1 Gap Junctional Communication and the Regulation of Multicellular Functions.- 2 Experimental In Vitro Approaches to the Study of Mouse Primordial Germ Cell Development.- 3 Spermatogonial Transplantation.- 4 Genetic Control of Meiosis and the Onset of Spermiogenesis in Drosophila.- 5 Chromatin Structure and Gene Expression During Spermatogenesis.- 6 The Control of Testis ACE Expression.- 7 Growth Hormone Releasing Hormone and Growth Hormone Releasing Hormone-Related Peptide in the Testis.- 8 Cyclic ADP-Ribose and Calcium Signalling.- 9 Human Gonadotropin Receptors: Pathophysiology, Pharmacology, and Molecular Mechanisms.- 10 Steroidogenic Acute Regulatory Protein and Steroidogenesis.- 11 Pem: an Androgen-Dependent Homeodomain Gene Expressed in the Testis and Epididymis.- 12 Studies on the Mechanism of Sperm Production.- 13 Role of c-kit in Egg Activation.- 14 Spermatogenesis-Specific Genes Deleted in Infertile Men: DAZ/DAZH Clinical Aspects and Animal Models.- 15 Follicle-Stimulating Hormone Receptor Mutation and Fertility.- Previous Volumes Published in this Series.
The organization of sarcomeric structures during muscle development involves regulated multistep assembly pathways. The myosin assembly factor UNC-45 functions both as a molecular chaperone and as an Hsp90 co-chaperone for myosin throughout muscle thick-filament formation. Consequently, mutations in unc-45 result in paralyzed worms with severe myofibril disorganization in striated body wall muscles. Our data suggest that functional muscle formation in Caenorhabditis elegans is linked to ubiquitin-dependent UNC-45 turnover, regulated by the E3 enzymes UFD-2 and CHN-1 in cooperation with the ubiquitin-selective chaperone CDC-48 (also known as p97 in human). Missense mutations in the gene encoding p97 are known to cause a dominant, late-onset hereditary inclusion body myopathy. Remarkably, we identified a conserved role of CDC-48/p97 in the process of myofiber differentiation and maintenance, which appears to have important implications for understanding defects in muscle formation and maintenance during pathological conditions.
Our studies with the yeast Saccharomyces cerevisiae have uncovered a number of general principles governing substrate selectivity and proteolysis by the ubiquitin-proteasome system. The initial work focused on the degradation of a transcription factor, the MATα2 repressor, but the pathways uncovered have a much broader range of targets. At least two distinct ubiquitination mechanisms contribute to α2 turnover. One of them depends on a large integral membrane ubiquitin ligase (E3) and a pair of ubiquitin-conjugating enzymes (E2s). The transmembrane E3 and E2 proteins must travel from their site of synthesis in the ER to the inner nuclear membrane in order to reach nuclear substrates such as α2. The 26S proteasome is responsible for α2 degradation, and several important features of proteasome assembly and active site formation were uncovered. Most recently, we have delineated major steps in 20S proteasome assembly and have also identified several novel 20S proteasome assembly factors. Surprisingly, alterations in 20S proteasome assembly lead to defects in the assembly of the proteasome regulatory particle (RP). The RP associates with the 20S proteasome to form the 26S proteasome. Our data suggest that the 20S proteasome can function as an assembly factor for the RP, which would make it the first such factor for RP assembly identified to date.
The ubiquitin-proteasome system (UPS) plays an essential role in a wide variety of cell regulatory signaling pathways. The clinical effectiveness of the proteasome inhibitor Velcade in the treatment of several human cancers underscores the importance of the UPS as a novel target area for pharmaceutical intervention. E3 ubiquitin ligases are key enzyme complexes that regulate and determine the ubiquitination of specific substrates, whose abnormal regulation has been implicated in multiple disease phenotypes. Targeting a selective E3 ligase may allow specific manipulation of distinct pathways and eventually lead to a better therapeutic index with reduced nonspecific side effects. Here, we aim to discuss the challenges of interfering with small molecules in this target class, as well as current strategies and progress in E3 ligase drug discovery.
Postmenopausal women that still have an uterus and suffer from hot flushes are treated with combinations of estrogens and progestins. Whereas estrogens are indispensable for treating postmenopausal symptoms, progestins are added to counteract the proliferative activity of estrogens on uterine epithelial cells. However, in the mammary gland, progestins, given together with estrogens, stimulate the proliferation of mammary epithelial cells. Therefore, progestins with reduced proliferative activity in the mammary gland would be of advantage for hormone therapy of postmenopausal women. In order to identify progestins with better tissue-selectivity, we exploited the activation of different signal transduction pathways by the classical progesterone receptor. We demonstrated that progestins with reduced non-genomic versus genomic activity in vitro show a better dissociation of uterine versus mammary gland effects in vivo than medroxyprogesterone acetate (MPA), a synthetic progestin that is widely used in hormone therapy.
The design of catalytic reactions that proceed with high enantioselectivity is an important goal in organic synthesis. Increased interest in this research area has resulted in substantial progress, particularly in the field of metal catalyzed transformations. In recent years small organic molecules have been used as organocatalysts for a variety of enantioselective reactions. Among these, secondary amine catalysts are the most widely applied and can be used in the activation of the nucleophilic component through enamine formation (enamine catalysis), or by formation of an iminum intermediate to activate the electrophile (iminium catalysis). Additionally, chiral diols and thioureas, as well as carbene- and DMAP-derivatives (hydrogen bonding-, nucleophilic catalysis), have been shown to be versatile catalysts for enantioselective transformations. An alternative to these strategies is the activation of an electrophile or nucleophile by use of a chiral Brønsted acid. Compared to amino-, carbene-, pyridine- and hydrogen-bonding catalyzed transformations, enantioselective Brønsted acid catalysis has only recently emerged as important and promising area of research. In the course of our research program we were able to contribute significantly to the field of enantioselective Brønsted acid catalysis over the last 2 years, and could demonstrate for the first time that in various enantioselective transformations chiral Brønsted acid catalysts can give better or at least comparable results to metal-catalyzed processes. In this chapter we will highlight some of our most recent results and will, additionally, describe how we initially entered the field of asymmetric Brønsted acid catalysis by starting of from a biomimetic approach using nature as a role model.
The mammary gland undergoes extensive epithelial expansion and differentiation during pregnancy, leading ultimately to the development of functional milk-producing alveolar lobules. This phase of mammary gland remodeling is controlled primarily by the cooperative interplay between hormonal signals initiated by both progesterone and prolactin. Abrogation of mammary epithelial expression of receptors for either one of the hormones results in failure of alveologenesis and an absence of pregnancy-induced tertiary ductal side branches in the case of progesterone receptor-null (PRKO) mammary glands. By combining gene array approaches to identify PR- and prolactin (PRL)-dependent downstream signaling pathways and by using genetic mouse models to address the consequences of abrogation and/or misexpression of potential downstream genes, recent studies have begun to illuminate key signaling pathways that mediate the morphogenic effects of these hormones during pregnancy-induced mammary gland remodeling. Analysis of deregulated expression of PR-dependent gene transcripts in PRKO mammary glands has revealed that convergence between progesterone and prolactin signaling occurs in part through progesterone-dependent induction of mammary epithelial PRL receptors to prime the mammary epithelium to respond to PRL. Additional genes activated by PRs encode epithelial paracrine growth factor signals that regulate ductal and alveolar epithelial proliferation and survival, lineage-restricted transcription factors that control luminal and alveolar cell fate establishment and maintenance, and gap junction proteins that play a critical role in alveolar morphogenesis by establishment of epithelial cell polarity. Finally, two distinct isoforms of PRs (PR-A and PR-B) are coexpressed in the mammary gland and display extensively overlapping but partially distinct gene regulatory properties in relaying the progesterone signal.
Metabolic phenotyping in large-scale population studies can yield crucial information regarding the impact and interaction of genetic and environmental factors with regard to the prevalence and risk of chronic diseases. Spectroscopic technologies such as nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) can be used to generate multi-parameter profiles of biological samples and together with automated sample delivery and mathematical modelling systems, can be used as a high throughput screening tool. The adaptation of these metabolic profiling tools from pre-clinical studies in animal models to population studies in man is explored and an overview of the current and future roles of metabolic phenotyping is described, including the idea of “Metabolome Wide Association Screening” focussing on key disease areas such as cardiovascular disease and metabolic syndrome, cancers and neurodegeneration.
The metabolic phenotype of tumor cells promote the proliferative state, which indicates that (a) cell transformation is associated with the activation of specific metabolic substrate channels toward nucleic acid synthesis and (b) increased expression phosphorylation, allosteric or transcriptional regulation of intermediary metabolic enzymes and their substrate availability together mediate unlimited growth. It is evident that cell transformation due to various K-ras point mutations is associated with the activation of specific metabolic substrate channels that increase glucose channeling toward nucleic acid synthesis. Therefore, phosphorylation, allosteric and transcriptional regulation of intermediary metabolic enzymes and their substrate availability together mediate cell transformation and growth. In this review, we summarize opposite changes in metabolic phenotypes induced by various cell-transforming agents, and tumor growth-inhibiting drugs or phytochemicals, or novel synthetic antileukemic drugs such as imatinib mesylate (Gleevec). Metabolic enzymes that further incite growth signaling pathways and thus promote malignant cell transformation serve as high-efficacy nongenetic novel targets for cancer therapies.
Studies of drug action classically assess biochemical activity in settings which typically contain the isolated target only. Recent technical advances in mass spectrometry-based analysis of proteins have enabled the quantitative analysis of sub-proteomes and entire proteomes, thus initiating a departure from the traditional single gene--single protein--single target paradigm. Here, we review chemical proteomics-based experimental strategies in kinase drug discovery to analyse quantitatively the interaction of small molecule compounds or drugs with a defined sub-proteome containing hundreds of protein kinases and related proteins. One novel approach is based on 'Kinobeads'--an affinity resin comprised of a cocktail of immobilized broad spectrum kinase inhibitors--to monitor quantitatively the differential binding of kinases and related nucleotide-binding proteins in the presence and absence of varying concentrations of a lead compound or drug of interest. Differential binding is detected by high throughput and sensitive mass spectroscopy techniques utilizing isobaric tagging reagents (iTRAQ), yielding quantitative and detailed target binding profiles. The method can be applied to the screening of compound libraries and to selectivity profiling of lead compounds directly against their endogenously expressed targets in a range of cell types and tissue lysates. In addition, the method can be used to map drug-induced changes in the phosphorylation state of the captured sub-proteome, enabling the analysis of signalling pathways downstream of target kinases.
The level of Myc proteins is a critical determinant of cellular proliferation and apoptosis. Ubiquitination of Myc plays a key role in controlling protein levels by stimulating proteasomal degradation of the protein. Some experiments suggest that ubiquitination may also regulate Myc function in addition to turnover. This review attempts to summarize current knowledge about this field.
N-Heterocyclic carbenes (NHC) have become an important class of organocatalysts and class of ligands for transition-metal catalysis. In organocatalyzed umpolung reactions, thiazolium salt-derived NHC have been used successfully for decades. Even so, during recent years there has been an increased interest in NHC-catalyzed transformations and many new reactions have been developed. This article focuses on the use of NHC in the conjugate umpolung of α,β-unsaturated aldehydes.
Metabolic stress is an important stimulus that promotes apoptosis-mediated tumor suppression. Metabolic stress arises in tumors from multiple factors that include insufficient nutrient supply caused by deficient angiogenesis and high metabolic demand of unrestrained cell proliferation. The high metabolic demand of tumor cells is only exacerbated by reliance on the inefficient process of glycolysis for energy production. Recently it has become clear that tumor cells survive metabolic stress through the catabolic process of autophagy. Autophagy also functions as a tumor suppression mechanism by preventing cell death and inflammation and by protecting the genome from damage and genetic instability. How autophagy protects the genome is not yet clear but may be related to its roles in sustaining metabolism or in the clearance of damaged proteins and organelles and the mitigation of oxidative stress. These findings illuminate the important role of metabolism in cancer progression and provide specific predictions for metabolic modulation in cancer therapy.
The main function of mature T cells is to recognize and respond to foreign antigens by a complex activation process involving differentiation of the resting cell to a proliferating lymphoblast actively secreting immunoregulatory lymphokines or displaying targeted cytotoxicity, ultimately leading to recruitment of other cell types and initiation of an effective immune response. In order to understand the physiology and pathophysiology of T lymphocytes, it is necessary to decode the biochemical processes that integrate signals from antigen, cytokine, integrin and death receptors. The principal upon which our work is based is to explore and identify gene products of distinct members of the AGC family of protein serine/threonine kinases as key players mediating cell growth regulation. Given the established important role of PKC theta as regulator of T cell fate and knowing that several other PKC isotypes are also expressed in T cells at a high level, we now summarize the physiological and non-redundant functions of PKC alpha, beta, delta, epsilon, zeta and theta isotypes in T cells. This review describes the current knowledge of the physiological and non-redundant functions of the PKC gene products in T cells.
In 1920s, Otto Warburg described the phenomenon of ‘aerobic glycolysis’, the ability of tumour cells to convert glucose to lactate in the presence of normal oxygen conditions. Warburg’s hypothesis of
Estrogen and progesterone play a critical role in normal and neoplastic development of the mammary gland. A long duration of estrogen and progesterone exposure is associated with increased breast cancer risk, and a short duration of the same doses of these hormones is associated with a reduced breast cancer risk. The protective effects of estrogen and progesterone have been extensively studied in animal models. Several studies have demonstrated that these hormones induce persistent and long-lasting alterations in gene expression in the mammary epithelial cells. In the experiments discussed herein, the protective effect of estrogen and progesterone is shown to occur in genetically engineered mice (the p53-null mammary gland). The protective effect is associated with a decrease in cell proliferation. The effects of hormones seem to manifest as a delay in premalignant progression. In the nontumor-bearing glands of hormone-treated mice, premalignant foci are present at the time the control glands are actively developing mammary tumors. If the hormone-treated cells are transplanted from the treated host to the untreated host, the cells resume their predetermined tumorigenic potential. The protective effect reflects both host-mediated factors (either stroma-determined or systemic factors) and mammary epithelial intrinsic changes. If normal, untreated p53 cells are transplanted into a host that has been previously treated with a short dose of hormones, the cells exhibit a significant delay in tumorigenesis. The relative contributions of host-mediated factors and mammary cell intrinsic factors remain to be determined. Current studies are moving this research area from the biological to the molecular realm and from the rodent models to human studies and offer the potential for directing prevention efforts at specific molecular targets.
Members of the inhibitor of apoptosis protein (IAP) family are key regulators of apoptosis as they bind and inhibit caspases and other pro-apoptotic factors. Recent findings suggest that these proteins play additional roles, e.g., in cell cycle regulation, angiogenesis, and carcinogenesis. Here, we review the function of BRUCE (BIR repeat-containing ubiquitin-conjugating enzyme), an unusual 528-kDa IAP with ubiquitin ligase activity, and describe its role in apoptosis and cytokinesis. Additionally, we discuss how these seemingly unrelated functions might be linked.
A major charter for modern nutrition is to provide a molecular basis for health outcome resulting from different food choices and how this could be designed to maintain individual health free of disease. Nutrigenomic techniques have been developed to generate information at various levels of biological organization, i.e. genes, proteins, and metabolites. Within this frame, metabonomics targets the molecular characterization of a living system through metabolic profiling. The metabolic profiles are explored with sophisticated data mining techniques mainly based on multivariate statistics, which can recover key metabolic information to be further linked to biochemical processes and physiological events. The power of metabonomics relies on its unique ability to assess functional changes in the metabolism of complex organisms stemming from multiple influences such as lifestyle and environmental factors. In particular, metabolic profiles encapsulate information on the metabolic activity of symbiotic partners, i.e. gut microflora, in complex organisms, which represent major determinant in nutrition and health. Therefore, applications of metabonomics to nutrition sciences led to the nutrimetabonomics approach for the classification of dietary responses in populations and the possibility of optimized or personalized nutritional management.
