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The DFNA15 deafness mutation affects POU4F3 protein stability, localization, and transcriptional activity.

ABSTRACT: A mutation in the POU4F3 gene (BRN-3.1, BRN3C) is responsible for DFNA15 (MIM 602459), autosomal-dominant nonsyndromic hearing loss. POU4F3 is a member of the POU family of transcription factors and is essential for inner-ear hair cell maintenance. To test the potential effects of the human POU4F3 mutation, we performed a series of experiments in cell culture to mimic the human mutation. Mutant POU4F3 loses most of its transcriptional activity and most of its ability to bind to DNA and does not function in a dominant-negative manner. Moreover, whereas wild-type POU4F3 is found exclusively in the nucleus, our studies demonstrate that the mutant protein is localized both to the nucleus and the cytoplasm. Two nuclear localization signals were identified; both are essential for proper nuclear entry of POU4F3 protein. We found that the mutant protein half-life is longer than that of the wild type. We propose that the combination of defects caused by the mutation on the function of the POU4F3 transcription factor eventually leads to hair cell morbidity in affected family H members.

SUBMITTER: Weiss S

PROVIDER: S-EPMC262385 | biostudies-literature | 2003 Nov

REPOSITORIES: biostudies-literature

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The DFNA15 deafness mutation affects POU4F3 protein stability, localization, and transcriptional activity.

Weiss Sigal S Gottfried Irit I Mayrose Itay I Khare Suvarna L SL Xiang Mengqing M Dawson Sally J SJ Avraham Karen B KB

Molecular and cellular biology 20031101 22

A mutation in the POU4F3 gene (BRN-3.1, BRN3C) is responsible for DFNA15 (MIM 602459), autosomal-dominant nonsyndromic hearing loss. POU4F3 is a member of the POU family of transcription factors and is essential for inner-ear hair cell maintenance. To test the potential effects of the human POU4F3 mutation, we performed a series of experiments in cell culture to mimic the human mutation. Mutant POU4F3 loses most of its transcriptional activity and most of its ability to bind to DNA and does not ...[more]

PMID: 14585957

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Project description:BackgroundMutations in PINK1 and PARKIN are the most common causes of recessive early-onset Parkinson's disease (EOPD). Together, the mitochondrial ubiquitin (Ub) kinase PINK1 and the cytosolic E3 Ub ligase PARKIN direct a complex regulated, sequential mitochondrial quality control. Thereby, damaged mitochondria are identified and targeted to degradation in order to prevent their accumulation and eventually cell death. Homozygous or compound heterozygous loss of either gene function disrupts this protective pathway, though at different steps and by distinct mechanisms. While structure and function of PARKIN variants have been well studied, PINK1 mutations remain poorly characterized, in particular under endogenous conditions. A better understanding of the exact molecular pathogenic mechanisms underlying the pathogenicity is crucial for rational drug design in the future.MethodsHere, we characterized the pathogenicity of the PINK1 p.I368N mutation on the clinical and genetic as well as on the structural and functional level in patients' fibroblasts and in cell-based, biochemical assays.ResultsUnder endogenous conditions, PINK1 p.I368N is expressed, imported, and N-terminally processed in healthy mitochondria similar to PINK1 wild type (WT). Upon mitochondrial damage, however, full-length PINK1 p.I368N is not sufficiently stabilized on the outer mitochondrial membrane (OMM) resulting in loss of mitochondrial quality control. We found that binding of PINK1 p.I368N to the co-chaperone complex HSP90/CDC37 is reduced and stress-induced interaction with TOM40 of the mitochondrial protein import machinery is abolished. Analysis of a structural PINK1 p.I368N model additionally suggested impairments of Ub kinase activity as the ATP-binding pocket was found deformed and the substrate Ub was slightly misaligned within the active site of the kinase. Functional assays confirmed the lack of Ub kinase activity.ConclusionsHere we demonstrated that mutant PINK1 p.I368N can not be stabilized on the OMM upon mitochondrial stress and due to conformational changes in the active site does not exert kinase activity towards Ub. In patients' fibroblasts, biochemical assays and by structural analyses, we unraveled two pathomechanisms that lead to loss of function upon mutation of p.I368N and highlight potential strategies for future drug development.

Project description:BACKGROUND:Breast cancer is the most common malignancy in women worldwide. Among the breast cancer subtypes, triple-negative breast cancer (TNBC) is the most aggressive and the most difficult to treat. One of the master regulators in TNBC progression is the architectural transcription factor HMGA1. This study aimed to further explore the HMGA1 molecular network to identify molecular mechanisms involved in TNBC progression. METHODS:RNA from the MDA-MB-231 cell line, silenced for HMGA1 expression, was sequenced and, with a bioinformatic analysis, molecular partners HMGA1 could cooperate with in regulating common downstream gene networks were identified. Among the putative partners, the FOXM1 transcription factor was selected. The relationship occurring between HMGA1 and FOXM1 was explored by qRT-PCR, co-immunoprecipitation and protein stability assays. Subsequently, the transcriptional activity of HMGA1 and FOXM1 was analysed by luciferase assay on the VEGFA promoter. The impact on angiogenesis was assessed in vitro, evaluating the tube formation ability of endothelial cells exposed to the conditioned medium of MDA-MB-231 cells silenced for HMGA1 and FOXM1 and in vivo injecting MDA-MB-231 cells, silenced for the two factors, in zebrafish larvae. RESULTS:Here, we discover FOXM1 as a novel molecular partner of HMGA1 in regulating a gene network implicated in several breast cancer hallmarks. HMGA1 forms a complex with FOXM1 and stabilizes it in the nucleus, increasing its transcriptional activity on common target genes, among them, VEGFA, the main inducer of angiogenesis. Furthermore, we demonstrate that HMGA1 and FOXM1 synergistically drive breast cancer cells to promote tumor angiogenesis both in vitro in endothelial cells and in vivo in a zebrafish xenograft model. Moreover, using a dataset of breast cancer patients we show that the co-expression of HMGA1, FOXM1 and VEGFA is a negative prognostic factor of distant metastasis-free survival and relapse-free survival. CONCLUSIONS:This study reveals FOXM1 as a crucial interactor of HMGA1 and proves that their cooperative action supports breast cancer aggressiveness, by promoting tumor angiogenesis. Therefore, the possibility to target HMGA1/FOXM1 in combination should represent an attractive therapeutic option to counteract breast cancer angiogenesis.

Dataset Information

The DFNA15 deafness mutation affects POU4F3 protein stability, localization, and transcriptional activity.

Publications

The DFNA15 deafness mutation affects POU4F3 protein stability, localization, and transcriptional activity.

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