Regulation of sarco-endoplasmic reticulum Ca(2+)-ATPases during platelet-derived growth factor-induced smooth muscle cell proliferation.

The role of the sarco-endoplasmic reticulum Ca(2+)-ATPases (SERCA) in the regulation of cell proliferation by Ca2+ was investigated by testing the effect of platelet-derived growth factor (PDGF) on cultured pig aorta smooth muscle cells. For this purpose, the PDGF-mediated rise in the Ca2+ concentration was first examined for its ability to induce the formation of prostaglandins from the specific membrane enzyme, cyclooxygenase. In parallel experiments, similar conditions (10 ng/ml PDGF for 24 h) were used to investigate the smooth muscle cell membrane SERCA2 isoforms. Total SERCA2 activity rose by 472% as reflected by their specific formation of phosphorylated intermediate (E approximately P). This rise correlated with an increase in the amount of SERCA2 proteins (100 kDa) as shown by Western blotting. With isoform-specific anti-SERCA2-a and anti-SERCA2-b antibodies, we demonstrated that the increase in total SERCA2 proteins concerned the minor isoform SERCA2-a, which rose 10-fold, whereas SERCA2-b proteins were not affected. Lastly, Northern blotting using riboprobes showed that PDGF treatment increased the SERCA2-a mRNA species by 82%, and concomitantly decreased the SERCA2-b mRNA by 28%, as a result of isoform switching. We conclude that up-regulation of the SERCA2-type Ca(2+)-ATPases occurs in PDGF-treated smooth muscle cells, which suggests that this enzymatic system plays an essential part in cell proliferation.     

Molecular cloning and sequencing of the plasma-membrane Ca2+ pump of pig smooth muscle.

cDNAs coding for the plasma-membrane Ca2+ pump have been isolated from a pig smooth-muscle cDNA library and sequenced. The open reading frame encodes a protein of 1220 amino acids, which corresponds to the one already described in a human teratoma cell line. We demonstrate here that this cDNA probably represents the only isoform of the plasma-membrane Ca2(+)-transport ATPase expressed in this smooth muscle. There is no evidence for the expression of any other plasma-membrane Ca2(+)-pump gene, or for the presence of other alternatively spliced isoforms. These results are in apparent contradiction to those obtained on protein levels which demonstrate the reaction of at least two different polypeptides with a panel of antibodies against the plasma-membrane ATPase. It is suggested that these two polypeptides could result from a post-translational modification of one single enzyme.     

Expression of N-linked sialyl Le(x) determinants and O-glycans in the carbohydrate moiety of human amniotic fluid transferrin during pregnancy

Transferrin, a glycoprotein involved in iron transport in body fluids, was isolated from amniotic fluid of a hydramniospatient by sequential anion-exchange chromatography and gel filtration. The N-glycans of human amniotic fluid transferrin (hAFT) were enzymatically liberated by PNGase-F digestion, isolated by gel filtration and fractionated by (high-pH) anion-exchange chromatography. After alkaline borohydride treatment of native hAFT, the released O-glycans were isolated by gel filtration and fractionated by anion-exchange chroma-tography. Structure elucidation of 14 N- and 2 O-glycans was performed by 500 or 600 MHz1H-NMR spectroscopy. Besides conventional N-glycans established earlier for human serum transferrin (hST), new (alpha1-3)-fucosylated N- glycans were found, representing sialyl Le(x) elements. Furthermore, as compared to hST, a higher degree of (alpha1-6)-fucosylation and an increase in branching from di- to triantennary compounds has been detected. The presence of O-glycans is demonstrated for the first time in transferrin.      

SYSTEMIC RELEASE OF SOLUBLE TNF RECEPTORS AFTER HIGH-DOSE TNF IN ISOLATED LIMB PERFUSION

Isolated limb perfusion (ILP) with high dose tumour necrosis factor (TNF), interferon γ and melphalan (TIM) is an efficient treatment for patients with regionally advanced melanoma and sarcoma. In 44 patients, we determined the kinetics of soluble TNF receptors (sTNF-RI and RII) plasma concentrations, and correlated them with systemic TNF and interleukin 6 (IL-6) levels and shock. Seven patients treated conventionally by ILP without cytokine served as controls.Elevated levels of both sTNF-Rs were observed within 30 min after beginning of the TIM-ILP. A first peak of sTNF-Rs levels was observed 3 h after ILP and was followed by a rapid decrease reaching a nadir at 12–14 h post ILP. This first peak was followed by a second, long-lasting elevation of both sTNF-Rs levels persisting for 4 to 5 days after TIM-ILP. Patients treated by ILP without TNF/interferon γ (IFN-γ) had no detectable increase in either sTNF-Rs or in circulating TNF, demonstrating that the release of TNF-Rs was dependent upon the administration of TNF/IFN-γ. High plasma levels of TNF and IL-6 were observed in patients that had more than 5% leakage during the TIM-ILP, but no significant correlation between TNF levels and the peak values of both sTNF-Rs was observed. The levels of TNF and IL-6 were, however, significantly related to each other. TNF systemic levels, but not sTNF-Rs concentrations, correlated significantly with the severity of the shock observed after TIM-ILP. Patients in which sTNF-RII concentration was in excess over circulating TNF, had no shock or grade I shock only, suggesting that sTNF-RII may play a protective, although limited, role in inhibiting activity of circulating TNF.     

Terminal phase of cytokinesis in D-98S cells

The events leading to the completion of cytokinesis after the formation of the midbody and intercellular bridge in D-98S cells were studied with light and electron microscopy. Pairs of daughter cells corresponding to different stages of cytokineses, as determined previously form time lapse films, were selected from embedded monolayers for serial sectioning. Separation of daughter cells is preceded by the reduction in diameter of the intercellular bridge from 1-1.5 μm to approx. 0.2 μm. Two processes contribute to this reduction: (a) The intercellular bridge becomes gradually thinner after telophase; a progressive breakdown of midbody structures accompanies this change; and (b) the more significant contribution to reduction in bridge diameter occurs through the localized constriction of a segment of the intercellular bridge.. The microtubules within the constricted portion of the bridge are forced closer together, and some microtubules disappear as this narrowing progresses. The plasma membrane over the narrowed segments is thrown into a series of wavelike ripples. Separation of daughter cells is achieved through movements of the cells which stretch and break the diameter-reduced bridge. The midbody is discarded after separation and begins to deteriorate. Occasional pairs of daughter cells were found in which incomplete karyokineses resulted in their nuclei being connected by a strand of nuclear material traversing the bridge and midbody. Such cells do not complete cytokinesis but merge together several hours after telophase. This merging of daughter cells coincides with the nearly complete breakdown of the midbody.     

Secretion and degradation of parathormone as a function of intracellular maturation of hormone pools

The biosynthesis, processing, and secretion of parthormone and the effect of calcium on these processes were measured in dispersed porcine parthyroid cells incubated with [(35)S]methionine. Proparathormone was detected at 10 min, the earliest time measured, and was rapidly and apparently quantitatively converted to parathormone. The half-life of the prohomormone pool was 15 min. Secretion of parathormone was detected by 20 min. In pulse-chase experiments there was a period between 20 and 40 min during which the wave of newly-synthesized parathormone was secreted. After 40 min during little additional radioactive hormone was secreted, but dibutyryl cyclic AMP, an agent that can mobilize stored parathormone, when added to the incubation mixtures enhanced radioactive parathormone secretion but only after 60 min, although it increased net hormone secretion as determined by radioimmunoassay to the same extent at all times studied. When the ionized calcium concentration of the medium was lowered, more radioactive hormone was secreted at all times but the effect was greatest on that hormone that was synthesized less than 60 min previously ; however, net hormone secretion in contrast to radioactive hormone was enhanced equally at all intervals. These data could mean that the refractoriness to secretion of parathormone 40-60 min of age was related to maturation of secretory container preparatory to storage. Low calcium (0.5 mM) stimulated hormone secretion up to fivefold compared to high calcium (3.0 mM) but did not affect synthesis of parathormone or proparathormne or conversion of the latter to hormone. During processing at least 70 percent of the intracellular parathormone was lost, presumably through proteolysis and this degradation was greater at high calcium. These data have been interpreted in light of the concept that two secretable pools of parathormone exist within the parathyroid.     

Limnological and ecological sensitivity of Rwenzori mountain lakes to climate warming

An increasing number of studies forecast that anthropogenic climate change poses serious consequences for the biodiversity and ecosystem functioning of high-elevation mountain lakes, through a series of both direct and indirect effects. The impacts of future climate warming on alpine ecosystems are of particular concern, given that warming is expected to be most pronounced at high elevations around the globe. Here, we evaluate the limnological and ecological sensitivity of high-elevation lakes in the Rwenzori Mountains (Uganda-D. R. Congo) to climate change. This is done by comparing the species assemblages of larval chironomid remains deposited recently in lake sediments with those deposited at the base of short cores (dated to within or shortly after the Little Ice Age) in 16 lakes. Chironomid-based reconstructions of mean annual air temperature (MATemp) are made using a variety of inference models (with transfer functions based on weighted averaging, weighted-averaging partial least squares, and a weighted modern analogue technique), and two different calibration data sets, one covering the full regional temperature gradient and one comprising only high-elevation Rwenzori lakes and ponds. The reconstructed historical temperature change ranges between a cooling of −2.03°C and a warming of +3.22°C (with n = 16 lakes × 3 models × 2 calibration data sets). However, excluding the atypical mid-elevation lake Mahoma (2,990 m altitude), we find a three-to-one ratio of cases of inferred warming against inferred cooling, and of the 24 Δ MATemp values exceeding 0.60°C, 23 are positive and only one is negative. Chironomid-inferred temperature changes mostly fall within the error range of the regional temperature inference models. A generalized linear mixed model analysis of the combined result from all lakes (except Mahoma) nevertheless indicates significantly warmer MATemp (on average +0.38 ± 0.11°C) at present compared to between ~85 and ~645 years ago. Inferred temperature changes are independent of whether lakes are located in glaciated or non-glaciated catchments, and of the age of the core base, suggesting that at least part of the signal is due to relatively recent, anthropogenic warming. The direction of faunal change at the lakes in relation to established species–environment relationships suggests that part of the observed shifts in species composition reflect lake-specific evolution in habitat features other than temperature, such as nutrients, pH or oxygen regime, which in our present calibration data set co-vary with temperature to a greater or lesser extent. The fairly uniform and marked historical warming trend in Rwenzori lakes documented by this study highlights their ecological vulnerability and their value as early warning systems for detecting the limnological and ecological effects of global warming.