SPOC: A widely distributed domain associated with cancer, apoptosis and transcription

BACKGROUND: The Split ends (Spen) family are large proteins characterised by N-terminal RNA recognition motifs (RRMs) and a conserved SPOC (Spen paralog and ortholog C-terminal) domain. The aim of this study is to characterize the family at the sequence level. RESULTS: We describe undetected members of the Spen family in other lineages (Plasmodium and Plants) and localise SPOC in a new domain context, in a family that is common to all eukaryotes using profile-based sequence searches and structural prediction methods. CONCLUSIONS: The widely distributed DIO (Death inducer-obliterator) family is related to cancer and apoptosis and offers new clues about SPOC domain functionality

The ETS Family Member TEL Binds to Nuclear Receptors RAR and RXR and Represses Gene Activation

Retinoic acid receptor (RAR) signaling is important for regulating transcriptional activity of genes involved in growth, differentiation, metabolism and reproduction. Defects in RAR signaling have been implicated in cancer. TEL, a member of the ETS family of transcription factors, is a DNA-binding transcriptional repressor. Here, we identify TEL as a transcriptional repressor of RAR signaling by its direct binding to both RAR and its dimerisation partner, the retinoid x receptor (RXR) in a ligand-independent fashion. TEL is found in two isoforms, created by the use of an alternative startcodon at amino acid 43. Although both isoforms bind to RAR and RXR in vitro and in vivo, the shorter form of TEL represses RAR signaling much more efficiently. Binding studies revealed that TEL binds closely to the DNA binding domain of RAR and that both Helix Loop Helix (HLH) and DNA binding domains of TEL are mandatory for interaction. We have shown that repression by TEL does not involve recruitment of histone deacetylases and suggest that polycomb group proteins participate in the process

Mechanisms of chromosomal instability and carcinogenesis

Most carcinomas present some form of genetic instability, either as a shortening or lengthening of PCR markers termed microsatellite instability or as a change in the relative intensity of paternal and maternal alleles termed chromosomal instability. Although chromosomal instability is found in the vast majority of carcinomas, its exact contribution to tumor formation has long been a matter of debate. The mutagenic effects associated with microsatellite instability might active known oncogenes, and therefore are an accepted cause of cellular transformation, but the mere numerical changes associated with chromosomal instability only seem to compromise cellular fitness. Whereas the mitotic origins of aneuploidy are now accepted, the role of spindle microtubules in chromosome breakage and translocations remains disputed. Nonetheless, a comparison of several proposed mechanisms of structural instability reveals a striking convergence towards a key role for merotelic kinetochore attachments, which is further corroborated by the pattern of copy number alterations in clinical tumors. The recent discovery of gene dosage effects and cancer stem cells hint at the deregulation of intertwined regulatory networks and a cellular response to reduced fitness as a possible carcinogenic mechanism related to chromosomal instability. These emerging paradigms of cancer however need to be validated by relevant experimental models.Peer reviewe

How to make the end of a gene, the simple way

Transcription termination of nearly all protein-coding genes in mammals requires 3’ end processing by a multiprotein complex that will cleave and polyadenylate the messenger RNA precursor. Because a variety of enzyme complexes intervene, 3’ end processing was thought to be fundamentally complex and subject to a multitude of regulatory effects. The possibility to select just one out of several polyadenylation sites, in particular, has caused much questioning and speculation. What appear to be separate mechanisms however can be combined into a defined set of rules, allowing for a relatively simple interpretation of 3’ end processing. Ultimately, readiness of the terminal exon splice site determines when a transcript reaches the maturity to select a nearby polyadenylation signal. Transcriptional pausing then acts in concert, extending the timeframe during which the transcription complex is close to polyadenylation sites. Since RNA polymerase pausing is governed by the same type of sequences in bacteria and metazoans, mammalian transcription termination resembles its prokaryote counterpart more than generally thought.Peer reviewe

Are aneuploidy and chromosome breakage caused by a CINgle mechanism?

Genetic instability is a hallmark of cancer. Most tumors show complex patterns of translocations, amplifications and deletions, which have occupied scientists for decades. A specific problem arises in carcinomas with a genetic defect termed chromosomal instability; these solid tumors undergo gains and losses of entire chromosomes, as well as segmental defects caused by chromosome breaks. To date, the apparent inconsistency between intact and broken chromosomes has precluded identification of an underlying mechanism. The recent identification of centromeric breaks alongside aneuploidy in cells with spindle defects indicates that a single mechanism could account for all genetic alterations characteristic of chromosomal instability. Since a poorly controlled spindle can cause merotelic attachments, kinetochore distortion, and subsequent chromosome breakage, spindle defects can generate the sticky ends necessary to start a breakage-fusion-bridge cycle. The characteristic breakpoint of spindle-generated damage, adjacent to the centromere, also explains the losses and gains of whole chromosome arms, which are especially prominent in low-grade tumors. The recent data indicate that spindle defects are an early event in tumor formation, and an important initiator of carcinogenesis.This work is financed by grants PS 09/00572 (Fondo de Investigación en Salud) and S-BIO-0189-2006 (Comunidad Autonoma de Madrid). The Department of Immunology and Oncology was founded and is supported by the Spanish National Research Council (CSIC) and by Pfizer.Peer reviewe

Epigenetic countermarks in mitotic chromosome condensation

Mitosis in metazoans is characterized by abundant phosphorylation of histone H3 and involves the recruitment of condensin complexes to chromatin. The relationship between the 2 phenomena and their respective contributions to chromosome condensation in vivo remain poorly understood. Recent studies have shown that H3T3 phosphorylation decreases binding of histone readers to methylated H3K4 in vitro and is essential to displace the corresponding proteins from mitotic chromatin in vivo. Together with previous observations, these data provide further evidence for a role of mitotic histone H3 phosphorylation in blocking transcriptional programs or preserving the ‘memory’ PTMs. Mitotic protein exclusion can also have a role in depopulating the chromatin template for subsequent condensin loading. H3 phosphorylation thus serves as an integral step in the condensation of chromosome arms.Research in K.v.W. laboratory is supported in part by grant SAF2013–42289-R from the Spanish Ministry of Economics and Competitiveness. C.M.G. is a CSIC predoctoral fellow financed by FPI grant BES-2014–068580. Research in the T.G.K. laboratory is supported by grants from the NIH, GM101664, GM106416, and GM100907.Peer reviewe

Dido3-dependent HDAC6 targeting controls cilium size

En la superficie de muchos tipos de células los mamíferos podemos encontrar cilios, los cuales participan en multitud de procesos fisiológicos que van desde el crecimiento celular y el desarrollo hasta la percepción del ambiente en el que se encuentran. Su importancia se pone de manifiesto si tenemos en cuenta algunas enfermedades causadas por defectos en estos orgánulos: el hidrocéfalo, la anosmia (pérdida del olfato) o la retinitis pigmentaria. El grupo de investigación del Centro Nacional de Biotecnología del CSIC dirigido por Karel H.M. van Wely estudia las proteínas involucradas en la formación y en el desensamblaje de los cilios. Si bien se conoce desde hace tiempo su regulación asociada a la mitosis de la céllulas, en este laboratorio del CNB se ha encontrado un mecanismo que regula el tamaño de los cilios cuando la célula no se está dividiendo. Los experimentos que ha realizado en este laboratorio Ainhoa Sánchez de Diego, publicados en la revista Nature Communications, muestran que cuando las céllulas no están creciendo la distribución subcelular de la deacetilasa HDAC6 es esencial para controlar el tamaño de los cilios.Primary cilia are involved in a variety of physiological processes such as sensing of the environment, cell growth, and development. Numerous developmental disorders and pathological arise from defects in these organelles. Multiple proteins that promote formation and disassembly of the primary cilium have been identified, but little is known about the mechanisms that control steady state cilium size. Here, we show that Dido3-dependent targeting of HDAC6 is a key determinant of cilium size in growth-arrested cells. The amount of either protein negatively correlates with cilium size, Dido3 availability at the centrosome governs ciliary HDAC6 levels, and redistribution of the two proteins controls tubulin acetylation. In turn, basal body localization of Dido3 and HDAC6 depend on the actin network, previously shown to limit cilium size independent of the cell cycle. These results show that not only kinase-dependent activation of a deacetylase but also its subcellular distribution controls substrate selection.This work is financed by grants PS09/00572 (Fondo de Investigación en Salud) and BFU2009-08395E, (Ministerio de Economía y Competitividad) to KvW, and grants 2010/BMD2502 (Comunidad Autónoma de Madrid) and SAF2010-21205 (Ministerio de Economía y Competitividad) to CMA.Peer reviewe

Preprotein Translocation by a Hybrid Translocase Composed of Escherichia coli and Bacillus subtilis Subunits

Bacterial protein translocation is mediated by translocase, a multisubunit membrane protein complex that consists of a peripheral ATPase SecA and a preprotein-conducting channel with SecY, SecE, and SecG as subunits. Like Escherichia coli SecG, the Bacillus subtilis homologue, YvaL, dramatically stimulated the ATP-dependent translocation of precursor PhoB (prePhoB) by the B. subtilis SecA-SecYE complex. To systematically determine the functional exchangeability of translocase subunits, all of the relevant combinations of the E. coli and B. subtilis secY, secE, and secG genes were expressed in E. coli. Hybrid SecYEG complexes were overexpressed at high levels. Since SecY could not be overproduced without SecE, these data indicate a stable interaction between the heterologous SecY and SecE subunits. E. coli SecA, but not B. subtilis SecA, supported efficient ATP-dependent translocation of the E. coli precursor OmpA (proOmpA) into inner membrane vesicles containing the hybrid SecYEG complexes, if E. coli SecY and either E. coli SecE or E. coli SecG were present. Translocation of B. subtilis prePhoB, on the other hand, showed a strict dependence on the translocase subunit composition and occurred efficiently only with the homologous translocase. In contrast to E. coli SecA, B. subtilis SecA binds the SecYEG complexes only with low affinity. These results suggest that each translocase subunit contributes in an exclusive manner to the specificity and functionality of the complex