A new human colon carcinoma line

Supported by the “Tumorzentrum Heidelberg-Mannheim”.     

Association of increased basement membrane invasiveness with absence of estrogen receptor and expression of vimentin in human breast cancer cell lines.

Lack of estrogen receptor (ER) and presence of vimentin (VIM) associate with poor prognosis in human breast cancer. We have explored the relationships between ER, VIM, and invasiveness in human breast cancer cell lines. In the matrigel outgrowth assay, ER+/VIM- (MCF-7, T47D, ZR-75-1), and ER-/VIM- (MDA-MB-468, SK-Br-3) cell lines were uninvasive, while ER-/VIM+ (BT549, MDA-MB-231, MDA-MB-435, MDA-MB-436, Hs578T) lines formed invasive, penetrating colonies. Similarly, ER-/VIM+ cell lines were significantly more invasive than either the ER+/VIM- or ER-/VIM- cell lines in the Boyden chamber chemoinvasion assay. Invasive activity in nude mice was only seen with ER-/VIM+ cell lines MDA-MB-231, MDA-MB-435 and MDA-MB-436. Hs578T cells (ER-/VIM+) showed hematogenous dissemination to the lungs in one of five mice, but lacked local invasion. The ER-/VIM+ MCF-7ADR subline was significantly more active than the MCF-7 cells in vitro, but resembled the wild-type MCF-7 parent in in vivo activity. Data from these cell lines suggest that human breast cancer progression results first in the loss of ER, and subsequently in VIM acquisition, the latter being associated with increased metastatic potential through enhanced invasiveness. The MCF-7ADR data provide evidence that this transition can occur in human breast cancer cells. Vimentin expression may provide useful insights into mechanisms of invasion and/or breast cancer cell progression.     

Cyclic nucleotides and intracellular-calcium homeostasis in human platelets.

The relationship between agonist-sensitive calcium compartments and those discharged by the Ca(2+)-ATPase inhibitor thapsigargin were studied in human platelets. In this context, calcium mobilization from intracellular pools and manganese influx was investigated in relation to the effect of altered cyclic-nucleotide levels. For maximal calcium release from intracellular stores, thapsigargin, compared to a receptor agonist like thrombin, requires the platelet's self-amplification mechanism, known to generate thromboxane A2. With this lipid mediator formed, thapsigargin released calcium and stimulated manganese influx in a manner similar to thrombin. Blocking the thromboxane receptor by addition of sulotroban (BM13.177) or, alternatively, increasing platelet cAMP or cGMP using prostacyclin or sodium nitroprusside, dramatically reduced the ability of thapsigargin to release calcium from intracellular compartments. The same experimental conditions significantly reduced the rate of manganese influx initiated by thapsigargin compared to thrombin. The experiments indicate that thapsigargin-sensitive compartments play only a minor role in inducing manganese influx compared to the receptor-sensitive compartment. Cyclic nucleotides accelerate the redistribution of an agonist-elevated platelet calcium into the thapsigargin-sensitive compartment, from which calcium can be released by inhibition of the Ca(2+)-ATPase. In human platelets, thapsigargin-induced calcium increase and influx were responsible for only part the calcium release resulting from inhibition of the corresponding ATPase; another part results from the indirect effect of thapsigargin acting via thromboxane-A2-receptor activation. Cyclic nucleotides are therefore an interesting regulatory device which can modify the thapsigargin response by not allowing the self-amplification mechanism of platelets to operate.     

Nitric oxide causes ADP-ribosylation and inhibition of glyceraldehyde-3-phosphate dehydrogenase.

Nitric oxide and nitric oxide-generating agents like 3-morpholinosydnonimine (SIN-1) stimulate the mono-ADP-ribosylation of a cytosolic, 39-kDa protein in various tissues. This protein was purified from human platelet cytosol by conventional and fast protein liquid chromatography techniques. N-terminal sequence analysis identified the isolated protein as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Nitric oxide stimulates the auto-ADP-ribosylation of GAPDH in a time and concentration-dependent manner with maximal effects after about 60 min. Associated with ADP-ribosylation is a loss of enzymatic activity. NAD(+)-free enzyme is not inhibited by SIN-1, indicating the absolute requirement of NAD+ as the substrate of the ADP-ribosylation reaction. Inhibition of the glycolytic enzyme GAPDH may be relevant as a cytotoxic effect of NO complementary to its inhibitory actions on iron-sulfur enzymes like aconitase and electron transport proteins of the respiratory chain.     

A TEA-insensitive flickering potassium channel active around the resting potential in myelinated nerve

A novel potassium-selective channel which is active at membrane potentials between -100 mV and +40 mV has been identified in peripheral myelinated axons of Xenopus laevis using the patch-clamp technique. At negative potentials with 105 mM-K on both sides of the membrane, the channel at 1 kHz resolution showed a series of brief openings and closings interrupted by longer closings, resulting in a flickery bursting activity. Measurements with resolution up to 10 kHz revealed a single-channel conductance of 49 pS with 105 mM-K and 17 pS with 2.5 mM-K on the outer side of the membrane. The channel was selective for K ions over Na ions (PNa/PK = 0.033). The probability of being within a burst in outside-out patches varied from patch to patch (> 0.2, but often > 0.9), and was independent of membrane potential. Open-time histograms were satisfactorily described with a single exponential (tau o = 0.09 msec), closed times with the sum of three exponentials (tau c = 0.13, 5.9, and 36.6 msec). Sensitivity to external tetraethylammonium was comparatively low (IC50 = 19.0 mM). External Cs ions reduced the apparent unitary conductance for inward currents at Em = -90 mV (IC50 = 1.1 mM). Ba and, more potently, Zn ions lowered not only the apparent single-channel conductance but also open probability. The local anesthetic bupivacaine with high potency reduced probability of being within a burst (IC50 = 165 nM). The flickering K channel is clearly different from the other five types of K channels identified so far in the same preparation. We suggest that this channel may form the molecular basis of the resting potential in vertebrate myelinated axons.     

Gene flow inferred from seed dispersal and pollinator behaviour compared to DNA analysis of restriction site variation in a patchy population of Lotus corniculatus L.

Summary Gene flow was investigated in a natural population of Lotus corniculatus L. (Fabaceae) using a combination of pollen and seed dispersal studies and a recombinant DNA technique. The population is spatially heterogeneous and grows with Empetrum nigrum. L. corniculatus is pollinated by the pollen-collecting bumblebee Bombus lapidarius L. Most pollinator flights occurred within patches, as bees usually visit nearest-neighbour plants, show no marked directionality, and forage mostly within patches. Gene flow by seeds is also limited, reinforcing the pattern of gene flow within patches. However, 2.6% of pollinator flights are between patches and considerable pollen carryover also occurs. Thus, gene flow between patches is potentially sufficient to retard or prevent genetic differentiation in spite of the patchy sub-structuring of the population. A sub-set of the population was analysed for restriction fragment length polymorphisms (RFLPs) to document the actual gene flow pattern of the population. The DNA analysis revealed significant levels of genetic differentiation between the patches. The level of gene flow that can be inferred from the distribution of genetic variation is surprisingly restricted, as compared to gene flow inferred from pollinator behaviour, and emphasizes that stochastic processes like genetic drift and founder effects may have a strong impact on the prevailing genetic structure.     

Homeosis in the mouse induced by a null mutation in the Hox-3.1 gene.

We have replaced the Hox-3.1 coding sequence with the E. coli lacZ gene by means of homologous recombination in embryonic stem cells and thus produced null mutant mice. Homozygous mice were born alive, but most of them died within a few days. In the trunk region of homozygotes, several skeletal segments were transformed into the likeness of more anterior ones, as observed in Drosophila with loss-of-function homeotic mutations. The most obvious transformations were the attachment of the 8th pair of ribs to the sternum and the appearance of a 14th pair of ribs on the 1st lumbar vertebra. The pattern of beta-galactosidase activity was identical in heterozygotes and homozygotes and reflected faithfully the Hox-3.1 expression pattern. Thus, the mutation modified the identity, rather than the position, of embryonic cells that would normally express Hox-3.1.     

Different concentrations of thyroid peroxidase and thyroglobulin in the nuclear envelope and the endoplasmic reticulum throughout the cytoplasm.

Thyroid peroxidase (TPO) and thyroglobulin (TG) represent two major glycoproteins of thyroid follicular cells performing biological functions such as iodination, transcytosis of thyroglobulin, and formation of thyroid hormones. They are involved in thyroid autoimmunity and thyroid inborn metabolic disorders. Studying these processes at a molecular level includes the determination of their precise intracellular distribution. An evaluation of the relative concentrations of TG and TPO in different subcellular compartments was carried out in stimulated human follicular cells using thin-frozen sections and the immunogold technique. It is documented that TG is transported from the endoplasmic reticulum and the Golgi apparatus to the follicular lumen by transport vesicles; most of it being present in the expanded endoplasmic reticulum throughout the cytoplasm. On the other hand, gold particles indicating TPO are adjacent to the membranes of the exocytotic pathway. They do not label the basolateral membrane but show the strongest density in the nuclear envelope and the apical membrane. The labeling density of TPO is about four times higher in the nuclear envelope than in the endoplasmic reticulum throughout the cytoplasm. In contrast, TG is concentrated three times higher in the rough endoplasmic reticulum throughout the cytoplasm than in the nuclear cisternae. Our results give the first quantitative evidence that TPO and TG are concentrated in different subcompartments of the endoplasmic reticulum. Because previous studies demonstrated the nuclear envelope as the site where the synthesis of endogenous peroxidase (Br?kelmann, J., D. W. Fawcett, Biol. Reprod. 1, 59-71 (1969)) begins, we suggest that synthesis of these functionally related proteins happens in specialized parts of the endoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exploration of disorder in protein structures by X-ray restrained molecular dynamics

Conformational disorder in crystal structures of ribonuclease-A and crambin is studied by including two independent structures in least-squares optimizations against X-ray data. The optimizations are carried out by X-ray restrained molecular dynamics (simulated annealing refinement) and by conventional least-squares optimization. Starting from two identical structures, the optimizations against X-ray data lead to significant deviations between the two, with rms backbone displacements of 0.45 A for refinement of ribonuclease at 1.53 A resolution, and 0.31 A for crambin at 0.945 A. More than 15 independent X-ray restrained molecular dynamics runs have been carried out for ribonuclease, and the displacements between the resulting structures are highly reproducible for most atoms. These include residues with two or more conformations with significant dihedral angle differences and alternative hydrogen bonding, as well as groups of residues that undergo displacements that are suggestive of rigid-body librations. The crystallographic R-values obtained are approximately 13%, as compared to 15.3% for a comparable refinement with a single structure. Least-squares optimization without an intervening restrained molecular dynamics stage is sufficient to reproduce most of the observed displacements. Similar results are obtained for crambin, where the higher resolution of the X-ray data allows for refinement of unconstrained individual anisotropic temperature factors. These are shown to be correlated with the displacements in the two-structure refinements.     

The homeodomain LIM protein Isl-1 is expressed in subsets of neurons and endocrine cells in the adult rat.

We have used immunocytochemical methods to localize the homeodomain LIM protein Isl-1 in the adult rat. Isl-1 immunoreactivity is expressed in polypeptide hormone-producing cells of the endocrine system, in neurons of the peripheral nervous system, and in a subset of brain nuclei. Isl-1 is also expressed in a subset of motoneurons in the spinal cord and brain stem, but not in regions of the central nervous system involved in sensory function or in neocortical areas. The pattern of expression of Isl-1 suggests that this gene may be involved in the specification and maintenance of differentiated phenotypical properties of these cells.