bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alpha‐fetoprotein‐mediated uptake of fatty acids by human T lymphocytes
Authors: Torres Juan M. , Anel Alberto , Uriel José 
Published: February 2005

AbstractThe binding to resting and activated T lymphocytes of two radiolabelled fatty acids (oleic and arachidonic) was studied in the presence or in the absence of alphafetoprotein (AFP) as carrier protein. Fatty acid binding by resting and activated T lymphocytes was determined at 4°C as a function of the concentration of fatty acid and AFP. Under the conditions employed, the following observations were made: (1) in the presence of AFP, fatty acids (oleic and arachidonic acid) are bound to cells by a two‐component pathway; one is a saturable process, evidenced when the fatty acid to AFP (FA/AFP) molar ratio was fixed at 1 and the concentration of the fatty acid and the protein varied from 0.1 to 3.2 μM, and the second is a nonsaturable function of FA/AFP molar ratio and was linearly related to the unbound fatty acid concentration in the medium over the entire range studied; (2) in the absence of AFP, the nonsaturable process appears to be the only component of fatty acid binding; (3) at all tested concentrations of free (unbound) fatty acid in the medium, net fatty acid binding by either resting or activated T cells was considerably greater in the presence than in the absence of AFP; (4) in the presence of AFP, fatty acid binding was much higher in activated T cells than in resting T cells, whereas in the absence of AFP, nonsignificant differences were observed between activated and resting T cells; and (5) the time course of fatty acid and AFP binding at 4°C revealed that, at equilibrium, the number of fatty acid molecules bound to the cell was much greater than that of AFP suggesting an accelerated dissociation of the fatty acid upon interaction of the AFP‐fatty acid complex with putative cell receptors.It is concluded to the existence of an AFP/AFP‐receptor pathway that facilitates the binding of fatty acids to T lymphocytes, particularly upon their blast transformation. This pathway may fulfill the increased requirement for fatty acids characteristic of proliferating cells and may serve to regulate the endocytosis of fatty acids with modulatory effects on lymphocyte function and to protect cells from their cytotoxic potential when internalized in excess.
Association of cytoplasmic free Ca2+ gradients with subcellular organelles
Authors: Wahl Miriam , Sleight Richard G. , Gruenstein Eric 
Published: February 2005

AbstractPrevious investigations have identified gradients of intracellular free (Ca2+)i (Ca2+)i in the cytoplasm of human fibroblasts. In this study we have compared the spatial distribution of these gradients with the subcellular distribution of cytoplasmic organelles. Using the Ca2+‐sensitive dye fura‐2 and organelle‐specific fluorescent dyes, we have found that the highest Ca2+ concentrations are found in the perinuclear cytoplasm and that these regions co‐localize with the Golgi apparatus. The area occupied by the endoplasmic reticulum, which includes the Golgi region plus an adjacent area, is also significantly elevated above the average cellular (Ca2+)i. Most mitochondria are located in regions different from those with the highest (Ca2+)i. A variety of phenomena which could have given rise to artifactual (Ca2+)i gradients have been ruled out, including compartmentalization of fura‐2 in subcellular organelles, incomplete hydrolysis of fura‐2AM esters, and the presence of pH gradients which might change the Ca2+ binding characteristics of fura‐2. The existence of gradients in (Ca2+)i between ER and Golgi containing regions of the cytoplasm supports the hypothesis (Sambrook:between Cell 61:197–199, 1990) that the traffic of membrane bound vesicles from ER to Golgi is directed by local variations in (Ca2+)i.
Identification of a new squamous cell differentiation marker and its suppression by retinoids
Authors: Lotan Reuben , Pieniazek Jack , George Margaret D. , Jetten Anton M. 
Published: February 2005

AbstractRabbit tracheobronchial epithelial cells (RbTE) can undergo squamous cell differentiation under defined culture conditions and, therefore, have been used as a model to study the regulation of squamous cell differentiation markers. In the present study, we identified a 20‐kDa protein, designated rSQ20, in the serumfree growth medium conditioned by RbTE cells undergoing squamous cell differentiation. The protein was also found in extracts of squamous differentiated cells. rSQ20 was labeled by cells incubated with [35S]methionine but not with [3H]glucosamine, suggesting that it is not a glycoprotein. Undifferentiated cells did not produce this protein. rSQ20 was detected in the conditioned medium of RbTE cells after they reached a confluent and growth‐arrested state, and thereafter its level increased markedly and concurrently with an increase in type I (epidermal) transglutaminase, an established marker of squamous cell differentiation. rSQ20 found in concentrated conditioned medium of squamous differentiated RbTE cells was eluted from a gel filtration column as a protein of 20 kDa, similar to that found by gel electrophoresis under denaturing conditions, suggesting that it is not a multimeric protein. A protein with an apparent molecular weight of 16 kDa (rSQ16), probably the product of partial proteolysis of rSQ20, was often found in various amounts in the conditioned medium of differentiated RbTE cells. β‐Alltransretinoic acid and other vitamin A analogues (retinoids), which suppress squamous cell differentiation, inhibited the expression of rSQ20 in RbTE cells. RbTE cells immortalized by transfection with SV40 large T antigen as well as malignantly transformed derivatives obtained from the immortalized cells by further transfection with v‐Ha‐ras secreted SQ20 and SQ16 when grown to high cell densities although their squamous differentiation was impaired. An analogous protein with an apparent molecular weight of 16 kDa, designated hSQ16, was detected in the medium of differentiated normal human bronchial epithelial (NHBE) cells and normal human epidermal keratinocytes (NHEK). No such protein could be detected in the medium in which undifferentiated NHBE or NHEK cells were grown. These results suggest that rSQ20 and hSQ16 are new markers of squamous cell differentiation. © 1992 Wiley‐Liss, Inc.
Transformation of renal tubule epithelial cells by simian virus‐40 is associated with emergence of Ca2+‐insensitive K+ channels and altered mitogenic sensitivity to K+ channel blockers
Authors: Teulon Jacques , Ronco Pierre M. , Geniteau‐Legendre Monique , Baudouin Béatrice , Estrade Simone , Cassingena Roland , Vandewalle Alain 
Published: February 2005

AbstractWe compared the pattern of K+ channels and the mitogenic sensitivity to K+ channel blocking agents in primary cultures of rabbit proximal tubule cells (PC.RC) (Ronco et al., 1990) and two derived SV‐40‐transformed cell lines exhibiting specific functions of proximal (RC.SV1) and more distal (RC.SV2) tubule cells (Vandewalle et al., 1989). First, K+ channel equipment surveyed by the patchclamp technique was modified after SV‐40 transformation in both cell lines; although a high conductance Ca2+‐activated K+ channel [K+200 (Ca2+)] remained the most frequently recorded K+ channel, the transformed state was characterized by emergence of three Ca2+‐insensitive K+ channels (150, 50, and 30 pS), virtually absent from primary culture, contrasting with reduced frequency of two Ca2+‐sensitive K+ channels (80 and 40 pS). Second, quinine (Q), tetraethylammonium ion (TEA) and charybdotoxin (CTX), at concentrations not affecting cell viability, all decreased 3H‐TdR incorporation and cell growth in PC.RC cultures, but only TEA had similar effects in transformed cells. The latter were further characterized by paradoxical effects of Q that induced a marked increase in thymidine incorporation. Q also exerted contrasting effects on channel activity: it inhibited the [K+200 (Ca2+)] when the channel was highly active, with a Ki (0.2 mM) similar to that measured for 3H‐TdR incorporation in PC.RC cells (0.3 mM), but increased the mean current through poorly active channels. TEA blocked all K+ channels with conductance ≥ 50 pS, including the [K+200 (Ca2+)], in a range of concentrations that substantially affected cell proliferation. The unique effect of TEA on SV‐40‐transformed cells might be related to broad inhibition of K+ channels. © 1992 Wiley‐Liss, Inc.
Model for the regulation of platelet volume and responsiveness by the trans‐membrane Na+/K+‐pump
Authors: Marx Gerard , Blankenfeld Avigdor , Panet Rivka , Gorodetsky Raphael 
Published: February 2005

AbstractThe correspondence between K+ uptake in platelets to their responsiveness was studied using 86Rb+ as an analogue of K+. An average 86Rb+ uptake rate of 0.73 (± 0.140) × 10−15 mole Rb+/min‐plt (n = 20) was observed. By the use of K+‐influx inhibitors, we were able to distinguish three distinct 86Rb+ uptake pathways: an ouabain‐sensitive (61% ± 2% inhibitable) pump and two equivalent channels, only one of which is sensitive to furosemide. Other platelet parameters were also examined in conjunction with K+‐uptake. Platelets incubated with ouabain exhibited an overall rise in their cell volume (MPV) with incubation time (ΔMPV = 7.4 × 10−17 L/min 1plt−1). Concomitantly, over 24 hours, a steady decrease in platelet number was recorded by blood cell coulter, which correlated inversely with the counts of particles, which by their size resemble white blood cells (r = 0.89). On a cellular level. incubation with ouabain induced greater expression of surface fibrinogen‐receptor (GPIIb), increased binding of FITC‐labelled fibrinogen, and increased responsiveness to ADP. Our observations suggest the following sequence of events: Ouabain turns off the Na+/K+‐ATPase pump, which leads to water accumulation in platelets and concomitant increased MPV. Greater expression of fibrinogen receptors on the distended platelet surface corresponds to spontaneous microaggregate formation as well as greater respon‐siveness to agonists. Our model links volume regulation, the expression of fibrinogen receptors, and the sensitivity of platelets to agonists to the activity of the Na+K+‐ATPase pump. © 1992 Wiley‐Liss, Inc.
Cytoskeletal events underlying dendrite formation by cultured pigment cells
Authors: Lacour Jean‐Philippe , Gordon Philip R. , Eller Mark , Bhawan Jag , Gilchrest Barbara A. 
Published: February 2005

AbstractIn contrast to neurite outgrowth, pigment cell dendrite formation is relatively unstudied. Keratinocyte‐conditioned medium (KCM) induces a striking dendricity in human melanocytes and B16 melanoma cells that is detectable within 30 min, maximal in 24–48 hr, and quantifiable by computerized image analysis. Cyto‐chalasin B (CB), known to disrupt actin microfilaments, completely blocks dendrite formation if added to cultures before or with KCM. This effect is rapidly reversible, and dendrites appear within 1 hr after refeeding with KCM alone. In contrast, CB treatment fails to disrupt existing dendrites previously induced by KCM. Agents known to cause microtubule disassembly (colchicine, nocodazole, or vinblastine) do not inhibit dendrite formation if added before or with KCM. In contrast, these agents disrupt established dendrites Inhibition of protein synthesis with cycloheximide or actinomycin D completely blocks dendrite formation, but if cultures are provided fresh KCM lacking protein synthesis inhibitors, dendrites reappear within 24 hr. Actin microfilaments visualized with a monoclonal antibody or rhodamine‐phalloidin are poorly organized in untreated cells, but form numerous fibers localized along dendrites in KCM‐treated cells. Microtubules visualized with a monoclonal anti‐tubulin antibody are localized in the center of dendrites. These cytoskeletal changes occur without altering β actin or β tubulin mRNA levels. Taken together, these data implicate actin microfilaments in dendrite outgrowth, but not in maintenance, and conversely microtubules in dendrite maintenance but not in formation. These keratinocyte‐induced changes involving β actin and β tubulin polymerization appear to require both new protein synthesis and post‐translational regulation. The observed similarities between melanocytes and other neural crest‐derived cells suggest that cutaneous pigment cells might serve as an alternative model for studies of neurite outgrowth. © 1992 Wiley‐Liss, Inc.
Interferon‐γ and interleukin‐1β inhibit adipoconversion in cultured rodent preadipocytes
Authors: Grégoire Francine , de Broux Nathalie , Hauser Nadine , Heremans Hubertine , van Damme Jo , Remacle Claude 
Published: February 2005

AbstractCytokines like tumor necrosis factor (TNF), interferon‐γ (IFN‐γ), and interleukin‐1 (IL‐1) are known to interfere with the differentiation of cultured cell lines of adipocyte precursors. In the present study, the effect of mouse and rat IFN‐γ, as well as human IL‐1β, was investigated on rodent preadipocytes in primary cultures, either in the presence of fetal bovine serum (FBS, 10%) or in serum‐free defined medium. IFN‐γ exerted an antiproliferative action that was more pronounced when cells reached confluency than during the growth phase of the culture. Morphological observation and quantifications of undifferentiated and differentiating cells revealed that IFN‐γ caused a decrease in the proportion of cells devoid of lipid droplets which would correspond to fibroblast‐like cells, whereas preadipocytes remained unaffected. IFN‐γ induced a marked retardation of adipoconversion, resulting in a partial inhibition of lipoprotein lipase (LPL) activity and a severe decrease in glycerol‐3‐phosphate dehydrogenase (GPDH) activity. The antiproliferative and anti‐LPL effects of IFN‐γ were neutralized by adding anti‐IFN‐γ antibodies, while these antibodies prevented only partially the depressing effect of IFN‐γ on GPDH activity. Contrary to IFN‐γ, IL‐1β slightly enhanced the proliferation in preadipocyte cultures. IL‐1β also depressed adipoconversion, inhibited markedly LPL activity, and partially reduced GPDH activity. These results show that the influence of cytokines on adipoconversion observed in preadipocyte cell lines can be tound in normal preadipocytes in culture. © 1992 Wiley‐Liss, Inc.
Proliferative and differentiative response of corneal and limbal epithelium to extracellular calcium in serum‐free clonal cultures
Authors: Kruse Friedrich E. , Tseng Scheffer C. G. 
Published: February 2005

AbstractAn increasing concentration of extracellular Ca2+ ([Ca2+]e) consistently induces epithelial differentiation, but its effect on proliferation remains variable. We investigated the effect of [Ca2+]e on two different cell populations: the peripheral corneal (PC) and limbal (L) epithelia, the latter containing corneal stem cells. Primary clonal (18 cells/cm2) cultures from rabbit limbal and peripheral corneal epithelia were established in serum‐free MCDB 151 medium containing growth‐promoting agents and 0.03, 0.3, or 1.8 mM Ca2+. During early culture life, colony size and the BrdU labelling‐index of L and PC, assayed on day 6, increased in response to increasing [Ca2+]e; cell attachment and colony‐forming efficiency remained unchanged for both L and PC epithelia. These results indicate that increasing [Ca2+]e, under these defined conditions, stimulates the proliferation of transient amplifying cells, but does not stimulate the differentiation of stem cells into clonal proliferation. A 10‐fold increase of the seeding density or prolongation of the culture up to day 14 or 21 changed the response to [Ca2+]e allowing better proliferation in lower [Ca2+]e. Only cells grown as a monolayer in 0.03 mM Ca2+ could still be passaged on day 14, whereas cells in higher [Ca2+]e showed increasing stratification and cell detachment and could not be passaged. Normal cellular differentiation accessed by the expression of a cornea‐type K3 keratin, recognized by the monoclonal antibody AE‐5, was enhanced by increasing [Ca2+]e. Abnormal differentiation featured by the formation of cornified envelopes was only observed in higher [Ca2+]e. These results indicate that [Ca2+]e promotes the proliferation of relatively undifferentiated transient amplifying cells under clonal, serum‐free culture conditions. Factors that enhance differentiation, such as seeding density or prolonged culture life, can modify this response and allow better proliferation in low [Ca2+]e. © 1992 Wiley‐Liss, Inc.
Characterization of Na+‐K+ homeostasis of cultured human skin fibroblasts in the presence and absence of fetal bovine serum
Authors: Hopp Laszlo , Lasker Norman , Bamforth Ronie , Aviv Abraham 
Published: February 2005

AbstractPreviously, we demonstrated that removal of fetal bovine serum (FBS) from the medium of human skin fibroblasts resulted in an accelerated 86Rb+ washout, decreased cellular K+, and increased Na+ contents. In the present study we examined the mechanism underlying these changes. The efflux rate constant for 86Rb+, and the cellular contents of Na+ and K+ were measured. Verapamil (K1/2= 15 μM) and chlorpromazine (K1/2 = 1 μM) reduced by approximately 70% the increased 86Rb+ washout evoked by FBS removal. The effect of the two drugs was additive at low, but not high, concentrations. Verapamil and chlorpromazine also attenuated the decrease in cellular K+ content and prevented the increase in cellular Na+ content associated with FBS depletion. Bumetanide (50 μM) was only partially effective in offsetting the enhanced 86Rb+ efflux and was completely without any effect on the cellular Na+ and K+ changes induced by FBS removal. In the presence of FBS, A‐23187 produced a slight and transient increase of the 86Rb+ washout. The protein kinase C activator phorbol 12‐myristate 13‐acetate enhanced the 86Rb+ efflux in FBS‐containing medium for a prolonged period but this increase was only a fraction of that caused by serum removal. Cellular Na+ and K+ contents were not changed by the phorbol ester. We conclude that FBS removal raises the cellular Na+ content, and enhances 86Rb+ efflux, through a calmodulin‐dependent pathway activated by calcium influx. © 1992 Wiley‐Liss, Inc.
Mechanism of human keratinocyte migration on fibronectin: Unique roles of RGD site and integrins
Authors: Kim Janice P. , Zhang Ken , Chen John D. , Wynn Kimberly C. , Kramer Randall H. , Woodley David T. 
Published: February 2005

AbstractThe migration of human keratinocytes over the wound bed plays an important role in the re‐epithelialization of cutaneous wounds. Fibronectin, a large glycoprotein matrix component that is abundant within cutaneous wound beds, promotes keratinocyte migration. However, the mechanisms by which keratinocytes migrate over fibronectin are unknown. In this study, we sought to identify specific sites within the fibronectin molecule that induce keratinocyte locomotion and to characterize the cell surface receptors involved. The data show that the domain within the fibronectin molecule that induces human keratinocyte migration is the 120 kD cell‐binding domain close to the carboxyl terminus. The 40 kD heparin‐binding domain near the carboxyl terminus and the 45 kD gelatin‐binding domain near the amino terminus did not promote keratinocyte migration. In addition, keratinocyte migration on both fibronectin and the 120 kD cell‐binding domain was completely inhibited by the presence of GRGDSP peptide, suggesting that keratinocyte migration on fibronectin is mediated by recognizing the RGD sequence located within the cell‐binding domain of fibronectin. Furthermore, keratinocytes were able to migrate directly on immobilized RGD substratum. Cell migration on fibronectin is mediated by the α5β1 integrin since antibodies blocking the α5 and the β1 subunits completely inhibited keratinocyte migration on fibronectin. In addition, we demonstrate that human keratinocytes express α5β1 integrin in culture by flow cytometry. © 1992 Wiley‐Liss, Inc.
Switching from differentiation to growth in hepatocytes: Control by extracellular matrix
Authors: Mooney David , Hansen Linda , Vacanti Joseph , Langer Robert , Farmer Stephen , Ingber Donald 
Published: February 2005

AbstractStudies were carried out to analyze how different extracellular matrix (ECM) molecules regulate hepatocyte growth and differentiation. Freshly isolated rat hepatocytes were cultured on non‐adhesive plastic dishes that were pre‐coated with defined densities of either laminin, fibronectin, type I collagen, or type IV collagen. Sparse cell plating densities were used to minimize cell‐cell contact formation and all studies were carried out in chemically defined medium that contained a saturating amount of soluble growth factors. Dishes coated with a low ECM density (1 ng/cm2) supported hepatocyte attachment, but did not promote cell spreading or growth. Computerized image analysis confirmed that over 80% of cells remained free of contact with other cells under these conditions. Yet, these round cells maintained high levels of albumin gene expression as well as elevated secretion rates for multiple liver‐specific proteins (albumin, transferrin, and fibrinogen), regardless of the type of ECM molecule used for cell attachment. When ECM coating densities were raised from 1 to 1,000 ng/cm2, cell spreading, expression of histone mRNA, DNA synthesis, and cell proliferation all increased in parallel. Activation of growth by high ECM densities was also accompanied by a concomitant down‐regulation of differentiated functions and again, dishes coated with all four types of ECM molecules produced similar effects. Thus, the ability to switch hepatocytes from differentiation to growth (i.e., between different genetic programs) is not limited to a single ECM molecule, a distinct three dimensional ECM geometry, or due to alteration of cell‐cell interactions. Rather, the regulatory signals conveyed by immobilized ECM molecules depend on the density at which they are presented and thus, on their ability to either prohibit or support cell spreading. © 1992 Wiley‐Liss, Inc.
1,25‐dihydroxy‐vitamin‐D3 enhances antiproliferative effect and transcription of TGF‐β1 on human keratinocytes in culture
Authors: Kim Hee‐Jong , Abdelkader Neamatallah , Katz Marion , McLane John A. 
Published: February 2005

AbstractBoth TGF‐β and 1,25‐dihydroxy‐vitamin‐D3 (1,25(OH)2D3) have been reported to decrease the proliferation of normal human keratinocytes. The effect and expression of TGF‐β in keratinocytes treated with 1,25(OH)2D3 was investigated. Human keratinocytes were grown in the presence of various concentrations of TGF‐β and/or 1,25(OH)2D3 prior to enumeration. TGF‐β, alone, has a half maximal dose of inhibition (ED50) of approximately 750 pg/ml after seven days in culture in Keratinocyte Growth Medium (KGM®; Clonetics) supplemented with 1.5 mM calcium. When 1,25(OH)2D3 (10−7M) was also added to cultures with various concentrations of TGF‐β, the ED50 shifted an average of 2‐fold less. The presence of TGF‐β (10 pg/ml) augmented the potency of 1,25(OH)2D3 by at least 10‐fold. In keratinocyte cultures, the antiproliferative effect of the two compounds together is synergistic. In keratinocytes grown for 1 week in the presence of 1,25(OH)2D3 at 10−6M, the TGF‐β1 message increased approximately 5‐fold. An increase is detected within 2 hours of exposure to 1,25(OH)2D3. There was only a 50% increase in the levels of TGF‐β2 and no detection of TGF‐β3. When keratinocyte cultures were treated with 1,25(OH)2D3 and neutralizing antibodies to TGF‐β, the induced‐antiproliferative activity was blocked by more than 50%. The keratinocytes produced more active than latent TGF‐β after growth with high doses of 1,25(OH)2D3. © 1992 Wiley‐Liss, Inc.