Efficient Gene Targeting Mediated by Adeno-Associated Virus and DNA Double-Strand Breaks

Gene targeting is the in situ manipulation of the sequence of an endogenous gene by the introduction of homologous exogenous DNA. Presently, the rate of gene targeting is too low for it to be broadly used in mammalian somatic cell genetics or to cure genetic diseases. Recently, it has been demonstrated that infection with recombinant adeno-associated virus (rAAV) vectors can mediate gene targeting in somatic cells, but the mechanism is unclear. This paper explores the balance between random integration and gene targeting with rAAV. Both random integration and spontaneous gene targeting are dependent on the multiplicity of infection (MOI) of rAAV. It has previously been shown that the introduction of a DNA double-stranded break (DSB) in a target gene can stimulate gene targeting by several-thousand-fold in somatic cells. Creation of a DSB stimulates the frequency of rAAV-mediated gene targeting by over 100-fold, suggesting that the mechanism of rAAV-mediated gene targeting involves, at least in part, the repair of DSBs by homologous recombination. Absolute gene targeting frequencies reach 0.8% with a dual vector system in which one rAAV vector provides a gene targeting substrate and a second vector expresses the nuclease that creates a DSB in the target gene. The frequencies of gene targeting that we achieved with relatively low MOIs suggest that combining rAAV vectors with DSBs is a promising strategy to broaden the application of gene targeting

Mapping Regions of RNF168 Required for its Degradation by ICP0

Viruses establish infection by overtaking host cell processes and developing mechanisms that promote viral replication. Herpes simplex virus undergoes lytic and latent cycles of infection throughout the lifespan of its host. The viral genome is transcriptionally silent during latency, but viral proteins are produced upon reactivation. Herpes simplex virus type 1 encodes the ICP0 protein, an E3 ubiquitin ligase required for reactivation from latency of the infectious virus. The immediate-early protein ICP0 regulates the herpes simplex virus by activating viral gene expression thereby initiating lytic infection. Cellular proteins are degraded by ICP0, promoting the virus to enter the lytic cycle. Two cellular histone ubiquitin ligases, RNF8 and RNF168 that promote recruitment of DNA repair factors to DNA damage sites. ICP0 viral expression counteracts RNF8 and RNF168 as anti-viral factors by their degradation. This study maps regions of RNF168 required for its degradation so that proteins involved in viral reactivation can be determined. RNF168 has been shown to organize the DNA damage response by increasing the local concentration of ubiquitinated proteins in damage sites to prolong the ubiquitination signal. As a chromatin-associated RING finger protein, RNF168 consists of a sequence of two motif interacting with ubiquitin (MIU) domains that allow RNF168 to be recruited to damage sites. Two constructs were created, which separated each MIU to test for degradation by ICP0, thus localizing how ICP0 targets cellular proteins. In understanding how ICP0 targets its cellular substrates, other proteins targeted by ICP0 with similar motifs may be identified

The MRN complex in double-strand break repair and telomere maintenance

AbstractGenomes are subject to constant threat by damaging agents that generate DNA double-strand breaks (DSBs). The ends of linear chromosomes need to be protected from DNA damage recognition and end-joining, and this is achieved through protein–DNA complexes known as telomeres. The Mre11–Rad50–Nbs1 (MRN) complex plays important roles in detection and signaling of DSBs, as well as the repair pathways of homologous recombination (HR) and non-homologous end-joining (NHEJ). In addition, MRN associates with telomeres and contributes to their maintenance. Here, we provide an overview of MRN functions at DSBs, and examine its roles in telomere maintenance and dysfunction

Optogenetic approaches to cell migration and beyond

Optogenetics, the use of genetically encoded tools to control protein function with light, can generate localized changes in signaling within living cells and animals. For years it has been focused on channel proteins for neurobiology, but has recently expanded to cover many different types of proteins, using a broad array of different protein engineering approaches. These methods have largely been directed at proteins involved in motility, cytoskeletal regulation and gene expression. This review provides a survey of non-channel proteins that have been engineered for optogenetics. Existing molecules are used to illustrate the advantages and disadvantages of the many imaginative new approaches that the reader can use to create light-controlled proteins

The HSV-1 ubiquitin ligase ICP0: modifying the cellular proteome to promote infection

Herpes simplex virus 1 (HSV-1) hijacks ubiquitination machinery to modify the cellular proteome to create an environment permissive for virus replication. HSV-1 encodes its own RING-finger E3 ubiquitin (Ub) ligase, Infected Cell Protein 0 (ICP0), that directly interfaces with component proteins of the Ub pathway to inactivate host immune defences and cellular processes that restrict the progression of HSV-1 infection. Consequently, ICP0 plays a critical role in the infectious cycle of HSV-1 that is required to promote the efficient onset of lytic infection and productive reactivation of viral genomes from latency. This review will describe the current knowledge regarding the biochemical properties and known substrates of ICP0 during HSV-1 infection. We will highlight the gaps in the characterization of ICP0 function and propose future areas of research required to understand fully the biological properties of this important HSV-1 regulatory protein

HSV-1 Remodels Host Telomeres to Facilitate Viral Replication

SummaryTelomeres protect the ends of cellular chromosomes. We show here that infection with herpes simplex virus 1 (HSV-1) results in chromosomal structural aberrations at telomeres and the accumulation of telomere dysfunction-induced DNA damage foci (TIFs). At the molecular level, HSV-1 induces transcription of telomere repeat-containing RNA (TERRA), followed by the proteolytic degradation of the telomere protein TPP1 and loss of the telomere repeat DNA signal. The HSV-1-encoded E3 ubiquitin ligase ICP0 is required for TERRA transcription and facilitates TPP1 degradation. Small hairpin RNA (shRNA) depletion of TPP1 increases viral replication, indicating that TPP1 inhibits viral replication. Viral replication protein ICP8 forms foci that coincide with telomeric proteins, and ICP8-null virus failed to degrade telomere DNA signal. These findings suggest that HSV-1 reorganizes telomeres to form ICP8-associated prereplication foci and to promote viral genomic replication

Differential Myocardial Gene Delivery by Recombinant Serotype-Specific Adeno-associated Viral Vectors

AbstractRecombinant cross-packaging of adeno-associated virus (AAV) genome of one serotype into other AAV serotypes has the potential to optimize tissue-specific gene transduction and expression in the heart. To evaluate the role of AAV1 to 5 virion shells on AAV2 transgene transduction, we constructed hybrid vectors in which each serotype capsid coding domain was cloned into a common vector backbone containing AAV2 replication genes. Constructs were tested for expression in: (1) adult murine heart in vivo using direct injection of virus, (2) neonatal and adult murine ventricular cardiomyocytes in vitro, and (3) adult human ventricular cardiomyocytes in vitro, using green fluorescent protein (GFP) as the measurable transgene. Serotype 1 virus demonstrated the highest transduction efficiency in adult murine cardiomyocytes both in vitro and in vivo, while serotype 2 virus had the greater transduction efficiency in neonatal cardiomyocytes in vitro. Prolonged in vivo myocardial GFP expression was observed for up to 12 months using serotype 1 and 2 vectors only. In human cardiomyocytes, serotype 1 vector was superior in transduction efficiency, followed by types 2, 5, 4, and 3. These data establish a hierarchy for efficient serotype-specific vector transduction in myocardial tissue. AAV1 serotype packaging results in more efficient transduction of genes in the murine and human adult heart, compared to other AAV serotypes. Our results suggest that adult human cardiac gene therapy may be enhanced by the use of serotype 1-specific AAV vectors

Antigen glycosylation regulates efficacy of CAR T cells targeting CD19

While chimeric antigen receptor (CAR) T cells targeting CD19 can cure a subset of patients with B cell malignancies, most patients treated will not achieve durable remission. Identification of the mechanisms leading to failure is essential to broadening the efficacy of this promising platform. Several studies have demonstrated that disruption of CD19 genes and transcripts can lead to disease relapse after initial response; however, few other tumor-intrinsic drivers of CAR T cell failure have been reported. Here we identify expression of the Golgi-resident intramembrane protease Signal peptide peptidase-like 3 (SPPL3) in malignant B cells as a potent regulator of resistance to CAR therapy. Loss of SPPL3 results in hyperglycosylation of CD19, an alteration that directly inhibits CAR T cell effector function and suppresses anti-tumor cytotoxicity. Alternatively, over-expression of SPPL3 drives loss of CD19 protein, also enabling resistance. In this pre-clinical model these findings identify post-translational modification of CD19 as a mechanism of antigen escape from CAR T cell therapy