Loss of heterozygosity of TRIM3 in malignant gliomas

EF1α-associated protein complexes affect dendritic spine plasticity by regulating microglial phagocytosis in Fmr1 knock-out mice

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. There is no specific treatment for FXS due to the lack of therapeutic targets. We report here that Elongation Factor 1α (EF1α) forms a complex with two other proteins: Tripartite motif-containing protein 3 (TRIM3) and Murine double minute (Mdm2). Both EF1α-Mdm2 and EF1α-TRIM3 protein complexes are increased in the brain of Fmr1 knockout mice as a result of FMRP deficiency, which releases the normal translational suppression of EF1α mRNA and increases EF1α protein levels. Increased EF1α-Mdm2 complex decreases PSD-95 ubiquitination (Ub-PSD-95) and Ub-PSD-95-C1q interaction. The elevated level of TRIM3-EF1α complex is associated with decreased TRIM3-Complement Component 3 (C3) complex that inhibits the activation of C3. Both protein complexes thereby contribute to a reduction in microglia-mediated phagocytosis and dendritic spine pruning. Finally, we created a peptide that disrupts both protein complexes and restores dendritic spine plasticity and behavioural deficits in Fmr1 knockout mice. The EF1α-Mdm2 and EF1α-TRIM3 complexes could thus be new therapeutic targets for FXS.

Advances in the antitumor mechanisms of tripartite motif-containing protein 3

The tripartite motif-containing (TRIM) protein family has steadily become a hotspot in tumor-related research. As a member of the E3 ubiquitin ligase family, TRIM is working on many crucial biological processes, including the regulation of tumor cell proliferation, metastasis, apoptosis, and autophagy. Among the diverse TRIM superfamily members, TRIM3 operates via different mechanisms in various types of tumors. This review primarily focuses on the current state of research regarding the antitumor mechanisms of TRIM3 in different cancers. A more in-depth study of TRIM3 may provide new directions for future antitumor treatments. Our review focuses on TRIM3 proteins and cancer. We searched for relevant articles on the mechanisms by which TRIM3 affects tumorigenesis and development from 1997 to 2023 and summarized the latest progress and future directions. Triad-containing motif protein 3 (TRIM3) is an important protein, which plays a key role in the process of tumorigenesis and development. The comprehensive exploration of TRIM3 is anticipated to pave the way for future advancements in antitumor therapy, which is expected to be a new hallmark for cancer detection and a novel target for drug action. TRIM3 is poised to become a significant milestone in cancer detection and a promising focal point for drug intervention. Recent years have witnessed notable progress in research aimed at unraveling the antitumor mechanism of TRIM3, with far-reaching implications for practical tumor diagnosis, treatment protocols, efficacy evaluation, economics, and pharmaceutical utilization.

Ribogenesis boosts controlled by HEATR1-MYC interplay promote transition into brain tumour growth

Cell commitment to tumourigenesis and the onset of uncontrolled growth are critical determinants in cancer development but the early events directing tumour initiating cell (TIC) fate remain unclear. We reveal a single-cell transcriptome profile of brain TICs transitioning into tumour growth using the brain tumour (brat) neural stem cell-based Drosophila model. Prominent changes in metabolic and proteostasis-associated processes including ribogenesis are identified. Increased ribogenesis is a known cell adaptation in established tumours. Here we propose that brain TICs boost ribogenesis prior to tumour growth. In brat-deficient TICs, we show that this dramatic change is mediated by upregulated HEAT-Repeat Containing 1 (HEATR1) to promote ribosomal RNA generation, TIC enlargement and onset of overgrowth. High HEATR1 expression correlates with poor glioma patient survival and patient-derived glioblastoma stem cells rely on HEATR1 for enhanced ribogenesis and tumourigenic potential. Finally, we show that HEATR1 binds the master growth regulator MYC, promotes its nucleolar localisation and appears required for MYC-driven ribogenesis, suggesting a mechanism co-opted in ribogenesis reprogramming during early brain TIC development.

It's a TRIM-endous view from the top: the varied roles of TRIpartite Motif proteins in brain development and disease

The tripartite motif (TRIM) protein family members have been implicated in a multitude of physiologies and pathologies in different tissues. With diverse functions in cellular processes including regulation of signaling pathways, protein degradation, and transcriptional control, the impact of TRIM dysregulation can be multifaceted and complex. Here, we focus on the cellular and molecular roles of TRIMs identified in the brain in the context of a selection of pathologies including cancer and neurodegeneration. By examining each disease in parallel with described roles in brain development, we aim to highlight fundamental common mechanisms employed by TRIM proteins and identify opportunities for therapeutic intervention.

Therapeutic Effectiveness of Anticancer Agents Targeting Different Signaling Molecules Involved in Asymmetric Division of Cancer Stem Cell

Intra-tumoral heterogeneity is maintained by cancer stem cells (CSCs) with dysregulated self-renewal and asymmetric cell division (ACD). According to the cancer stem cell theory, by ACD a CSC can generate two daughter progenies with different fates such as one cancer stem cell and one differentiated cell. Therefore, this type of mitotic division supports vital process of the maintenance of CSC population. But this CSC pool reservation by ACD complicates the treatment of cancer patients, as CSCs give rise to aggressive clones which are prone to metastasis and drug-insensitivity. Hence, identification of therapeutic modalities which can target ACD of cancer stem cell is an intriguing part of cancer research. In this review, other than the discussion about the extrinsic inducers of ACD role of different proteins, miRNAs and lncRNAs in this type of cell division is also mentioned. Other than these, mode of action of the proven and potential drugs targeting ACD of CSC is also discussed here.

Emerging Roles of TRIM Family Proteins in Gliomas Pathogenesis

Simple Summary

Gliomas remain challenging tumors due to their increased heterogeneity, complex molecular profile, and infiltrative phenotype that are often associated with a dismal prognosis. In a constant search for molecular changes and associated mechanisms, the TRIM protein family has emerged as an important area of investigation because of the regulation of vital cellular processes involved in brain pathophysiology that may possibly lead to brain tumor development. Herein, we discuss the diverse role of TRIM proteins in glioma progression, aiming to detect potential targets for future intervention.

Abstract

Gliomas encompass a vast category of CNS tumors affecting both adults and children. Treatment and diagnosis are often impeded due to intratumor heterogeneity and the aggressive nature of the more malignant forms. It is therefore essential to elucidate the molecular mechanisms and explore the intracellular signaling pathways underlying tumor pathology to provide more promising diagnostic, prognostic, and therapeutic tools for gliomas. The tripartite motif-containing (TRIM) superfamily of proteins plays a key role in many physiological cellular processes, including brain development and function. Emerging evidence supports the association of TRIMs with a wide variety of cancers, exhibiting both an oncogenic as well as a tumor suppressive role depending on cancer type. In this review, we provide evidence of the pivotal role of TRIM proteins in gliomagenesis and exploit their potential as prognostic biomarkers and therapeutic targets.

Tripartite Motif Containing 3 inhibits the aggressive behaviors of papillary thyroid carcinoma and indicates lower recurrence risk

BACKGROUND

Tripartite Motif Containing 3 (TRIM3) has been reported to be downregulated in several malignancies. However, its prognostic significance in thyroid cancer remains unknown.

OBJECTIVE

Here we aimed to investigate TRIM3's expression and its involvement in papillary thyroid carcinoma (PTC).

METHODS

Clinicopathological analyses were performed in patients with PTC. Expression of TRIM3 protein was evaluated by IHC. The prognostic role of TRIM3 in PTC patients was assessed by univariate and multivariate analyses. Cell proliferation and invasion were tested in two PTC cell lines following overexpression or knockdown.

RESULTS

TRIM3 was decreased in PTC tissues compared to adjacent thyroid tissues on both mRNA and protein levels. Additionally, low expression of TRIM3 was significantly related to tumor size, lymph node metastasis and TNM stage. Moreover, TRIM3 was identified as an independent prognosis factor by multivariate analysis. Cellular data revealed that TRIM3 can inhibit the proliferation and invasion of PTC cells. Consistently, TRIM3 can upregulate the expression level of E-cadherin, while downregulate N-cadherin, Vimentin, and cyclin D1 expression.

CONCLUSIONS

TRIM3 expression was downregulated in PTC tissues comparing with that in adjacent nontumorous thyroid tissues. Lower TRIM3 expression in PTC can contribute independently to a poorer prognosis by enhancing PTC proliferation and invasion, highlighting its potential as a novel therapeutic target and prognostic biomarker.

The tumour suppressor brain tumour (Brat) regulates linker histone dBigH1 expression in the Drosophila female germline and the early embryo

Linker histones H1 are essential chromatin components that exist as multiple developmentally regulated variants. In metazoans, specific H1s are expressed during germline development in a tightly regulated manner. However, the mechanisms governing their stage-dependent expression are poorly understood. Here, we address this question in Drosophila, which encodes for a single germline-specific dBigH1 linker histone. We show that during female germline lineage differentiation, dBigH1 is expressed in germ stem cells and cystoblasts, becomes silenced during transit-amplifying (TA) cystocytes divisions to resume expression after proliferation stops and differentiation starts, when it progressively accumulates in the oocyte. We find that dBigH1 silencing during TA divisions is post-transcriptional and depends on the tumour suppressor Brain tumour (Brat), an essential RNA-binding protein that regulates mRNA translation and stability. Like other oocyte-specific variants, dBigH1 is maternally expressed during early embryogenesis until it is replaced by somatic dH1 at the maternal-to-zygotic transition (MZT). Brat also mediates dBigH1 silencing at MZT. Finally, we discuss the situation in testes, where Brat is not expressed, but dBigH1 is translationally silenced too.

Analysis of human total antibody repertoires in TIF1γ autoantibody positive dermatomyositis

We investigate the accumulated microbial and autoantigen antibody repertoire in adult-onset dermatomyositis patients sero-positive for TIF1γ (TRIM33) autoantibodies. We use an untargeted high-throughput approach which combines immunoglobulin disease-specific epitope-enrichment and identification of microbial and human antigens. We observe antibodies recognizing a wider repertoire of microbial antigens in dermatomyositis. Antibodies recognizing viruses and Poxviridae family species are significantly enriched. The identified autoantibodies recognise a large portion of the human proteome, including interferon regulated proteins; these proteins cluster in specific biological processes. In addition to TRIM33, we identify autoantibodies against eleven further TRIM proteins, including TRIM21. Some of these TRIM proteins share epitope homology with specific viral species including poxviruses. Our data suggest antibody accumulation in dermatomyositis against an expanded diversity of microbial and human proteins and evidence of non-random targeting of specific signalling pathways. Our findings indicate that molecular mimicry and epitope spreading events may play a role in dermatomyositis pathogenesis.

Megremis, Walker at al. identify immunogenic epitopes in dermatomyositis patients. They identify antibodies recognizing a wider diversity of microbial antigens including poxviruses, and autoantibodies recognizing a large portion of the human proteome. Shared epitope homology between viral and human proteins suggests that molecular mimicry and epitope spreading events may play a role in dermatomyositis pathogenesis.

Targeting Loss of Heterozygosity: A Novel Paradigm for Cancer Therapy

Loss of heterozygosity (LOH) is a common genetic event in the development of cancer. In certain tumor types, LOH can affect more than 20% of the genome, entailing loss of allelic variation in thousands of genes. This reduction of heterozygosity creates genetic differences between tumor and normal cells, providing opportunities for development of novel cancer therapies. Here, we review and summarize (1) mutations associated with LOH on chromosomes which have been shown to be promising biomarkers of cancer risk or the prediction of clinical outcomes in certain types of tumors; (2) loci undergoing LOH that can be targeted for development of novel anticancer drugs as well as (3) LOH in tumors provides up-and-coming possibilities to understand the underlying mechanisms of cancer evolution and to discover novel cancer vulnerabilities which are worth a further investigation in the near future.

Decreased expression of TRIM3 gene predicts a poor prognosis in gastric cancer

BACKGROUND/AIMS

Tripartite motif-containing 3 (TRIM3) is a member of the TRIM protein family which is known to be involved in development of numerous tumor types. However, the prognostic role of TRIM3 in gastric cancer (GC) remained to be clarified. The aim of this study was to evaluate the expression pattern and prognostic significance of TRIM3 gene and its relationship with β-catenin, CyclinD, and BCL2 expression in patients with GC.

METHODS

A total of 40 fresh primary gastric cancer tumors and their matched adjacent noncancerous tissues were selected from the First Affiliated Hospital of Mashhad University. Real-time quantitative RT-PCR was performed to evaluate differences in TRIM3 expression in GC and normal tissues. The correlation between TRIM3 expression level and patients' overall survival, some clinicopathological variables, and β-catenin, CyclinD, and BCL-2 genes expression level were also studied. Moreover, patients were divided in two groups according to the TRIM3 expression levels: low and high.

RESULTS

Compared to noncancerous tissues, TRIM3 expression in GC tissues was significantly increased (fold change = 1.58). Kaplan-Meier survival analysis revealed a significant difference of patient survival according to TRIM3 expression status (P = 0.012). Low TRIM3 expression was associated with shorter overall survival and was an independent predictor for poor prognosis in GC patients (HR, 1.25; 95%CI, 1.02-1.60; P = 0.045). Expression of TRIM3 was negatively correlated with expression of β-catenin, BCL-2, and CyclinD as genes for proliferation, apoptosis, and the cell cycle in GC patients.

CONCLUSIONS

This study demonstrates that decreased level of TRIM3 mRNA expression is associated with poor prognosis in patients with gastric cancer. TRIM3 may play a protective role in gastric cancer by relieving the effects of cancer progressive genes and could be considered for further investigations as a prognostic biomarker.

TRIM-NHL as RNA Binding Ubiquitin E3 Ligase (RBUL): Implication in development and disease pathogenesis

TRIM proteins are RING domain-containing modular ubiquitin ligases, unique due to their stimuli specific expression, localization, and turnover. The TRIM family consists of more than 76 proteins, including the TRIM-NHL sub-family which possesses RNA binding ability along with the inherent E3 Ligase activity, hence can be classified as a unique class of RNA Binding Ubiquitin Ligases (RBULs). Having these two abilities, TRIM-NHL proteins can play important role in a wide variety of cellular processes and their dysregulation can lead to complex and systemic pathological conditions. Increasing evidence suggests that TRIM-NHL proteins regulate RNA at the transcriptional and post-transcriptional level having implications in differentiation, development, and many pathological conditions. This review explores the evolving role of TRIM-NHL proteins as TRIM-RBULs, their ubiquitin ligase and RNA binding ability regulating cellular processes, and their possible role in different pathophysiological conditions.

Costameric integrin and sarcoglycan protein levels are altered in a Drosophila model for Limb-girdle muscular dystrophy type 2H

Mutations in two different domains of the ubiquitously expressed TRIM32 protein give rise to two clinically separate diseases, one of which is Limb-girdle muscular dystrophy type 2H (LGMD2H). Uncovering the muscle-specific role of TRIM32 in LGMD2H pathogenesis has proven difficult, as neurogenic phenotypes, independent of LGMD2H pathology, are present in TRIM32 KO mice. We previously established a platform to study LGMD2H pathogenesis using Drosophila melanogaster as a model. Here we show that LGMD2H disease-causing mutations in the NHL domain are molecularly and structurally conserved between fly and human TRIM32. Furthermore, transgenic expression of a subset of myopathic alleles (R394H, D487N, and 520fs) induce myofibril abnormalities, altered nuclear morphology, and reduced TRIM32 protein levels, mimicking phenotypes in patients afflicted with LGMD2H. Intriguingly, we also report for the first time that the protein levels of βPS integrin and sarcoglycan δ, both core components of costameres, are elevated in TRIM32 disease-causing alleles. Similarly, murine myoblasts overexpressing a catalytically inactive TRIM32 mutant aberrantly accumulate α- and β-dystroglycan and α-sarcoglycan. We speculate that the stoichiometric loss of costamere components disrupts costamere complexes to promote muscle degeneration.

Modeling Neurodegenerative Disorders in Drosophila melanogaster

Drosophila melanogaster provides a powerful genetic model system in which to investigate the molecular mechanisms underlying neurodegenerative diseases. In this review, we discuss recent progress in Drosophila modeling Alzheimer's Disease, Parkinson's Disease, Amyotrophic Lateral Sclerosis (ALS), Huntington's Disease, Ataxia Telangiectasia, and neurodegeneration related to mitochondrial dysfunction or traumatic brain injury. We close by discussing recent progress using Drosophila models of neural regeneration and how these are likely to provide critical insights into future treatments for neurodegenerative disorders.

Reclassification of Mongolian Diffuse Gliomas According to the Revised 2016 World Health Organization Central Nervous System Tumor Classification

Background

The 2016 World Health Organization (WHO) classification of central nervous system (CNS) tumors has been modified to incorporate the IDH mutation and 1p/19q co-deletion in the diagnosis of diffuse gliomas. In this study, we aimed to evaluate the feasibility and prognostic significance of the revised 2016 WHO classification of CNS tumors in Mongolian patients with diffuse gliomas.

Methods

A total of 124 cases of diffuse gliomas were collected, and tissue microarray blocks were made. IDH1 mutation was tested using immunohistochemistry, and 1p/19q co-deletion status was examined using fluorescence in situ hybridization analysis.

Results

According to the 2016 WHO classification, 124 cases of diffuse brain glioma were reclassified as follows: 10 oligodendroglioma, IDH^mut and 1p/19q co-deleted; three anaplastic oligodendroglioma, IDH^mut and 1p/19q co-deleted; 35 diffuse astrocytoma, IDH^mut, 11 diffuse astrocytoma, IDH^wt, not otherwise specified (NOS); 22 anaplastic astrocytoma, IDH^mut, eight anaplastic astrocytoma, IDH^wt, NOS; and 35 glioblastoma, IDH^wt, NOS, respectively. The 2016 WHO classification presented better prognostic value for overall survival in patients with grade II tumors than traditional histological classification. Among patients with grade II tumors, those with oligodendroglioma IDH^mut and 1p/19q co-deleted and diffuse astrocytoma IDH^mut showed significantly higher survival than those with diffuse astrocytoma IDH^wt, NOS (p<.01).

Conclusions

Mongolian diffuse gliomas could be reclassified according to the new 2016 WHO classification. Reclassification revealed substantial changes in diagnosis of both oligodendroglial and astrocytic entities. We have confirmed that the revised 2016 WHO CNS tumor classification has prognostic significance in Mongolian patients with diffuse gliomas, especially those with grade II tumors.

A Novel Mutation in Brain Tumor Causes Both Neural Over-Proliferation and Neurodegeneration in Adult Drosophila

A screen for neuroprotective genes in Drosophila melanogaster led to the identification of a mutation that causes extreme, progressive loss of adult brain neuropil in conjunction with massive brain overgrowth. We mapped the mutation to the brain tumor (brat) locus, which encodes a tripartite motif-NCL-1, HT2A, and LIN-41 (TRIM-NHL) RNA-binding protein with established roles limiting stem cell proliferation in developing brain and ovary. However, a neuroprotective role for brat in the adult Drosophila brain has not been described previously. The new allele, brat^cheesehead (brat^chs), carries a mutation in the coiled-coil domain of the TRIM motif, and is temperature-sensitive. We demonstrate that mRNA and protein levels of neural stem cell genes are increased in heads of adult brat^chs mutants and that the over-proliferation phenotype initiates prior to adult eclosion. We also report that disruption of an uncharacterized gene coding for a presumptive prolyl-4-hydroxylase strongly enhances the over-proliferation and neurodegeneration phenotypes. Together, our results reveal an unexpected role for brat that could be relevant to human cancer and neurodegenerative diseases.

Exosomal TRIM3 is a novel marker and therapy target for gastric cancer

Background

Exosomes are critically involved in cancer development and progression. The exosomal contents have been suggested as ideal cancer biomarkers. In this study, we investigated the expression of exosomal proteins in the serum of gastric cancer patients and their roles in gastric cancer.

Methods

The proteomic profile of exosomes from the serum of gastric cancer patients was detected by using LC-MS/MS. The expression of TRIM3 in exosomes from the serum of gastric cancer patients and healthy controls was assessed by ELISA and western blot. Immunohistochemistry was used to detect TRIM3 expression in gastric cancer tissues and their matching adjacent tissues. The growth and migration abilities of gastric cancer cells with TRIM3 overexpression or knockdown in vitro were evaluated by colony formation assay and transwell migration assay. The effects of TRIM3 overexpression or knockdown on gastric cancer growth and metastasis in vivo were investigated by using subcutaneous xenograft tumor and peritoneal metastasis mouse model. The effects of TRIM3-overexpressing exosomes on gastric cancer growth and metastasis in vitro and in vivo were also evaluated.

Results

We found that the expression levels of TRIM3 mRNA and protein were decreased in gastric cancer tissues compared to the matched control tissues. In addition, the levels of TRIM3 protein in the serum exosomes of gastric cancer patients were lower than that in healthy controls. We demonstrated that TRIM3 overexpression reduced while TRIM3 knockdown promoted the growth and metastasis of gastric cancer in vitro and in vivo through the regulation of stem cell factors and EMT regulators. Moreover, exosomes-mediated delivery of TRIM3 protein could suppress gastric cancer growth and metastasis in vitro and in vivo.

Conclusions

Taken together, our findings suggest that exosomal TRIM3 may serve as a biomarker for gastric cancer diagnosis and the delivery of TRIM3 by exosomes may provide a new avenue for gastric cancer therapy.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0825-0) contains supplementary material, which is available to authorized users.

The asymmetrically segregating lncRNA cherub is required for transforming stem cells into malignant cells

Tumor cells display features that are not found in healthy cells. How they become immortal and how their specific features can be exploited to combat tumorigenesis are key questions in tumor biology. Here we describe the long non-coding RNA cherub that is critically required for the development of brain tumors in Drosophila but is dispensable for normal development. In mitotic Drosophila neural stem cells, cherub localizes to the cell periphery and segregates into the differentiating daughter cell. During tumorigenesis, de-differentiation of cherub-high cells leads to the formation of tumorigenic stem cells that accumulate abnormally high cherub levels. We show that cherub establishes a molecular link between the RNA-binding proteins Staufen and Syncrip. As Syncrip is part of the molecular machinery specifying temporal identity in neural stem cells, we propose that tumor cells proliferate indefinitely, because cherub accumulation no longer allows them to complete their temporal neurogenesis program.

Many biological signals control how cells grow and divide. However, cancer cells do not obey these growth-restricting signals, and as a result large tumors may develop.

Recent experiments have suggested that stem cells – the precursors to the different types of specialized cells found in the body – are particularly important for generating tumors. A stem cell normally divides unequally to form a self-renewing cell and a more specialized cell (often a progenitor cell that will give rise to increasingly specialized cell types). The timing of when the specialization occurs can be key to guiding the ultimately produced cell progenies to their final identity. However, in a tumor cells can retain the ability to self-renew. Ultimately, the resulting ‘tumor stem cells’ become immortal and proliferate indefinitely. It is not fully understood why this uncontrolled proliferation occurs.

Just like mammals (including humans), fruit flies can develop tumors. Some of the DNA mutations responsible for tumor development were already identified in flies as early as in the 1970s. This has made fruit flies a well-studied model system for uncovering the principle defects that cause tumors to form.

Landskron et al. have now studied the neural stem cells found in brain tumors in fruit flies. Additional DNA mutations were not responsible for these cells becoming immortal. Instead, certain RNA molecules – products that are ‘transcribed’ from the DNA – were present in different amounts in tumor cells. The RNA that showed the greatest increase in tumor cells is a so-called long non-coding RNA named cherub. This RNA molecule has no important role in normal fruit flies, but is critical for tumor formation.

Landskron et al. found that during cell division cherub segregates from the neural stem cells to the newly formed progenitor cells, where it breaks down over time. Progenitor cells that contain high levels of cherub give rise to tumor-generating neural stem cells. At the molecular level, cherubhelps two proteins to interact with each other: one called Syncrip that makes the neural stem cells take on a older identity, and another one (Staufen) that tethers it to the cell membrane. By restricting Syncrip to a particular location in the cell, cherub alters the timing of stem cell specialization, which contributes to tumor formation.

Overall, the results presented by Landskron et al. reveal a new role for long non-coding RNAs: controlling the localization of the proteins that determine the fate of the cell. They also highlight a critical link between the timing of stem cell development and the proliferation of the cells. Further work is now needed to test whether the same control mechanism works in species other than fruit flies.

Characterization and biological function analysis of the TRIM47 gene from common carp (Cyprinus carpio)

The TRIM family protein was known to play an important role in many cellular processes, including potential antiviral activity, which has attracted lots of attention. In this study, a TRIM47 homolog from common carp (Cyprinus carpio) was cloned and the full length coding DNA sequence (CDS) of this gene was analyzed, results showed that there was a 97% similarity between common carp and zebrafish (Danio rerio), but only 18% similarity with that of human (Homo sapiens) and mouse (Mus musculus). The tissue distribution analysis showed TRIM47 had the highest mRNA level in the brain, a few immune related organs such as liver and kidney also had a relatively high level of TRIM47 expression. SVCV infection decreased TRIM47 mRNA level significantly both in vitro and in vivo, but its expression was not affected by the virus at the protein level. The recombinant plasmid pcDNA4-TRIM47-His was constructed, the subcellular localization in FHM cells showed that TRIM47 uniformly distributed in the cytoplasm at the form of tiny spots, and partially localized in the mitochondria. Overexpression TRIM47 in FHM cells significantly decreased the mRNA level of SVCV-G gene, and it was accompanied with the increasing of IFN1, a member of type I IFN, at the case of SVCV stimulation. In summary, our results had first demonstrated that TRIM47 of the common carp played an important role in viral resistance processes as well as the regulation of IFN signaling pathway.

The tripartite motif-containing protein 3 on the proliferation and cytokine secretion of rheumatoid arthritis fibroblast-like synoviocytes

Recent studies have revealed fibroblast-like synoviocytes (FLS) as a pivotal effector cell in the inflamed joint of rheumatoid arthritis (RA) patients. FLS exhibit high proliferation rates and constitutive expression of cytokines, contributing to the pathogenesis of RA. In this study, we found that the expression of tripartite motif-containing protein 3 (TRIM3), a candidate tumor suppressor gene, was lower in synovial tissue samples of RA patients than in that of healthy controls. We then investigated the role of TRIM3 on the proliferation and cytokine secretion of primary cultured FLS from RA patients. Enforced expression of TRIM3 in RA FLS led to significantly decreased cell proliferation as indicated by Cell Counting Kit-8 assay, reduced secretion of tumor necrosis factor-α (TNF)-α, interleukin (IL)-1β and IL-6 as indicated by enzyme-linked immunosorbent assays, and decreased p38 phosphorylation as assessed by western blot analysis. The proteins promoting cell cycles (cyclin D1 and PCNA) were downregulated and the protein negatively regulating cell cycle progression (p53 and p21) was upregulated after TRIM3 overexpression. Importantly, TRIM3 knockdown had reverse effects on cell proliferation, which was suppressed by the p38-specific inhibitor SB203580. In conclusion, the current results demonstrated the downregulation of TRIM3 expression in RA synovial tissues. Importantly, TRIM3 exerted an anti-proliferation role in RA FLS via p38 signaling pathway.

Molecular Programs Underlying Asymmetric Stem Cell Division and Their Disruption in Malignancy

Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two unequal daughter cells. One retains its stem cell identity while the other becomes specialized through a differentiation program and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell in order to direct their destiny. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and non-canonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer.

Potential role of TRIM3 as a novel tumour suppressor in colorectal cancer (CRC) development

OBJECTIVE

Colorectal cancer (CRC) is the third leading cause of cancer-related mortality in the United States. Recent cancer genome-sequencing efforts and complementary functional studies have led to the identification of a collection of candidate 'driver' genes involved in CRC tumorigenesis. Tripartite motif (TRIM3) is recently identified as a tumour suppressor in glioblastoma but this tumour-suppressive function has not been investigated in CRC.

MATERIAL AND METHODS

In this study, we investigated the potential role of TRIM3 as a tumour suppressor in CRC development by manipulating the expression of TRIM3 in two authentic CRC cell lines, HCT116 and DLD1, followed by various functional assays, including cell proliferation, colony formation, scratch wound healing, soft agar, and invasion assays. Xenograft experiment was performed to examine in vivo tumour-suppressive properties of TRIM3.

RESULTS

Small-interfering RNA (siRNA) mediated knockdown of TRIM3 conferred growth advantage in CRC cells. In contrast, overexpression of TRIM3 affected cell survival, cell migration, anchorage independent growth and invasive potential in CRC cells. In addition, TRIM3 was found to be down-regulated in human colon cancer tissues compared with matched normal colon tissues. Overexpression of TRIM3 significantly inhibited tumour growth in vivo using xenograft mouse models. Mechanistic investigation revealed that TRIM3 can regulate p53 protein level through its stabilisation.

CONCLUSIONS

TRIM3 functions as a tumour suppressor in CRC progression. This tumour-suppressive function is exerted partially through regulation of p53 protein. Therefore, this protein may represent a novel therapeutic target for prevention or intervention of CRC.

Molecular Characterization, Tissue Distribution and Expression, and Potential Antiviral Effects of TRIM32 in the Common Carp (Cyprinus carpio)

Tripartite motif-containing protein 32 (TRIM32) belongs to the tripartite motif (TRIM) family, which consists of a large number of proteins containing a RING (Really Interesting New Gene) domain, one or two B-box domains, and coiled coil motif followed by different C-terminal domains. The TRIM family is known to be implicated in multiple cellular functions, including antiviral activity. However, it is presently unknown whether TRIM32 of common carp (Cyprinus carpio) has the antiviral effect. In this study, the sequence, expression, and antiviral function of TRIM32 homolog from common carp were analyzed. The full-length coding sequence region of trim32 was cloned from common carp. The results showed that the expression of TRIM32 (mRNA) was highest in the brain, remained stably expressed during embryonic development, and significantly increased following spring viraemia of carp virus (SVCV) infection. Transient overexpression of TRIM32 in affected Epithelioma papulosum cyprinid cells led to significant decrease of SVCV production as compared to the control group. These results suggested a potentially important role of common carp TRIM32 in enhancing host immune response during SVCV infection both in vivo and in vitro.

TRIM-NHL proteins in development and disease

TRIM-NHL proteins are key regulators of developmental transitions, for example promoting differentiation, while inhibiting cell growth and proliferation, in stem and progenitor cells. Abnormalities in these proteins have been also associated with human diseases, particularly affecting muscular and neuronal functions, making them potential targets for therapeutic intervention. The purpose of this review is to provide a systematic and comprehensive summary on the most studied TRIM-NHL proteins, highlighting examples where connections were established between structural features, molecular functions and biological outcomes.

Efficient exploration of pan-cancer networks by generalized covariance selection and interactive web content

Statistical network modeling techniques are increasingly important tools to analyze cancer genomics data. However, current tools and resources are not designed to work across multiple diagnoses and technical platforms, thus limiting their applicability to comprehensive pan-cancer datasets such as The Cancer Genome Atlas (TCGA). To address this, we describe a new data driven modeling method, based on generalized Sparse Inverse Covariance Selection (SICS). The method integrates genetic, epigenetic and transcriptional data from multiple cancers, to define links that are present in multiple cancers, a subset of cancers, or a single cancer. It is shown to be statistically robust and effective at detecting direct pathway links in data from TCGA. To facilitate interpretation of the results, we introduce a publicly accessible tool (cancerlandscapes.org), in which the derived networks are explored as interactive web content, linked to several pathway and pharmacological databases. To evaluate the performance of the method, we constructed a model for eight TCGA cancers, using data from 3900 patients. The model rediscovered known mechanisms and contained interesting predictions. Possible applications include prediction of regulatory relationships, comparison of network modules across multiple forms of cancer and identification of drug targets.

Cancer stem cell division: when the rules of asymmetry are broken

Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two daughter cells and simultaneously directs the differential fate of both: one retains its stem cell identity while the other becomes specialized and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and noncanonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer. The universe is asymmetric and I am persuaded that life, as it is known to us, is a direct result of the asymmetry of the universe or of its indirect consequences. The universe is asymmetric. -Louis Pasteur.

Human Brat ortholog TRIM3 is a tumor suppressor that regulates asymmetric cell division in glioblastoma

Cancer stem cells, capable of self-renewal and multipotent differentiation, influence tumor behavior through a complex balance of symmetric and asymmetric cell divisions. Mechanisms regulating the dynamics of stem cells and their progeny in human cancer are poorly understood. In Drosophila, mutation of brain tumor (brat) leads to loss of normal asymmetric cell division by developing neural cells and results in a massively enlarged brain composed of neuroblasts with neoplastic properties. Brat promotes asymmetric cell division and directs neural differentiation at least partially through its suppression on Myc. We identified TRIM3 (11p15.5) as a human ortholog of Drosophila brat and demonstrate its regulation of asymmetric cell division and stem cell properties of glioblastoma (GBM), a highly malignant human brain tumor. TRIM3 gene expression is markedly reduced in human GBM samples, neurosphere cultures, and cell lines and its reconstitution impairs growth properties in vitro and in vivo. TRIM3 expression attenuates stem-like qualities of primary GBM cultures, including neurosphere formation and the expression of stem cell markers CD133, Nestin, and Nanog. In GBM stem cells, TRIM3 expression leads to a greater percentage dividing asymmetrically rather than symmetrically. As with Brat in Drosophila, TRIM3 suppresses c-Myc expression and activity in human glioma cell lines. We also demonstrate a strong regulation of Musashi-Notch signaling by TRIM3 in GBM neurospheres and neural stem cells that may better explain its effect on stem cell dynamics. We conclude that TRIM3 acts as a tumor suppressor in GBM by restoring asymmetric cell division.

The ability of TRIM3 to induce growth arrest depends on RING-dependent E3 ligase activity

Mutation of the TRIM (tripartite motif)-NHL family members brat and mei-P26 perturb the differentiation of transit-amplifying progenitor cells resulting in tumour-like phenotypes. The NHL (named after the NCL1, HT2A and LIN41 repeat) domain is essential for their growth suppressive activity, and they can induce cell-cycle exit in a RING-independent manner. TRIM3 is the only bona fide tumour suppressor in the mammalian TRIM-NHL subfamily and similar to the other members of this family, its ability to inhibit cell proliferation depends on the NHL domain. However, whether the RING domain was required for TRIM3-dependent cell-cycle exit had not been investigated. In the present study, we establish that the RING domain is required for TRIM3-induced growth suppression. Furthermore, we show that this domain is necessary to promote ubiquitination of p21 in a reconstituted in vitro system where UbcH5a is the preferred E2. Thus the ability of TRIM3 to suppress growth is associated with its ability to ubiquitinate proteins.

Brain tumor specifies intermediate progenitor cell identity by attenuating β-catenin/Armadillo activity

During asymmetric stem cell division, both the daughter stem cell and the presumptive intermediate progenitor cell inherit cytoplasm from their parental stem cell. Thus, proper specification of intermediate progenitor cell identity requires an efficient mechanism to rapidly extinguish the activity of self-renewal factors, but the mechanisms remain unknown in most stem cell lineages. During asymmetric division of a type II neural stem cell (neuroblast) in the Drosophila larval brain, the Brain tumor (Brat) protein segregates unequally into the immature intermediate neural progenitor (INP), where it specifies INP identity by attenuating the function of the self-renewal factor Klumpfuss (Klu), but the mechanisms are not understood. Here, we report that Brat specifies INP identity through its N-terminal B-boxes via a novel mechanism that is independent of asymmetric protein segregation. Brat-mediated specification of INP identity is critically dependent on the function of the Wnt destruction complex, which attenuates the activity of β-catenin/Armadillo (Arm) in immature INPs. Aberrantly increasing Arm activity in immature INPs further exacerbates the defects in the specification of INP identity and enhances the supernumerary neuroblast mutant phenotype in brat mutant brains. By contrast, reducing Arm activity in immature INPs suppresses supernumerary neuroblast formation in brat mutant brains. Finally, reducing Arm activity also strongly suppresses supernumerary neuroblasts induced by overexpression of klu. Thus, the Brat-dependent mechanism extinguishes the function of the self-renewal factor Klu in the presumptive intermediate progenitor cell by attenuating Arm activity, balancing stem cell maintenance and progenitor cell specification.

Asymmetric cell division of stem and progenitor cells during homeostasis and cancer

Stem and progenitor cells are characterized by their ability to self-renew and produce differentiated progeny. A fine balance between these processes is achieved through controlled asymmetric divisions and is necessary to generate cellular diversity during development and to maintain adult tissue homeostasis. Disruption of this balance may result in premature depletion of the stem/progenitor cell pool, or abnormal growth. In many tissues, including the brain, dysregulated asymmetric divisions are associated with cancer. Whether there is a causal relationship between asymmetric cell division defects and cancer initiation is as yet not known. Here, we review the cellular and molecular mechanisms that regulate asymmetric cell divisions in the neural lineage and discuss the potential connections between this regulatory machinery and cancer.

TRIM3, a tumor suppressor linked to regulation of p21(Waf1/Cip1.)

The TRIM family of genes is largely studied because of their roles in development, differentiation and host cell antiviral defenses; however, roles in cancer biology are emerging. Loss of heterozygosity of the TRIM3 locus in ∼20% of human glioblastomas raised the possibility that this NHL-domain containing member of the TRIM gene family might be a mammalian tumor suppressor. Consistent with this, reducing TRIM3 expression increased the incidence of and accelerated the development of platelet-derived growth factor -induced glioma in mice. Furthermore, TRIM3 can bind to the cdk inhibitor p21(WAF1/CIP1). Thus, we conclude that TRIM3 is a tumor suppressor mapping to chromosome 11p15.5 and that it might block tumor growth by sequestering p21 and preventing it from facilitating the accumulation of cyclin D1-cdk4.

Neural stem cells in Drosophila: molecular genetic mechanisms underlying normal neural proliferation and abnormal brain tumor formation

Neural stem cells in Drosophila are currently one of the best model systems for understanding stem cell biology during normal development and during abnormal development of stem cell-derived brain tumors. In Drosophila brain development, the proliferative activity of neural stem cells called neuroblasts gives rise to both the optic lobe and the central brain ganglia, and asymmetric cell divisions are key features of this proliferation. The molecular mechanisms that underlie the asymmetric cell divisions by which these neuroblasts self-renew and generate lineages of differentiating progeny have been studied extensively and involve two major protein complexes, the apical complex which maintains polarity and controls spindle orientation and the basal complex which is comprised of cell fate determinants and their adaptors that are segregated into the differentiating daughter cells during mitosis. Recent molecular genetic work has established Drosophila neuroblasts as a model for neural stem cell-derived tumors in which perturbation of key molecular mechanisms that control neuroblast proliferation and the asymmetric segregation of cell fate determinants lead to brain tumor formation. Identification of novel candidate genes that control neuroblast self-renewal and differentiation as well as functional analysis of these genes in normal and tumorigenic conditions in a tissue-specific manner is now possible through genome-wide transgenic RNAi screens. These cellular and molecular findings in Drosophila are likely to provide valuable genetic links for analyzing mammalian neural stem cells and tumor biology.

Characterization and biological function analysis of the trim3a gene from zebrafish (Danio rerio)

The biological significance of tripartite motif (TRIM) proteins is increasingly being appreciated due to their roles in a broad range of biological processes that associated with innate immunity. In this study, we have described the structural and functional analysis of TRIM3a from zebrafish. Annotation of domain architectures found that the TRIM3a fulfills the TRIM-NHL rule of domain composition with a Filamin/ABP280 domain and NHL repeats at its C-terminal region. In addition, the mRNA expression level of TRIM3a was the highest in brain, and with a relatively higher level in spleen, liver, and gill. A strong expression starting at 36 h post fertilization (hpf) was observed by real-time PCR and could be detected in brain by in situ hybridization, suggesting that TRIM3a protein might play an important role in brain development in zebrafish. Considering that TRIM3a has a RING finger domain, we expressed and purified the TRIM3a protein and performed ubiquitylation assays, our results showed that TRIM3a underwent self-polyubiquitylation in combination with E1, UbcH5c, biotin-ubiquitin in vitro. Meanwhile, TRIM3a-R without the RING domain was expressed and purified as well, in vitro ubiquitylation assays showed that the self-ubiquitylation of TRIM3a was dependent on its RING domain, suggesting that TRIM3a might function as a RING finger E3 ubiquitin ligase.

Genome-wide analysis of self-renewal in Drosophila neural stem cells by transgenic RNAi

The balance between stem cell self-renewal and differentiation is precisely controlled to ensure tissue homeostasis and prevent tumorigenesis. Here we use genome-wide transgenic RNAi to identify 620 genes potentially involved in controlling this balance in Drosophila neuroblasts. We quantify all phenotypes and derive measurements for proliferation, lineage, cell size, and cell shape. We identify a set of transcriptional regulators essential for self-renewal and use hierarchical clustering and integration with interaction data to create functional networks for the control of neuroblast self-renewal and differentiation. Our data identify key roles for the chromatin remodeling Brm complex, the spliceosome, and the TRiC/CCT-complex and show that the alternatively spliced transcription factor Lola and the transcriptional elongation factors Ssrp and Barc control self-renewal in neuroblast lineages. As our data are strongly enriched for genes highly expressed in murine neural stem cells, they are likely to provide valuable insights into mammalian stem cell biology as well.

Drosophila melanogaster as a model system for human brain cancers

Glioblastomas (GBM), the most common primary brain tumors, infiltrate the brain, grow rapidly, and are refractory to current therapies. Signature genetic lesions in glioblastomas include mutation of the epidermal growth factor receptor tyrosine kinase (EGFR) receptor tyrosine kinase and activating mutations in components of the PI-3 kinase (PI3K) pathway. Despite years of study, how these pathways specifically regulate glial pathogenesis is unclear. To address the genetic and cellular origins of this disease, a novel Drosophila GBM model has been developed in which glial progenitor cells give rise to proliferative and invasive neoplastic cells that create transplantable tumors in response to constitutive co-activation of the EGFR-Ras and PI3K pathways. Standing with a rich literature demonstrating the direct relevance of Drosophila to studies on human cancer, neurological disease, and neurodevelopment, this model represents a robust cell-type specific Drosophila neurological disease model in which malignant cells are created by mutations in genetic pathways thought to be driving forces in a homologous human disease. Using lineage analysis and cell-type specific markers, neoplastic glial cells were found to originate from committed glial progenitor cells, rather than from multipotent neuroblasts. Genetic analyses demonstrated that EGFR-Ras and PI3K induce fly glial neoplasia through activation of a combinatorial genetic network composed, in part, of other genetic pathways also commonly mutated in human glioblastomas. In the future, large-scale forward genetic screens with this model may reveal new insights into the origins and treatments of human glioblastoma.

Brat promotes stem cell differentiation via control of a bistable switch that restricts BMP signaling

Drosophila ovarian germline stem cells (GSCs) are maintained by Dpp signaling and the Pumilio (Pum) and Nanos (Nos) translational repressors. Upon division, Dpp signaling is extinguished, and Nos is downregulated in one daughter cell, causing it to switch to a differentiating cystoblast (CB). However, downstream effectors of Pum-Nos remain unknown, and how CBs lose their responsiveness to Dpp is unclear. Here, we identify Brain Tumor (Brat) as a potent differentiation factor and target of Pum-Nos regulation. Brat is excluded from GSCs by Pum-Nos but functions with Pum in CBs to translationally repress distinct targets, including the Mad and dMyc mRNAs. Regulation of both targets simultaneously lowers cellular responsiveness to Dpp signaling, forcing the cell to become refractory to the self-renewal signal. Mathematical modeling elucidates bistability of cell fate in the Brat-mediated system, revealing how autoregulation of GSC number can arise from Brat coupling extracellular Dpp regulation to intracellular interpretation.

The relevance of symmetric and asymmetric cell divisions to human central nervous system diseases

During development of the embryonic central nervous system (CNS), large numbers of neurons and glia are generated from the neuroepithelium and its progenitor derivatives as a result of symmetric and asymmetric cell divisions. We describe the biology of symmetric and asymmetric cell divisions in the CNS as gleaned from animal models, and discuss the relevance of these processes to human CNS development and disease.

American Association for Cancer Research Genetics and Biology of Brain Cancers 2009, December 13-15, 2009, San Diego, CA

Molecularly targeted therapies promise to transform the treatment of cancer patients, including those with brain tumors. A deeper understanding of the biology of brain tumors has led to a palpable excitement that new and more effective treatments are on the horizon for these deadly diseases. This conference brought basic, genomic, and translational scientists together with clinicians to discuss how to develop more effective molecularly targeted therapies for brain tumor patients based on a mechanistic understanding of the molecular circuitry and biology of the disease.

Association weight matrix for the genetic dissection of puberty in beef cattle

We describe a systems biology approach for the genetic dissection of complex traits based on applying gene network theory to the results from genome-wide associations. The associations of single-nucleotide polymorphisms (SNP) that were individually associated with a primary phenotype of interest, age at puberty in our study, were explored across 22 related traits. Genomic regions were surveyed for genes harboring the selected SNP. As a result, an association weight matrix (AWM) was constructed with as many rows as genes and as many columns as traits. Each {i, j} cell value in the AWM corresponds to the z-score normalized additive effect of the ith gene (via its neighboring SNP) on the jth trait. Columnwise, the AWM recovered the genetic correlations estimated via pedigree-based restricted maximum-likelihood methods. Rowwise, a combination of hierarchical clustering, gene network, and pathway analyses identified genetic drivers that would have been missed by standard genome-wide association studies. Finally, the promoter regions of the AWM-predicted targets of three key transcription factors (TFs), estrogen-related receptor gamma (ESRRG), Pal3 motif, bound by a PPAR-gamma homodimer, IR3 sites (PPARG), and Prophet of Pit 1, PROP paired-like homeobox 1 (PROP1), were surveyed to identify binding sites corresponding to those TFs. Applied to our case, the AWM results recapitulate the known biology of puberty, captured experimentally validated binding sites, and identified candidate genes and gene-gene interactions for further investigation.

Identification of BERP (brain-expressed RING finger protein) as a p53 target gene that modulates seizure susceptibility through interacting with GABA(A) receptors

p53 is a central player in responses to cellular stresses and a major tumor suppressor. The identification of unique molecules within the p53 signaling network can reveal functions of this important transcription factor. Here, we show that brain-expressed RING finger protein (BERP) is a gene whose expression is up-regulated in a p53-dependent manner in human cells and in mice. We generated BERP-deficient mice by gene targeting and demonstrated that they exhibit increased resistance to pentylenetetrazol-induced seizures. Electrophysiological and biochemical studies of cultured cortical neurons of BERP-deficient mice showed a decrease in the amplitude of GABA(A) receptor (GABA(A)R)-mediated miniature inhibitory postsynaptic currents as well as reduced surface protein expression of GABA(A)Rs containing the gamma2-subunit. However, BERP deficiency did not decrease GABA(A)Rgamma2 mRNA levels, raising the possibility that BERP may act at a posttranscriptional level to regulate the intracellular trafficking of GABA(A)Rs. Our results indicate that BERP is a unique p53-regulated gene and suggest a role for p53 within the central nervous system.

Genetic mechanisms regulating stem cell self-renewal and differentiation in the central nervous system of Drosophila

Recent studies using the Drosophila central nervous system as a model have identified key molecules and mechanisms underlying stem cell self-renewal and differentiation. These studies suggest that proteins like Aurora-A, atypical protein kinase C, Prospero and Brain tumor act as key regulators in a tightly coordinated interplay between mitotic spindle orientation and asymmetric protein localization. These data also provide initial evidence that both processes are coupled to cell cycle progression and growth control, thereby regulating a binary switch between proliferative stem self-renewal and differentiative progenitor cell specification. Considering the evolutionary conservation of some of the mechanisms and molecules involved, these data provide a rationale and genetic model for understanding stem cell self-renewal and differentiation in general. The new data gained in Drosophila may therefore lead to conceptual advancements in understanding the aetiology and treatment of human neurological disorders such as brain tumor formation and neurodegenerative diseases.

Lessons from development: A role for asymmetric stem cell division in cancer

Asymmetric stem cell division has emerged as a major regulatory mechanism for physiologic control of stem cell numbers. Reinvigoration of the cancer stem cell theory suggests that tumorigenesis may be regulated by maintaining the balance between asymmetric and symmetric cell division. Therefore, mutations affecting this balance could result in aberrant expansion of stem cells. Although a number of molecules have been implicated in regulation of asymmetric stem cell division, here, we highlight known tumor suppressors with established roles in this process. While a subset of these tumor suppressors were originally defined in developmental contexts, recent investigations reveal they are also lost or mutated in human cancers. Mutations in tumor suppressors involved in asymmetric stem cell division provide mechanisms by which cancer stem cells can hyperproliferate and offer an intriguing new focus for understanding cancer biology. Our discussion of this emerging research area derives insight from a frontier area of basic science and links these discoveries to human tumorigenesis. This highlights an important new focus for understanding the mechanism underlying expansion of cancer stem cells in driving tumorigenesis.