PubMed Health⌕ Search

Biomedical subjects

P Crespo

Publications and source records attributed to P Crespo.

At least 19 recordsLinked to original sources
PubMed2006

Fe impurities weaken the ferromagnetic behavior in Au nanoparticles.

In this Letter, we report on a crucial experiment showing that magnetic impurities reduce the ferromagnetic order temperature in thiol-capped Au glyconanoparticles (GNPs). The spontaneous magnetization of AuFe GNPs exhibits a fast decrease with temperature that contrasts with the almost constant value of the magnetization observed in Au NPs. Moreover, hysteresis disappears below 300 K. Both features indicate that Fe impurities reduce the high local anisotropy field responsible for the ferromagnetic behavior in Au GNPs. As a consequence, the amazing ferromagnetism in Au NPs should not be associated with the presence of magnetic impurities.

Journal Article↗
PubMed2006

Origin of orbital ferromagnetism and giant magnetic anisotropy at the nanoscale.

The origin of orbital magnetism recently observed in different nanostructured films and particles is discussed as a consequence of spin-orbit coupling. It is shown that contact potentials induced at the thin film surface by broken symmetries, as domain boundaries in self-assembled monolayers, lead to orbital states that in some cases are of large radius. The component of the angular momentum normal to the surface can reach very high values that decrease the total energy by decreasing spin-orbit interaction energy. Intraorbital ferromagnetic spin correlations induce orbital momenta alignment. The estimated values of the magnetic moments per atom are in good agreement with the experimental observations in thiol capped gold films and nanoparticles.

Journal Article↗
PubMed2006

Total hip arthroplasty infected by Brucella: a report of two cases.

Infection caused by Brucella following total joint arthroplasty is very rare. We present 2 cases of brucellar infection following total hip arthroplasty (THA). A 66-year-old woman who had prolonged contact with cattle presented with pain at the thigh and groin areas. The patient had undergone an uncemented THA for a hip fracture 3 years previously. Cultures of articular liquid were positive for Brucella abortus. The implant was loosened and was managed with a 2-stage re-implantation. A 71-year-old man presented with painless suppuration of the hip joint through the scar from previous surgeries. Radiography demonstrated a well-integrated THA. When postoperative cultures were found positive for Brucella melitensis, antibiotic treatment of rifampicin 900 mg, streptomycin 1 g, and doxycycline 200 mg daily were prescribed. At 5.5-year and 5-year follow-up, respectively, both patients were asymptomatic and free of infection with well-integrated implants. As the Brucella pathogen is highly susceptible to antibiotics, standard 2-stage revision arthroplasty for loosened implant or debridement and antibiotic treatment for well-fixed implant should suffice.

Aged↗
PubMed2005

Metallic magnetic nanoparticles.

In this paper, we reviewed some relevant aspects of the magnetic properties of metallic nanoparticles with small size (below 4 nm), covering the size effects in nanoparticles of magnetic materials, as well as the appearance of magnetism at the nanoscale in materials that are nonferromagnetic in bulk. These results are distributed along the text that has been organized around three important items: fundamental magnetic properties, different fabrication procedures, and characterization techniques. A general introduction and some experimental results recently obtained in Pd and Au nanoparticles have also been included. Finally, the more promising applications of magnetic nanoparticles in biomedicine are indicated. Special care was taken to complete the literature available on the subject.

Anisotropy↗
PubMed2004

Permanent magnetism, magnetic anisotropy, and hysteresis of thiol-capped gold nanoparticles.

We report on the experimental observation of magnetic hysteresis up to room temperature in thiol-capped Au nanoparticles with 1.4 nm size. The coercive field ranges from 860 Oe at 5 K to 250 Oe at 300 K. It is estimated that the Au atoms exhibit a magnetic moment of mu=0.036mu(B). However, Au nanoparticles with similar size but stabilized by means of a surfactant, i.e., weak interaction between protective molecules and Au surface atoms, are diamagnetic, as bulk Au samples are. The apparent ferromagnetism is consequently associated with 5d localized holes generated through Au-S bonds. These holes give rise to localized magnetic moments that are frozen in due to the combination of the high spin-orbit coupling (1.5 eV) of gold and the symmetry reduction associated with two types of bonding: Au-Au and Au-S.

Journal Article↗
PubMed2004

Dose quantification from in-beam positron emission tomography.

Positron emission tomography (PET) imaging of the radioactivity distributions induced by therapeutic irradiation is at present the only feasible method for an in situ and non-invasive monitoring of radiooncology treatments with ion beams. The clinical implementation of this imaging technology at the experimental carbon ion therapy facility at the Gesellschaft für Schwerionenforschung (GSI) at Darmstadt, Germany is outlined and an interactive approach for a PET guided quantification of local dose deviations with respect to the treatment plan is presented.

Humans↗
PubMed2003

Ferromagnetism in fcc twinned 2.4 nm size Pd nanoparticles.

The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0.02 emu/g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.

Journal Article↗
PubMed2001

Maintenance of CDC42 GDP-bound state by Rho-GDI inhibits MAP kinase activation by the exchange factor Ras-GRF. evidence for Ras-GRF function being inhibited by Cdc42-GDP but unaffected by CDC42-GTP.

The function of the Ras guanine nucleotide exchange factor Ras-GRF/cdc25(Mn) is subject to tight regulatory processes. We have recently shown that the activation of the Ras/MAPK pathway by Ras-GRF is controlled by the Rho family GTPase Cdc42 through still unknown mechanisms. Here, we report that retaining Cdc42 in its GDP-bound state by overexpressing Rho-GDI inhibits Ras-GRF-mediated MAPK activation. Conversely, Ras-GRF basal and LPA- or ionomycin-stimulated activities were unaffected by a constitutively active GTP-bound Cdc42. Moreover, the Cdc42 downstream effectors MLK3, ACK1, PAK1, and WASP had no detectable influence on Ras-GRF-mediated MAPK activation. In contrast, promoting GDP release from Cdc42 with the Rho family GEF Dbl or with ionomycin suppressed the restraint exerted by Cdc42 on Ras-GRF activity. We conclude that Cdc42-GDP inhibits Ras-GRF-induced MAPK activation, but neither Cdc42-GTP nor the Cdc42 downstream effectors affect Ras-GRF performance. Interestingly, the loss of the GDP-bound state by Cdc42 abolishes its inhibitory effects on Ras-GRF function. These results suggest that the Cdc42 mechanism of action may not be solely restricted to activation of downstream signaling cascades when GTP-loaded. Furthermore, the GDP-bound form may be acting as an inhibitory molecule down-modulating parallel signaling routes such as the Ras/MAPK pathway.

Animals↗
PubMed2000

Role of the cAMP and MAPK pathways in the transformation of mouse 3T3 fibroblasts by a TSHR gene constitutively activated by point mutation.

Constitutive activating mutations of the TSHR gene, have been detected in about 30 per cent of hyperfunctioning human thyroid adenomas and in a minority of differentiated thyroid carcinomas. The mutations activating the TSHR gene(s) in the thyroid carcinomas, were located at the codon 623 changing an Ala to a Ser (GCC-->TCC) or in codon 632 changing a Thr to Ala or Ile (ACC-->GCC or ACC-->ATC). In order to study if the constitutively activated TSHR gene(s) has played a role in the determination of the malignant phenotype presented by these tumors, we investigated: (1) the transforming capacity after transfection of mouse 3T3 cells, of a TSHR cDNA activated by an Ala-->Ser mutation in codon 623 or an Thr-->Ile mutation in codon 632 and (2) the pathway(s) eventually responsible(s) for the malignant phenotype of the cells transformed by these constitutively activated TSHR cDNAs. Our results show that (1) the TSHR(M623) or (M632) cDNAs give rise to 3T3 clones presenting a fully neoplastic phenotype (growth in agar and nude mouse tumorigenesis); this phenotype was weaker in the cells transformed by the 632 cDNA; (2) suggest that the fully transformed phenotype of our 3T3 cells, may be the consequence of the additive effect of the activation of at least two different pathways: the cAMP pathway through G(alpha)s and the Ras dependent MAPK pathway through G(beta)gamma and PI3K and (3) show that the PI3K isoform playing a key role as an effector in the MAPK pathway activation in our 3T3-transformed cells is PI3Kgamma. Signaling from PI3Kgamma to MAPK appears to require in our murine cellular system a tyrosine kinase (still not characterized), Shc, Grb2, Sos, Ras and Raf. It is proposed that the constitutively activated TSHR genes detected in the thyroid carcinomas, may have played an oncogenic role, participating in their development through these two pathways.

3T3 Cells↗
PubMed2000

The Rho family GTPase Cdc42 regulates the activation of Ras/MAP kinase by the exchange factor Ras-GRF.

The Ras guanine-nucleotide exchange factor Ras-GRF/Cdc25(Mn) harbors a complex array of structural motifs that include a Dbl-homology (DH) domain, usually found in proteins that interact functionally with the Rho family GTPases, and the role of which is not yet fully understood. Here, we present evidence that Ras-GRF requires its DH domain to translocate to the membrane, to stimulate exchange on Ras, and to activate mitogen-activated protein kinase (MAPK). In an unprecedented fashion, we have found that these processes are regulated by the Rho family GTPase Cdc42. We show that GDP- but not GTP-bound Cdc42 prevents Ras-GRF recruitment to the membrane and activation of Ras/MAPK, although no direct association of Ras-GRF with Cdc42 was detected. We also demonstrate that catalyzing GDP/GTP exchange on Cdc42 facilitates Ras-GRF-induced MAPK activation. Moreover, we show that the potentiating effect of ionomycin on Ras-GRF-mediated MAPK stimulation is also regulated by Cdc42. These results provide the first evidence for the involvement of a Rho family G protein in the control of the activity of a Ras exchange factor.

3T3 Cells↗
PubMed2000

Distinct carboxy-termini confer divergent characteristics to the mitogen-activated protein kinase p38alpha and its splice isoform Mxi2.

The p38 family of mitogen-activated protein kinases is composed of several isoforms. Mxi2 is a splicing variant of p38alpha that harbors a unique carboxy-terminus. Here we show that this sole divergence results in remarkable differences between Mxi2 and p38alpha. Mxi2 is distinctively activated by stress stimuli and potently activated by mitogens. Mxi2 affinity for bona fide p38 substrates is remarkably diminished and Mxi2 activity is largely unaffected by the phosphatase CL100. Also, Mxi2 sensitivity to inhibition by SB203580 is greatly reduced. Interestingly, we show that the p38 C-terminus is involved in conferring sensitivity to this compound. Overall, our results point to the p38 carboxy-terminus as a key determinant of the biochemical properties of this family of kinases.

Alternative Splicing↗
PubMed2000

Stress-induced activation of c-Jun N-terminal kinase in sensory ganglion neurons: accumulation in nuclear domains enriched in splicing factors and distribution in perichromatin fibrils.

In response to cellular stress, the activation of the JNK cascade mediates phosphorylation of c-Jun that promotes its transactivation, which in turn activates the transcription of specific genes. In an experimental model of neuronal stress in vivo, by means of immunofluorescence and kinase assays we have found a reversible activation of JNK induced by the administration of the anti-cancer drug Adriamycin. In control neurons, a considerable basal level of the active, phosphorylated JNK was detected in neuronal nuclei, with a speckled distribution in addition to a diffuse nucleoplasmic signal. Adriamycin-induced neuronal stress was associated with a notable increase of this nuclear immunostaining, indicating activation of the JNK pathway which was confirmed by the increase of JNK enzymatic activity, while no changes in the total JNK were detected by Western blots. The JNK neuronal response to stress was also accompanied by an increase in the nuclear immunoreactivity for c-Jun and also by the de novo appearance of a strong nuclear phospho-c-Jun signal. These effects tend to revert to the control situation after 24 h of Adriamycin treatment. The nuclear compartmentalization of phospho-JNK and its substrate c-Jun was analyzed by confocal laser microscopy. Phospho-JNK strongly colocalizes with snRNPs in nuclear speckles, while the former was not concentrated in the coiled bodies. Upon stress induction, both c-Jun and phospho-c-Jun show a nucleoplasmic distribution in euchromatin domains, with the nucleoli free of immunolabeling. Furthermore, the nuclear speckles enriched in phospho-JNK exhibit a very low or undetectable signal with both c-Jun antibodies. Immunogold electron microscopy confirms the accumulation of phospho-JNK in interchromatin granule clusters (nuclear speckles), while in the nucleoplasm this kinase is mainly localized in perichromatin fibrils. Both c-Jun and phospho-c-Jun were also detected in perichromatin fibrils. Double labeling experiments show the colocalization of phospho-JNK and phospho-c-Jun in certain perichromatin fibrils. These results indicate that the neuronal response to the Adriamycin-induced stress is mediated by the activation of the JNK pathway. The accumulation of phospho-JNK in nuclear speckles raises the possibility that this kinase may be involved in the phosphorylation of an unknown splicing factor. Moreover, the colocalization of phospho-JNK and c-Jun in perichromatin fibrils, which are associated with sites of active transcription, suggests that these nuclear structures may be putative sites for the phosphorylation of JNK substrates.

Animals↗
PubMed2000

Myeloid leukemia cell growth and differentiation are independent of mitogen-activated protein kinase ERK1/2 activation.

The mitogen-activated protein kinase ERK1/2 pathway is essential in the control of cell proliferation and differentiation in most cellular systems. As such, it has been considered a potential target for antineoplastic therapy. For this purpose, we have examined the role of ERK activation in myeloid leukemia cell growth and differentiation. Using a representative set of myeloid leukemia cell lines, we show that cell proliferation was not accompanied by increases on ERK1/2 activation, and mitogenic stimulation did not enhance ERK activity. Moreover, abolition of ERK function by the inhibitor PD98059 or by a dominant inhibitory mutant ERK2 had no significant effects on proliferation. With the aid of various differentiation inducers, we found that within the same cell line, differentiation to a given lineage could occur with and without ERK1/2 activation, depending on the stimulus. Also, a differentiator could have the same effect in the presence or absence of ERK stimulation, depending on the cell line. ERK inhibition did not affect the differentiation elicited by stimuli whose effects were accompanied by ERK activation. Finally, constitutive ERK activity was also ineffective on proliferation and differentiation. Thus, our results indicate that ERK1/2 activation is not an essential requirement for leukemic cell growth and differentiation.

Cell Differentiation↗
PubMed2000

H-, K- and N-Ras inhibit myeloid leukemia cell proliferation by a p21WAF1-dependent mechanism.

Mutated ras genes are frequently found in human cancer. However, it has been shown that oncogenic ras inhibits growth of primary cells, through pathways involving p53 and the cell cycle inhibitors p16INK4a and p19ARF. We have analysed the effect of the ectopic expression of the three mammalian ras genes on the proliferation of K562 leukemia cells, which are deficient for p53, p16INK4a, p15INK4b and p19ARF genes. We have found that high expression levels of both wild-type and oncogenic H-, K- and N-ras inhibit the clonogenic growth of K562 cells. Induction of H-rasV12 expression in K562 transfectants retards growth and this effect is accompanied with an increase of p21WAF1 mRNA and protein levels. Furthermore, p21WAF1 promoter is activated potently by oncogenic ras and less pronounced by wild-type ras. This induction is p53-independent since a p21WAF1 promoter devoid of the p53 responsive elements is still activated by Ras. Finally, inhibition of p21WAF1 expression by an antisense construct partially overcomes the growth inhibitory action of oncogenic H-ras. Altogether, these results indicate that the antiproliferative effect of ras in myeloid leukemia cells is associated to the induction of p21WAF1 expression and suggest the existence of p19ARF and p16INK4a-independent pathways for ras-mediated growth inhibition.

Acute Disease↗
PubMed2000

Ras proteins in the control of the cell cycle and cell differentiation.

The Ras family of small GTPases includes three closely related proteins: H-, K-, and N-Ras. Ras proteins are involved in the transduction of signals elicited by activated surface receptors, acting as key components by relaying signals downstream through diverse pathways. Mutant, constitutively activated forms of Ras proteins are frequently found in cancer. While constitutive Ras activation induces oncogenic-like transformation in immortalized fibroblasts, it causes growth arrest in primary vertebrate cells. Induction of p53 and cyclin-dependent kinase inhibitors such as p15INK4b, p16INK4a, p19ARF, and p21WAF1 accounts for this response. Interestingly, while ras has usually been regarded as a transforming oncogene, the analysis of Ras function in most of the cellular systems studied so far indicates that the promotion of differentiation is the most prominent effect of Ras. While in some cell types, particularly muscle, Ras inhibits differentiation, in others such as neuronal, adipocytic, or myeloid cells, Ras induces differentiation, in some cases accompanied by growth arrest. Several possible mechanisms for the pleiotropic effects' of Ras in animal cells are discussed.

Animals↗
PubMed1999

Signal transduction elements of TC21, an oncogenic member of the R-Ras subfamily of GTP-binding proteins.

TC21 is a Ras-like GTPase with high oncogenic potential that is found mutated in some human tumors and overexpressed in breast cancer cell lines. We have conducted cellular and biochemical studies in order to understand the role of this protein in signal transduction and to unveil the signaling elements that participate in the TC21 pathway. Using gene transfer experiments, we demonstrate here that the TC21 oncogene can induce both cellular transformation in mouse fibroblasts and neuronal-like differentiation in rat PC12 cells. Interestingly, the proto-oncogenic version of TC21 shows also a lower, but significant, activity in both biological processes. We also demonstrate that the similarity of the cellular responses induced by TC21 and Ras derive from the utilization of overlapping pathways. Thus, the exchange of guanosine nucleotides in wild type TC21 is catalyzed by Ras exchange factors. Moreover, TC21 binds physically to c-Raf-1 in a GTP-dependent manner. Finally, overexpression of TC21G23V in NIH3T3 cells results in the activation of c-Raf-1 and the MAPK and the JNK branches of serine/threonine cascades. From these results, we conclude that TC21 promotes Ras-like responses in diverse cell types due to the use of overlapping, if not identical, signaling elements of the Ras oncogenic pathway.

3T3 Cells↗
PubMed1999

Identification and chromosomal location of two human genes encoding enzymes potentially involved in proteolytic maturation of farnesylated proteins.

Two human cDNAs encoding proteins similar to yeast enzymes involved in proteolytic processing of farnesylated proteins like a-factor mating pheromone and Ras2p have been cloned from an ovary cDNA library. These proteins have been tentatively called Face-1 and Face-2 (farnesylated protein-converting enzymes 1 and 2), respectively, and are integral membrane proteins, belonging to distinct families of metalloproteinases. Northern blot analysis of poly(A)+ RNAs isolated from a wide variety of human tissues demonstrated that both genes are expressed in all examined tissues, which suggests that these enzymes play housekeeping roles in normal processes. Fluorescence in situ hybridization experiments showed that the human FACE-1 gene maps to 1p34, whereas FACE-2 is located at 11q13, a region frequently amplified in human carcinomas and lymphomas. On the basis of these results, we suggest that inhibition of Face-1 and/or Face-2 could be part of strategies directed to block the functioning of prenylated proteins activated in oncogenic processes, including Ras proteins.

Amino Acid Sequence↗