Molecular details of aluminium-amyloid ß peptide interaction by nuclear magnetic resonance.

Alzheimer's disease (AD) is a devastating neurodegenerative condition that poses major challenges to human health. Both amyloid ß (Aß) and metal ions such as aluminium are implicated in the development of AD. By the means of NMR, the interactions of Al3+ with Aß1-28 peptide as well as the Aß1-28 analogues were studied, and the key binding sites of Al3+ in Aß determined. NMR data showed Al3+ interacts with Aß1-28 at the NH and αH of numerous residues by exhibiting upfield shifts. Using Aß analogues where His6, His13 and His14 were individually replaced by alanine residue(s), including Aß H6A, Aß H13A, Aß H14A, and Aß H6,13,14A, the results demonstrated that the histidine residues (His6, His13 and His14) and N-terminal Asp1 were involved in the Al3+ coordination. These findings provide, for the first time, the details of the molecular interaction between Al3+ and Aß, which points to the potential role of Al3+ in Aß aggregation, hence in AD development.

Protein kinase CK2 is involved in zinc homeostasis in breast and prostate cancer cells.

The intracellular zinc profiles of breast and prostate cancer cells are diametrically opposed, with hyper-accumulation of zinc in breast cancer, and low level in prostate cancer. This phenomenon is poorly understood. This study employs two breast and two prostate cancer cell lines to investigate the role of protein kinase CK2 in regulating zinc homeostasis. CK2 was targeted by its specific inhibitors 4,5,6,7-tetrabromobenzotriazole (TBB) and CX-4945, and by the specific siRNA against each of the three CK2 genes. The effect of zinc exposure after the above CK2 manipulation was observed by MTT [3-(4,5-dimethyliazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] cell viability assay and confocal microscopy for intracellular zinc level. The results demonstrate that CK2 is involved in regulating zinc homeostasis in breast and prostate cancer cells as both TBB and CX-4945 substantially decreased cell viability upon zinc exposure. siRNA-mediated knockdown of the three CK2 subunits (α, α' and ß) revealed their discrete roles in regulating zinc homeostasis in breast and prostate cancer cells. Knockdown of CK2α' decreased the intracellular zinc level of breast cancer cells and in turn increased the cell viability while the opposite findings were obtained for the prostate cancer cells. Knockdown of CK2ß expression substantially increased the zinc level in breast cancer cell lines whilst decreased the zinc level in prostate cancer cells. Taken together, this study shows that CK2 is involved in zinc homeostasis of breast and prostate cancer cells and opens a new avenue for research on these cancers.

Unravelling the role of protein kinase CK2 in metal toxicity using gene deletion mutants.

Metal ions, biologically essential or toxic, are present in the surrounding environment of living organisms. Understanding their uptake, homeostasis or detoxification is critical in cell biology and human health. In this study, we investigated the role of protein kinase CK2 in metal toxicity using gene deletion strains of Saccharomyces cerevisiae against a panel of six metal ions. The deletion of CKA2, the yeast orthologue of mammalian CK2α', leads to a pronounced resistant phenotype against Zn2+ and Al3+, whilst the deletion of CKB1 or CKB2 results in tolerance to Cr6+ and As3+. The individual deletion mutants of CK2 subunits (CKA1, CKA2, CKB1 and CKB2) did not have any benefit against Co2+ and Cd2+. The metal ion content in the treated cells was then measured by inductively coupled plasma mass spectrometry. Two contrasting findings were obtained for the CKA2 deletion mutant (cka2Δ) against Al3+ or Zn2+. Upon exposure to Al3+, cka2Δ had markedly lower Al3+ content than the wild type and other CK2 mutants, congruous to the resistant phenotype of cka2Δ against Al3+, indicating that CKA2 is responsible for Al3+ uptake. Upon zinc exposure the same mutant showed similar Zn2+ content to the wild type and cka1Δ. Strikingly, the selective inhibitor of CK2 TBB (4,5,6,7-tetrabromo-1H-benzotriazole) abolished the resistant phenotype of cka2Δ against Zn2+. Hence, the CK2 subunit CKA1 plays a key role in Zn2+ sequestration of the cell. Given that both zinc and CK2 are implicated in cancer development, the findings herein are of significance to cancer research and anticancer drug development.

Revelation of molecular basis for chromium toxicity by phenotypes of Saccharomyces cerevisiae gene deletion mutants.

Chromium toxicity is increasingly relevant to living organisms such as humans, due to the environmental contamination of chromium and the application of stainless steel-based medical devices like hip prostheses. Despite the investigations in past years, the molecular details for chromium toxicity remain to be delineated. In this study, we seek to gain insights into the molecular aspects of chromium toxicity by screening a genome-wide deletion set of individual genes in Saccharomyces cerevisiae against hexavalent chromium [Cr(vi)] using chromium trioxide. From the primary data collected in this study, two lists of deletion mutants in response to Cr(vi) exposure were obtained, one for the sensitive phenotype and the other for the resistant phenotype. The functional analysis of the genes corresponding to the sensitive mutants reveals the key features of Cr(vi) toxicity, which include genotoxicity, protein damage, disruption of energy and sulfur metabolisms. DNA repair, ubiquitination-mediated protein degradation, iron homeostasis and growth attenuation are the intrinsic facets of the cell's detoxification mechanisms. Protein kinase CK2 is, for the first time, found to be involved in regulating chromium toxicity by reducing the uptake of Cr(vi). Taken together, the findings provide meaningful details into the basic understanding of chromium toxicity in terms of its uptake, modes of action, cellular detoxification and molecular regulatory mechanisms.

Molecular insight into arsenic toxicity via the genome-wide deletion mutant screening of Saccharomyces cerevisiae.

Arsenic is omnipresent in soil, air, food and water. Chronic exposure to arsenic is a serious problem to human health. In-depth understanding of this metalloid's toxicity is a fundamental step towards development of arsenic-free foods and measures for bioremediation. By screening the complete set of gene deletion mutants (4873) of Saccharomyces cerevisiae, this study uncovered 75 sensitive and 39 resistant mutants against arsenite [As(III)]. Functional analysis of the corresponding genes revealed the molecular details for its uptake, toxicity and detoxification. On the basis of the hypersensitivity of yap3Δ, the transcription factor, Yap3p, is for the first time linked to the cell's detoxification against As(III). Apart from confirming the previously described role of the mitogen-activated protein kinase (MAPK) Hog1 pathway in combating arsenic toxicity, the results show that the regulatory subunits (Ckb1p and Ckb2p) of protein kinase CK2 are also involved in the process, suggesting possible crosstalk between the two key protein kinases. The sensitivity to As(III) conferred by deletion of the genes involved in protein degradation and chromatin remodelling demonstrates protein damage is the key mode of toxicity for the metalloid. Furthermore, the resistant phenotype of fps1Δ, snf3Δ and pho81Δ against As(III) links arsenic uptake with the corresponding plasma membrane-bound transporters-aquaglyceroporin (Fps1p), hexose (Snf3p) and phosphate transporters. The molecular details obtained in this screen for As(III) uptake, detoxification and toxicity provide the basis for future investigations into arsenic-related problems in the environment, agriculture and human health.