C-terminal region of protein kinase CK2 alpha: How the structure can affect function and stability of the catalytic subunit

Regulation of eukaryotic protein kinases by Pin1, a peptidyl-prolyl isomerase

The peptidyl-prolyl isomerase Pin1 cooperates with proline-directed kinases and phosphatases to regulate multiple oncogenic pathways. Pin1 specifically recognizes phosphorylated Ser/Thr-Pro motifs in proteins and catalyzes their cis-trans isomerization. The Pin1-catalyzed conformational changes determine the stability, activity, and subcellular localization of numerous protein substrates. We conducted a survey of eukaryotic protein kinases that are regulated by Pin1 and whose Pin1 binding sites have been identified. Our analyses reveal that Pin1 target sites in kinases do not fall exclusively within the intrinsically disordered regions of these enzymes. Rather, they fall into three groups based on their location: (i) within the catalytic kinase domain, (ii) in the C-terminal kinase region, and (iii) in regulatory domains. Some of the kinases downregulated by Pin1 activity are tumor-suppressing, and all kinases upregulated by Pin1 activity are functionally pro-oncogenic. These findings further reinforce the rationale for developing Pin1-specific inhibitors as attractive pharmaceuticals for cancer therapy.

CK2 phosphorylates TNFAIP1 to affect its subcellular localization and interaction with PCNA

TNFAIP1 is a protein which can be induced by tumor necrosis factoralpha (TNFalpha) and interleukin-6 (IL-6), it may play roles in DNA synthesis, DNA repair, cell apoptosis and human diseases. However, very little has been known about how TNFAIP1 acts in these physiological processes. In this paper, CK2beta was identified as a partner of TNFAIP1 by screening the HeLa cDNA library in yeast two-hybrid system with TNFAIP1 as a bait. Furthermore, it was demonstrated that CK2 could phosphorylate TNFAIP1 in vitro and in vivo, which facilitated the distribution of TNFAIP1 in nucleus and enhanced its interaction with PCNA. It is suggested that the phosphorylation of TNFAIP1 may be required for its functions.

New liver cell mutants defective in the endocytic pathway

To isolate mutant liver cells defective in the endocytic pathway, a selection strategy using toxic ligands for two distinct membrane receptors was utilized. Rare survivors termed trafficking mutants (Trf2-Trf7) were stable and more resistant than the parental HuH-7 cells to both toxin conjugates. They differed from the previously isolated Trf1 HuH-7 mutant as they expressed casein kinase 2 alpha'' (CK2alpha'') which is missing from Trf1 cells and which corrects the Trf1 trafficking phenotype. Binding of (125)I-asialoorosomucoid (ASOR) and cell surface expression of asialoglycoprotein receptor (ASGPR) were reduced approximately 20%-60% in Trf2-Trf7 cells compared to parental HuH-7, without a reduction in total cellular ASGPR. Based on (125)I-transferrin binding, cell surface transferrin receptor activity was reduced between 13% and 88% in the various mutant cell lines. Distinctive phenotypic traits were identified in the differential resistance of Trf2-Trf7 to a panel of lectins and toxins and to UV light-induced cell death. By following the endocytic uptake and trafficking of Alexa(488)-ASOR, significant differences in endosomal fusion between parental HuH-7 and the Trf mutants became apparent. Unlike parental HuH-7 cells in which the fusion of endosomes into larger vesicles was evident as early as 20 min, ASOR endocytosed into the Trf mutants remained within small vesicles for up to 60 min. Identifying the biochemical and genetic mechanisms underlying these phenotypes should uncover novel and unpredicted protein-protein or protein-lipid interactions that orchestrate specific steps in membrane protein trafficking.

Molecular characterization and function analysis of MT-10 and MT-20 metallothionein isoforms from Mytilus galloprovincialis

Structure and function of molluscan metallothioneins (MTs) are still poorly understood. The sea mussel Mytilus galloprovincialis displays two MT isoforms which differ in both primary sequences and physiological functions. MT-10 is the constitutive isoform, whereas MT-20 is mainly induced by cadmium (Cd). Both MTs were produced as recombinant proteins and showed identical Cd content and similar Cd-binding properties. Conversely, circular dichroism disclosed marked differences in the secondary conformations of the two Cd(7)-MTs. The possible relapses of these structural differences on protein stability and function were assessed. MT-10 presented a higher thermal stability and a more compact structure than MT-20, as it was inferred by absorption and emission spectroscopy studies. Moreover, the kinetics of Cd-release clearly indicated that MT-10 is much more sensitive to oxidation than is MT-20. The observed differences between MT-10 and MT-20 are discussed in terms of the different physiological roles exerted by the two isoforms in mussel.