Germline mutation in the NBR1 gene involved in autophagy detected in a family with renal tumors.

Hereditary Renal Cell Carcinomas (RCC) are caused by mutations in predisposing genes, the major ones including VHL, FLCN, FH and MET. However, many families with inherited RCC have no germline mutation in these genes. Using Whole Exome Sequencing on germline DNA from a family presenting three different histological renal tumors (an angiomyolipoma, a clear-cell RCC and an oncocytic papillary RCC), we identified a frameshift mutation in the Neighbor of BRCA1 gene 1 (NBR1), segregating with the tumors. NBR1 encodes a cargo receptor protein involved in autophagy. Genetic and functional analyses suggested a pathogenic impact of the mutation. Indeed, functional study performed in renal cell lines showed that the mutation alters NBR1 interactions with some of its partners (such as p62/SQSTM1), leading to a dominant negative effect. This results in an altered autophagic process and an increased proliferative capacity in renal cell lines. Our study suggests that NBR1 may be a new predisposing gene for RCC, however its characterization needs to be further investigated in order to confirm its role in renal carcinogenesis.

FBXO32 links ubiquitination to epigenetic reprograming of melanoma cells.

Ubiquitination by serving as a major degradation signal of proteins, but also by controlling protein functioning and localization, plays critical roles in most key cellular processes. Here, we show that MITF, the master transcription factor in melanocytes, controls ubiquitination in melanoma cells. We identified FBXO32, a component of the SCF E3 ligase complex as a new MITF target gene. FBXO32 favors melanoma cell migration, proliferation, and tumor development in vivo. Transcriptomic analysis shows that FBXO32 knockdown induces a global change in melanoma gene expression profile. These include the inhibition of CDK6 in agreement with an inhibition of cell proliferation and invasion upon FBXO32 silencing. Furthermore, proteomic analysis identifies SMARC4, a component of the chromatin remodeling complexes BAF/PBAF, as a FBXO32 partner. FBXO32 and SMARCA4 co-localize at loci regulated by FBXO32, such as CDK6 suggesting that FBXO32 controls transcription through the regulation of chromatin remodeling complex activity. FBXO32 and SMARCA4 are the components of a molecular cascade, linking MITF to epigenetics, in melanoma cells.

Contribution of de novo and mosaic TP53 mutations to Li-Fraumeni syndrome.

BACKGROUND: Development of tumours such as adrenocortical carcinomas (ACC), choroid plexus tumours (CPT) or female breast cancers before age 31 or multiple primary cancers belonging to the Li-Fraumeni (LFS) spectrum is, independently of the familial history, highly suggestive of a germline TP53 mutation. The aim of this study was to determine the contribution of de novo and mosaic mutations to LFS. METHODS AND RESULTS: Among 328 unrelated patients harbouring a germline TP53 mutation identified by Sanger sequencing and/or QMPSF, we could show that the mutations had occurred de novo in 40 cases, without detectable parental age effect. Sanger sequencing revealed two mosaic mutations in a child with ACC and in an unaffected father of a child with medulloblastoma. Re-analysis of blood DNA by next-generation sequencing, performed at a depth above 500X, from 108 patients suggestive of LFS without detectable TP53 mutations, allowed us to identify 6 additional cases of mosaic TP53 mutations, in 2/49 children with ACC, 2/21 children with CPT, in 1/31 women with breast cancer before age 31 and in a patient who developed an osteosarcoma at age 12, a breast carcinoma and a breast sarcoma at age 35. CONCLUSIONS: This study performed on a large series of TP53 mutation carriers allows estimating the contribution to LFS of de novo mutations to at least 14% (48/336) and suggests that approximately one-fifth of these de novo mutations occur during embryonic development. Considering the medical impact of TP53 mutation identification, medical laboratories in charge of TP53 testing should ensure the detection of mosaic mutations.

A germline oncogenic MITF mutation and tumor susceptibility.

MITF (Microphthalmia-associated transcription factor) is a lineage specific transcription factor that plays a critical role in melanocyte homeostasis and whose deregulation has been shown to contribute to melanoma disease. A germline mutation in MITF, impairing SUMOylation and predisposing to cutaneous malignant melanoma, was recently identified. Interestingly, an association of the MITF mutation with coexisting melanoma and renal cell carcinoma was also shown. Collectively, these data suggest that MITF has an important oncogenic function in tumorigenesis of multiple tissues/melanocytes and kidney cells.

Characteristics of the coexistence of melanoma and renal cell carcinoma.

BACKGROUND: Patients with melanoma (MM) have an increased risk of kidney cancer, and there is an excess risk of MM among patients with renal cell carcinoma (RCC). The objective of the current study was to analyze a series of 42 patients with both MM and RCC to identify clinical and pathologic features as well as risk factors of this association. METHODS: Clinical and pathologic characteristics of 42 patients who developed both MM and RCC (the MM + RCC series) were compared with 2 published series in each cancer alone: a series of 293 patients with MM (MM series) and a series of 1527 patients with RCC (RCC series). RESULTS: RCC was diagnosed concomitantly or after MM in 83% of patients in the MM + RCC series. Those patients displayed a high proportion of asymptomatic RCC at diagnosis (70%) and a higher frequency of stage I tumors (61%) than patients in the RCC series. Compared with the MM series, patients in the MM + RCC series more often were men, had a higher frequency of blond/red hair, had poor tanning ability, and had a higher number of nevi. In addition, patients in the MM + RCC series had a high aggregation of other malignancies (mainly skin cancers) and a significantly higher frequency of family history of MM (P = .005). Only 2 cyclin-dependent kinase 2A gene (CDKN2A) germline mutations were identified among patients in the MM + RCC series who also were members of MM-prone families. CONCLUSIONS: The high aggregation of cancers among patients in the MM + RCC series and the familial clustering of MM argued for a genetic predisposition that may be partly independent of CDKN2A.

Incomplete penetrance of the predisposition to medulloblastoma associated with germ-line SUFU mutations.

METHODS AND RESULTS: Germline SUFU mutations were identified in two families with several children under 3 years of age diagnosed with medulloblastoma. All medulloblastomas in which the histology was reviewed were of the desmoplastic subtype, including three with the rare extensive nodularity subtype. In both families, the mutation detected in the SUFU gene was a frameshift mutation. Among the 25 mutation carriers identified in the two families, seven developed medulloblastomas. CONCLUSIONS: This report highlights three features of SUFU related tumours. These are mainly medulloblastomas with extensive nodularity or typical desmoplastic/nodular medulloblastomas. These tumours mostly, if not exclusively, appear during the first 3 years of life. The penetrance of the mutation is incomplete.

Significant contribution of germline BRCA2 rearrangements in male breast cancer families.

Although screening for large deletions or duplications of the BRCA1 gene is becoming a routine component of the molecular diagnosis of familial breast cancer, little is known about the occurrence of such rearrangements in the BRCA2 gene. Because of the high frequency of BRCA2 mutations in breast cancer families with at least one case of male breast cancer, we selected a cohort of 39 such families, tested negative for mutations in the coding regions of BRCA1 and BRCA2, and developed an assay for BRCA2 rearrangements, based on quantitative multiplex PCR of short fluorescent fragments (QMPSF). We found three rearrangements: (1) a deletion of exons 12 and 13; (2) a duplication of exons 1 and 2; and (3) a complete deletion of BRCA2. We determined the boundaries of the deletion of exons 12 and 13, showing that it resulted from an unequal recombination between Alu sequences. We mapped the complete BRCA2 deletion, which extends over at least 298 kb and showed that it does not affect APRIN/AS3, previously characterized as a tumor suppressor gene, but it comprises several loci corresponding to proven or putative transcripts of unknown functional significance. These data suggest that screening for BRCA2 rearrangements should be done, especially in male breast cancer families tested negative for BRCA1 and BRCA2 mutations.