NS1 interaction with CKII alpha: novel protein complex mediating parvovirus-induced cytotoxicity

Parvovirus interference with intracellular signalling: mechanism of PKCeta activation in MVM-infected A9 fibroblasts

Autonomous parvoviruses are strongly dependent on the phosphorylation of the major non-structural protein NS1 by members of the protein kinase C (PKC) family. Besides being accompanied with changes in the overall phosphorylation pattern of NS1 and acquiring new modifications at consensus PKC sites, ongoing minute virus of mice (MVM) infections lead to the appearance of new phosphorylated cellular protein species. This prompted us to investigate whether MVM actively interferes with phosphoinositol-dependent kinase (PDK)/PKC signalling. The activity, subcellular localization and phosphorylation status of the protein kinases PDK1, PKCeta and PKClambda were measured in A9 cells in the presence or absence of MVM infection. Parvovirus infection was found to result in activation of both PDK1 and PKCeta, as evidenced by changes in their subcellular distribution and overall (auto)phosphorylation. We show evidence that activation of PKCeta by PDK1 is driven by atypical PKClambda. By modifying the hydrophobic motif of PKCeta, PKClambda appeared to control docking and consecutive phosphorylation of PKCeta's activation-loop by PDK1, a process that was inhibited in vivo in the presence of a dominant-negative PKClambda mutant.

A viral adaptor protein modulating casein kinase II activity induces cytopathic effects in permissive cells

Autonomous parvoviruses induce severe morphological and physiological alterations in permissive host cells, eventually leading to cell lysis and release of progeny virions. Viral cytopathic effects (CPE) result from specific rearrangements and destruction of cytoskeletal micro- and intermediate filaments. We recently reported that inhibition of endogenous casein kinase II (CKII) protects target cells from parvovirus minute virus of mice (MVM)-induced CPE, pointing to this kinase as an effector of MVM toxicity. The present work shows that the parvoviral NS1 protein mediates CKII-dependent cytoskeletal alterations and cell death. NS1 can act as an adaptor molecule, linking the cellular protein kinase CKIIalpha to tropomyosin and thus modulating the substrate specificity of the kinase. This action results in an altered tropomyosin phosphorylation pattern both in vitro and in living cells. The capacity of NS1 to induce CPE was impaired by mutations abolishing binding with either CKIIalpha or tropomyosin. The cytotoxic adaptor function of NS1 was confirmed with fusion peptides, where the tropomyosin-binding domain of NS1 and CKIIalpha are physically linked. These adaptor peptides were able to mimic NS1 in its ability to induce death of transformed MVM-permissive cells.