The WTX Tumor Suppressor Interacts with the Transcriptional Corepressor TRIM28

Satellite cell-derived TRIM28 is pivotal for mechanical load- and injury-induced myogenesis

Satellite cells are skeletal muscle stem cells that contribute to postnatal muscle growth, and they endow skeletal muscle with the ability to regenerate after a severe injury. Here we discover that this myogenic potential of satellite cells requires a protein called tripartite motif-containing 28 (TRIM28). Interestingly, different from the role reported in a previous study based on C2C12 myoblasts, multiple lines of both in vitro and in vivo evidence reveal that the myogenic function of TRIM28 is not dependent on changes in the phosphorylation of its serine 473 residue. Moreover, the functions of TRIM28 are not mediated through the regulation of satellite cell proliferation or differentiation. Instead, our findings indicate that TRIM28 regulates the ability of satellite cells to progress through the process of fusion. Specifically, we discover that TRIM28 controls the expression of a fusogenic protein called myomixer and concomitant fusion pore formation. Collectively, the outcomes of this study expose the framework of a novel regulatory pathway that is essential for myogenesis.

The role of satellite cell-derived TRIM28 in mechanical load- and injury-induced myogenesis

Satellite cells are skeletal muscle stem cells that contribute to postnatal muscle growth, and they endow skeletal muscle with the ability to regenerate after a severe injury. Here we discovered that this myogenic potential of satellite cells requires a protein called tripartite motif-containing 28 (TRIM28). Unexpectedly, multiple lines of both in vitro and in vivo evidence revealed that the myogenic function of TRIM28 is not dependent on changes in the phosphorylation of its serine 473 residue. Moreover, the functions of TRIM28 were not mediated through the regulation of satellite cell proliferation or differentiation. Instead, our findings indicate that TRIM28 regulates the ability of satellite cells to progress through the process of fusion. Specifically, we discovered that TRIM28 controls the expression of a fusogenic protein called myomixer and concomitant fusion pore formation. Collectively, the outcomes of this study expose the framework of a novel regulatory pathway that is essential for myogenesis.

Recent advances in Wilms' tumor predisposition

Wilms' tumor (WT), the most common childhood kidney cancer, develops in association with an underlying germline predisposition in up to 15% of cases. Germline alterations affecting the WT1 gene and epigenetic alterations affecting the 11p15 locus are associated with a selective increase in WT risk. Nevertheless, WT also occurs in the context of more pleiotropic cancer predispositions, such as DICER1, Li-Fraumeni and Bloom syndrome, as well as Fanconi anemia. Recent germline genomic investigations have increased our understanding of the host genetic factors that influence WT risk, with sequencing of rare familial cases and large WT cohorts revealing an expanding array of predisposition genes and associated genetic conditions. Here, we describe evidence implicating WT1, the 11p15 locus, and the recently identified genes CTR9, REST and TRIM28 in WT predisposition. We discuss the clinical features, mode of inheritance and biological aspects of tumorigenesis, when known. Despite these described associations, many cases of familial WT remain unexplained. Continued investigations are needed to fully elucidate the landscape of germline genetic alterations in children with WT. Establishing a genetic diagnosis is imperative for WT families so that individuals harboring a predisposing germline variant can undergo surveillance, which should enable the early detection of tumors and use of less intensive treatments, thereby leading to improved overall outcomes.

The translational values of TRIM family in pan-cancers: From functions and mechanisms to clinics

Cancer is the second leading cause of human death across the world. Tripartite motif (TRIM) family, with E3 ubiquitin ligase activities in majority of its members, is reported to be involved in multiple cellular processes and signaling pathways. TRIM proteins have critical effects in the regulation of biological behaviors of cancer cells. Here, we discussed the current understanding of the molecular mechanism of TRIM proteins regulation of cancer cells. We also comprehensively reviewed published studies on TRIM family members as oncogenes or tumor suppressors in the oncogenesis, development, and progression of a variety of types of human cancers. Finally, we highlighted that certain TRIM family members are potential molecular biomarkers for cancer diagnosis and prognosis, and potential therapeutic targets.

TRIM28 variants and Wilms' tumour predisposition

TRIM28 was recently identified as a Wilms' tumour (WT) predisposition gene, with germline pathogenic variants identified in around 1% of isolated and 8% of familial WT cases. TRIM28 variants are associated with epithelial WT, but the presence of other tumour components or anaplasia does not exclude the presence of a germline or somatic TRIM28 variant. In children with WT, TRIM28 acts as a classical tumour suppressor gene, with both alleles generally disrupted in the tumour. Therefore, loss of TRIM28 (KAP1/TIF1beta) protein expression in tumour tissue by immunohistochemistry is an effective strategy to identify patients carrying pathogenic TRIM28 variants. TRIM28 is a ubiquitously expressed corepressor that binds transcription factors in a context‐, species‐, and cell‐type‐specific manner to control the expression of genes and transposable elements during embryogenesis and cellular differentiation. In this review, we describe the inheritance patterns, histopathological and clinical features of TRIM28‐associated WT, as well as potential underlying mechanisms of tumourigenesis during embryonic kidney development. Recognizing germline TRIM28 variants in patients with WT can enable counselling, genetic testing, and potential early detection of WT in other children in the family. A further exploration of TRIM28‐associated WT will help to unravel the diverse and complex mechanisms underlying WT development. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

TRIM28 Regulates Dlk1 Expression in Adipogenesis

The tripartite motif-containing protein 28 (TRIM28) is a transcription corepressor, interacting with histone deacetylase and methyltransferase complexes. TRIM28 is a crucial regulator in development and differentiation. We would like to investigate its function and regulation in adipogenesis. Knockdown of Trim28 by transducing lentivirus-carrying shRNAs impairs the differentiation of 3T3-L1 preadipocytes, demonstrated by morphological observation and gene expression analysis. To understand the molecular mechanism of Trim28-mediated adipogenesis, the RNA-seq was performed to find out the possible Trim28-regulated genes. Dlk1 (delta-like homolog 1) was increased in Trim28 knockdown 3T3-L1 cells both untreated and induced to differentiation. Dlk1 is an imprinted gene and known as an inhibitor of adipogenesis. Further knockdown of Dlk1 in Trim28 knockdown 3T3-L1 would rescue cell differentiation. The epigenetic analysis showed that DNA methylation of Dlk1 promoter and differentially methylated regions (DMRs) was not altered significantly in Trim28 knockdown cells. However, compared to control cells, the histone methylation on the Dlk1 promoter was increased at H3K4 and decreased at H3K27 in Trim28 knockdown cells. Finally, we found Trim28 might be recruited by transcription factor E2f1 to regulate Dlk1 expression. The results imply Trim28-Dlk1 axis is critical for adipogenesis.

TRIM28 congenital predisposition to Wilms' tumor: novel mutations and presentation in a sibling pair

Wilms’ tumor is the most common renal malignancy in children. In addition to staging, molecular risk stratification, such as loss of heterozygosity (LOH) in Chromosomes 1 and 16, is being increasingly used. Although genetic predisposition syndromes have been well-characterized in some Wilms’ tumors, recent sequencing and biology efforts are expanding the classification of this malignancy. Here we present a case of siblings with remarkably similar presentations of bilateral Wilms’ tumor at ∼12 mo of age. Thorough exam after the younger sibling was diagnosed did not reveal any signs to suggest one of the known Wilms’ predisposition syndromes. Both were treated with standard therapies with good response and long-term sustained complete remission of 53 and 97 mo, respectively. Whole-exome sequencing was performed on a tumor sample from each patient and matched blood from one, revealing a shared truncation mutation of TRIM28 in all three samples with heterozygosity in the germline sample. TRIM28 loss has been recently implicated in early-stage Wilms’ tumors with epithelioid morphology. These siblings expand the phenotype for presentation with multifocal disease with retained excellent response to standard therapy.

Identification of new Wilms tumour predisposition genes: an exome sequencing study

BACKGROUND

Wilms tumour is the most common childhood renal cancer and is genetically heterogeneous. While several Wilms tumour predisposition genes have been identified, there is strong evidence that further predisposition genes are likely to exist. Our study aim was to identify new predisposition genes for Wilms tumour.

METHODS

In this exome sequencing study, we analysed lymphocyte DNA from 890 individuals with Wilms tumour, including 91 affected individuals from 49 familial Wilms tumour pedigrees. We used the protein-truncating variant prioritisation method to prioritise potential disease-associated genes for further assessment. We evaluated new predisposition genes in exome sequencing data that we generated in 334 individuals with 27 other childhood cancers and in exome data from The Cancer Genome Atlas obtained from 7632 individuals with 28 adult cancers.

FINDINGS

We identified constitutional cancer-predisposing mutations in 33 individuals with childhood cancer. The three identified genes with the strongest signal in the protein-truncating variant prioritisation analyses were TRIM28, FBXW7, and NYNRIN. 21 of 33 individuals had a mutation in TRIM28; there was a strong parent-of-origin effect, with all ten inherited mutations being maternally transmitted (p=0·00098). We also found a strong association with the rare epithelial subtype of Wilms tumour, with 14 of 16 tumours being epithelial or epithelial predominant. There were no TRIM28 mutations in individuals with other childhood or adult cancers. We identified truncating FBXW7 mutations in four individuals with Wilms tumour and a de-novo non-synonymous FBXW7 mutation in a child with a rhabdoid tumour. Biallelic truncating mutations in NYNRIN were identified in three individuals with Wilms tumour, which is highly unlikely to have occurred by chance (p<0·0001). Finally, we identified two de-novo KDM3B mutations, supporting the role of KDM3B as a childhood cancer predisposition gene.

INTERPRETATION

The four new Wilms tumour predisposition genes identified-TRIM28, FBXW7, NYNRIN, and KDM3B-are involved in diverse biological processes and, together with the other 17 known Wilms tumour predisposition genes, account for about 10% of Wilms tumour cases. The overlap between these 21 constitutionally mutated predisposition genes and 20 genes somatically mutated in Wilms tumour is limited, consisting of only four genes. We recommend that all individuals with Wilms tumour should be offered genetic testing and particularly, those with epithelial Wilms tumour should be offered TRIM28 genetic testing. Only a third of the familial Wilms tumour clusters we analysed were attributable to known genes, indicating that further Wilms tumour predisposition factors await discovery.

FUNDING

Wellcome Trust.

TRIM28 haploinsufficiency predisposes to Wilms tumor

Two percent of patients with Wilms tumors have a positive family history. In many of these cases the genetic cause remains unresolved. By applying germline exome sequencing in two families with two affected individuals with Wilms tumors, we identified truncating mutations in TRIM28. Subsequent mutational screening of germline and tumor DNA of 269 children affected by Wilms tumor was performed, and revealed seven additional individuals with germline truncating mutations, and one individual with a somatic truncating mutation in TRIM28. TRIM28 encodes a complex scaffold protein involved in many different processes, including gene silencing, DNA repair and maintenance of genomic integrity. Expression studies on mRNA and protein level showed reduction of TRIM28, confirming a loss-of-function effect of the mutations identified. The tumors showed an epithelial-type histology that stained negative for TRIM28 by immunohistochemistry. The tumors were bilateral in six patients, and 10/11 tumors are accompanied by perilobar nephrogenic rests. Exome sequencing on eight tumor DNA samples from six individuals showed loss-of-heterozygosity (LOH) of the TRIM28-locus by mitotic recombination in seven tumors, suggesting that TRIM28 functions as a tumor suppressor gene in Wilms tumor development. Additionally, the tumors showed very few mutations in known Wilms tumor driver genes, suggesting that loss of TRIM28 is the main driver of tumorigenesis. In conclusion, we identified heterozygous germline truncating mutations in TRIM28 in 11 children with mainly epithelial-type Wilms tumors, which become homozygous in tumor tissue. These data establish TRIM28 as a novel Wilms tumor predisposition gene, acting as a tumor suppressor gene by LOH.

A unique subset of low-risk Wilms tumors is characterized by loss of function of TRIM28 (KAP1), a gene critical in early renal development: A Children's Oncology Group study

This study explores the genomic alterations that contribute to the formation of a unique subset of low-risk, epithelial differentiated, favorable histology Wilms tumors (WT), tumors that have been characterized by their expression of post-induction renal developmental genes (Subset 1 WT). We demonstrate copy neutral loss of heterozygosity involving 19q13.32-q13.43, unaccompanied by evidence for imprinting by DNA methylation. We further identified loss-of-function somatic mutations in TRIM28 (also known as KAP1), located at 19q13, in 8/9 Subset 1 tumors analyzed. An additional germline TRIM28 mutation was identified in one patient. Retrospective evaluation of previously analyzed WT outside of Subset 1 identified an additional tumor with anaplasia and both TRIM28 and TP53 mutations. A major function of TRIM28 is the repression of endogenous retroviruses early in development. We depleted TRIM28 in HEK293 cells, which resulted in increased expression of endogenous retroviruses, a finding also demonstrated in TRIM28-mutant WT. TRIM28 has been shown by others to be active during early renal development, and to interact with WTX, another gene recurrently mutated in WT. Our findings suggest that inactivation of TRIM28 early in renal development contributes to the formation of this unique subset of FHWTs, although the precise manner in which TRIM28 impacts both normal renal development and oncogenesis remains elusive.

WTX inhibits gastric cancer migration through the reversal of epithelial-mesenchymal transition

The aim of the present study was to investigate whether the expression of Wilms' tumor gene on X chromosome (WTX) affected the epithelial-mesenchymal transition (EMT) process and migration of gastric cancer cells. Stable WTX-overexpressing AGS cells (AGS.W) were established and analyzed by flow cytometry. The efficiency of the overexpression was verified by fluorescence microscopy, reverse transcription-quantitative polymerase chain reaction and western blotting. To analyze the expression of EMT-associated proteins, western blotting and immunofluorescence assays were performed. The migratory capability of the cells was detected by Transwell wound-healing assays, respectively. Compared with that of the control cells (AGS.veh), WTX expression was notably increased at mRNA (P<0.05) and protein levels (P<0.05) in the AGS.W gastric cancer cells. Morphological observations indicated that AGS.W cells transformed into spindle shapes, compared to AGS.veh cells, which maintained round or oval shapes. Furthermore, western blotting and immunofluorescence validated that the expression level of the epithelial marker epithelial-cadherin was significantly increased, whereas the expression levels of the mesenchymal markers neural-cadherin, β-catenin and vimentin were significantly decreased in the AGS.W cells compared with those in the AGS.veh cells. In addition, the overexpression of WTX decreased the migratory ability of AGS.W cells compared with AGS.veh cells. Exogenous expression of WTX inhibited gastric cancer cell migration by reversing EMT. The results of the present study describe a molecular feature that may be a promising target for future gastric cancer therapy strategies.

Germline mutations and somatic inactivation of TRIM28 in Wilms tumour

Wilms tumour is a childhood tumour that arises as a consequence of somatic and rare germline mutations, the characterisation of which has refined our understanding of nephrogenesis and carcinogenesis. Here we report that germline loss of function mutations in TRIM28 predispose children to Wilms tumour. Loss of function of this transcriptional co-repressor, which has a role in nephrogenesis, has not previously been associated with cancer. Inactivation of TRIM28, either germline or somatic, occurred through inactivating mutations, loss of heterozygosity or epigenetic silencing. TRIM28-mutated tumours had a monomorphic epithelial histology that is uncommon for Wilms tumour. Critically, these tumours were negative for TRIM28 immunohistochemical staining whereas the epithelial component in normal tissue and other Wilms tumours stained positively. These data, together with a characteristic gene expression profile, suggest that inactivation of TRIM28 provides the molecular basis for defining a previously described subtype of Wilms tumour, that has early age of onset and excellent prognosis.

The germline and somatic molecular events associated with Wilms tumour, a childhood kidney cancer, have been progressively defined over the past three decades. Among the uncharacterised tumours are a group of tumours that have monomorphic epithelial histology, familial association, distinctively clustered gene-expression patterns, early age of diagnosis, and excellent prognosis. Here, we describe germline mutations and loss of function of TRIM28 in familial Wilms tumours, along with somatic loss of function in a non-familial Wilms tumour. All TRIM28-mutant tumours showed the rare monomorphic epithelial histology, suggesting that loss of TRIM28 expression could be a useful marker to define a group of tumours with excellent prognosis. Future studies could lead to identification and reassurance of families that carry TRIM28 mutations, and to the use of reduced intensity of treatment for children who develop TRIM28-null tumours.

A knock-in mouse line conditionally expressing the tumor suppressor WTX/AMER1

WTX/AMER1 is an important developmental regulator, mutations in which have been identified in a proportion of patients suffering from the renal neoplasm Wilms' tumor and in the bone malformation syndrome Osteopathia Striata with Cranial Sclerosis (OSCS). Its cellular functions appear complex and the protein can be found at the membrane, within the cytoplasm and the nucleus. To understand its developmental and cellular function an allelic series for Wtx in the mouse is crucial. Whereas mice carrying a conditional knock out allele for Wtx have been previously reported, a gain-of-function mouse model that would allow studying the molecular, cellular and developmental role of Wtx is still missing. Here we describe the generation of a novel mouse strain that permits the conditional activation of WTX expression. Wtx fused to GFP was introduced downstream a stop cassette flanked by loxP sites into the Rosa26 locus by gene targeting. Ectopic WTX expression is reported after crosses with several Cre transgenic mice in different embryonic tissues. Further, functionality of the fusion protein was demonstrated in the context of a Wtx null allele.

Expression of tripartite motif-containing protein 28 in primary breast carcinoma predicts metastasis and is involved in the stemness, chemoresistance, and tumor growth

The prediction of who develops metastasis has been the most difficult aspect in the management of breast cancer patients. The lymph node metastasis has been the most useful predictor of prognosis and patient management. However, a good proportion of patients with lymph node positivity remain disease free for 5 years or more, while about a third of those who were lymph node negative develop distant metastasis within the same period. This warrants a robust biomarker(s), preferably gene expression based. In order to elucidate gene-based biomarkers for prognosis of breast cancers, gene expression profiling of primary tumors and follow-up for over 5 years has been performed. The analysis revealed a network of genes centered around the tripartite motif-containing protein 28 as an important indicator of disease progression. Short hairpin RNA-mediated knockdown of tripartite motif-containing protein 28 in breast cancer cells revealed a decreased expression of epithelial-to-mesenchymal transition markers and increased expression of epithelial markers, decreased migration and invasion, and increased chemosensitivity to doxorubicin, 5-fluorouracil, and methotrexate. Furthermore, knockdown of tripartite motif-containing protein 28 resulted in the decrease of stemness as revealed by sphere formation assay as well as decreased expression of CD44 and Bmi1. Moreover, tripartite motif-containing protein 28 knockdown significantly reduced the tumor size and lung metastasis in orthotopic tumor xenograft assay in immunocompromised mice. The tumor size was further reduced when these mice were treated with doxorubicin. These data provide evidence for tripartite motif-containing protein 28 as a biomarker and a potential therapeutic target for breast cancer.

Tripartite motif containing 28 (TRIM28) promotes breast cancer metastasis by stabilizing TWIST1 protein

TRIM28 regulates its target genes at both transcriptional and posttranscriptional levels. Here we report that a TRIM28-TWIST1-EMT axis exists in breast cancer cells and TRIM28 promotes breast cancer metastasis by stabilizing TWIST1 and subsequently enhancing EMT. We find that TRIM28 is highly expressed in both cancer cell lines and advanced breast cancer tissues, and the levels of TRIM28 and TWIST1 are positively correlated with the aggressiveness of breast carcinomas. Overexpression and depletion of TRIM28 up- and down-regulates the protein, but not the mRNA levels of TWIST1, respectively, suggesting that TRIM28 upregulates TWIST1 post-transcriptionally. Overexpression of TRIM28 in breast cancer cell line promotes cell migration and invasion. Knockdown of TRIM28 reduces the protein level of TWIST1 with concurrent upregulation of E-cadherin and downregulation of N-cadherin and consequently inhibits cell migration and invasion. Furthermore, Immunoprecipitation and GST pull-down assays demonstrated that TRIM28 interacts with TWIST1 directly and this interaction is presumed to protect TWIST1 from degradation. Our study revealed a novel mechanism in breast cancer cells that TRIM28 enhances metastasis by stabilizing TWIST1, suggesting that targeting TRIM28 could be an efficacious strategy in breast cancer treatment.