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Résumé Chez une enfant anormale, on observe un excès de matériel chromosomique sur la paire 1:1q+, et une translocation t(1q+;10q-) est dépistée dans la famille.L'analyse du caryotype après «dénaturation thermique ménagée» a permis d'individualiser le chromosome C anormal (10q-), de définir l'emplacement exact des points de cassure et de lier essentiellement l'état pathologique du patient à une trisomie partielle du bras long du chromosome 10.Cette trisomie se traduit principalement par une arriération mentale, une hypotrophie, des anomalies oculaires, une fente palatine, une mal-implantation des oreilles, un micrognathisme, des anomalies du squelette et une cardiopathie.
Chargée de Recherche I.N.S.E.R.M. Chef de Service à l'Institut Pasteur de Lyon.
Chargés de Recherche C.N.R.S. 相似文献
Partial trisomy 10 due to hereditary translocation t(1;10) (q44;q22)
Summary A chromosome 1q+was observed in an abnormal girl. A balanced t(1q+;10q-) was found in the family.Application of a controlled thermic denaturation technique allowed recognition of the abnormal C as a 10q-and localization of the break points (1q44 and 10q22).The partial trisomy 10q of the proband had induced mental retardation, severe retardation of growth, ocular anomalies, agenesis of the palate, low implantation of the ears, micrognathia bone anomalies and cardiac malformation.
Zusammenfassung Bei einem Mädchen mit Mißbildungen wurde ein Chromosom 1q+beobachtet. Eine balancierte t(1q+, 10q-) fand sich in der Familie.Die Identifikation des abnormen C als 10q- wurde durch Anwendung kontrollierter Wärmedenaturierung erreicht; auf diesem Wege wurden auch die Bruchpunkte identifiziert.Die partielle Trisomie 10q hatte bei dem Probanden einen geistigen Entwicklungsrückstand, eine schwere Wachstumsstörung, Augenanomalien, Fehlen des Gaumens, tief ansetzende Ohren, eine Mikrognathie, Knochenanomalien und eine Herzmißbildung zur Folge.
Chargée de Recherche I.N.S.E.R.M. Chef de Service à l'Institut Pasteur de Lyon.
Chargés de Recherche C.N.R.S. 相似文献
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Ku-Chi Tsao Cheng-Fen Tu Shyh-Jye Lee Ruey-Bing Yang 《The Journal of biological chemistry》2013,288(7):5017-5026
scube1 (signal
peptide-CUB (complement protein C1r/C1s, Uegf, and
Bmp1)-EGF domain-containing protein
1), the founding member of a novel secreted and cell
surface SCUBE protein family, is expressed predominantly in various developing
tissues in mice. However, its function in primitive hematopoiesis remains
unknown. In this study, we identified and characterized zebrafish
scube1 and analyzed its function by injecting antisense
morpholino-oligonucleotide into embryos. Whole-mount in situ
hybridization revealed that zebrafish scube1 mRNA is maternally
expressed and widely distributed during early embryonic development. Knockdown
of scube1 by morpholino-oligonucleotide down-regulated the
expression of marker genes associated with early primitive hematopoietic
precursors (scl) and erythroid (gata1 and
hbbe1), as well as early (pu.1) and late
(mpo and l-plastin) myelomonocytic
lineages. However, the expression of an early endothelial marker
fli1a and vascular morphogenesis appeared normal in
scube1 morphants. Overexpression of bone morphogenetic
protein (bmp) rescued the expression of scl in
the posterior lateral mesoderm during early primitive hematopoiesis in
scube1 morphants. Biochemical and molecular analysis
revealed that Scube1 could be a BMP co-receptor to augment BMP signaling. Our
results suggest that scube1 is critical for and functions at
the top of the regulatory hierarchy of primitive hematopoiesis by modulating BMP
activity during zebrafish embryogenesis. 相似文献
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Farah H. Bardai Valerie Price Marcus Zaayman Lulu Wang Santosh R. D'Mello 《The Journal of biological chemistry》2012,287(42):35444-35453
Both neuroprotective and neurotoxic roles have previously been described for histone deacetylase-1 (HDAC1). Here we report that HDAC1 expression is elevated in vulnerable brain regions of two mouse models of neurodegeneration, the R6/2 model of Huntington disease and the Ca2+/calmodulin-dependent protein kinase (CaMK)/p25 double-transgenic model of tauopathic degeneration, suggesting a role in promoting neuronal death. Indeed, elevating HDAC1 expression by ectopic expression promotes the death of otherwise healthy cerebellar granule neurons and cortical neurons in culture. The neurotoxic effect of HDAC1 requires interaction and cooperation with HDAC3, which has previously been shown to selectively induce the death of neurons. HDAC1-HDAC3 interaction is greatly elevated under conditions of neurodegeneration both in vitro and in vivo. Furthermore, the knockdown of HDAC3 suppresses HDAC1-induced neurotoxicity, and the knockdown of HDAC1 suppresses HDAC3 neurotoxicity. As described previously for HDAC3, the neurotoxic effect of HDAC1 is inhibited by treatment with IGF-1, the expression of Akt, or the inhibition of glycogen synthase kinase 3β (GSK3β). In addition to HDAC3, HDAC1 has been shown to interact with histone deacetylase-related protein (HDRP), a truncated form of HDAC9, whose expression is down-regulated during neuronal death. In contrast to HDAC3, the interaction between HDRP and HDAC1 protects neurons from death, an effect involving acquisition of the deacetylase activity of HDAC1 by HDRP. We find that elevated HDRP inhibits HDAC1-HDAC3 interaction and prevents the neurotoxic effect of either of these two proteins. Together, our results suggest that HDAC1 is a molecular switch between neuronal survival and death. Its interaction with HDRP promotes neuronal survival, whereas interaction with HDAC3 results in neuronal death. 相似文献
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Ivano Bertini Marco Fragai Claudio Luchinat Maxime Melikian Efstratios Mylonas Niko Sarti Dmitri I. Svergun 《The Journal of biological chemistry》2009,284(19):12821-12828
The presence of extensive reciprocal conformational freedom between the
catalytic and the hemopexin-like domains of full-length matrix
metalloproteinase-1 (MMP-1) is demonstrated by NMR and small angle x-ray
scattering experiments. This finding is discussed in relation to the
essentiality of the hemopexin-like domain for the collagenolytic activity of
MMP-1. The conformational freedom experienced by the present system, having
the shortest linker between the two domains, when compared with similar
findings on MMP-12 and MMP-9 having longer and the longest linker within the
family, respectively, suggests this type of conformational freedom to be a
general property of all MMPs.Matrix metalloproteinases
(MMP)2 are
extracellular hydrolytic enzymes involved in a variety of processes including
connective tissue cleavage and remodeling
(1–3).
All 23 members of the family are able to cleave simple peptides derived from
connective tissue components such as collagen, gelatin, elastin, etc. A subset
of MMPs is able to hydrolyze more resistant polymeric substrates, such as
cross-linked elastin, and partially degraded collagen forms, such as gelatin
and type IV collagens (4).
Intact triple helical type I–III collagen is only attacked by
collagenases MMP-1, MMP-8, and MMP-13 and by MMP-2 and MMP-14
(5–12).
Although the detailed mechanism of cleavage of single chain peptides by MMP
has been largely elucidated
(13–19),
little is known about the process of hydrolysis of triple helical collagen. In
fact, triple helical collagen cannot be accommodated in the substrate-binding
groove of the catalytic site of MMPs
(9).All MMPs (but MMP-7) in their active form are constituted by a catalytic
domain (CAT) and a hemopexin-like domain (HPX)
(20–22).
The CAT domain contains two zinc ions and one to three calcium ions. One zinc
ion is at the catalytic site and is responsible for the activity, whereas the
other metal ions have structural roles. The isolated CAT domains retain full
catalytic activity toward simple peptides and single chain polymeric
substrates such as elastin, whereas hydrolysis of triple helical collagen also
requires the presence of the HPX domain
(9,
23–25).
It has been shown that the isolated CAT domain regains a small fraction of the
activity of the full-length (FL) protein when high amounts of either
inactivated full-length proteins or isolated HPX domains are added to the
assay solution (9). Finally, it
has been shown that the presence of the HPX domain alone alters the CD
spectrum of triple helical collagen in a way that suggests its partial
unwinding (26,
27). It is tempting to
speculate that full-length collagenases attack collagen by first locally
unwinding the triple helical structure with the help of the HPX domain and
then cleaving the resulting, exposed, single filaments
(9,
28).Until 2007, three-dimensional structures of full-length MMPs had been
reported only for collagenase MMP-1
(29–31)
and gelatinase MMP-2 (32). The
structures of the two proteins are very similar and show a compact arrangement
of the two domains, which are connected by a short linker (14 and 20 amino
acids, respectively). It is difficult to envisage that rigid and compact
molecules of this type can interact with triple helical collagen in a way that
can lead to first unwinding and then cleavage of individual filaments. It has
been recently suggested that such concerted action could occur much more
easily if the two domains could enjoy at least a partial conformational
independence (9). Slight
differences in the reciprocal orientation of the CAT and HPX domains of MMP-1
in the presence (29) and
absence (30,
31) of the prodomain were
indeed taken as a hint that the two domains could experience relative mobility
(29).Two recent solution studies have shown that conformational independence is
indeed occurring in gelatinase MMP-9
(33) and elastase MMP-12
(34), whereas the x-ray
structure of the latter (34)
is only slightly less compact than those of MMP-1
(29–31)
and MMP-2 (32). Among MMPs,
MMP-9 features an exceptionally long linker (68 amino acid)
(33,
35), which in fact constitutes
a small domain by itself (the O-glycosylated domain)
(33), and therefore, this
inspiring observation can hardly be taken as evidence that conformational
freedom is a general characteristic of the two-domain MMPs. MMP-12 features a
much more normal 16-amino acid linker, thereby making more probable a general
functional role for this conformational freedom
(34). However, both MMP-9 and
MMP-12 retain their full catalytic activity against their substrates even when
deprived of the HPX domain (9).
Therefore, the question remains of whether conformational freedom is also a
required characteristic for those MMPs that are only active as full-length
proteins, i.e. collagenases. Interestingly, the three collagenases
(MMP-1, MMP-8, and MMP-13) have the shortest linker (14 amino acids) among all
MMPs. Demonstrating or negating the presence of conformational freedom in one
of these collagenases would therefore constitute a significant step forward to
formulate mechanistic hypotheses on their collagenolytic activity.Our recent studies on MMP-12 in solution
(34) have shown that a
combination of NMR relaxation studies and small angle x-ray scattering (SAXS)
is enough to show the presence and the extent of the relative conformational
freedom of the two domains of MMPs. Here we apply the same strategy to
full-length MMP-1 and show that sizable conformational freedom is indeed
experienced even by this prototypical collagenase, although somewhat less
pronounced than that observed for MMP-12. 相似文献
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Bruno D. Fonseca Chadi Zakaria Jian-Jun Jia Tyson E. Graber Yuri Svitkin Soroush Tahmasebi Danielle Healy Huy-Dung Hoang Jacob M. Jensen Ilo T. Diao Alexandre Lussier Christopher Dajadian Niranjan Padmanabhan Walter Wang Edna Matta-Camacho Jaclyn Hearnden Ewan M. Smith Yoshinori Tsukumo Akiko Yanagiya Masahiro Morita Emmanuel Petroulakis Jose L. González Greco Hernández Tommy Alain Christian K. Damgaard 《The Journal of biological chemistry》2015,290(26):15996-16020
The mammalian target of rapamycin complex 1 (mTORC1) is a critical regulator of protein synthesis. The best studied targets of mTORC1 in translation are the eukaryotic initiation factor-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1). In this study, we identify the La-related protein 1 (LARP1) as a key novel target of mTORC1 with a fundamental role in terminal oligopyrimidine (TOP) mRNA translation. Recent genome-wide studies indicate that TOP and TOP-like mRNAs compose a large portion of the mTORC1 translatome, but the mechanism by which mTORC1 controls TOP mRNA translation is incompletely understood. Here, we report that LARP1 functions as a key repressor of TOP mRNA translation downstream of mTORC1. Our data show the following: (i) LARP1 associates with mTORC1 via RAPTOR; (ii) LARP1 interacts with TOP mRNAs in an mTORC1-dependent manner; (iii) LARP1 binds the 5′TOP motif to repress TOP mRNA translation; and (iv) LARP1 competes with the eukaryotic initiation factor (eIF) 4G for TOP mRNA binding. Importantly, from a drug resistance standpoint, our data also show that reducing LARP1 protein levels by RNA interference attenuates the inhibitory effect of rapamycin, Torin1, and amino acid deprivation on TOP mRNA translation. Collectively, our findings demonstrate that LARP1 functions as an important repressor of TOP mRNA translation downstream of mTORC1. 相似文献
11.
Veronica Nin Claudia C. S. Chini Carlos Escande Verena Capellini Eduardo N. Chini 《The Journal of biological chemistry》2014,289(9):5518-5527
Liver gluconeogenesis is essential to provide energy to glycolytic tissues during fasting periods. However, aberrant up-regulation of this metabolic pathway contributes to the progression of glucose intolerance in individuals with diabetes. Phosphoenolpyruvate carboxykinase (PEPCK) expression plays a critical role in the modulation of gluconeogenesis. Several pathways contribute to the regulation of PEPCK, including the nuclear receptor Rev-erbα and the histone deacetylase SIRT1. Deleted in breast cancer 1 (DBC1) is a nuclear protein that binds to and regulates both Rev-erbα and SIRT1 and, therefore, is a candidate to participate in the regulation of PEPCK. In this work, we provide evidence that DBC1 regulates glucose metabolism and the expression of PEPCK. We show that DBC1 levels decrease early in the fasting state. Also, DBC1 KO mice display higher gluconeogenesis in a normal and a high-fat diet. DBC1 absence leads to an increase in PEPCK mRNA and protein expression. Conversely, overexpression of DBC1 results in a decrease in PEPCK mRNA and protein levels. DBC1 regulates the levels of Rev-erbα, and manipulation of Rev-erbα activity or levels prevents the effect of DBC1 on PEPCK. In addition, Rev-erbα levels decrease in the first hours of fasting. Finally, knockdown of the deacetylase SIRT1 eliminates the effect of DBC1 knockdown on Rev-erbα levels and PEPCK expression, suggesting that the mechanism of PEPCK regulation is, at least in part, dependent on the activity of this enzyme. Our results point to DBC1 as a novel regulator of gluconeogenesis. 相似文献
12.
Lifu Wang John C. Lawrence Jr. Thomas W. Sturgill Thurl E. Harris 《The Journal of biological chemistry》2009,284(22):14693-14697
mTORC1 contains multiple proteins and plays a central role in cell growth
and metabolism. Raptor (regulatory-associated protein of mammalian target of
rapamycin (mTOR)), a constitutively binding protein of mTORC1, is essential
for mTORC1 activity and critical for the regulation of mTORC1 activity in
response to insulin signaling and nutrient and energy sufficiency. Herein we
demonstrate that mTOR phosphorylates raptor in vitro and in
vivo. The phosphorylated residues were identified by using phosphopeptide
mapping and mutagenesis. The phosphorylation of raptor is stimulated by
insulin and inhibited by rapamycin. Importantly, the site-directed mutation of
raptor at one phosphorylation site, Ser863, reduced mTORC1 activity
both in vitro and in vivo. Moreover, the Ser863
mutant prevented small GTP-binding protein Rheb from enhancing the
phosphorylation of S6 kinase (S6K) in cells. Therefore, our findings indicate
that mTOR-mediated raptor phosphorylation plays an important role on
activation of mTORC1.Mammalian target of rapamycin
(mTOR)2 has been shown
to function as a critical controller in cellular growth, survival, metabolism,
and development (1). mTOR, a
highly conserved Ser-Thr phosphatidylinositol 3-kinase-related protein kinase,
structurally forms two distinct complexes, mTOR complex 1 (mTORC1) and mTOR
complex 2 (mTORC2), each of which catalyzes the phosphorylation of different
substrates (1). The best
characterized substrates for mTORC1 are eIF4E-binding protein (4E-BP, also
known as PHAS) and p70 S6 kinase (S6K)
(1), whereas mTORC2
phosphorylates the hydrophobic and turn motifs of protein kinase B
(Akt/protein kinase B) (2) and
protein kinase C (3,
4). mTORC1 constitutively
consists of mTOR, raptor, and mLst8/GβL
(1), whereas the proline-rich
Akt substrate of 40 kDa (PRAS40) is a regulatory component of mTORC1 that
disassociates after growth factor stimulation
(5,
6). Raptor is essential for
mTORC1 activity by providing a substrate binding function
(7) but also plays a regulatory
role on mTORC1 with stimuli of growth factors and nutrients
(8). In response to insulin,
raptor binding to substrates is elevated through the release of the
competitive inhibitor PRAS40 from mTORC1
(9,
10) because PRAS40 and the
substrates of mTORC1 (4E-BP and S6K) appear to bind raptor through a consensus
sequence, the TOR signaling (TOS) motif
(10–14).
In response to amino acid sufficiency, raptor directly interacts with a
heterodimer of Rag GTPases and promotes mTORC1 localization to the
Rheb-containing vesicular compartment
(15).mTORC1 integrates signaling pathways from growth factors, nutrients,
energy, and stress, all of which generally converge on the tuberous sclerosis
complex (TSC1-TSC2) through the phosphorylation of TSC2
(1). Growth factors inhibit the
GTPase-activating protein activity of TSC2 toward the small GTPase Rheb via
the PI3K/Akt pathway (16,
17), whereas energy depletion
activates TSC2 GTPase-activating protein activity by stimulating AMP-activated
protein kinase (AMPK) (18).
Rheb binds directly to mTOR, albeit with very low affinity
(19), and upon charging with
GTP, Rheb functions as an mTORC1 activator
(6). mTORC1 complexes isolated
from growth factor-stimulated cells show increased kinase activity yet do not
contain detectable levels of associated Rheb. Therefore, how Rheb-GTP binding
to mTOR leads to an increase in mTORC1 activity toward substrates, and what
the role of raptor is in this activation is currently unknown. More recently,
the AMPK and p90 ribosomal S6 kinase (RSK) have been reported to directly
phosphorylate raptor and regulate mTORC1 activity. The phosphorylation of
raptor directly by AMPK reduced mTORC1 activity, suggesting an alternative
regulation mechanism independent of TSC2 in response to energy supply
(20). RSK-mediated raptor
phosphorylation enhances mTORC1 activity and provides a mechanism whereby
stress may activate mTORC1 independent of the PI3K/Akt pathway
(21). Therefore, the
phosphorylation status of raptor can be critical for the regulation of mTORC1
activity.In this study, we investigated phosphorylation sites in raptor catalyzed by
mTOR. Using two-dimensional phosphopeptide mapping, we found that
Ser863 and Ser859 in raptor were phosphorylated by mTOR
both in vivo and in vitro. mTORC1 activity in vitro
and in vivo is associated with the phosphorylation of
Ser863 in raptor. 相似文献
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15.
Guanylate-binding Protein 1 (Gbp1) Contributes to Cell-autonomous Immunity against Toxoplasma gondii
Elizabeth M. Selleck Sarah J. Fentress Wandy L. Beatty Daniel Degrandi Klaus Pfeffer Herbert W. Virgin IV John D. MacMicking L. David Sibley 《PLoS pathogens》2013,9(4)
IFN-γ activates cells to restrict intracellular pathogens by upregulating cellular effectors including the p65 family of guanylate-binding proteins (GBPs). Here we test the role of Gbp1 in the IFN-γ-dependent control of T. gondii in the mouse model. Virulent strains of T. gondii avoided recruitment of Gbp1 to the parasitophorous vacuole in a strain-dependent manner that was mediated by the parasite virulence factors ROP18, an active serine/threonine kinase, and the pseudokinase ROP5. Increased recruitment of Gbp1 to Δrop18 or Δrop5 parasites was associated with clearance in IFN-γ-activated macrophages in vitro, a process dependent on the autophagy protein Atg5. The increased susceptibility of Δrop18 mutants in IFN-γ-activated macrophages was reverted in Gbp1−/− cells, and decreased virulence of this mutant was compensated in Gbp1−/− mice, which were also more susceptible to challenge with type II strain parasites of intermediate virulence. These findings demonstrate that Gbp1 plays an important role in the IFN-γ-dependent, cell-autonomous control of toxoplasmosis and predict a broader role for this protein in host defense. 相似文献
16.
Evidence for 1-(Malonylamino)cyclopropane-1-Carboxylic Acid Being
the Major Conjugate of Aminocyclopropane-1-Carboxylic Acid in Tomato
Fruit 总被引:1,自引:0,他引:1
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Tomato (Lycopersicon esculentum Miller) fruit discs fed with [2,3-14C]1-aminocyclopropane-1-carboxylic acid (ACC) formed 1-malonyl-ACC (MACC) as the major conjugate of ACC in fruit throughout all ripening stages, from immature-green through the red-ripe stage. Another conjugate of ACC, γ-glutamyl-ACC (GACC), was formed only in mature-green fruit in an amount about 10% of that of MACC; conjugation of ACC into GACC was not detected in fruits at other ripening stages. No GACC formation was observed from etiolated mung bean (Vigna radiata [L.] Wilczek) hypocotyls, etiolated common vetch (Vicia sativum L.) epicotyls, or pea (Pisum sativum L.) root tips, etiolated epicotyls, and green stem tissue, where active conversion of ACC into MACC was observed. GACC was, however, formed in vitro in extracts from fruit of all ripening stages. GACC formation in an extract from red fruit at pH 7.15 was only about 3% of that at pH 8.0, the pH at which most assays were run. Our present in vivo data support the previous contention that MACC is the major conjugate of ACC in plant tissues, whereas GACC is a minor, if any, conjugate of ACC. Thus, our data do not support the proposal that GACC formation could be more important than MACC formation in tomato fruit. 相似文献
17.
《Origins of life and evolution of the biosphere》1992,22(1-4):191-242
18.
A Role for the Proton-coupled Folate Transporter (PCFT-SLC46A1) in Folate
Receptor-mediated
Endocytosis 总被引:1,自引:0,他引:1
Rongbao Zhao Sang Hee Min Yanhua Wang Estela Campanella Philip S. Low I. David Goldman 《The Journal of biological chemistry》2009,284(7):4267-4274
Recently, this laboratory identified a proton-coupled folate transporter
(PCFT), with optimal activity at low pH. PCFT is critical to intestinal folate
absorption and transport into the central nervous system because there are
loss-of-function mutations in this gene in the autosomal recessive disorder,
hereditary folate malabsorption. The current study addresses the role PCFT
might play in another transport pathway, folate receptor (FR)-mediated
endocytosis. FRα cDNA was transfected into novel PCFT+ and
PCFT– HeLa sublines. FRα was shown to bind and trap
folates in vesicles but with minimal export into the cytosol in
PCFT– cells. Cotransfection of FRα and PCFT resulted in
enhanced folate transport into cytosol as compared with transfection of
FRα alone. Probenecid did not inhibit folate binding to FR, but
inhibited PCFT-mediated transport at endosomal pH, and blocked
FRα-mediated transport into the cytosol. FRα and PCFT co-localized
to the endosomal compartment. These observations (i) indicate that PCFT plays
a role in FRα-mediated endocytosis by serving as a route of export of
folates from acidified endosomes and (ii) provide a functional role for PCFT
in tissues in which it is expressed, such as the choroid plexus, where the
extracellular milieu is at neutral pH.Loss of function mutations of the proton-coupled folate transporter
(PCFT),2 which
functions optimally at low pH, are the molecular basis for the autosomal
recessive disorder, hereditary folate malabsorption (HFM)
(1–4).
Infants present with this disorder several months after birth with marked
folate deficiency anemia, hypogammaglobulinemia with immune deficiency and
infections, neurological deficits, and often seizures
(5). PCFT is highly expressed
at the apical brush-border membrane of the duodenum and proximal jejunum
(6–9)
where the pH at the microclimate of the surface of this epithelium is low (pH
5.8–6.0), and folates are absorbed
(1,
7,
10,
11). Hence, the failure to
absorb folates in the absence of this transporter in HFM is expected. However,
PCFT expression, and its associated folate transport activity at low pH, is
observed in many tissues where the transport interface is presumed to be at pH
7.4 (12). Of particular
interest is the mechanism by which PCFT mediates transport of folates into the
central nervous system (CNS) where this transporter is expressed in brain and
choroid plexus (1,
7,
13). Transport into the CNS is
impaired in patients with HFM who have very low cerebrospinal fluid (CSF)
folate levels and marked reversal of the blood:CSF folate gradient which is
normally 2–3:1 (5).Folates are also transported into cells by a receptor-mediated process.
Folate receptor-α (FRα) is anchored to cell membranes via a
glycosylphosphatidylinositol domain. Uptake begins with folate binding to
receptor at the cell surface followed by invagination of the membrane and the
formation of endosomes that traffic along microtubules to a perinuclear
compartment before returning to the plasma membrane
(14–16).
During transit in the cytoplasm, endosomes acidify to a pH of
∼6.0–6.5 (17),
folate is released from the receptor and exported from the intact endosome
into the cytoplasm. This putative exporter was shown to require a
trans-endosomal pH gradient
(18–20).The current report addresses the hypothesis that PCFT is an endosomal
folate exporter and thereby plays a role in FRα-mediated endocytosis
(1,
2,
21,
22), that the ubiquitous
expression of PCFT in mammalian tissues may be related to this function, and
that loss of this function may be a basis for the low CSF folate levels in
HFM. The experimental approach utilized a series of HeLa sublines, developed
in this laboratory, in which constitutive expression of FRα is
negligible. HeLa R5 cells lack reduced folate carrier (RFC) function due to a
genomic deletion of this gene
(23). A derivative of R5
cells, HeLa R1-11 cells lack, in addition, PCFT expression, while an R1-11
revertant re-expresses PCFT
(24). The impact of PCFT on
FRα-mediated endocytosis, achieved by transfection of the receptor into
these cell lines, was assessed under conditions in which there was negligible
PCFT-mediated transport directly across the plasma membrane into cells. 相似文献
19.
20.
Drosophila Heterochromatin Protein 1 (HP1)/Origin
Recognition Complex (ORC) Protein Is Associated with HP1 and ORC and
Functions in Heterochromatin-induced Silencing 总被引:5,自引:0,他引:5
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Mohammed Momin Shareef Chadwick King Mona Damaj RamaKrishna Badagu Da Wei Huang Rebecca Kellum 《Molecular biology of the cell》2001,12(6):1671-1685
Heterochromatin protein 1 (HP1) is a conserved component of the highly compact chromatin of higher eukaryotic centromeres and telomeres. Cytogenetic experiments in Drosophila have shown that HP1 localization into this chromatin is perturbed in mutants for the origin recognition complex (ORC) 2 subunit. ORC has a multisubunit DNA-binding activity that binds origins of DNA replication where it is required for origin firing. The DNA-binding activity of ORC is also used in the recruitment of the Sir1 protein to silence nucleation sites flanking silent copies of the mating-type genes in Saccharomyces cerevisiae. A fraction of HP1 in the maternally loaded cytoplasm of the early Drosophila embryo is associated with a multiprotein complex containing Drosophila melanogaster ORC subunits. This complex appears to be poised to function in heterochromatin assembly later in embryonic development. Here we report the identification of a novel component of this complex, the HP1/ORC-associated protein. This protein contains similarity to DNA sequence-specific HMG proteins and is shown to bind specific satellite sequences and the telomere-associated sequence in vitro. The protein is shown to have heterochromatic localization in both diploid interphase and mitotic chromosomes and polytene chromosomes. Moreover, the gene encoding HP1/ORC-associated protein was found to display reciprocal dose-dependent variegation modifier phenotypes, similar to those for mutants in HP1 and the ORC 2 subunit. 相似文献