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L A López

Publications and source records attributed to L A López.

14 recordsLinked to original sources
PubMed2002

Sesquiterpene lactone dehydroleucodine selectively induces transient arrest in G2 in Allium cepa root meristematic cells.

Dehydroleucodine is a sesquiterpene lactone recently isolated from aerial parts of a medicinal herb, Artemisia douglasiana Besser. We have previously shown that 25 and 100 microM dehydroleucodine slowed down onion root growth by 30 and 70%, respectively, affecting neither cell viability nor cell elongation. In the present study we analyze the effect of dehydroleucodine on cell cycle phases in onion (Allium cepa L.) root meristematic cells synchronized with caffeine or caffeine and hydroxyurea. Synchronized root cells treated with 100 and 200 microM dehydroleucodine present an interphase lengthening of 5.2 h and 8.2 h, respectively. The S-phase length, estimated by [3H]thymidine incorporation assay, was 6 h for both control roots and roots that had been immersed in dehydroleucodine. The peak of [3H]leucine incorporation was observed 6 h after release from synchronization in controls and in dehydroleucodine-treated roots, indicating that protein synthesis in G2 was not affected. Thus, these results show that dose-dependently dehydroleucodine selectively induces a transient arrest of meristematic cell in G2 and that dehydroleucodine can be used experimentally as a cell cycle suppressor.

Caffeine↗
PubMed2001

The sesquiterpene lactone dehydroleucodine reversibly inhibits Allium cepa L. root growth.

Here, we prove that dehydroleucodine, a sesquiterpene lactone, at low concentrations (25-100 microM) slowed down the Allium cepa L root growth by 22-70% respectively neither affecting cell viability nor cell size. Removal of the drug after 24 h incubation restored the normal growth rate of the roots. Higher concentrations (200 microM) of dehydroleucodine were deleterious for the roots. As cell size did not change, it is most likely that dehydroleucodine affected some event of cell division cycle making it longer. Thus, dehydroleucodine could be a useful tool to slow down cell proliferation.

Cell Size↗
PubMed1999

Endoglin overexpression modulates cellular morphology, migration, and adhesion of mouse fibroblasts.

Endoglin is the gene mutated in hereditary hemorrhagic telangiectasia type 1 (HHT1), a dominantly inherited vascular disorder. Endoglin glycoprotein is a component of the transforming growth factor type beta (TGF-beta) receptor system which is highly expressed by endothelial cells, and at lower levels on fibroblasts and smooth muscle cells, suggesting the involvement of these lineages in the HHT1 vascular dysplasia. Overexpression of endoglin in mouse NCTC929 fibroblasts led to decreased migration in chemotactic and wound healing assays, as well as changes in the cellular morphology. When plated on uncoated surfaces, endoglin transfectants formed intercellular clusters, endoglin being not specifically localized to the cell-cell junctions, but homogenously distributed on the cellular surface. Although the expression of alpha5beta1 integrin and of an activation epitope of beta1 integrin were unchanged, a polyclonal antibody to alpha5beta1 integrin was able to inhibit cluster formation, suggesting the involvement of integrin ligand/s. In fact, coating with fibronectin, laminin, or an RGD-containing 80 kDa fragment of fibronectin were able to prevent the cellular clustering. Furthermore, synthesis of plasminogen activator inhibitor 1 (PAI-1), and to a weak extent that of fibronectin, were inhibited in endoglin transfectants. Thus, the presence of endoglin in mouse NCTC929 fibroblasts is associated with reduced production of certain extracellular matrix (ECM) components, which might explain their altered morphology, migration and intercellular cluster formation.

Animals↗
PubMed1998

1H MRS markers of tumour growth in intrasplenic tumours and liver metastasis induced by injection of HT-29 cells in nude mice spleen.

We have characterized, by in vitro magnetic resonance spectroscopy (MRS), the metabolite pattern of perchloric acid (PCA) extracts of intrasplenic tumours and hepatic metastasis, produced by intra-spleen injection of the human colorectal carcinoma cell line HT-29 and its metastatic variant HT-29 MMM into nude mice. Our aim was to gain further understanding of colorectal tumour metabolism as a basis for future in vivo studies of human colon cancer by 1H MRS. Metabolite PCA extract analysis showed a good reproduction of the spectral pattern observed in human primary colon tumours, while they were very different from the spectral pattern of the host tissues (spleen and liver). The main differences between host and tumour tissues involved taurine, phosphocholine (PC), phosphoethanolamine (PE), creatine, glycogen and glucose. Creatine is the most promising marker to follow tumour growth because of its practical absence in the nude mice host tissues. Detection of variable levels of this compound and of taurine in hepatic foci in man, are suggested as possible diagnostic markers. No correlation could be found between spectral pattern differences and the different ability to metastasize of the two HT-29 cell lines used. Furthermore, indirect evidence for a functional link between taurine and myo-inositol in colon tumour cells is presented. In summary, our data suggest that the nude mice model may be a suitable system for the MRS study of the changes taking place in host tissues upon tumour progression.

Animals↗
PubMed1997

Heat shock proteins and cell proliferation in human breast cancer biopsy samples.

Human breast cancers may overexpress certain heat shock protein (hsp) family members, proteins which are involved with cell proliferation and differentiation as well as with disease prognosis and drug resistance. Here, we have studied the relationship between the expression of two hsps (hsp27 and hsp70) and the proliferative activity of tumor cells in 40 biopsies from breast cancer patients. Twenty of these tumors were selected for a detailed colocalization study. Immunocytochemistry was done using specific antibodies against hsp27 and hsp70. Cell proliferation was studied analyzing the expression of proliferating cell nuclear antigen (PCNA) (late G1, S, and G2 phases of the cell cycle) and the number of silver-staining nucleolar organizer regions (AgNORs) (G1 phase). The colocalization study revealed a statistically significant inverse correlation between hsp27 expression and cell proliferation in 16/19 (84%) of the cases evaluated by PCNA immunostaining, and in 11/16 (69%) of the cases evaluated by AgNORs. In contrast, a statistically significant positive correlation between hsp70 expression and elevated cell proliferation was seen in almost 85% of the cases evaluated by PCNA staining, and in almost 50% of the cases evaluated by AgNORs. Moreover, in 22% (9/40) of the breast cancer samples examined, hsp70 was clearly associated with the mitotic spindle. A Western blot analysis revealed that hsp70 was coprecipitated with taxol-polymerized tubulin. The association of hsp70 with the mitotic spindle was not clearly noted in lung carcinoma samples (N = 20) or in normal cells displaying elevated mitotic activity. These studies thus demonstrate that in a significant percentage of clinical breast cancers hsp27 overexpression is inversely correlated with cell proliferation, while hsp70 is clearly associated with the mitotic spindle and cell proliferation. These results add evidence to the concept that in human breast cancers hsp27 may be involved in cell growth arrest and increased differentiation while, in contrast, hsp70 may be involved in cell proliferation; further studies will be necessary to elucidate these possible cause-and-effect relationships.

Adult↗
PubMed1996

Endoglin modulates cellular responses to TGF-beta 1.

Endoglin is a homodimeric membrane glycoprotein which can bind the beta 1 and beta 3 isoforms of transforming growth factor-beta (TGF-beta). We reported previously that endoglin is upregulated during monocyte differentiation. We have now observed that TGF-beta itself can stimulate the expression of endoglin in cultured human monocytes and in the U-937 monocytic line. To study the functional role of endoglin, stable transfectants of U-937 cells were generated which overexpress L- or S- endoglin isoforms, differing in their cytoplasmic domain. Inhibition of cellular proliferation and downregulation of c-myc mRNA which are normally induced by TGF-beta 1 in U-937 cells were totally abrogated in L-endoglin transfectants and much reduced in the S-endoglin transfectants. Inhibition of proliferation by TGF-beta 2 was not altered in the transfectants, in agreement with the isoform specificity of endoglin. Additional responses of U-937 cells to TGF-beta 1, including stimulation of fibronectin synthesis, cellular adhesion, platelet/endothelial cell adhesion molecule 1 (PECAM-1) phosphorylation, and homotypic aggregation were also inhibited in the endoglin transfectants. However, modulation of integrin and PECAM-1 levels and stimulation of mRNA levels for TGF-beta 1 and its receptors R-I, R-II, and betaglycan occurred normally in the endoglin transfectants. No changes in total ligand binding were observed in L-endoglin transfectants relative to mock, while a 1.5-fold increase was seen in S-endoglin transfectants. The degradation rate of the ligand was the same in all transfectants. Elucidating the mechanism by which endoglin modulates several cellular responses to TGF-beta 1 without interfering with ligand binding or degradation should increase our understanding of the complex pathways which mediate the effects of this factor.

Antigens, CD↗
PubMed1995

A microtubule-associated protein (MAP2) kinase restores microtubule motility in embryonic brain.

Motility driven by the microtubule motors, kinesin and cytoplasmic dynein, is inhibited by MAP2 (López, L. A., and Sheetz, M. P. (1993) Cell Motil. Cytoskeleton 24, 1-16). The MAP2 inhibition is reversed by a kinase that is co-purified with chicken embryonic MAP2, completely releasing MAP2 from the microtubules. We have identified this activity with a kinase, embryonic MAP2 kinase (M(r) = 100,000), which phosphorylates MAP2 at serine amino acid residues. This kinase is c-AMP independent and inhibited by potassium fluoride and glycerol 2-phosphate. Only the phosphorylation produced by embryonic MAP2 kinase can change the affinity of MAP2 by microtubules. Bovine MAP2 kinase, Cdc2 kinase, mitogenic activated protein kinase, and the NIMA kinase are able to phosphorylate MAP2 but do not change the affinity for microtubules. In vivo, embryonic MAP2 kinase could play a major role in the regulation of motility and positioning of membranous organelles within the cells even at substoichiometric levels.

Animals↗
PubMed1991

Stereotaxic injection of tetanus toxin in rat central nervous system causes alteration in normal levels of monoamines.

A single intraventricular injection of tetanus toxin produced a time-dependent elevation of serotonin levels in brain and spinal cord of adult rats. This tetanus toxin-induced increase was produced in areas of high density of serotonergic innervation, such as the hypothalamus, hippocampus, and spinal cord. Little or no effect was found in the thalamus, cerebellum, and frontal cortex, areas that are poorly innervated by serotonergic terminals. The responses of catecholamines (no change in dopamine level and generalized decrease in norepinephrine) pointed to a specific action of tetanus toxin on the serotonergic system. Stereotaxic injections of tetanus toxin in dorsal or magnus raphe nuclei did not have an evident effect on biogenic amine levels in the brain and spinal cord, respectively. Because direct stereotaxic injections of the toxin in the hypothalamus or hippocampus produced significant serotonin increases in both areas, it is proposed that tetanus toxin interacts with presynaptic targets to produce serotonin accumulation; this is probably due in part to an activation of tryptophan 5-hydroxylase.

Animals↗
PubMed1990

In vitro depolymerization dynamics of brain endogenous microtubules.

A subcellular fraction containing fragments of endogenous microtubules stabilized in 50% glycerol was separated by diferential centrifugation of rat brain homogenates. The pellets were suspended in glycerol-deficient media, and microtubule depolymerization was monitored by measuring the decrease of sedimentable tubulin. Concomitantly, the number and size of microtubules in the suspensions were followed via electron microscopy. Depolymerization was accompanied by a proportional decrease in the number of microtubules, whereas the average size did not change significantly. After approximately 20 min, a subpopulation of microtubules became stable and did not suffer further depolymerization. These results indicate that upon dilution some microtubules completely depolymerize, whereas others remain stable in the glycerol-deficient medium. The degree of depolymerization depended on both the volume of the resuspension media and on the final glycerol concentration. The results suggest that the depolymerization of the remaining microtubules is prevented by stabilizing factors released from depolymerizing microtubules. Tubulin dimers are not one of these factors, since depolymerization was not altered by the addition of colchicine or by changing the concentration of free tubulin in the medium.

Animals↗
PubMed1986

Separation of microtubule populations in rat brain homogenates by differential centrifugation.

Subcellular fractions were separated from rat homogenates at 600 g for 5 min (P1), 15,000 g for 10 min (P2), 48,000 g for 60 min (P3), 100,000 g for 150 min (P4) and a final supernatant (S). They contained 5.0, 14.3, 14.7, 24.7 and 41.3% of the total tubulin in the homogenate measured by colchicine binding. The microtubules recovered in a pool of fractions P1 + P2 + P3 underwent a faster depolymerization than those of P4 when the sediments were suspended in buffered solutions, poor in the stabilizing agent glycerol. As was observed with the electron microscope, P4 was richer than the other fractions in microtubules associated with membranous structures (MTA) by filamentous lateral connections. Subcellular distribution and lability properties may be the result of the connection of microtubules with membranous structures; the attached membranes would decrease the sedimentation velocity of microtubules, and lateral bridges could increase microtubular stability. Differences in length were not a cause of microtubule separation since this parameter did not vary among the microtubule of the different fractions or between MTA and non-associated microtubules of the same fraction.

Animals↗
PubMedDate not supplied

[Opinions of primary care managers on sources of influence on medical practice. Differences with physicians' opinions].

OBJECTIVES: To determine the opinion of primary healthcare managers on the importance and legitimacy of different sources of influence in medical practice, and to compare the results with the opinions of physicians in healthcare teams. MATERIAL AND METHODS DESIGN: cross-sectional study. POPULATION: primary healthcare managers in the Spanish public health system (area managers, medical and nursing directors) and in the Andalusian health service (district director, nursing coordinators and epidemiology and program coordinators). The sample comprised the total population of 302. As dependent variables, a series of questions was designed to gather the interviewees' opinions on different strategies, institutions and/or collectives that exert some kind of influence on medical practice. The degree of importance of each factor was summarized into a set of 9 items. The subjects were asked to score each item from 1 (most important) to 9 (least important). To assess the legitimacy of these scores, 16 items were presented measured using a Likert-type 7-point scale (1: not at all legitimate; 7: very legitimate). A self-administered questionnaire was used, sent by mail. Non-parametric tests (Friedman and Kruskall-Wallis) were used for statistical analysis of the data. RESULTS: The response rate was 79.8%. Using the Friedman test for an ordinal 9-point scale, analysis of the mean ranges for each item revealed that the most important sources of influence for the primary healthcare managers interviewed were: the devising of management protocols by the doctors themselves; discussion with colleagues; feedback from patients, and attending training courses, and reading articles and scientific journals. The institutions or groups with the greatest legitimacy to influence medical practice were: users or citizens; internal audits; peers; scientific associations, and the managers themselves. CONCLUSIONS: The sources of influence considered to have the greatest importance and legitimacy in influencing medical practice concern the professional medical system (self-defined protocols, discussion with colleagues, etc.). Managers accept the use of business managerial tools as well as the influence of social actors to a greater extent than do physicians. This finding could indicate differences in the value systems between primary healthcare physicians and managers.

Administrative Personnel↗