Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have identified three truncating, two splice-site, and three missense variants at conserved amino acids in the CUL4B gene on Xq24 in 8 of 250 families with X-linked mental retardation (XLMR). During affected subjects' adolescence, a syndrome emerged with delayed puberty, hypogonadism, relative macrocephaly, moderate short stature, central obesity, unprovoked aggressive outbursts, fine intention tremor, pes cavus, and abnormalities of the toes. This syndrome was first described by Cazebas et al., in a family that was included in our study and that carried a CUL4B missense variant. CUL4B is a ubiquitin E3 ligase subunit implicated in the regulation of several biological processes, and CUL4B is the first XLMR gene that encodes an E3 ubiquitin ligase. The relatively high frequency of CUL4B mutations in this series indicates that it is one of the most commonly mutated genes underlying XLMR and suggests that its introduction into clinical diagnostics should be a high priority.
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PMID:Mutations in CUL4B, which encodes a ubiquitin E3 ligase subunit, cause an X-linked mental retardation syndrome associated with aggressive outbursts, seizures, relative macrocephaly, central obesity, hypogonadism, pes cavus, and tremor. 1723 39

We reevaluated a previously reported family with an X-linked mental retardation syndrome and attempted to identify the underlying genetic defect. Screening of candidate genes in a 10-Mb region on Xq25 implicated CUL4B as the causative gene. CUL4B encodes a scaffold protein that organizes a cullin-RING (really interesting new gene) ubiquitin ligase (E3) complex in ubiquitylation. A base substitution, c.1564C-->T, converted a codon for arginine into a premature termination codon, p.R388X, and rendered the truncated peptide completely devoid of the C-terminal catalytic domain. The nonsense mutation also results in nonsense-mediated mRNA decay in patients. In peripheral leukocytes of obligate carriers, a strong selection against cells expressing the mutant allele results in an extremely skewed X-chromosome inactivation pattern. Our findings point to the functional significance of CUL4B in cognition and in other aspects of human development.
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PMID:Mutation in CUL4B, which encodes a member of cullin-RING ubiquitin ligase complex, causes X-linked mental retardation. 1727 78

CUL4A and CUL4B, which are derived from the same ancestor, CUL4, encode scaffold proteins that organize cullin-RING ubiquitin ligase (E3) complexes. Recent genetic studies have shown that germ line mutation in CUL4B can cause mental retardation, short stature, and other abnormalities in humans. CUL4A was observed to be overexpressed in breast and hepatocellular cancers, although no germ line mutation in human CUL4A has been reported. Although CUL4A has been known to be involved in a number of cellular processes, including DNA repair and cell cycle regulation, little is known about whether CUL4B has similar functions. In this report, we tested the functional importance of CUL4B in cell proliferation and characterized the nuclear localization signal (NLS) that is essential for its function. We found that RNA interference silencing of CUL4B led to an inhibition of cell proliferation and a prolonged S phase, due to the overaccumulation of cyclin E, a substrate targeted by CUL4B for ubiquitination. We showed that, unlike CUL4A and other cullins that carry their NLS in their C termini, NLS in CUL4B is located in its N terminus, between amino acid 37 and 40, KKRK. This NLS could bind to importin alpha1, alpha3, and alpha5. NLS-deleted CUL4B was distributed in cytoplasm and failed to promote cell proliferation. Therefore, the nuclear localization of CUL4B mediated by NLS is critical for its normal function in cell proliferation.
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PMID:Characterization of nuclear localization signal in the N terminus of CUL4B and its essential role in cyclin E degradation and cell cycle progression. 1980 44

Cabezas syndrome (MIM 300354) is a recently identified syndromic form of X-linked mental retardation (XLMR) caused by mutations in the CUL4B gene. In total, nine XLMR families carrying mutations in the CUL4B gene have been described to date. Here, we present a detailed clinical phenotype of three affected brothers of Polish descent. Based on the symptoms, we made a clinical diagnosis of Cabezas syndrome, which was subsequently confirmed by identification of a novel nonsense mutation (c.2107A-->T, p.703K-->X) in exon 18 of the CUL4B gene. The mutation was inherited from an asymptomatic mother and was present in all three affected brothers. The patients presented with typical features of Cabezas syndrome, such as severe mental retardation, speech impairment, hyperactivity, seizures, intention tremor, inguinal hernia, small feet, and craniofacial dysmorphism. In addition to previously described symptoms, syndactyly of the second and third toes and skin manifestations (hyperhydrosis and keratosis pilaris) were present in our cases. Our report provides further support that Cabezas syndrome is a recognizable syndromic form of XLMR. We conclude that the CUL4B gene should be screened in males with severe speech impairment and primary intention tremor, especially if characteristic facial dysmorphism is also present.
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PMID:A novel nonsense mutation in CUL4B gene in three brothers with X-linked mental retardation syndrome. 2000 52

The CUL4B gene encodes a member of Cullin-RING ubiquitin ligase complex. Point mutations in CUL4B were identified recently in patients with syndromic X-linked mental retardation (XLMR). Here, using oligoarray-based comparative genomic hybridization (array CGH), we identified a de novo deletion of the CUL4B gene in a boy with syndromic mental retardation, minor facial anomalies, short stature, delayed puberty, hypogonadism, relative macrocephaly, gait ataxia, and pes cavus, all manifestations described previously in patients with CUL4B point mutations. Interestingly, our patient also presented with aortic valvular "dysplasia" and vertebral anomalies similar to those seen in Scheuermann disease, both of which may also be part of this syndrome. This report further suggests that point mutations and deletions of the CUL4B gene lead to a recognizable phenotype. The association of facial anomalies, short stature, hypogonadism, and gait ataxia in a mentally retarded boy should prompt molecular analyses of the CUL4B gene.
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PMID:Deletion of the CUL4B gene in a boy with mental retardation, minor facial anomalies, short stature, hypogonadism, and ataxia. 2001 35

CUL4A and B encode subunits of E3-ubiquitin ligases implicated in diverse processes including nucleotide excision repair, regulating gene expression and controlling DNA replication fork licensing. But, the functional distinction between CUL4A and CUL4B, if any, is unclear. Recently, mutations in CUL4B were identified in humans associated with mental retardation, relative macrocephaly, tremor and a peripheral neuropathy. Cells from these patients offer a unique system to help define at the molecular level the consequences of defective CUL4B specifically. We show that these patient-derived cells exhibit sensitivity to camptothecin (CPT), impaired CPT-induced topoisomerase I (Topo I) degradation and ubiquitination, thereby suggesting Topo I to be a novel Cul4-dependent substrate. Consistent with this, we also find that these cells exhibit increased levels of CPT-induced DNA breaks. Furthermore, over-expression of known CUL4-dependent substrates including Cdt1 and p21 appear to be a feature of these patient-derived cells. Collectively, our findings highlight the interplay between CUL4A and CUL4B and provide insight into the pathogenesis of CUL4B-deficiency in humans.
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PMID:Mutations in Cullin 4B result in a human syndrome associated with increased camptothecin-induced topoisomerase I-dependent DNA breaks. 2006 23

Cullin's encode the structural components for one of the most abundant E3 ubiquitin ligase families in eukaryotes accounting for as many as 400 distinct E3 ubiquitin ligases. Because of their modular assembly involving combinations of multiple distinct adaptor and substrate receptor proteins, it comes as no surprise that these E3's are implicated in a plethora of fundamental biochemical processes ranging from DNA replication and repair to transcription and development. Herein, we focus on one member of the cullin family, namely the Cullin 4-RING E3 ligases (CRL4's). More specifically, we overview what has been learned about some of the functions of CRL4's from various model systems. We discuss the unexpected association of defective CUL4B with syndromal X-linked mental retardation in humans and speculate on the biochemical consequences and clinical implications of defective CRL4 function. In particular, mutations in CUL4B highlight a previously unappreciated role for CRL4's in neuronal function and cognition in humans.
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PMID:CUL4B-deficiency in humans: understanding the clinical consequences of impaired Cullin 4-RING E3 ubiquitin ligase function. 2135 45

In this issue, Nakagawa and Xiong (2011) reveal a mechanism targeting WDR5 for proteolysis dependent on the X-linked mental retardation gene, CUL4B. This provides a link between the stability of a chromatin factor and gene expression implicated in neurological pathogenesis.
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PMID:CUL4B: trash talking at chromatin. 2181 45

CUL4B, encoding a scaffold protein for the assembly of Cullin4B-Ring ubiquitin ligase (CRL4B) complexes, is frequently mutated in X-linked mental retardation (XLMR) patients. Here, we show that CUL4B, but not its paralog, CUL4A, targets WDR5, a core subunit of histone H3 lysine 4 (H3K4) methyltransferase complexes, for ubiquitylation and degradation in the nucleus. Knocking down CUL4B increases WDR5 and trimethylated H3K4 (H3K4me3) on the neuronal gene promoters and induces their expression. Furthermore, CUL4B depletion suppresses neurite outgrowth of PC12 neuroendocrine cells, which can be rescued by codepletion of WDR5. XLMR-linked mutations destabilize CUL4B and impair its ability to support neurite outgrowth of PC12 cells. Our results identify WDR5 as a critical substrate of CUL4B in regulating neuronal gene expression and suggest epigenetic change as a common pathogenic mechanism for CUL4B-associated XLMR.
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PMID:X-linked mental retardation gene CUL4B targets ubiquitylation of H3K4 methyltransferase component WDR5 and regulates neuronal gene expression. 2181 41

Mutations of the CUL4B ubiquitin ligase gene are causally linked to syndromic X-linked mental retardation (XLMR). However, the pathogenic role of CUL4B mutations in neuronal and developmental defects is not understood. We have generated mice with targeted disruption of Cul4b, and observed embryonic lethality with pronounced growth inhibition and increased apoptosis in extra-embryonic tissues. Cul4b, but not its paralog Cul4a, is expressed at high levels in extra-embryonic tissues post implantation. Silencing of CUL4B expression in an extra-embryonic cell line resulted in the robust accumulation of the CUL4 substrate p21(Cip1/WAF) and G2/M cell cycle arrest, which could be partially rescued by silencing of p21(Cip1/WAF). Epiblast-specific deletion of Cul4b prevented embryonic lethality and gave rise to viable Cul4b null mice. Therefore, while dispensable in the embryo proper, Cul4b performs an essential developmental role in the extra-embryonic tissues. Our study offers a strategy to generate viable Cul4b-deficient mice to model the potential neuronal and behavioral deficiencies of human CUL4B XLMR patients.
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PMID:Essential role of the CUL4B ubiquitin ligase in extra-embryonic tissue development during mouse embryogenesis. 2245 36


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