A potential copper-regulatory role for cytosolic expression of the DNA repair protein XRCC5

The Role of Copper Chaperone Atox1 in Coupling Redox Homeostasis to Intracellular Copper Distribution

Human antioxidant protein 1 (Atox1) is a small cytosolic protein with an essential role in copper homeostasis. Atox1 functions as a copper carrier facilitating copper transfer to the secretory pathway. This process is required for activation of copper dependent enzymes involved in neurotransmitter biosynthesis, iron efflux, neovascularization, wound healing, and regulation of blood pressure. Recently, new cellular roles for Atox1 have emerged. Changing levels of Atox1 were shown to modulate response to cancer therapies, contribute to inflammatory response, and protect cells against various oxidative stresses. It has also become apparent that the activity of Atox1 is tightly linked to the cellular redox status. In this review, we summarize biochemical information related to a dual role of Atox1 as a copper chaperone and an antioxidant. We discuss how these two activities could be linked and contribute to establishing the intracellular copper balance and functional identity of cells during differentiation.

Phosphorylation of hnRNP K by cyclin-dependent kinase 2 controls cytosolic accumulation of TDP-43

Cytosolic accumulation of TAR DNA binding protein 43 (TDP-43) is a major neuropathological feature of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). However, the mechanisms involved in TDP-43 accumulation remain largely unknown. Previously, we reported that inhibitors of cyclin-dependent kinases (CDKs) prevented cytosolic stress granule accumulation of TDP-43, correlating with depletion of heterogeneous ribonucleoprotein (hnRNP) K from stress granules. In the present study, we further investigated the relationship between TDP-43 and hnRNP K and their control by CDKs. Inhibition of CDK2 abrogated the accumulation of TDP-43 into stress granules. Phosphorylated CDK2 co-localized with accumulated TDP-43 and phosphorylated hnRNP K in stress granules. Inhibition of CDK2 phosphorylation blocked phosphorylation of hnRNP K, preventing its incorporation into stress granules. Due to interaction between hnRNP K with TDP-43, the loss of hnRNP K from stress granules prevented accumulation of TDP-43. Mutation of Ser216 and Ser284 phosphorylation sites on hnRNP K inhibited hnRNP K- and TDP-43-positive stress granule formation in transfected cells. The interaction between hnRNP K and TDP-43 was further confirmed by the loss of TDP-43 accumulation following siRNA-mediated inhibition of hnRNP K expression. A substantial decrease of CDK2 and hnRNP K expression in spinal cord motor neurons in ALS patients demonstrates a potential key role for these proteins in ALS and TDP-43 accumulation, indicating that further investigation of the association between hnRNP K and TDP-43 is warranted. Understanding how kinase activity modulates TDP-43 accumulation may provide new pharmacological targets for disease intervention.

The relationship of copper to DNA damage and damage prevention in humans

Copper ions are well suited to facilitate formation of reactive oxygen species (ROS) that can damage biomolecules, including DNA and chromatin. That this can occur in vitro with isolated DNA or chromatin,or by exposure of cultured mammalian cells to copper complexed with various agents, has been well demonstrated. Whether that is likely to occur in vivo is not as clear. This review addresses the question of whether and how copper ions or complexes – in forms that could be present in vivo, damage DNA and chromosome structure and/or promote epigenetic changes that can lead to pathology and diseases, including cancer and neurological conditions such as Alzheimer's disease, Lewy body dementias, and spongiform encephalopathies. This question is considered in light of our knowledge that copper-dependent enzymes are important contributors to antioxidant defense, and that the mammalian organism has robust mechanisms for maintaining constant levels of copper not only in body fluids but in its major organs. Overall,and except in unusual genetic states that lead to copper overload in specific cells (particularly those in liver), it appears that excessive intake of copper is not a significant factor in the development of disease states.

Role of Ku70 and Bax in epigallocatechin-3-gallate-induced apoptosis of A549 cells in vivo

EGCG (epigallocatechin-3-gallate), the major catechin found in green tea, has been demonstrated to inhibit proliferation and induce apoptosis in a number of types of tumors. Recent studies reveal that EGCG has various anticancer effects. This study investigated a further possible molecular mechanism of the anticancer effects of EGCG in murine lung cancer xenografts. In the study, A549 human lung cancer cells were injected into nude mice. Tumor volume was used to measure cancer cell growth. The weight of the animals was used to assess the toxicity of the drugs. The expression of protein and mRNA was assayed by western blot analysis and RT-PCR, respectively. The interaction between Bax and Ku70 was determined by immunoprecipitation. Our results suggest that EGCG induced A549 lung cancer cell apoptosis in vivo, and had less toxic effects compared to classical anticancer drugs. EGCG may inhibit the surrogate markers of proliferation and apoptosis (caspase 3) in A549 tumor xenografts in vivo. In addition, EGCG downregulated the expression of Bcl-xl and upregulated the expression of Bax mRNA and protein. Further experiments indicated that EGCG downregulated the protein expression of Ku70 and interrupted the binding of Ku70 and Bax. This is the first study demonstrating that the induction of apoptosis by EGCG may be caused by the downregulation of Ku70 and that EGCG disrupts the interaction between Ku70 and Bax in lung cancer.