The Bcr-Abl tyrosine kinase activates various signaling pathways including nuclear factor B that mediate proliferation, transformation, and apoptosis resistance in Bcr-Abl ؉ myeloid leukemia cells. Here we report that protein kinase (PK) D2, a serine threonine kinase of the PKD family, is a novel substrate of Bcr-Abl. PKD2 was found to be the major isoform of the PKD family expressed in chronic myeloid leukemia cells and is tyrosine phosphorylated by Bcr-Abl in its pleckstrin homology domain. A mutant that mimicks tyrosine phosphorylation of PKD2 in the pleckstrin homology domain activates nuclear factor B independently of its catalytic activity. Furthermore, our data show that Bcr-Abl-induced activation of the nuclear factor B cascade in LAMA84 cells is largely mediated by tyrosine-phosphorylated PKD2. These data present a novel mechanism of Bcr-Abl-induced nuclear factor B activation in myeloid leukemia. Targeting PKD2 tyrosine phosphorylation, not its kinase activity, could be a novel therapeutic approach for the treatment of Bcr-Abl ؉ myeloid leukemia.

Protein kinase D2 (PKD2) belongs to the PKD family of serine/threonine kinases that is activated by phorbol esters and G protein-coupled receptors (GPCRs). Its C-terminal regulatory domain comprises two cysteine-rich domains (C1a/C1b) followed by a pleckstrin homology (PH) domain. Here, we examined the role of the regulatory domain in PKD2 phorbol ester binding, catalytic activity, and subcellular localization: The PH domain is a negative regulator of kinase activity. C1a/C1b, in particular C1b, is required for phorbol ester binding and gastrin-stimulated PKD2 activation, but it has no inhibitory effect on the catalytic activity. Gastrin triggers nuclear accumulation of PKD2 in living AGS-B cancer cells. C1a/C1b, not the PH domain, plays a complex role in the regulation of nucleocytoplasmic shuttling: We identified a nuclear localization sequence in the linker region between C1a and C1b and a nuclear export signal in the C1a domain. In conclusion, our results define the critical components of the PKD2 regulatory domain controlling phorbol ester binding, catalytic activity, and nucleocytoplasmic shuttling and reveal marked differences to the regulatory properties of this domain in PKD1. These findings could explain functional differences between PKD isoforms and point to a functional role of PKD2 in the nucleus upon activation by GPCRs.

Protein kinase D2 (PKD2), a member of the PKD family of serine/threonine kinases, is localized in various subcellular compartments including the nucleus where the kinase accumulates upon activation of G-protein-coupled receptors. We define three critical post-translational modifications required for nuclear accumulation of PKD2 in response to activation of the CCK2 receptor (CCK2R): phosphorylation at Ser706 and Ser710 within the activation loop by PKCg leading to catalytic activity and phosphorylation at Ser244 within the zinc-finger domain, which is crucial for blocking nuclear export of active PKD2 by preventing its interaction with the Crm-1 export machinery. We identify CK1d and e as upstream activated kinases by CCK2R that phosphorylate PKD2 at Ser244. Moreover, nuclear accumulation of active PKD2 is a prerequisite for efficient phosphorylation of its nuclear substrate, HDAC7. Only nuclear, active PKD2 mediates CCK2R-induced HDAC7 phosphorylation and Nur77 expression. Thus, we define a novel, compartment-specific signal transduction pathway downstream of CCK2R that phosphorylates PKD2 at three specific sites, results in nuclear accumulation of the active kinase and culminates in efficient phosphorylation of nuclear PKD2 substrates in human gastric cancer cells.

The genetic trajectory leading to viral attenuation was studied in a canine parvovirus (CPV) strain grown on dog kidney cells for 115 transfers. Consensus sequences of viral populations at passages 0, 3, 30, 50, 80, and 115 were obtained from PCR products covering 86% of the genome; clones from each of the 80th and 115th passages were also sequenced, covering 69% of the genome. Sixteen changes were fixed in the 115th-passage virus sample. Levels of polymorphism were strikingly different over time, in part because of a plaque-cloning step at passage 112 that reduced variation: passage 80 had 19 variants common among the clones, but passage 115 had only a single common variant. Several mutations increased in the culture at the same time, with most reaching fixation only after the 80th passage. The pattern of evolution was consistent with recombination and not with separate selective sweeps of individual mutations. Thirteen of the changes observed were identical to or at the same positions as changes observed in other isolates of CPV or feline panleukopenia virus.The most successful viral vaccines use live attenuated virus strains. For more than a century, attenuation has involved propagation of a virus under novel conditions so that it becomes less pathogenic to its original host as it evolves under the new conditions (9, 10). Despite the antiquity of this method and its remarkable success in generating many vaccines that are widely used in humans and other animals, little is known about the process by which the attenuating mutations arise and evolve. In addition, there are some drawbacks to this method: the outcome of an attempted attenuation is largely unpredictable, and a successfully attenuated virus may revert to virulence, depending on the nature of the attenuating mutation(s). Although newer approaches show promise, many contemporary vaccines are still being developed by these classic methods.A better understanding of the classical attenuation process might thus suggest protocols to eliminate some disadvantages of these methods of attenuation. One of the obvious gaps in our understanding of attenuation is at the genetic level. Until recently, the molecular changes underlying the shift from virulence to attenuation were almost completely unknown for most attenuated vaccine viruses. Even now, the dynamics over an attenuation episode have yet to be described. To begin filling this gap, we examined the genetic evolution that occurred during the passaging of canine parvovirus (CPV) in tissue culture to give rise to a successfully attenuated vaccine that has been used effectively for 20 years.

The N-terminal cytosolic T1 domain of the mammalian voltage gated potassium channel Kv1.4 is strongly involved in the tetramerization of the Kv1.4 subunit that is required for forming a functional ion channel. The T1 domain forms a stable tetramer of 48 kDa in solution that cannot be dissociated into monomers. In spite of the high molecular mass it was possible to completely assign the backbone and part of the side chain resonances by multidimensional NMR spectroscopy on uniformly (2)H, (13)C, (15)N enriched protein. The secondary structure analysis derived from the chemical shifts is in line with the expectations from X-ray structures of related proteins.