TRIM28 inactivation in epithelial nephroblastoma is frequent and often associated with predisposing TRIM28 germline variants

Distinct pathways for genetic and epigenetic predisposition in familial and bilateral Wilms tumor

BACKGROUND

Genetic predisposition is particularly common in children with the kidney cancer, Wilms tumor. In 10% of these children, this manifests as a family history of Wilms tumor or bilateral disease. The frequency and spectrum of underlying changes have not been systematically investigated.

METHODS

We analyzed 129 children with suspected Wilms tumor predisposition, 20 familial cases, and 109 children with bilateral disease, enrolled over 30 years in the German SIOP93-01/GPOH and SIOP2001 studies. We used whole exome, whole genome, and targeted DNA sequencing, together with MLPA and targeted methylation assays on tumor, blood, and normal kidney to determine predisposing changes.

RESULTS

Predisposing variants were identified in 117/129 children, comprising DNA variants (57%) and epigenetic changes (34%). Most children had predisposition variants in genes previously implicated in Wilms tumor: most prominently WT1 (n = 35) and less frequently TRIM28, REST, DIS3L2, CTR9, DICER1, CDC73, and NONO. Nine children carried germline mutations in cancer predisposition genes not considered Wilms tumor predisposition genes, such as CHEK2, CDKN2A, BLM, BRCA2, STK11, and FMN2. Predisposition via epigenetic BWS-IC1 alterations occurred as early somatic events, reflected by partial (mosaic) loss of imprinting or loss of heterozygosity at the IGF2/H19 locus in normal kidney or blood. These patients rarely had a clinical diagnosis of Beckwith-Wiedemann syndrome (BWS). Especially WT1-driven tumors follow a stereotypical pathway of germline WT1 mutations becoming homozygous in renal precursor lesions through 11p LOH, which concomitantly activates imprinted IGF2 expression, with subsequent WNT pathway activation leading to tumor growth. There is a high rate of multicentric tumors, which may have previously been missed in unilateral tumors. While Wilms tumor predisposition genes relied on somatic inactivation of the second allele, this was different for general cancer predisposition genes. The latter cases were often associated with additional oncogenic alterations, similar to tumors with epigenetic predisposition.

CONCLUSIONS

We identified two main mechanisms of Wilms tumor predisposition: either germline genetic alterations of Wilms tumor and, less frequently, general cancer genes; or postzygotic mosaic imprinting defects activating IGF2. These findings inform future genetic screening and risk assessment of affected children and lend support to liquid biopsy screening for enhanced therapeutic stratification.

TRIM28 in cancer and cancer therapy

TRIM28 (tripartite motif protein 28) was initially believed to be a transcription inhibitor that plays an important role in DNA damage repair (DDR) and in maintaining cancer cellular stemness. As research has continued to deepen, several studies have found that TRIM28 not only has ubiquitin E3 ligase activity to promote degradation of substrates, but also can promote SUMOylation of substrates. Although TRIM28 is highly expressed in various cancer tissues and has oncogenic effects, there are still a few studies indicating that TRIM28 has certain anticancer effects. Additionally, TRIM28 is subject to complex upstream regulation. In this review, we have elaborated on the structure and regulation of TRIM28. At the same time, highlighting the functional role of TRIM28 in tumor development and emphasizing its impact on cancer treatment provides a new direction for future clinical antitumor treatment.

Wilms tumour resulting from paternal transmission of a TRIM28 pathogenic variant-A first report

Wilms tumour (nephroblastoma) is a renal embryonal tumour that is frequently caused by constitutional variants in a small range of cancer predisposition genes. TRIM28 has recently been identified as one such gene. Previously, observational data strongly suggested a parent of origin effect, whereby Wilms tumour only occurred following maternal inheritance of a pathogenic genetic variant. However, here we report a child with bilateral Wilms tumour who had inherited a pathogenic TRIM28 variant from their father. This finding suggests that genetic counselling for paternally inherited pathogenic variants in TRIM28 should include discussion of a potential risk of Wilms tumour.