Objective. Increased chondrocyte nitric oxide (NO) and peroxynitrite production appears to modulate decreased matrix synthesis and increased mineralization in osteoarthritis (OA). Because NO inhibits mitochondrial respiration, this study was undertaken to directly assess the potential role of chondrocyte mitochondrial oxidative phosphorylation (OXPHOS) in matrix synthesis and mineralization.Methods. We studied cultured human articular chondrocytes and immortalized costal chondrocytes (TC28 cells). We also assessed the effects of antimycin A and oligomycin (inhibitors of mitochondrial complexes III and V, respectively) on chondrocyte mitochondrial respiration, ATP synthesis, and inorganic pyrophosphate (PPi) generation, and the mineralizing potential of released matrix vesicles (MV).Results. Articular chondrocytes and TC28 cells respired at comparable rates. Peroxynitrite and NO donors markedly suppressed respiration and ATP generation in chondrocytes. Because NO exerts multiple effects on chondrocytes, we investigated the primary functions of mitochondrial respiration and OXPHOS. To do so, we identified minimally cytotoxic doses of antimycin and oligomycin, which both induced intracellular ATP depletion (by 50-80%), attenuated collagen and proteoglycan synthesis, and blocked transforming growth factor ␤ from increasing intracellular ATP and elaboration of PPi, a critical inhibitor of hydroxyapatite deposition. Antimycin and oligomycin also abrogated the ability of the ATP-hydrolyzing enzyme plasma cell membrane glycoprotein 1 (PC-1) to increase chondrocyte PPi generation. Finally, MV from cells treated with antimycin or oligomycin contained less PPi and precipitated >50% more 45 Ca.Conclusion. Chondrocyte mitochondrial reserve, as NO-sensitive mitochondrial respiration-mediated ATP production, appears to support matrix synthesis and PPi elaboration and to regulate MV composition and mineralizing activity. NO-induced depression of chondrocyte respiration could modulate matrix loss and secondary cartilage mineralization in OA.The pathogenesis of osteoarthritis (OA) includes elaboration of increased amounts of nitric oxide (NO), as a consequence of up-regulation of chondrocyteinducible NO synthase induced by interleukin-1 (IL-1) and other factors (1-3). In chondrocytes, increased NO generation promotes OA (3,4) through effects that include inhibition of chondrocyte cytoskeletal actin polymerization and ␤1 integrin-dependent signaling (5,6), decreased expression of IL-1 receptor antagonist and transforming growth factor ␤ (TGF␤) (7,8), suppression of chondrocyte collagen and proteoglycan synthesis (9,10), activation of metalloproteinases (11), and suppression of proliferation as well as promotion of apoptosis (4,12). Cytokine-induced and NO-induced oxidative stress, the potentiation of injury by other oxidants, the formation of peroxynitrite from NO and O 2 Ϫ , and the nitration of proteins mediate several of the aforementioned effects of NO on chondrocytes (3,4,10,13,14).

The nucleotide sequence was determined for the chicken egg white lysozyme mRNA and for the exons of the gene together with their flanking intron regions. The exon pattern is to some degree related to the structural subdivision of the final protein product. However, the relationship of exons to functional units of the enzyme is better established. Exon 2 codes for amino acids 28-82, which include the catalytically active residues and a cluster of amino acids which bind rings C, D, E, and F of the oligosaccharide substrate. Exon 3 codes for amino acids 82-108, which give additional substrate specificity determine the cleavage frame for the alternating Nacetyiglucosamine/N-acetylmuramic acid chain, and increase the catalytic efficiency of the active center. Exons 1 and 4, respectively, code for translational signal sequences on the mRNA, for the signal peptide of prelysozyme, and for the amino-and carboxy-terminal regions of the enzyme. These regions increase the stability of the molecule but are not directly involved in the catalytic function.

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MicroRNAs (miRNAs) negatively regulate expression of target transcripts by hybridization to complementary sites of their messenger RNA targets. Chen et al. have described several putative functional single nucleotide polymorphisms (SNPs) in miRNA target sites. Here, we selected 11 miRNA target site SNPs located in 3' untranslated regions of genes involved in cancer and breast cancer to analyze their impact on breast cancer risk using a large familial study population. Whereas no association was observed for 10 SNPs, a significant association was revealed for the variant affecting a miRNA target site in the estrogen receptor (ESR) 1. Age stratification showed that the association was stronger in premenopausal women [C versus T: odds ratio (OR) = 0.60, confidence interval (CI) = 0.41-0.89, P = 0.010]. Furthermore, the effect was stronger in high-risk familial cases (C versus T: OR = 0.42, CI = 0.25-0.71, P = 0.0009). Clinical studies have shown that elimination of ESR1 significantly reduces breast cancer risk. Thus, therapies that inhibit ESR1 are used for breast cancer treatment. According to in silico analysis, ESR1_rs2747648 affects the binding capacity of miR-453, which is stronger when the C allele is present. In contrast, the T allele attenuates the binding of miR-453, which might lead to a reduced miRNA-mediated ESR1 repression, in consequence higher ESR1 protein levels and an increased breast cancer risk. Thus, the breast cancer protective effect observed for the C allele in premenopausal women is biologically reasonable. The analysis of large study populations in multicentre collaboration will be needed to verify the association and answer questions regarding the possible impact of this variant on therapeutic and clinical outcome.

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ZM447439 (ZM) is a potent and selective inhibitor of aurora-A and -B kinase with putative anti-tumoral activity. Inhibitors of aurora kinases were shown to induce apoptosis in vitro and in vivo. To investigate the underlying mechanisms, cell death pathways triggered by ZM was analysed in HCT-116 colorectal cancer cells. Through correlation of polyploidization and apoptosis in different knockout cells, the interrelation of these cellular responses to ZM was investigated. ZM induced apoptosis in a concentration- and time-dependent manner. ZM-induced apoptosis was associated with an upregulation of p53, breakdown of the mitochondrial membrane potential (DeltaPsim) and activation of caspase-3. To precisely define key components for ZM-induced apoptosis, knockout cells lacking p53, Bak, Bax or both Bak and Bax were used. Lack of p53 reduced ZM-induced apoptosis and breakdown of DeltaPsim, while lack of Bak, Bax or both almost completely inhibited apoptosis and breakdown of DeltaPsim. Since no difference in apoptosis induction was detectable between HCT-116 cells lacking Bak, Bax or both, apoptosis induction depended non-redundantly on both Bak and Bax. Phenomenally, ZM induced notable polyploidization in all examined cells, especially in p53-/- cells. A correlation between polyploidization and apoptosis was observed in wild-type, and also in p53-/- cells, albeit with a modest extent of apoptosis. Moreover, in Bak-/-, Bax-/- and Bak/Bax-/- cells apoptosis was totally inhibited in spite of the strongest polyploidization, suggesting apoptosis may be a secondary event following polyploidization in HCT-116 cells. Thus ZM-induced apoptosis depends not only on polyploidization, but also on the intracellular apoptotic signaling.

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