David S. Latchman

The Transcriptional Co-activators CREB-binding Protein (CBP) and p300 Play a Critical Role in Cardiac Hypertrophy That Is Dependent on Their Histone Acetyltransferase Activity

The CBP and p300 proteins are transcriptional co-activators that are involved in a variety of transcriptional pathways in development and in response to specific signaling pathways. We have previously demonstrated that the ability of both these factors to stimulate transcription is greatly enhanced by treatment of cardiac cells with the hypertrophic agent phenylephrine (PE). Here, we show that inhibition of either CBP or p300 with antisense or dominant negative mutant constructs inhibits PE-induced hypertrophy as assayed by atrial naturetic protein production, cardiac cell protein:DNA ratio and cell size. Furthermore, we show that overexpression of CBP or p300 can induce hypertrophy and that this effect requires their histone acetyltransferase (HAT) activity. Moreover, we show that PE can directly enhance CBP HAT activity and that artificial enhancement of HAT activity is sufficient to induce hypertrophy. Hence, CBP and p300 play an essential role in hypertrophy induced by PE, and this effect is mediated via PE-induced enhancement of their HAT activity. This is the first time a role for these factors, and their HAT activity, in hypertrophy has been directly demonstrated.

The Expression of Constitutively Active Isotypes of Protein Kinase C to Investigate Preconditioning

The role of protein kinase C (PKC) in ischemic preconditioning remains controversial because of difficulties with both its measurement and pharmacological manipulation. We investigated preconditioning in isolated neonatal rat cardiocytes by expressing constitutively active isotypes of PKC. Observations at differing durations of simulated ischemia suggested β-galactosidase (β-gal) activity reflected viability within transfected myocytes. Preconditioning with 90 min of ischemia significantly increased β-gal activity and myocyte survival after 6 h of ischemia; an effect abolished by PKC inhibitors. After co-transfection with plasmids encoding β-gal and either constitutively active mutants of PKC-δ, PKC-α, wild type PKC-δ, or empty vector, cardiocytes were subjected to 6 h of ischemia. Only PKC-δ, rendered constitutively active by a limited deletion within the pseudosubstrate domain, consistently increased resistance to simulated ischemia (β-gal activity was 85.6 ± 11.9% versus 53.7 ± 6.5% (p ≤ 0.01) and dead myocytes 46.8 ± 3.4%versus 68.7 ± 2.8% (p ≤ 0.01)). Since transfection was apparent in only 5–12% of cells, the results suggested a protective bystander effect that was confirmed by co-culture of transfected myocytes with untransfected myocytes. In neonatal cardiocytes expression of active PKC-δ increases resistance to simulated ischemia. This observation may provide further insight into the mechanism and possible avenues for therapeutic exploitation of preconditioning.

Focal cerebral ischaemia increases the levels of several classes of heat shock proteins and their corresponding mRNAs

The induction of focal cerebral ischaemia in rats by middle cerebral artery occlusion has previously been shown to increase, over time, the mRNA levels of the heat shock proteins (HSPs) 27 and 70. However, the levels of HSP90 mRNA remain constant. In contrast, during global ischaemia, HSP70 and HSP90 mRNA levels are both raised, particularly in the CA1 neurons in the hippocampus, an area that is resistant to the insult in comparison to the surrounding regions. HSP27 mRNA is raised in the neuroglia in the subregions of the hippocampus. However, the protein levels of HSP27, 70 and 90 have not been characterised in focal ischaemia. With this data in mind, we have carried out a comparative study of HSP27, 56, 60, 70 and 90 mRNA and protein levels during focal cerebral ischaemia in rats, up to 24 h post-occlusion. We have shown that HSP70 and HSP27 mRNA levels are increased and also that HSP60 mRNA levels (which had also not previously been characterised in this model of focal ischaemia) are significantly raised. HSP90 and HSP56 mRNAs were not significantly elevated. On Western blot analysis, the inducible HSP72 protein was first detected at 8 h post-occlusion, HSP27 protein was detected only at 24 h post-occlusion and HSP60 protein, although constitutive, appeared to increase at 24 h post-occlusion. HSP56 protein levels appeared to rise on the occluded side, but HSP90 protein levels remained constant.

Pure populations of transduced primary human cells can be produced using GFP expressing herpes virus vectors and flow cytometry

Herpes simplex virus (HSV) has often been suggested as a vector for gene delivery to the nervous system although it is also capable of infecting many other cell types. HSV also has the ability to package large genetic insertions so the expression of multiple genes from a single virus is possible. Here we show that a green fluorescent protein (GFP) expressing HSV1 vector can transduce two primary human cell types – quiescent human CD34+ hematopoietic progenitor cells and dendritic cells – which are both hard to transduce by other means. We also show that GFP is an effective marker when expressed from an HSV vector in vivo in the mouse brain. When GFP is expressed together with a second gene (in this case lacZ) from a sin-gle virus, transduced GFP-positive CD34+ hematopoietic progenitor cells or dendritic cells can both be generated at an effective efficiency of 100% for the second gene. Here transduction with the vector is combined with flow cytometry allowing GFP-positive cells to be sorted from the untransduced population. Such completely transduced populations of quiescent CD34+ hematopoietic progenitor and dendritic cells cannot easily be achieved by other means, and might thus allow experimental or therapeutic protocols to be carried out requiring high-level transduction which would not otherwise be possible. Such an approach using HSV vectors might also be applicable to other cell types for which transduction is as yet unreliable or of low efficiency.

Delivery of a constitutively active form of the heat shock factor using a virus vector protects neuronal cells from thermal or ischaemic stress but not from apoptosis

The heat shock proteins (HSPs) are induced by stressful stimuli and have a protective effect. Different HSPs protect with different efficiencies against different stresses indicating that optimal protection would be obtained with a non‐stressful agent which induced a range of HSPs. We have prepared a herpesvirus vector expressing a constitutively active mutant form of heat shock factor 1 (HSF1) which, unlike the wild‐type form of this transcription factor, does not require stress for its activation. Upon infection of neuronal cells, this virus induced a more restricted range of HSPs than in non‐neuronal cells. Infection with the virus protected neuronal cells against subsequent thermal or ischaemic stress in accordance with its ability to induce HSP70 expression but did not protect them against apoptotic stimuli. The mechanisms of these effects and their significance for the use of HSF to manipulate HSP gene expression is discussed.

Gene transfer using a disabled herpes virus vector containing the EMCV IRES allows multiple gene expression in vitro and in vivo.

The design of recombinant HSV-1 vectors for delivery of transgenes to the central nervous system is undergoing constant development. Problems associated with the construction and use of such vectors include the requirement for detection of recombinant versus nonrecombinant virus in vitro and also the identification of transduced cells in vivo. This could be overcome by the insertion of reporter genes such as lacZ or green fluorescent protein (GFP) under a separate promoter to the transgene to be expressed. In this case, however, reporter gene expression does not necessarily confirm transgene expression as a separate RNA must be produced. This study reports the use of an encephalomyocarditis virus internal ribosome entry site (IRES) to enable the translation of two reporter genes from a single mRNA transcript driven by the same promoter within a disabled HSV vector, and discusses the potential advantages of this approach.

Potential and limitations of a gamma 34.5 mutant of herpes simplex 1 as a gene therapy vector in the CNS.

Direct injection of viral vectors into the central nervous system has become a valuable technique for exploring the function of neurological systems and is a potential therapy for neural disease. To this end a number of herpes simplex virus (HSV)-derived vectors are currently being developed for the introduction of foreign DNA into the brain. In this study a non-neurovirulent HSV 17+ mutant, variant 1716, deleted in the γ34.5 gene and expressing the marker gene lacZ under the control of the latency-associated transcripts promoter was injected stereotactically into the central nervous system of two strains of rat (AO and PVG). We show (1) that transgene expression was low at the site of injection, in the striatum, at all times studied (12 h to 30 days after injection); (2) dramatically more transgene expression was observed at distant sites which contain neurons projecting directly to the site of injection, with maximal expression at these sites being at 1–2 days; (3) immunostaining with a polyclonal anti-HSV antibody and with an antibody which detects a 65 kDa HSV DNA binding protein (the product of the UL42 gene of the virus) demonstrated that viral gene products could be detected at the injection site as early as 12 h and up to 1 week after injection. Moreover these could also be detected at several secondary sites not all of which have direct connections with the injection site. These findings suggest that γ34.5 negative vectors have potential for gene transfer but may require further attenuation to limit viral antigen expression before they can be used successfully for gene therapy in the brain.