Hydroxylation of demethoxy-Q6 constitutes a control point in yeast coenzyme Q6 biosynthesis

Coenzyme Q is a lipid molecule required for respiration and antioxidant protection. Q biosynthesis in Saccharomyces cerevisiae requires nine proteins (Coq1p–Coq9p). We demonstrate in this study that Q levels are modulated during growth by its conversion from demethoxy-Q (DMQ), a late intermediate. Similar conversion was produced when cells were subjected to oxidative stress conditions. Changes in Q₆/DMQ₆ ratio were accompanied by changes in COQ7 gene mRNA levels encoding the protein responsible for the DMQ hydroxylation, the penultimate step in Q biosynthesis pathway. Yeast coq null mutant failed to accumulate any Q late biosynthetic intermediate. However, in coq7 mutants the addition of exogenous Q produces the DMQ synthesis. Similar effect was produced by over-expressing ABC1/COQ8. These results support the existence of a biosynthetic complex that allows the DMQ₆ accumulation and suggest that Coq7p is a control point for the Q biosynthesis regulation in yeast. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Received 04 September 2008; received after revision 22 October 2008; accepted 23 October 2008     

Myosin I: From yeast to human

Myosin I is a non-filamentous, single-headed, actin-binding motor protein and is present in a wide range of species from yeast to man. The role of these class I myosins have been studied extensively in simple eukaryotes, showing their role in diverse processes such as actin cytoskeleton organization, cell motility, and endocytosis. Recently, studies in metazoans have begun to reveal more specialized functions of myosin I. It will be a major challenge in the future to examine the physiological functions of each class I myosin in different cell types of metazoans.     

Bile Acids: Chemistry, Pathochemistry, Biology, Pathobiology, and Therapeutics

Bile acids and bile alcohols in the form of their conjugates are amphipathic end products of cholesterol metabolism with multiple physiological functions. The great variety of bile acids and bile alcohols that are present in vertebrates are tabulated. Bile salts have an enterohepatic circulation resulting from efficient vectorial transport of bile salts through the hepatocyte and the ileal enterocyte; such transport leads to the accumulation of a pool of bile salts that cycles between the liver and intestine. Bile salt anions promote lipid absorption, enhance tryptic cleavage of dietary proteins, and have antimicrobial effects. Bile salts are signaling molecules, activating nuclear receptors in the hepatocyte and ileal enterocyte, as well as an increasing number of G-protein coupled receptors. Bile acids are used therapeutically to correct deficiency states, to decrease the cholesterol saturation of bile, or to decrease the cytotoxicity of retained bile acids in cholestatic liver disease.     

Modulation of natural killer cell cytotoxicity and cytokine release by the drug glatiramer acetate

Glatiramer acetate (GA or Copaxone) is a drug used to treat experimental autoimmune encephalomyelitis in mice and multiple sclerosis in human. Here, we describe a new mechanism of action for this drug. GA enhanced the cytolysis of human NK cells against autologous and allogeneic immature and mature monocyte-derived dendritic cells (DCs). This drug reduced the percentages of mature DCs expressing CD80, CD83, HLA-DR or HLA-I. In contrast, it did not modulate the percentages of NK cells expressing NKG2D, NKp30, or NKp44. Nonetheless, anti-NKp30 or anti-CD86 inhibited GA-enhanced human NK cell lysis of immature DCs. Hence, CD86, and NKp30 are important for NK cell lysis of immature DCs, whereas CD80, CD83, HLA-DR and HLA-I are important for the lysis of mature DCs when GA is used as a stimulus. Further, GA inhibited the release of IFN-γ 24 h but increased the release of TNF-α 48 h after incubation with NK cells. Received 13 November 2008; received after revision 10 February 2009; accepted 18 February 2009     

Calmodulin-associated post-translational regulation of rat organic cation transporter 2 in the kidney is gender dependent

In this work, regulation of organic cation transporter type 2 from rat (rOCT2) stably transfected in HEK293 cells was investigated by microfluorimetry with 4-(4-(dimethylamino)styryl)-N-methylpyridinium as substrate. The transport mediated by rOCT2 was specifically stimulated by PKA, phosphatidylinositol-3-kinase, p56^lck tyrosine kinase, mitogen-extracellular-signal-regulated-kinase-1/2, calmodulin (CaM), and CaM-kinase-II. The regulatory pattern of rOCT2 differs markedly quantitatively and qualitatively from that of other OCT isoforms. Only CaM-dependent upregulation is conserved throughout the OCT family. For this reason, CaM regulation of rOCT2 was also investigated in isolated S3-segments (known to express only rOCT2) of male and female rat proximal tubules. Inhibition of CaM by calmidazolium significantly decreased rOCT2 activity (−49.0 ± 13.6%, n = 4) in male but not female (9.0 ± 13.0%, n = 4) rats. Real-time PCR and Western blot investigations of CaM expression in rat kidneys showed that male animals have significantly higher CaM expression. This is the first study describing post-translational gender-dependent rOCT2 regulation. Received 26 February 2009; accepted 16 March 2009     

The Role of the Agouti-Related Protein in Energy Balance Regulation

The Agouti-Related Protein (AgRP) is a powerful orexigenic peptide that increases food intake when ubiquitously overexpressed or when administered centrally. AgRP-deficiency, on the other hand, leads to increased metabolic rate and a longer lifespan when mice consume a high fat diet. In humans, AgRP polymorphisms have been consistently associated with resistance to fatness in Blacks and Whites and resistance to the development of type-2 diabetes in African Blacks. Systemically administered AgRP accumulates in the liver, the adrenal gland and fat tissue while recent findings suggest that AgRP may also have inverse agonist effects, both centrally and peripherally. AgRP could thus modulate energy balance via different actions. Its absence or reduced functionality may offer a benefit both in terms of bringing about negative energy balance in obesigenic environments, as well as leading to an increased lifespan.     

The many faces of semaphorins: from development to pathology

The semaphorin family is a large group of proteins controlling cell migration and axonal growth cone guidance. These proteins are bi-functional signals capable of growth promotion or growth inhibition. Initially described in the nervous system, the majority of studies related to semaphorins and semaphorin signalling are nowadays performed in model systems outside the nervous system. Here, we provide an exhaustive review of the many faces of semaphorins both during developmental, regulatory and pathological processes. Indeed, because of their crucial fundamental roles, the semaphorins and their receptors represent important targets for the development of drugs directed at a variety of diseases. Received 22 August 2008; received after revision 22 September 2008; accepted 24 September 2008 L. Roth, E. Koncina, S. Satkauskas: These authors contributed equally to this work.     

AID in antibody perfection

Expressed immunoglobulin (Ig) genes undergo alterations in sequence and genomic structure in order to optimize antibody function. A single B cell-specific factor, activation-induced deaminase (AID), initiates these changes by deamination of cytosine to uracil. Uracil in DNA is encountered commonly, and conserved pathways are responsible for its faithful repair. However, at the Ig loci of B cells, AID-initiated damage is processed to produce three distinct outcomes: somatic hypermutation, class switch recombination and gene conversion. This review focuses on the role of AID in Ig gene diversification, emphasizing how AID functions within the mechanism of the Ig gene diversification pathway; and highlights open questions for future research, particularly the most provocative current question: what makes a gene a target for AID-initiated mutagenesis?     

Gene expression in spermiogenesis

Germ cells convey parental genes to the next generation, and only germ cells perform meiosis, which is a mechanism that preserves the parental genes. The fusion of the products of germ cell meiosis, the haploid sperm and egg, creates the next generation. Sperm are the haploid germ cells that contribute genes to the egg. In preparation for this, the haploid round spermatids produced by meiosis undergo drastic morphological changes to become sperm. During this process of spermiogenesis, the nuclear form of the haploid germ cell takes shape, the mitochondria are rearranged in a specific manner, the flagellum develops and the acrosome forms. Spermatogenesis is supported by precise and orderly regulation of gene expression during the changes in chromatin structure, when protamine replaces histone. In this report, we summarize the molecular mechanisms involved in spermiogenesis.Received 2 September 2004; received after revision 7 October 2004; accepted 7 October 2004     

Dissection of the molecular mechanisms that control the nuclear accumulation of transport factors importin-α and CAS in stressed cells

The physiological state of eukaryotic cells controls nuclear trafficking of numerous cargos. For example, stress results in the inhibition of classical protein import, which is characterized by the redistribution of several transport factors. As such, importin-alpha and cellular apoptosis susceptibility protein (CAS) accumulate in nuclei of heat-shocked cells; however, the mechanisms underlying this relocation are not fully understood. We now show that heat upregulates the initial docking of importin-alpha at the nuclear envelope and stimulates the translocation of CAS into the nuclear interior. Moreover, heat exposure compromises the exit of importin-alpha from nuclei and drastically increases its retention in the nucleoplasm, whereas CAS nuclear exit and retention are less affected. Taken together, our results support the idea that heat shock regulates importin-alpha and CAS nuclear accumulation at several levels. The combination of different stress-induced changes leads to the nuclear concentration of both transport factors in heat-stressed cells.