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Free access

Denis Nonclercq, Fabrice Journé, Ioanna Laïos, Carole Chaboteaux, Robert-Alain Toillon, Guy Leclercq and Guy Laurent

We used the Crm1 inhibitor leptomycin B (LMB) to examine a possible involvement of nuclear export in estrogen receptor α (ER) level and function in MCF-7 breast carcinoma cells. As revealed by immunofluorescence microscopy and western blotting with anti-ER antibodies, LMB produced an accumulation of ER in cell nuclei. LMB also partly abrogated ER elimination resulting from Hsp90 disruption and 17β-estradiol (E2)-induced ER downregulation. By contrast, it was ineffective on ER downregulation caused by the pure anti-estrogen fulvestrant. Finally, LMB inhibited E2-induced progesterone receptor expression and the expression of an estrogen response element-driven luciferase reporter gene in unstimulated and E2-stimulated cells. Altogether, the data reported here suggest that: i) ER undergoes nuclear export directly or indirectly involving exportin Crm1; ii) degradation of unliganded and of agonist-bound ER probably occurs in an extranuclear compartment, while it is not the case for ER bound to a pure anti-estrogen; and iii) optimal ER-mediated gene transactivation seems to require nucleocytoplasmic shuttle of the receptor.

Open access

S Das, I Sepahi, A Duthie, S Clark and J C Crockett

The interaction of receptor activator of NFκB (RANK), a member of the tumour necrosis factor receptor superfamily, with RANK ligand is crucial for the formation, function and survival of osteoclasts. The role of the cytoplasmic oligomerisation domain (pre-ligand assembly domain; PLAD or ‘IVVY’ motif) in the ligand-dependent activation of downstream NFκB signalling has not been studied previously. The discovery of truncating mutations of TNFRSF11A (W434X and G280X that lack the PLAD) as the cause of rare cases of osteoclast-poor osteopetrosis offered the opportunity for functional study of this region. Recapitulating the W434X mutation by transcription activator-like effector nuclease (TALEN)-mediated targeted disruption of Tnfrsf11a within the region homologous to W434X in the mouse macrophage-like cell line RAW264.7 impaired formation of osteoclast-like cells. Using overexpression studies, we demonstrated that, in contrast to WT-RANK, the absence of the PLAD in G280X-RANK and W434X-RANK prevented ligand-independent but not ligand-dependent oligomerisation. Cells expressing W434X-RANK, in which only two of the three TRAF6-binding motifs are present, continued to exhibit ligand-dependent NFκB signalling. Hence, the absence of the PLAD did not prevent ligand-induced trimerisation and subsequent NFκB activation of RANK, demonstrating that therapeutic targeting of the PLAD in the prevention of osteoporosis may not be as effective as proposed previously.

Free access

Pilar Argente-Arizón, Santiago Guerra-Cantera, Luis Miguel Garcia-Segura, Jesús Argente and Julie A Chowen

The search for new strategies and drugs to abate the current obesity epidemic has led to the intensification of research aimed at understanding the neuroendocrine control of appetite and energy expenditure. This intensified investigation of metabolic control has also included the study of how glial cells participate in this process. Glia, the most abundant cell type in the central nervous system, perform a wide spectrum of functions and are vital for the correct functioning of neurons and neuronal circuits. Current evidence indicates that hypothalamic glia, in particular astrocytes, tanycytes and microglia, are involved in both physiological and pathophysiological mechanisms of appetite and metabolic control, at least in part by regulating the signals reaching metabolic neuronal circuits. Glia transport nutrients, hormones and neurotransmitters; they secrete growth factors, hormones, cytokines and gliotransmitters and are a source of neuroprogenitor cells. These functions are regulated, as glia also respond to numerous hormones and nutrients, with the lack of specific hormonal signaling in hypothalamic astrocytes disrupting metabolic homeostasis. Here, we review some of the more recent advances in the role of glial cells in metabolic control, with a special emphasis on the differences between glial cell responses in males and females.

Free access

Daniel Raleigh, Xiaoxue Zhang, Benoît Hastoy and Anne Clark

Islet amyloid polypeptide (IAPP) forms cytotoxic oligomers and amyloid fibrils in islets in type 2 diabetes (T2DM). The causal factors for amyloid formation are largely unknown. Mechanisms of molecular folding and assembly of human IAPP (hIAPP) into β-sheets, oligomers and fibrils have been assessed by detailed biophysical studies of hIAPP and non-fibrillogenic, rodent IAPP (rIAPP); cytotoxicity is associated with the early phases (oligomers/multimers) of fibrillogenesis. Interaction with synthetic membranes promotes β-sheet assembly possibly via a transient α-helical molecular conformation. Cellular hIAPP cytotoxicity can be activated from intracellular or extracellular sites. In transgenic rodents overexpressing hIAPP, intracellular pro-apoptotic signals can be generated at different points in β-cell protein synthesis. Increased cellular trafficking of proIAPP, failure of the unfolded protein response (UPR) or excess trafficking of misfolded peptide via the degradation pathways can induce apoptosis; these data indicate that defects in intracellular handling of hIAPP can induce cytotoxicity. However, there is no evidence for IAPP overexpression in T2DM. Extracellular amyloidosis is directly related to the degree of β-cell apoptosis in islets in T2DM. IAPP fragments, fibrils and multimers interact with membranes causing disruption in vivo and in vitro. These findings support a role for extracellular IAPP in β-sheet conformation in cytotoxicity. Inhibitors of fibrillogenesis are useful tools to determine the aberrant mechanisms that result in hIAPP molecular refolding and islet amyloidosis. However, currently, their role as therapeutic agents remains uncertain.

Free access

Elena Ivanova and Gavin Kelsey

Genomic imprinting is an important and enigmatic form of gene regulation in mammals in which one copy of a gene is silenced in a manner determined by its parental history. Imprinted genes range from those with constitutive monoallelic silencing to those, typically more remote from imprinting control regions, that display developmentally regulated, tissue-specific or partial monoallelic expression. This diversity may make these genes, and the processes they control, more or less sensitive to factors that modify or disrupt epigenetic marks. Imprinted genes have important functions in development and physiology, including major endocrine/neuroendocrine axes. Owing to is central role in coordinating growth, metabolism and reproduction, as well as evidence from genetic and knockout studies, the hypothalamus may be a focus for imprinted gene action. Are there unifying principles that explain why a gene should be imprinted? Conflict between parental genomes over limiting maternal resources, but also co-adaptation between mothers and offspring, have been invoked to explain the evolution of imprinting. Recent reports suggest there may be many more genes imprinted in the hypothalamus than hitherto expected, and it will be important for these new candidates to be validated and to determine whether they conform to current notions of how imprinting is regulated. In fully evaluating the role of imprinted genes in the hypothalamus, much work needs to be done to identify the specific neuronal populations in which particular genes are expressed, establish whether there are pathways in common and whether imprinted genes are involved in long-term programming of hypothalamic functions.

Free access

CM Perks, PV Newcomb, MR Norman and JM Holly

Interaction of epithelial cells with the extracellular matrix is mediated through integrin receptors, which transmit signals regulating cell growth, differentiation and death. Occupation of these receptors, via Arg-Gly-Asp (RGD) recognition sequences, leads to activation of focal adhesion kinase (FAK). We treated human breast cancer cell lines with RGD-containing peptides, which can disrupt integrin attachment, and investigated alterations in FAK phosphorylation, cell detachment and death. Cells grown in vitro were treated with insulin-like growth factor-binding protein-1 (IGFBP-1) and a small, synthetic RGD-containing peptide (Gly-Arg-Gly-Asp-Thr-Pro) and its negative control peptide RGE (Arg-Gly-Glu-Ser) for either 30 min followed by immunoprecipitation of cell lysates with anti-phosphotyrosine and Western immunoblotting with anti-FAK or for 24 h followed by cell counting, immunocytochemistry and flow cytometry. Both IGFBP-1 (0-800 ng/ml) and the synthetic RGD-containing peptide (1-100 microg/ml) caused significant dephosphorylation of FAK. Furthermore, after 24 h both peptides caused detachment from the matrix and the induction of apoptosis. We conclude from these data that IGFBP-1 can interact with integrin receptors to induce FAK dephosphorylation and subsequently influence attachment and cell death.

Free access

Sasha R Howard

Delayed puberty represents the clinical presentation of a final common pathway for many different pathological mechanisms. In the majority of patients presenting with significantly delayed puberty, there is a clear family history of delayed or disturbed puberty, and pubertal timing is known to be a trait with strong heritability. Thus, genetic factors clearly play a key role in determining the timing of puberty, and mutations in certain genes are recognised as responsible for delayed or absent puberty in a minority of patients. Through the identification of causal genetic defects such as these we have been able to learn a great deal about the pathogenesis of disrupted puberty and its genetic regulation. Firstly, deficiency in key genes that govern the development of the gonadotropin-releasing hormone system during fetal development may result in a spectrum of conditions ranging from isolated delayed puberty to absent puberty with anosmia. Secondly, a balance of inhibitory and excitatory signals, acting upstream of GnRH secretion, are vital for the correct timing of puberty. These act to repress the hypothalamic–pituitary–gonadal axis during mid-childhood and allow it to reactivate at puberty, and alterations in this equilibrium can cause delayed (or precocious) puberty. Thirdly, disturbances of energy metabolism inputs to the kisspeptin–GnRH system may also lead to late onset of puberty associated with changes in body mass.

Free access

Richard C Lindsey, Charles H Rundle and Subburaman Mohan

Insulin-like growth factor 1(IGF1) and ephrin ligand (EFN)–receptor (EPH) signaling are both crucial for bone cell function and skeletal development and maintenance. IGF1 signaling is the major mediator of growth hormone-induced bone growth, but a host of different signals and factors regulate IGF1 signaling at the systemic and local levels. Disruption of the Igf1 gene results in reduced peak bone mass in both experimental animal models and humans. Additionally, EFN–EPH signaling is a complex system which, particularly through cell–cell interactions, contributes to the development and differentiation of many bone cell types. Recent evidence has demonstrated several ways in which the IGF1 and EFN–EPH signaling pathways interact with and depend upon each other to regulate bone cell function. While much remains to be elucidated, the interaction between these two signaling pathways opens a vast array of new opportunities for investigation into the mechanisms of and potential therapies for skeletal conditions such as osteoporosis and fracture repair.

Restricted access

Leandro Nieto, Mariana Fuertes, Josefina Rosmino, Sergio Senin and Eduardo Arzt

Retinoic acid (RA), an active metabolite of Vitamin A, and bone morphogenetic protein 4 (BMP-4) pathways control the transcription of pro-opiomelanocortin (Pomc), the precursor of ACTH. We describe a novel mechanism by which RA and BMP-4 act together in the context of pituitary corticotroph tumoral cells to regulate Pomc transcription. BMP-4 and RA exert a potentiated inhibition on Pomc gene expression. This potentiation of the inhibitory action on Pomc transcription was blocked by the inhibitory SMADs of the BMP-4 pathway (SMAD6 and SMAD7), a negative regulator of BMP-4 signaling (TOB1) and a blocker of RA pathway (COUP-TFI). AtT-20 corticotrophinoma cells express RA receptors (RARB, RXRA and RXRG) which associate with factors of BMP-4 (SMAD4 and SMAD1) signaling cascade in transcriptional complexes that block Pomc transcription. COUP-TFI and TOB1 disrupt these complexes. Deletions and mutations of the Pomc promoter and a specific DNA-binding assay show that the complexes bind to the RARE site in the Pomc promoter. The enhanced inhibitory interaction between RA and BMP-4 pathways occurs also in another relevant corticotroph gene promoter, the corticotropin-releasing hormone receptor 1 (Crh-r1). The understanding of the molecules that participate in the control of corticotroph gene expression contribute to define more precise targets for the treatment of corticotrophinomas.

Free access

A J Notini, R A Davey, J F McManus, K L Bate and J D Zajac

Androgens mediate their effects in target cells via the androgen receptor (AR), which acts predominantly as a ligand-dependent transcription factor. In addition, androgens induce rapid activation of second messenger signal transduction cascades, and this is thought to occur via non-genomic mechanisms. We have used the Cre/loxP system to generate an AR knockout (ARKO) mouse targeting exon 3, which encodes the second zinc finger of the DNA-binding domain. To generate universal ARKO mice, floxed AR mice were mated with CMV-Cre mice, which express Cre recombinase ubiquitously. Deletion of the floxed allele in our mice does not disrupt the reading frame, and has been designed so that the mutant AR can bind ligand but not target genes. ARKO males displayed a complete androgen insensitivity phenotype, with female external genitalia and a reduction in body weight compared with wild-type males (P < 0.001). Testes of ARKO males were smaller than control males (P < 0.0001) and were located intra-abdominally. We have demonstrated that genotypically XY mice lacking the second zinc finger of the AR have a female phenotype, and we conclude that the genomic actions of the AR (mediated by DNA binding) are indispensable for normal male sexual differentiation.