Ubiquitin-dependent proteolysis plays an essential role in the regulation of a variety of cellular processes, including cell proliferation, differentiation, and apoptosis (1-3). Ubiquitin (Ub) 3 is covalently attached to target proteins by a cascade enzyme system consisting of Ub-activating (E1), conjugating (E2), and ligating (E3) enzymes (1, 4). Ub E3 ligases that confer the substrate specificity have been grouped into two families; the HECT-domain family that is defined by its homology to E6-associated protein (E6AP) and the RING family carrying RING-finger domain that is essential for the Ub ligase activity (5, 6). One of the well defined RING E3 ligases is the Skp1/Cul1/F-box protein complex, in which Cul1 serves as a scaffold molecule that interacts with Skp1 and a small RING-finger protein Roc1, also known as Hrt1 and Rbx1 (7-9). F-box proteins are recruited to the complex by binding to the Skp1 adaptor protein.At least six Cul members have been identified: Cul1, Cul2, Cul3, Cul4A, Cul4B, and Cul5 (10). Of these, Cul3 is known to mediate the degradation of several proteins, such as cyclin E (11), but the molecular composition of Cul3-based Ub ligase was unknown. Recently, a large family of proteins having BTB (Bric-a-brac/Tramtrack/Broad complex) domain has been identified as novel Cul3-interacting proteins (12). Most BTB proteins, but not all, have additional domains for proteinprotein interaction, such as zinc fingers, Kelch repeats, and MATH motifs. Furthermore, a subset of proteins containing BTB domain has been identified to function as substrate-specific adaptors that bind to Cul3. Specifically, MEL-26, a homolog of human SPOP (speckle-type POZ protein) in Caenorhabditis elegans, was first identified as a BTB protein that serves as a specific adaptor of MEI-1 for the ubiquitination by Cul3-based Ub ligase and subsequent degradation by the proteasome (13). MEI-1 is a subunit of the katanin-like microtubule severing heterodimer MEI-1/MEI-2 that localizes to the spindles and the chromosomes during meiosis (14). SPOP BTB protein has also been shown to mediate the ubiquitination of the Polycomb group BMI and the variant histone MacroH2A (15). In addition, Keap1 BTB protein was shown to recruit Nrf2 to . Nrf2 is a transcription factor that regulates the expression of anti-oxidant genes upon oxidative stress. In Schizosaccharomyces pombe, Btb1p, Btb2p, and Btb3p interact with Cul3, but their functions remain unknown (20). Therefore, so far only a few protein substrates have been shown to interact with BTB proteins for their ubiquitination by Cul3-based Ub ligases.Daxx was originally identified as a protein that binds to the death domain of Fas receptor by yeast two-hybrid screening (21). Daxx interacts with the apoptosis signal-regulating kinase 1 (ASK1) and promotes Fas-mediated apoptosis through the activation of Jun N-terminal kinase (22). Subsequent studies have also shown that Daxx behaves as a proapoptotic protein under various stress conditions (21,(23)(24)(25). On the contrary, homozygous deletio...

Fragile X syndrome (FXS) results in intellectual disability (ID) most often caused by silencing of the fragile X mental retardation 1 (FMR1) gene. The resulting absence of fragile X mental retardation protein 1 (FMRP) leads to both pre-and postsynaptic defects, yet whether the pre-and postsynaptic functions of FMRP are independent and have distinct roles in FXS neuropathology remain poorly understood. Here, we demonstrate an independent presynaptic function for FMRP through the study of an ID patient with an FMR1 missense mutation. This mutation, c.413G > A (R138Q), preserves FMRP's canonical functions in RNA binding and translational regulation, which are traditionally associated with postsynaptic compartments. However, neuronally driven expression of the mutant FMRP is unable to rescue structural defects at the neuromuscular junction in fragile x mental retardation 1 (dfmr1)-deficient Drosophila, suggesting a presynaptic-specific impairment. Furthermore, mutant FMRP loses the ability to rescue presynaptic action potential (AP) broadening in Fmr1 KO mice. The R138Q mutation also disrupts FMRP's interaction with the large-conductance calciumactivated potassium (BK) channels that modulate AP width. These results reveal a presynaptic-and translation-independent function of FMRP that is linked to a specific subset of FXS phenotypes.F ragile X syndrome (FXS) is the most common single-gene disorder responsible for intellectual disability (ID) in patients (1). Along with cognitive dysfunction, the syndrome typically presents with several other comorbidities, including behavioral and social impairments (anxiety and autism spectrum disorder), neurological defects (seizures and abnormal sleep patterns), and morphological abnormalities (dysmorphic facies and macroorchidism). Most patients inherit the syndrome through a maternal repeat expansion mutation that transcriptionally silences the FMR1 gene and results in loss of the gene product, FMRP.FMRP has complex multifaceted functions at synapses both in pre-and postsynaptic compartments. As an RNA binding protein, FMRP is best known for its function as a translation regulator in dendrites (2). Loss of FMRP has been linked to various forms of long-term synaptic plasticity defects that depend on local protein synthesis in the postsynaptic neuron (3). In addition to disrupted metabotropic glutamate receptor signaling, which has been shown across multiple brain regions (4-7), FMRP is necessary for activitydependent protein synthesis downstream of other signaling receptor pathways, including ACh, dopamine, and TrkB (8-10).Although postsynaptic control of translation is believed to be the dominant function of FMRP, it is unable to explain all of the pathophysiology observed in FXS animal models. For instance, in Drosophila, presynaptic expression of the FMR1 homolog, dfmr1, completely rescues the synaptic overgrowth phenotype at the neuromuscular junction (NMJ) in dfmr1-null mutants (11-13). In rodent brain, FMRP has been found in structures called fragile-X granules, which are ...

H3K36 methylation by Set2 targets Rpd3S histone deacetylase to transcribed regions of mRNA genes, repressing internal cryptic promoters and slowing elongation. Here we explore the function of this pathway by analysing transcription in yeast undergoing a series of carbon source shifts. Approximately 80 mRNA genes show increased induction upon SET2 deletion. A majority of these promoters have overlapping lncRNA transcription that targets H3K36me3 and deacetylation by Rpd3S to the mRNA promoter. We previously reported a similar mechanism for H3K4me2-mediated repression via recruitment of the Set3C histone deacetylase. Here we show that the distance between an mRNA and overlapping lncRNA promoter determines whether Set2–Rpd3S or Set3C represses. This analysis also reveals many previously unreported cryptic ncRNAs induced by specific carbon sources, showing that cryptic promoters can be environmentally regulated. Therefore, in addition to repression of cryptic transcription and modulation of elongation, H3K36 methylation maintains optimal expression dynamics of many mRNAs and ncRNAs.

Summary Injured peripheral neurons successfully activate a pro-regenerative transcriptional program to enable axon regeneration and functional recovery. How transcriptional regulators co-ordinate the expression of such program remains unclear. Here we show that hypoxia-inducible factor 1α (HIF-1α) controls multiple injury-induced genes in sensory neurons and contribute to the preconditioning lesion effect. Knockdown of HIF-1α in vitro or conditional knock out in vivo impairs sensory axon regeneration. The HIF-1α target gene Vascular Endothelial Growth Factor A (VEGFA) is expressed in injured neurons and contributes to stimulate axon regeneration. Induction of HIF-1α using hypoxia enhances axon regeneration in vitro and in vivo in sensory neurons. Hypoxia also stimulates motor neuron regeneration and accelerates neuromuscular junction re-innervation. This study demonstrates that HIF-1α represents a critical transcriptional regulator in regenerating neurons and suggests hypoxia as a tool to stimulate axon regeneration.

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Heterogeneous ribonucleoprotein-K (hnRNP-K) is normally ubiquitinated by HDM2 for proteasome-mediated degradation. Under DNA-damage conditions, hnRNP-K is transiently stabilized and serves as a transcriptional co-activator of p53 for cell-cycle arrest. However, how the stability and function of hnRNP-K is regulated remained unknown. Here, we demonstrated that UV-induced SUMOylation of hnRNP-K prevents its ubiquitination for stabilization. Using SUMOylation-defective mutant and purified SUMOylated hnRNP-K, SUMOylation was shown to reduce hnRNP-K's affinity to HDM2 with an increase in that to p53 for p21-mediated cell-cycle arrest. PIAS3 served as a small ubiquitin-related modifier (SUMO) E3 ligase for hnRNP-K in an ATR-dependent manner. During later periods after UV exposure, however, SENP2 removed SUMO from hnRNP-K for its destabilization and in turn for release from cell-cycle arrest. Consistent with the rise-and-fall of both SUMOylation and stability of hnRNP-K, its ability to interact with PIAS3 was inversely correlated to that with SENP2 during the time course after UV exposure. These findings indicate that SUMO modification plays a crucial role in the control of hnRNP-K's function as a p53 co-activator in response to DNA damage by UV.

Several methods of physiotherapy have been advanced for apogeotropic type benign positional vertigo involving the horizontal semicircular canal (HC-BPV). The aim of this study was to determine the therapeutic efficacies of the proposed maneuvers in apogeotropic HC-BPV. Using a prospective randomized trial involving seven nationwide dizziness clinics in Korea, we compared the immediate efficacies of head-shaking and modified Semont maneuvers in 103 consecutive patients with apogeotropic HC-BPV. We also determined an additional therapeutic benefit of mastoid oscillation while the patients without response to both maneuvers were performing the Brandt-Daroff exercise. Successful treatment was defined as resolution of positional vertigo and nystagmus, or as transition into geotropic HC-BPV. Results showed that head shaking was more effective than the modified Semont maneuver (37.3 vs. 17.3%, P = 0.02). However, therapeutic efficacy did not differ between the maneuvers after the initial non-responders switched over to the other maneuver (23.3 vs. 25.0%, P = 0.861). Mastoid oscillation provided no additional benefit while the patients without response to both maneuvers were performing the Brandt-Daroff exercise. Most positional vertigos resolved within a week (89.4%) irrespective of the treatment modalities applied and all showed resolution within 28 days. The head-shaking maneuver described here proved more effective than the modified Semont maneuver in treating apogeotropic HC-BPV. Mastoid vibration conferred no additional benefit during the Brandt-Daroff exercise.

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