Identification of a cytoplasmic interaction partner of the large regulatory proteins Rep78/Rep68 of adeno-associated virus type 2 (AAV-2)

Multiple potassium channel tetramerization domain (KCTD) family members interact with Gβγ, with effects on cAMP signaling

G protein-coupled receptors (GPCRs) initiate an array of intracellular signaling programs by activating heterotrimeric G proteins (Gα and Gβγ subunits). Therefore, G protein modifiers are well positioned to shape GPCR pharmacology. A few members of the potassium channel tetramerization domain (KCTD) protein family have been found to adjust G protein signaling through interaction with Gβγ. However, comprehensive details on the KCTD interaction with Gβγ remain unresolved. Here, we report that nearly all the 25 KCTD proteins interact with Gβγ. In this study, we screened Gβγ interaction capacity across the entire KCTD family using two parallel approaches. In a live cell bioluminescence resonance energy transfer-based assay, we find that roughly half of KCTD proteins interact with Gβγ in an agonist-induced fashion, whereas all KCTD proteins except two were found to interact through coimmunoprecipitation. We observed that the interaction was dependent on an amino acid hot spot in the C terminus of KCTD2, KCTD5, and KCTD17. While KCTD2 and KCTD5 require both the Bric-à-brac, Tramtrack, Broad complex domain and C-terminal regions for Gβγ interaction, we uncovered that the KCTD17 C terminus is sufficient for Gβγ interaction. Finally, we demonstrated the functional consequence of the KCTD-Gβγ interaction by examining sensitization of the adenylyl cyclase-cAMP pathway in live cells. We found that Gβγ-mediated sensitization of adenylyl cyclase 5 was blunted by KCTD. We conclude that the KCTD family broadly engages Gβγ to shape GPCR signal transmission.

Conserved properties of Drosophila Insomniac link sleep regulation and synaptic function

Sleep is an ancient animal behavior that is regulated similarly in species ranging from flies to humans. Various genes that regulate sleep have been identified in invertebrates, but whether the functions of these genes are conserved in mammals remains poorly explored. Drosophila insomniac (inc) mutants exhibit severely shortened and fragmented sleep. Inc protein physically associates with the Cullin-3 (Cul3) ubiquitin ligase, and neuronal depletion of Inc or Cul3 strongly curtails sleep, suggesting that Inc is a Cul3 adaptor that directs the ubiquitination of neuronal substrates that impact sleep. Three proteins similar to Inc exist in vertebrates—KCTD2, KCTD5, and KCTD17—but are uncharacterized within the nervous system and their functional conservation with Inc has not been addressed. Here we show that Inc and its mouse orthologs exhibit striking biochemical and functional interchangeability within Cul3 complexes. Remarkably, KCTD2 and KCTD5 restore sleep to inc mutants, indicating that they can substitute for Inc in vivo and engage its neuronal targets relevant to sleep. Inc and its orthologs localize similarly within fly and mammalian neurons and can traffic to synapses, suggesting that their substrates may include synaptic proteins. Consistent with such a mechanism, inc mutants exhibit defects in synaptic structure and physiology, indicating that Inc is essential for both sleep and synaptic function. Our findings reveal that molecular functions of Inc are conserved through ~600 million years of evolution and support the hypothesis that Inc and its orthologs participate in an evolutionarily conserved ubiquitination pathway that links synaptic function and sleep regulation.

Sleep is ubiquitous among animals and is regulated in a similar manner across phylogeny, but whether conserved molecular mechanisms govern sleep is poorly defined. The Insomniac protein is vital for sleep in Drosophila and is a putative adaptor for the Cul3 ubiquitin ligase. We show that two mammalian orthologs of Insomniac can restore sleep to flies lacking Insomniac, indicating that the molecular functions of these proteins are conserved through evolution. Our comparative analysis reveals that Insomniac and its mammalian orthologs can localize to neuronal synapses and that Insomniac impacts synaptic structure and physiology. Our findings suggest that Insomniac and its mammalian orthologs are components of an evolutionarily conserved ubiquitination pathway that links synaptic function and the regulation of sleep.

Interactions of cullin3/KCTD5 complexes with both cytoplasmic and nuclear proteins: Evidence for a role in protein stabilization

Based on its specific interaction with cullin3 mediated by an N-terminal BTB/POZ homologous domain, KCTD5 has been proposed to function as substrate adapter for cullin3 based ubiquitin E3 ligases. In the present study we tried to validate this hypothesis through identification and characterization of additional KCTD5 interaction partners. For the replication protein MCM7, the zinc finger protein ZNF711 and FAM193B, a yet poorly characterized cytoplasmic protein, we could demonstrate specific interaction with KCTD5 both in yeast two-hybrid and co-precipitation studies in mammalian cells. Whereas trimeric complexes of cullin3 and KCTD5 with the respective KCTD5 binding partner were formed, KCTD5/cullin3 induced polyubiquitylation and/or proteasome-dependent degradation of these binding partners could not be demonstrated. On the contrary, KCTD5 or Cullin3 overexpression increased ZNF711 protein stability.

Viral and Cellular Components of AAV2 Replication Compartments

Adeno-associated virus 2 (AAV2) is a helpervirus-dependent parvovirus with a bi-phasic life cycle comprising latency in absence and lytic replication in presence of a helpervirus, such as adenovirus (Ad) or herpes simplex virus type 1 (HSV-1). Helpervirus-supported AAV2 replication takes place in replication compartments (RCs) in the cell nucleus where virus DNA replication and transcription occur. RCs consist of a defined set of helper virus-, AAV2-, and cellular proteins. Here we compare the profile of cellular proteins recruited into AAV2 RCs or identified in Rep78-associated complexes when either Ad or HSV-1 is the helpervirus, and we discuss the potential roles of some of these proteins in AAV2 and helpervirus infection.

NBA1/MERIT40 and BRE interaction is required for the integrity of two distinct deubiquitinating enzyme BRCC36-containing complexes

BRCC36-deubiquitinating enzyme (DUB) forms two different complexes through interactions with two different adaptor proteins Abraxas and ABRO1 in cells. Abraxas mainly localizes in the nucleus, mediating the interaction of BRCC36 with BRCA1. ABRO1 is mainly localized in the cytoplasm. Because it lacks the BRCA1-interacting motif, the ABRO1 complex does not interact with BRCA1. Both BRCC36-containing complexes contain common components including BRE and NBA1/MERIT40. Here, we found that the two complexes are assembled in a similar manner and NBA1 and BRE interaction is critical for maintaining the integrity of both of the complexes. Knockdown of NBA1 or BRE leads to decreased levels of components of the two BRCC36-containing complexes. We provided evidence that NBA1 interacts with BRE through a C-terminal conserved motif of the NBA1 protein and a C-terminal UEV domain of the BRE protein. Furthermore, the NBA1-BRE interaction is required for cellular resistance to ionizing irradiation and NBA1's role in recruiting BRCA1 to DNA damage sites. Together, these studies reveal critical interactions required for the formation and function of BRCC36-containing DUB complexes.

Doxorubicin augments rAAV-2 transduction in rat neuronal cells

Doxorubicin, an approved drug for cancer therapy, was recently found to be a potent agent to augment adeno-associated virus (AAV)-mediated transgene expression, especially in airway cells. Recombinant AAV type 2 (rAAV-2) has been shown to preferentially transduce neural tissues and is considered as the primary viral vector for the treatments of various neurodegenerative diseases including Parkinson's disease (PD). The goal of this study is to investigate whether doxorubicin can be applied to increase the efficacy of rAAV-2 transduction in the central nervous system. We co-administrated doxorubicin with AV2.luc/EGFP into the rat striatum, a preferred target site for PD gene therapy, and found that doxorubicin augmented rAAV-2 transduction dramatically without significant cytotoxicity and alteration of rAAV-2 tropism. By evaluating the effects of doxorubicin on rAAV-2 transduction in PC12 and MN9D neuronal cells, we found that doxorubicin appeared to promote the nuclear accumulation of rAAV-2, but did not affect viral binding or uptake. Our data suggested that doxorubicin might play an important role in modulating rAAV-2 intracellular trafficking in neuron-like cells. Our study also provided the initial in vivo evidence to facilitate AAV-mediated gene expression in the midbrain with the treatment of doxorubicin.

Pentameric assembly of potassium channel tetramerization domain-containing protein 5

We report the X-ray crystal structure of human potassium channel tetramerization domain-containing protein 5 (KCTD5), the first member of the family to be so characterized. Four findings were unexpected. First, the structure reveals assemblies of five subunits while tetramers were anticipated; pentameric stoichiometry is observed also in solution by scanning transmission electron microscopy mass analysis and analytical ultracentrifugation. Second, the same BTB (bric-a-brac, tramtrack, broad complex) domain surface mediates the assembly of five KCTD5 and four voltage-gated K(+) (Kv) channel subunits; four amino acid differences appear crucial. Third, KCTD5 complexes have well-defined N- and C-terminal modules separated by a flexible linker that swivels by approximately 30 degrees; the C-module shows a new fold and is required to bind Golgi reassembly stacking protein 55 with approximately 1 microM affinity, as judged by surface plasmon resonance and ultracentrifugation. Fourth, despite the homology reflected in its name, KCTD5 does not impact the operation of Kv4.2, Kv3.4, Kv2.1, or Kv1.2 channels.