Parvovirus Host Cell Interactions: Development of Novel (Onko)Toxins on the Base of Parvomimetics.
Dr. Jürg P. F. Nüesch
In the past, my Group has investigated the properties and activities of the multifunctional parvoviral non-structural protein NS1 (1-8, 13-15). The variety of different tasks performed during infection suggested that this protein is regulated by post-translational modifications, particularly phosphorylation (9, 10, 14). Thus, we started to investigate the interconnection between NS1 regulation through cellular protein kinases and the impact of the viral infection on intracellular signalling (11, 12, 16, 17, 20). This led to the identification of PKC lambda and PKC eta as NS1 regulating protein kinases (12, 17). Vice-versa we obtained strong indication that MVM itself is able to influence activity and intracellular distribution of these kinases, mediated through the activator kinase PDK-1. The investigation of the MVM PDK/PKC Interrelationship consists one of our current projects (20).
A main interest of our Department consists in the exploitment of the natural oncotropism and oncolytic activity of autonomous parvovirus for cancer gene therapy. In the frame of this topic my Group is interested in the determination of NS1 functions involved in Cytotoxicity (13). Interestingly, we could show that NS1-toxicity is modulated through distinct (PKC-) phosphorylation sites (13, 18), which led to the generation of replication competent mutant MVMp viruses with altered toxic potential. Such virus variations might be beneficial for distinct approaches in cancer gene therapy (21). Analyzing the mechanisms of NS1-induced cytotoxicity we found that the host cell cytoskeleton is a main target of MVM(NS1) induced cell death (19). Thereby we are currently investigating three aspects of MVM induced disregulation of the cytoskeleton dynamics: (i) Destruction of actin filaments (ii) alterations of tropomyosin and (iii) the maintenance of microtubules upon MVM infection of A9 cells.
Besides characterization of the signalling pathways involved in the MVM induced perturbation of the cytoskeleton, we are interested to identify distinct parvoviral (NS1) related triggers leading to the disruption of the cell integrity (cytopathic effect [CPE]). So far we found that NS1 directly interacts with CKII alpha, thereby altering the substrate specificity of this cellular kinase (manuscript in preparation). This novel parvoviral enzymatic activity, seems to be a key-element for MVM induced CPE, since a variety of cellular proteins involved in cell signalling and cytoskeleton dynamics appear to be targets of this unique kinase. Finally, the identification of this MVM feature triggering CPE led us to the design parvomimetics (23), which are currently tested in heterologous virus systems as oncotoxins, an applied aspect of our basic research.