non-Hodgkin lymphomas diagnosed annually and is associated with a poor prognosis. The average overall survival of patients with MCL is 5 years, and for most patients who progress on targeted agents, survival remains at a dismal 3 to 8 months. There is a major unmet need to identify new therapeutic approaches that are well tolerated to improve treatment outcomes and quality of life. The protein arginine methyltransferase 5 (PRMT5) enzyme is overexpressed in MCL and promotes growth and survival. Inhibition of PRMT5 drives antitumor activity in MCL cell lines and preclinical murine models. PRMT5 inhibition reduced the activity of prosurvival AKT signaling, which led to the nuclear translocation of FOXO1 and modulation of its transcriptional activity. Chromatin immunoprecipitation and sequencing identified multiple proapoptotic BCL-2 family members as FOXO1-bound genomic loci. We identified BAX as a direct transcriptional target of FOXO1 and demonstrated its critical role in the synergy observed between the selective PRMT5 inhibitor, PRT382, and the BCL-2 inhibitor, venetoclax. Single-agent and combination treatments were performed in 9 MCL lines. Loewe synergy scores showed significant levels of synergy in most MCL lines tested. Preclinical, in vivo evaluation of this strategy in multiple MCL models showed therapeutic synergy with combination venetoclax/PRT382 treatment with an increased survival advantage in 2 patient-derived xenograft models (P ≤ .0001, P ≤ .0001). Our results provide mechanistic rationale for the combination of PRMT5 inhibition and venetoclax to treat patients with MCL.

Memory phase-specific genes in the Mushroom Bodies identified using CrebB-target DamID

The formation of long-term memories requires changes in the transcriptional program and de novo protein synthesis. One of the critical regulators for long-term memory (LTM) formation and maintenance is the transcription factor CREB. Genetic studies have dissected the requirement of CREB activity within memory circuits, however less is known about the genetic mechanisms acting downstream of CREB and how they may contribute defining LTM phases. To better understand the downstream mechanisms, we here used a targeted DamID approach (TaDa). We generated a CREB-Dam fusion protein using the fruit fly Drosophila melanogaster as model. Expressing CREB-Dam in the mushroom bodies (MBs), a brain center implicated in olfactory memory formation, we identified genes that are differentially expressed between paired and unpaired appetitive training paradigm. Of those genes we selected candidates for an RNAi screen in which we identified genes causing increased or decreased LTM.

Multi-Omic Analysis of CIC's Functional Networks Reveals Novel Interaction Partners and a Potential Role in Mitotic Fidelity

CIC encodes a transcriptional repressor and MAPK signalling effector that is inactivated by loss-of-function mutations in several cancer types, consistent with a role as a tumour suppressor. Here, we used bioinformatic, genomic, and proteomic approaches to investigate CIC's interaction networks. We observed both previously identified and novel candidate interactions between CIC and SWI/SNF complex members, as well as novel interactions between CIC and cell cycle regulators and RNA processing factors. We found that CIC loss is associated with an increased frequency of mitotic defects in human cell lines and an in vivo mouse model and with dysregulated expression of mitotic regulators. We also observed aberrant splicing in CIC-deficient cell lines, predominantly at 3' and 5' untranslated regions of genes, including genes involved in MAPK signalling, DNA repair, and cell cycle regulation. Our study thus characterises the complexity of CIC's functional network and describes the effect of its loss on cell cycle regulation, mitotic integrity, and transcriptional splicing, thereby expanding our understanding of CIC's potential roles in cancer. In addition, our work exemplifies how multi-omic, network-based analyses can be used to uncover novel insights into the interconnected functions of pleiotropic genes/proteins across cellular contexts.

Prenatal social support in low-risk pregnancy shapes placental epigenome

BACKGROUND

Poor social support during pregnancy has been linked to inflammation and adverse pregnancy and childhood health outcomes. Placental epigenetic alterations may underlie these links but are still unknown in humans.

METHODS

In a cohort of low-risk pregnant women (n = 301) from diverse ethnic backgrounds, social support was measured using the ENRICHD Social Support Inventory (ESSI) during the first trimester. Placental samples collected at delivery were analyzed for DNA methylation and gene expression using Illumina 450K Beadchip Array and RNA-seq, respectively. We examined association between maternal prenatal social support and DNA methylation in placenta. Associated cytosine-(phosphate)-guanine sites (CpGs) were further assessed for correlation with nearby gene expression in placenta.

RESULTS

The mean age (SD) of the women was 27.7 (5.3) years. The median (interquartile range) of ESSI scores was 24 (22-25). Prenatal social support was significantly associated with methylation level at seven CpGs (P_FDR < 0.05). The methylation levels at two of the seven CpGs correlated with placental expression of VGF and ILVBL (P_FDR < 0.05), genes known to be involved in neurodevelopment and energy metabolism. The genes annotated with the top 100 CpGs were enriched for pathways related to fetal growth, coagulation system, energy metabolism, and neurodevelopment. Sex-stratified analysis identified additional significant associations at nine CpGs in male-bearing pregnancies and 35 CpGs in female-bearing pregnancies.

CONCLUSIONS

The findings suggest that prenatal social support is linked to placental DNA methylation changes in a low-stress setting, including fetal sex-dependent epigenetic changes. Given the relevance of some of these changes in fetal neurodevelopmental outcomes, the findings signal important methylation targets for future research on molecular mechanisms of effect of the broader social environment on pregnancy and fetal outcomes.

TRIAL REGISTRATION

NCT00912132 ( ClinicalTrials.gov ).

A FOXO1-dependent transcription network is a targetable vulnerability of mantle cell lymphomas

Targeting lineage-defined transcriptional dependencies has emerged as an effective therapeutic strategy in cancer treatment. Through screening for molecular vulnerabilities of mantle cell lymphoma (MCL), we identified a set of transcription factors (TFs) including FOXO1, EBF1, PAX5, and IRF4 that are essential for MCL propagation. Integrated chromatin immunoprecipitation and sequencing (ChIP-Seq) with transcriptional network reconstruction analysis revealed FOXO1 as a master regulator that acts upstream in the regulatory TF hierarchy. FOXO1 is both necessary and sufficient to drive MCL lineage commitment through supporting the lineage-specific transcription programs. We further show that FOXO1, but not its close paralog FOXO3, can reprogram myeloid leukemia cells and induce B-lineage gene expression. Finally, we demonstrate that cpd10, a small molecule identified from an enriched FOXO1 inhibitor library, induces a robust cytotoxic response in MCL cells in vitro and suppresses MCL progression in vivo. Our findings establish FOXO1 inhibition as a therapeutic strategy targeting lineage-driven transcriptional addiction in MCL.

CIC missense variants contribute to susceptibility for spina bifida

Neural tube defects (NTDs) are congenital malformations resulting from abnormal embryonic development of the brain, spine, or spinal column. The genetic etiology of human NTDs remains poorly understood despite intensive investigation. CIC, homolog of the Capicua transcription repressor, has been reported to interact with ataxin-1 (ATXN1) and participate in the pathogenesis of spinocerebellar ataxia type 1. Our previous study demonstrated that CIC loss of function (LoF) variants contributed to the cerebral folate deficiency syndrome by downregulating folate receptor 1 (FOLR1) expression. Given the importance of folate transport in neural tube formation, we hypothesized that CIC variants could contribute to increased risk for NTDs by depressing embryonic folate concentrations. In this study, we examined CIC variants from whole-genome sequencing (WGS) data of 140 isolated spina bifida cases and identified eight missense variants of CIC gene. We tested the pathogenicity of the observed variants through multiple in vitro experiments. We determined that CIC variants decreased the FOLR1 protein level and planar cell polarity (PCP) pathway signaling in a human cell line (HeLa). In a murine cell line (NIH3T3), CIC loss of function variants downregulated PCP signaling. Taken together, this study provides evidence supporting CIC as a risk gene for human NTD.

A cuproptosis-related lncRNAs signature for prognosis, chemotherapy, and immune checkpoint blockade therapy of low-grade glioma

Cuproptosis is a new type of cell death that is associated with mitochondrial respiration of the tricarboxylic acid cycle. Previous studies showed that long non-coding RNAs (lncRNAs) regulated low-grade glioma (LGG) progression. However, the potential applications of cuproptosis-related lncRNAs (CRLs) in LGG were not explored. A comprehensive analysis was performed in The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) cohorts. We first screened two distinct cuproptosis subtypes based on prognostic CRLs using consensus clustering. To facilitate individualized survival prediction in LGG, we constructed a prognostic signature (including CRNDE, HAR1A, and FAM181A-AS1) in the TCGA dataset. The prognostic signature exhibited excellent predictive ability and reliability, which was validated in the CGGA_325 and CGGA_693 datasets. Notably, patients in the high-risk group had increased immune cell infiltration and expression of immune checkpoints, which indicated that they may benefit more from immune checkpoint blockade (ICB) therapy. Finally, the prognostic signature screened the population with sensitivity to chemotherapy and ICB therapy. In summary, this study initially explored the mechanism of CRLs in LGG and provides some insights into chemotherapy and ICB therapy of LGG.

CIC-DUX4 sarcomas

PURPOSE OF REVIEW

CIC-DUX4 sarcoma (CDS) is a high-grade undifferentiated round cells sarcoma that belongs to the undifferentiated round cell sarcomas family. It represents less than one percent of sarcomas, defining a rarest among rare malignancies. It affects young adults, displaying soft tissue mass. Considered very aggressive, a high proportion of cases display an advanced disease with lung metastasis at diagnosis. Here we discuss recent progress in molecular characterization of CDS, the main tracks of CDS biology and the current and future prospects of therapeutic approaches.

RECENT FINDINGS

CDS is characterized by a specific oncogenic translocation CIC::DUX4 that induce ETV4 overexpression. Patients with CDS show an aggressive clinical course and have a significantly unfavorable outcome compared to Ewing sarcoma. As of today, there is a lack of consensus on whether they should be treated with an Ewing-like approach, as currently done by most sites, or regarded as high-grade soft tissue sarcoma (STS). Anyway, when feasible, combination regimens including anthracycline and alkylating agents should be favored and patients should not benefit from a therapeutic de-escalation. Overall, registration within clinical trials and prospective registries is recommended.

SUMMARY

Overall, CDS showed a poor prognosis regardless of the patterns of treatment that warrant biological studies to better understand the disease.

Novel CIC variants identified in individuals with neurodevelopmental phenotypes

Heterozygous pathogenic variants in CIC, which encodes a transcriptional repressor, have been identified in individuals with neurodevelopmental phenotypes. To date, 11 CIC variants have been associated with the CIC-related neurodevelopmental syndrome. Here, we describe three novel and one previously reported CIC variants in four individuals with neurodevelopmental delay. Notably, we report for the first time a de novo frameshift variant specific to the long isoform of CIC (CIC-L, NM_001304815.1:c.1100dup, p.Pro368AlafsTer16) in an individual with speech delay, intellectual disability, and autism spectrum disorder. Our investigation into the function of CIC-L reveals that partial loss of CIC-L leads to transcriptional derepression of CIC target genes. We also describe a missense variant (NM_015125.3:c.683G>A, p.Arg228Gln) in an individual with a history of speech delay and relapsed pre-B acute lymphoblastic leukemia. Functional studies of this variant suggest a partial loss of CIC transcriptional repressor activity. Our study expands the list of CIC pathogenic variants and contributes to the accumulating evidence that CIC haploinsufficiency or partial loss of function is a pathogenic mechanism causing neurodevelopmental phenotypes.

Integrative multi-omic analysis reveals neurodevelopmental gene dysregulation in CIC-knockout and IDH1 mutant cells

Capicua (CIC)'s transcriptional repressor function is implicated in neurodevelopment and in oligodendroglioma (ODG) aetiology. However, CIC's role in these contexts remains obscure, primarily from our currently limited knowledge regarding its biological functions. Moreover, CIC mutations in ODG invariably co‐occur with a neomorphic IDH1/2 mutation, yet the functional relationship between these two genetic events is unknown. Here, we analysed models derived from an E6/E7/hTERT‐immortalized (i.e. p53‐ and RB‐deficient) normal human astrocyte cell line. To examine the consequences of CIC loss, we compared transcriptomic and epigenomic profiles between CIC wild‐type and knockout cell lines, with and without mutant IDH1 expression. Our analyses revealed dysregulation of neurodevelopmental genes in association with CIC loss. CIC ChIP‐seq was also performed to expand upon the currently limited ensemble of known CIC target genes. Among the newly identified direct CIC target genes were EPHA2 and ID1, whose functions are linked to neurodevelopment and the tumourigenicity of in vivo glioma tumour models. NFIA, a known mediator of gliogenesis, was discovered to be uniquely overexpressed in CIC‐knockout cells expressing mutant IDH1‐R132H protein. These results identify neurodevelopment and specific genes within this context as candidate targets through which CIC alterations may contribute to the progression of IDH‐mutant gliomas. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Capicua Regulates Dendritic Morphogenesis Through Ets in Hippocampal Neurons in vitro

Capicua (Cic), a transcriptional repressor frequently mutated in brain cancer oligodendroglioma, is highly expressed in adult neurons. However, its function in the dendritic growth of neurons in the hippocampus remains poorly understood. Here, we confirmed that Cic was expressed in hippocampal neurons during the main period of dendritogenesis, suggesting that Cic has a function in dendrite growth. Loss-of-function and gain-of function assays indicated that Cic plays a central role in the inhibition of dendritic morphogenesis and dendritic spines in vitro. Further studies showed that overexpression of Cic reduced the expression of Ets in HT22 cells, while in vitro knockdown of Cic in hippocampal neurons significantly elevated the expression of Ets. These results suggest that Cic may negatively control dendrite growth through Ets, which was confirmed by ShRNA knockdown of either Etv4 or Etv5 abolishing the phenotype of Cic knockdown in cultured neurons. Taken together, our results suggest that Cic inhibits dendritic morphogenesis and the growth of dendritic spines through Ets.

Capicua regulates the development of adult-born neurons in the hippocampus

New neurons continuously arise from neural progenitor cells in the dentate gyrus of the adult hippocampus to support ongoing learning and memory formation. To generate functional adult-born neurons, neural progenitor cells proliferate to expand the precursor cell pool and differentiate into neurons. Newly generated cells then undergo postmitotic maturation to migrate to their final destination and develop elaborate dendritic branching, which allows them to receive input signals. Little is known about factors that regulate neuronal differentiation, migration, and dendrite maturation during adult hippocampal neurogenesis. Here, we show that the transcriptional repressor protein capicua (CIC) exhibits dynamic expression in the adult dentate gyrus. Conditional deletion of Cic from the mouse dentate gyrus compromises the adult neural progenitor cell pool without altering their proliferative potential. We further demonstrate that the loss of Cic impedes neuronal lineage development and disrupts dendritic arborization and migration of adult-born neurons. Our study uncovers a previously unrecognized role of CIC in neurogenesis of the adult dentate gyrus.

Cellular stress signaling activates type-I IFN response through FOXO3-regulated lamin posttranslational modification

Neural stem/progenitor cells (NSPCs) persist over the lifespan while encountering constant challenges from age or injury related brain environmental changes like elevated oxidative stress. But how oxidative stress regulates NSPC and its neurogenic differentiation is less clear. Here we report that acutely elevated cellular oxidative stress in NSPCs modulates neurogenic differentiation through induction of Forkhead box protein O3 (FOXO3)-mediated cGAS/STING and type I interferon (IFN-I) responses. We show that oxidative stress activates FOXO3 and its transcriptional target glycine-N-methyltransferase (GNMT) whose upregulation triggers depletion of s-adenosylmethionine (SAM), a key co-substrate involved in methyl group transfer reactions. Mechanistically, we demonstrate that reduced intracellular SAM availability disrupts carboxymethylation and maturation of nuclear lamin, which induce cytosolic release of chromatin fragments and subsequent activation of the cGAS/STING-IFN-I cascade to suppress neurogenic differentiation. Together, our findings suggest the FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signaling cascade as a critical stress response program that regulates long-term regenerative potential.

Neural stem and progenitor cells (NSPCs) encounter constant stresses during aging, such as elevated oxidative stress. Here the authors show that oxidative stress induced reduction in NSPC neural differentiation is mediated by a FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signalling cascade initiated by FOXO3 oxidation.

Impact of Capicua on Pancreatic Cancer Progression

BACKGROUND

The transcription factor capicua (CIC) regulates mammalian development and homeostasis. Growing evidence shows that CIC suppresses various human cancers by directly repressing the downstream cancer-related target genes. This study investigated the clinical and biologic significance of CIC expression in pancreatic cancer (PC).

METHODS

The study reviewed 132 patients with PC who underwent curative resection. The patients were divided into two groups according to CIC immunoreactivity score by immunohistochemistry, and the associations between CIC expression, clinicopathologic characteristics, and postoperative prognosis were investigated. Moreover, the influence of CIC expression on the malignant potential of PC cells was assessed with cell proliferation, motility assays, and use of quantitative real time-polymerase chain reaction and Western blot on the downstream target genes of CIC in knockdown experiments.

RESULTS

The low-CIC expression group showed a higher proportion of lymphatic invasion (72.9% vs. 53.1%; p = 0.024), intrapancreatic neural invasion (94.1% vs. 81.3%; p = 0.021), and extrapancreatic plexus invasion (30.9% vs. 7.8%; p = 0.0006) than the high-CIC expression group as well as significantly worse overall survival (p = 0.0002) and recurrence-free survival (p = 0.0041) rates. Low CIC expression was an independent risk factor for poor prognosis (p = 0.038). Pancreatic cancer cells with knockdown CIC significantly enhanced cell motilities and cell cycle progression, promoted expression levels of ETV4 and MMP-9, and induced EMT.

CONCLUSIONS

The study elucidated the association of low CIC expression with a poor prognosis for patients with PC and suggested that the CIC-ETV4-MMP-9 axis might control PC progression.

TRIM25 promotes Capicua degradation independently of ERK in the absence of ATXN1L

Background

Aberrations in Capicua (CIC) have recently been implicated as a negative prognostic factor in a multitude of cancer types through the derepression of targets downstream of the mitogen-activated protein kinase (MAPK) signaling cascade, such as oncogenic E26 transformation-specific (ETS) transcription factors. The Ataxin-family protein ATXN1L has previously been reported to interact with CIC in both developmental and disease contexts to facilitate the repression of CIC target genes and promote the post-translational stability of CIC. However, little is known about the mechanisms at the base of ATXN1L-mediated CIC post-translational stability.

Results

Functional in vitro studies utilizing ATXN1L^KO human cell lines revealed that loss of ATXN1L leads to the accumulation of polyubiquitinated CIC protein, promoting its degradation through the proteasome. Although transcriptomic signatures of ATXN1L^KO cell lines indicated upregulation of the mitogen-activated protein kinase pathway, ERK activity was found to contribute to CIC function but not stability. Degradation of CIC protein following loss of ATXN1L was instead observed to be mediated by the E3 ubiquitin ligase TRIM25 which was further validated using glioma-derived cell lines and the TCGA breast carcinoma and liver hepatocellular carcinoma cohorts.

Conclusions

The post-translational regulation of CIC through ATXN1L and TRIM25 independent of ERK activity suggests that the regulation of CIC stability and function is more intricate than previously appreciated and involves several independent pathways. As CIC status has become a prognostic factor in several cancer types, further knowledge into the mechanisms which govern CIC stability and function may prove useful for future therapeutic approaches.

Capicua in Human Cancer

Capicua (CIC) is a highly conserved transcriptional repressor that is differentially regulated through mitogen-activated protein kinase (MAPK) signaling or genetic alteration across human cancer. CIC contributes to tumor progression and metastasis through direct transcriptional control of effector target genes. Recent findings indicate that CIC dysregulation is mechanistically linked and restricted to specific cancer subtypes, yet convergence on key downstream transcriptional nodes are critical for CIC-regulated oncogenesis across these cancers. In this review, we focus on how differential regulation of CIC through functional and genetic mechanisms contributes to subtype-specific cancer phenotypes and we propose new therapeutic strategies to effectively target CIC-altered cancers.