Showing papers by "University of Virginia published in 1988"

Improved tools for biological sequence comparison.

Abstract: We have developed three computer programs for comparisons of protein and DNA sequences. They can be used to search sequence data bases, evaluate similarity scores, and identify periodic structures based on local sequence similarity. The FASTA program is a more sensitive derivative of the FASTP program, which can be used to search protein or DNA sequence data bases and can compare a protein sequence to a DNA sequence data base by translating the DNA data base as it is searched. FASTA includes an additional step in the calculation of the initial pairwise similarity score that allows multiple regions of similarity to be joined to increase the score of related sequences. The RDF2 program can be used to evaluate the significance of similarity scores using a shuffling method that preserves local sequence composition. The LFASTA program can display all the regions of local similarity between two sequences with scores greater than a threshold, using the same scoring parameters and a similar alignment algorithm; these local similarities can be displayed as a "graphic matrix" plot or as individual alignments. In addition, these programs have been generalized to allow comparison of DNA or protein sequences based on a variety of alternative scoring matrices.

The Cognitive Structure of Emotions

Abstract: 1. Introduction The study of emotion Types of evidence for theories of emotion Some goals for a cognitive theory of emotion 2. Structure of the theory The organisation of emotion types Basic emotions Some implications of the emotions-as-valenced-reactions claim 3. The cognitive psychology of appraisal The appraisal structure Central intensity variables 4. The intensity of emotions Global variables Local variables Variable-values, variable-weights, and emotion thresholds 5. Reactions to events: I. The well-being emotions Loss emotions and fine-grained analyses The fortunes-of-others emotions Self-pity and related states 6. Reactions to events: II. The prospect-based emotions Shock and pleasant surprise Some interrelationships between prospect-based emotions Suspense, resignation, hopelessness, and other related states 7. Reactions to agents The attribution emotions Gratitude, anger, and some other compound emotions 8. Reactions to objects The attraction emotions Fine-grained analyses and emotion sequences 9. The boundaries of the theory Emotion words and cross-cultural issues Emotion experiences and unconscious emotions Coping and the function of emotions Computational tractability.

Politics of Strategic Decision Making in High-Velocity Environments: Toward a Midrange Theory

Abstract: How do politics affect the strategic decision processes of top executives in the “high-velocity” microcomputer industry? We induced a midrange theory linking power, politics, and performance from a...

Strategic decision processes in high velocity environments: four cases in the microcomputer industry

Abstract: How do executives make strategic decisions in industries where the rate of technological and competitive change is so extreme that market information is often unavailable or obsolete, where strategic windows are opening and shutting quickly, and where the cost of error is involuntary exit? How do top management teams divide the decision making responsibility? And how is risk of strategic error mitigated? What we report here is a set of hypotheses induced from a field investigation of four microcomputer firms, where we studied how each of the top management teams went about making major decisions. Our goal was to extend prior work on strategic decision making to what we term high velocity environments. Our results consist of a set of paradoxes which the successful firms resolve and the unsuccessful firms do not. We found an imperative to make major decisions carefully, but to decide quickly; to have a powerful, decisive CEO and a simultaneously powerful top management team; to seek risk and innovation, but...

Angiotensin II induces hypertrophy, not hyperplasia, of cultured rat aortic smooth muscle cells.

Abstract: We have explored the hypothesis that contractile agonists are important regulators of smooth muscle cell growth by examining the effects of one potent contractile agonist, angiotensin II (AII), on both cell proliferation and cellular hypertrophy. AII neither stimulated proliferation of cells made quiescent in a defined serum-free media nor augmented cell proliferation induced by serum or platelet-derived growth factor. However, AII did induce cellular hypertrophy of postconfluent quiescent cultures following 4 days of treatment, increasing smooth muscle cell protein content by 20% as compared with vehicle-treated controls. AII-induced hypertrophy was maximal at 1 microM, had an ED50 of 5 nM, and was blocked by the specific AII receptor antagonist Sar1,Ile8 AII. The cellular hypertrophy was due to an increase in protein synthesis, which was elevated within 6-9 hours following AII treatment, while no changes in protein degradation were apparent. AII was even more effective in inducing hypertrophy of subconfluent cultures, causing a 38% increase in protein content after 4 days of treatment (1 microM) and showing a maximal response at concentrations as low as 0.1 nM. Interestingly, in subconfluent cultures, AII treatment (1 microM, 4 days) was associated with a 50% increase in the fraction of cells with 4C DNA content with the virtual absence of cells in S-phase of the cell cycle, consistent with either arrest of cells in the G2 phase of the cell cycle or development of tetraploidy.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-stimulated MAP-2 kinase phosphorylates and activates ribosomal protein S6 kinase II

Abstract: Ribosomal protein S6 is a component of the eukaryotic 40S ribosomal subunit that becomes phosphorylated on multiple serine residues in response to a variety of mitogens, including insulin, growth factors, and transforming proteins of many oncogenic viruses. Recently, an activated S6 kinase (S6 KII) has been purified to homogeneity from Xenopus eggs1, and characterized immunologically2 and at the molecular level3. Purified S6 KII can be deactivated in vitro by incubation with either protein phosphatase 1 or protein phosphatase 2A. Reactivation and phosphorylation of S6 KII occurs in vitro with an insulin-stimulated micro-tubule-associated protein-2 (MAP-2) protein kinase which is itself a phosphoprotein that can be deactivated by protein phosphatase 2A. These studies suggest that a step in insulin signalling involves sequential activation by phosphorylation of at least two serine/threonine protein kinases.

Dynamic but Structural Equation Modeling of Repeated Measures Data

Abstract: The term “dynamic” is broadly defined as a pattern of change. Many scientists have searched for dynamics by calculating df/dt: the ratio of changes or differences d in a function f relative to changes in time t.This simple dynamic equation was used in the 16th and 17th century motion experiments of Galileo, in the 17th and 18th century gravitation experiments of Newton, and in the 19th century experiments of many physicists and chemists (see Morris, 1985). I also use this dynamic equation, but here I examine multivariate psychological change data using the 20th century developments of latent variable structural equation modeling.

Automobile Accidents Involving Patients with Obstructive Sleep Apnea

Abstract: Although patients with obstructive sleep apnea often report falling asleep while driving, the frequency of auto accidents involving these patients has not been rigorously studied. Therefore, we compared the driving records of 29 patients with obstructive sleep apnea with those of 35 subjects without sleep apnea. The patients with sleep apnea had a sevenfold greater rate of automobile accidents than did the subjects without apnea (p < 0.01). The percentage of persons with one or more accidents was also greater in the patients with apnea than in the control subjects without apnea (31% versus 6%, p < 0.01). The percentage of persons having one or more accidents in which they were at fault was also greater in the patients with apnea than in the control subjects (24% versus 3%, p < 0.02). The automobile accident rate of the patients with sleep apnea was 2.6 times the accident rate of all licensed drivers in the state of Virginia (p < 0.02). In addition, 24% of patients with sleep apnea reported falling asleep ...

Analytic nearest-neighbor model for fcc metals

Abstract: The implications of the mathematical format of the embedded-atom method of computer modeling of metals have been studied with use of a simple nearest-neighbor analytic model for the fcc lattice. The physical inputs into the model are the atomic volume, the cohesive energy, the bulk modulus, the average shear modulus, the vacancy-formation energy, and the slope at the nearest-neighbor distance of the spherically averaged free-atom electron density calculated with Hartree-Fock theory. The model employs an exponential repulsion between nearest-neighboring atoms, an exponentially decreasing function for the free-atom electron density, and a universal equation relating the crystal energy and the lattice constant. The anisotropy ratio of the cubic shear moduli is constrained to be 2 with this model. The dependence of the energies for unrelaxed configurations for vacancy formation, divacancy binding, and low-index plane surfaces on the model parameters has been analyzed. The average shear modulus plays a dominant role in determining these energies relative to the bulk modulus or the cohesive energy because the slope of the embedding function at the equilibrium electron density is linear in the average shear modulus. Embedding functions are not uniquely determined in specific models, and it is shown that the embedding functions used inmore » several models are essentially equivalent.« less

Biomass‐burning emissions and associated haze layers over Amazonia

Abstract: The characteristics of haze layers, which were visually observed over the central Amazon Basin during many of the Amazon Boundary Layer Experiment 2A flights in July/August 1985, were investigated by remote and in situ measurements, using the broad range of instrumentation and sampling equipment on board the Electra aircraft. It was found that these layers strongly influenced the chemical and optical characteristics of the atmosphere over the eastern Amazon Basin. Relative to the regional background, the concentrations of CO, CO2, O3, and NO were significantly elevated in the plumes and haze layers, with the NO/CO ratio in fresh plumes much higher than in the aged haze layers. The haze aerosol was composed predominantly of organic material, NH4, K(+), NO3(-), SO4(2-), and organic anions (formate, acetate, and oxalate).

Splice site selection, rate of splicing, and alternative splicing on nascent transcripts.

Abstract: Based on ultrastructural analysis of actively transcribing genes seen in electron micrographs, we present evidence that pre-mRNA splicing occurs with a reasonable frequency on the nascent transcripts of early Drosophila embryo genes and that splice site selection may generally precede polyadenylation. The details of the process observed are in agreement with results from in vitro splicing systems but differ in the more rapid completion of in vivo splicing. For those introns that are removed cotranscriptionally, a series of events is initiated following 3' splice site synthesis, beginning with ribonucleoprotein (RNP) particle formation at the 3' splice site within 48 sec, intron loop formation within 2 min, and splicing within 3 min. The initiation of the process is correlated with 3' splice site synthesis but is independent of 5' splice site synthesis, the position of the intron within the transcript, and the age or length of the transcript. In some cases, introns are removed from the 5' end of a transcript before introns are synthesized at the 3' end, supporting a possible role for the order of transcription in splice site pairing. In general, our observations are consistent with the 'first-come-first-served' principle of splice site selection, although an observed example of exon skipping indicates that alternative splicing possibilities can be accommodated within this general framework.

Synthesis and Properties of Metallic Glasses That Contain Aluminum

Abstract: The synthesis and properties of a class of metallic glasses containing up to 90 atomic percent aluminum are reported. The unusual formability of the glasses and their structural features are pointed out. Mechanical properties including tensile fracture strength and Young's modulus are reported along with crystallization temperatures. The unusually high strengths of the aluminum glasses can be of significant importance in obtaining high-strength low-density materials.

Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.

Abstract: Studies in man have shown that the episodic release of growth hormone (GH) is infrequent and erratic, and unlike that in the rat does not appear to have discernible ultradian periodicities. However, these observations in nonfasted subjects may be invalid since mixed nutrients have unpredictable effects on GH release. Moreover, in the fed state basal GH levels are frequently undetectable, thus rendering the identification of low amplitude pulses unreliable. Accordingly, the 24-h pulsatile pattern of GH secretion obtained from repetitive venous sampling in six normal adult male subjects was examined during a control fed day and during the first and fifth days of a 5-d fast. The GH data were analyzed using two distinct methods: a discrete pulse detection algorithm (Cluster analysis) and Fourier expansion time-series, which allows fixed periodicities of secretory activity to be resolved. The 5-d fast resulted in a significant increase in discrete GH pulse frequency (5.8 +/- 0.7 vs. 9.9 +/- 0.7 pulses/24 h, P = 0.028), 24 h integrated GH concentration (2.82 +/- 0.50 vs. 8.75 +/- 0.82 micrograms.min/ml; P = 0.0002), and maximal pulse amplitude (5.9 +/- 1.1 vs. 12.3 +/- 1.6 ng/ml, P less than 0.005). While multiple low-amplitude sinusoidal periodicities were present on the control fed day, time-series analysis revealed enhancement of circadian and ultradian cycles on the first and fifth days of fasting. Concomitantly, fasting resulted in a decline (day 1 vs. day 5) in serum concentrations of somatomedin C (1.31 +/- 0.22 vs. 0.77 +/- 0.18 U/ml) and glucose (4.9 +/- 0.2 vs. 3.2 +/- 0.2 mmol/liter), and a marked rise in free fatty acid (0.43 +/- 0.12 vs. 1.55 +/- 0.35 mmol/liter) and acetoacetate (35 +/- 6 vs. 507 +/- 80 nmol/liter). We conclude that the acute nutritional status is an important determinant of spontaneous pulsatile GH secretion in man. Fast-induced enhancement of GH release is achieved through combined frequency (discrete pulses) and amplitude (sinusoidal periodicities) modulation. Such alterations in somatotropic hormone release may play an important role in substrate homeostasis during starvation.

Cell-cell adhesion mediated by CD8 and MHC class I molecules.

Abstract: CD4 and CDS are cell-surface glycoproteins expressed on mutually exclusive subsets of peripheral T cells. T cells that express CD4 have T-cell antigen receptors that are specific for antigens presented by major histocompatibility complex class II molecules, whereas T cells that express CDS have receptors specific for antigens presented by MHC class I molecules (reviewed in ref. 1). Based on this correlation and on the observation that anti-CD4 and anti-CDS antibodies inhibit T-cell function, it has been suggested that CD4 and CDS increase the avidity of T cells for their targets by binding to MHC class II or MHC class I molecules respectively2,3. Also, CD4 and CDS may become physically associated with the T-cell antigen receptor, forming a higher-affinity complex for antigen and MHC molecules4–8, and could be involved in signal transduction5,6,9,10. Cell-cell adhesion dependent CD4 and MHC II molecules has recently been demonstrated11. To determine whether CDS can interact with MHC class I molecules in the absence of the T-cell antigen receptor, we have developed a cell-cell binding assay that measures adhesion of human B-cell lines expressing MHC class I molecules to transfected cells expressing high levels of human CDS. In this system, CDS and class I molecules mediate cell-cell adhesion, showing that CDS directly binds to MHC class I molecules.

Cross-bridge phosphorylation and regulation of latch state in smooth muscle

Abstract: We have developed a minimum kinetic model for cross-bridge interactions with the thin filament in smooth muscle. The model hypothesizes two types of cross-bridge interactions: 1) cycling phosphorylated cross bridges and 2) noncycling dephosphorylated cross bridges ("latch bridges"). The major assumptions are that 1) Ca2+-dependent myosin phosphorylation is the only postulated regulatory mechanism, 2) each myosin head acts independently, and 3) latch bridges are formed by dephosphorylation of an attached cross bridge. Rate constants were resolved by fitting data on the time courses of myosin phosphorylation and stress development. Comparison of the rate constants indicates that latch-bridge detachment is the rate-limiting step. Model simulations predicted a hyperbolic dependence of steady-state stress on myosin phosphorylation, which corresponded with the experimental observation of high values of stress with low levels of phosphorylation in intact tissues. Model simulations also predicted the experimental observation that an initial phosphorylation transient only accelerates stress development, with no effect on the final steady-state levels of stress. Because the only Ca2+-dependent regulatory mechanism in this model was activation of myosin light chain kinase, these results are consistent with the hypothesis that myosin phosphorylation is both necessary and sufficient for the development of the latch state.

Aggregation of chromaffin granules by calpactin at micromolar levels of calcium

Abstract: Several cytosolic proteins bind to secretory granule membranes in a Ca2+-dependent manner and thus may be involved in the mediation of membrane interactions during exocytosis. One of these proteins, calpactin, is a tetramer consisting of two heavy chains of relative molecular mass (Mr) 36K (p36) and two light chains of 10K (p10). We report here that calpactin promotes the Ca2+-dependent aggregation and fatty acid-dependent fusion of chromaffin granule membranes at a level of Ca2+ that is lower than that reported for other granule-aggregating proteins, and which parallels the Ca2+ requirement for secretion from permeabilized chromaffin cells. We found subunits of calpactin to be inactive in promoting granule aggregation. Two distinct 33K proteolytic fragments of p36, differing at their N termini, also promote granule aggregation but with different Ca2+ sensitivities from calpactin. These differences suggest that the N-terminal portion of p36 modulates the Ca2+/lipid binding sites in the core portion of p36 (ref.5).

Data diversity: an approach to software fault tolerance

Abstract: Data diversity is described, and the results of a pilot study are presented. The regions of the input space that cause failure for certain experimental programs are discussed, and data reexpression, the way in which alternate input data sets can be obtained, is examined. A description is given of the retry block which is the data-diverse equivalent of the recovery block, and a model of the retry block, together with some empirical results is presented. N-copy programming which is the data-diverse equivalent of N-version programming is considered, and a simple model and some empirical results are also given. >

Rates of needle-stick injury caused by various devices in a university hospital.

Abstract: We identified characteristics of devices that caused needle-stick injuries in a university hospital over a 10-month period. Hospital employees who reported needle sticks were interviewed about the types of devices causing injury and the circumstances of the injuries. Of 326 injuries studied, disposable syringes accounted for 35 percent, intravenous tubing and needle assemblies for 26 percent, prefilled cartridge syringes for 12 percent, winged steel-needle intravenous sets for 7 percent, phlebotomy needles for 5 percent, intravenous catheter stylets for 2 percent, and other devices for 13 percent. When the data were corrected for the number of each type of device purchased, disposable syringes had the lowest rate of needle sticks (6.9 per 100,000 syringes purchased). Devices that required disassembly had rates of injury of up to 5.3 times the rate for disposable syringes. One third of the injuries were related to recapping. Competing hazards were often cited as reasons for recapping. They included the risk of disassembling a device with an uncapped, contaminated needle and the difficulty of safely carrying several uncapped items to a disposal box in a single trip. New designs could provide safer methods for covering contaminated needles. Devices should be designed so that the worker's hands remain behind the needle as it is covered, the needle should be covered before disassembly of the device, and the needle should remain covered after disposal. Such improvements could reduce the incentives for recapping needles and lower the risk of needle-stick injuries among health care workers.

Inhibition of the inflammatory action of interleukin-1 and tumor necrosis factor (alpha) on neutrophil function by pentoxifylline.

Abstract: Inflammatory cytokines, including interleukin-1 and tumor necrosis factor, are produced by monocytes and macrophages in response to microorganisms and microbial products such as endotoxins. The cytokines stimulate neutrophil adherence, degranulation, and superoxide production but inhibit neutrophil migration. We studied the modulation of cytokine-induced neutrophil activation by pentoxifylline and its principle metabolites. Lipopolysaccharide-stimulated mononuclear-leukocyte-conditioned medium containing inflammatory cytokines, purified human interleukin-1, or recombinant human tumor necrosis factor increased neutrophil adherence to nylon fiber, primed neutrophils for increased superoxide production in response to N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP), increased neutrophil lysozyme release stimulated by FMLP, and decreased directed migration of neutrophils to FMLP. Pentoxifylline and its principle metabolites at or near therapeutically achievable levels were able to counteract these effects. Pentoxifylline inhibited the increase in free intracellular calcium in polymorphonuclear leukocytes stimulated by FMLP and increased binding of FMLP to neutrophils at 37 degrees C but not at 4 degrees C. By blocking the inflammatory action of interleukin-1 and tumor necrosis factor on neutrophils, pentoxifylline may diminish the tissue damage caused by neutrophils in such conditions as septic shock, adult respiratory distress syndrome, cardiopulmonary bypass lung damage, and myocardial reperfusion injury.

High-frequency quasi-resonant converter technologies

Abstract: Resonant switch topologies operating under the principle of zero-current switching (ZCS) and zero-voltage switching (ZVS) are introduced to minimize switching losses, stresses, and noises. Using the resonant switch concept, a host of new quasi-resonant converters (QRCs) are derived from conventional PWM converters. They are capable of operating in the megahertz range, with a significant improvement in performance and power density. Performances of ZCS and ZVS QRCs are compared. Power stages, gate drives, and feedback controls are discussed. >

Simple embedded atom method model for fcc and hcp metals

Abstract: A procedure based on the embedded atom method (EAM) is presented for developing atomistic models for use in computer simulation calculations, with an emphasis on simple but general schemes for matching experimental data with fitting parameters. Both the electron density function and the two-body potential are taken as exponentially decreasing functions and the model is derived for any choice of cutoff distance. The model has been applied successfully to seven fcc and three hcp metals, but the extension to bcc metals was unsuccessful because of difficulty in matching the shear anisotropy ratio.

Insulin-stimulated microtubule-associated protein kinase is phosphorylated on tyrosine and threonine in vivo

Abstract: Exposure of 3T3-L1 cells to insulin stimulates a soluble, serine(threonine)-specific protein kinase that phosphorylates microtubule-associated protein 2 (MAP-2) in vitro. The enzyme, termed MAP kinase, was isolated from insulin-treated or control cells radiolabeled with 32Pi. A 40-kDa phosphoprotein was found to elute in exact correspondence with enzymatic activity during hydrophobic interaction and gel filtration chromatography of extracts from cells stimulated with insulin. Both MAP kinase activity and the phosphoprotein were absent in fractions prepared from untreated cells. The 32P incorporated into the 40-kDa protein was stable during treatment with alkali. Phospho amino acid analysis confirmed that the radiolabel was primarily incorporated into phosphotyrosine and to a lesser extent phosphothreonine. In addition, MAP kinase was incompletely but specifically adsorbed by antibodies to phosphotyrosine. We conclude, based on these data and additional studies from this laboratory, that MAP kinase is phosphorylated on tyrosine in vivo. The data are consistent with the possibility that MAP kinase may be a substrate for the insulin receptor or another insulin-regulated tyrosine kinase.

Occupation of submerged aquatic vegetation by fishes: testing the roles of food and refuge

Abstract: We conducted a series of field experiments to examine the roles of refuge and food availability in explaining the distribution and abundance of fish in tidal freshwater marsh creeks. Two hypotheses were tested: (1) relative predation pressure is less in SAV than in unvegetated areas and (2) fish food availability is greater in SAV than in nearby unvegetated areas. Tethering experiments using mummichogs (Fundulus heteroclitus) in vegetated and unvegetated areas revealed that relative predation pressure was significantly less in areas with SAV. Banded killifish (Fundulus diaphanus) maintained in vegetated enclosures consumed prey associated with SAV, whereas those held in unvegetated pens had empty stomachs. No differences were found in the number of prey eaten by bluespotted sunfish (Enneacanthus gloriosus) or mummichogs when confined in vegetated or unvegetated enclosures. However, larger prey were consumed by bluespotted sunfish and mummichogs maintained in vegetated enclosures. These data suggest that foraging profitability is significantly enhanced by feeding in the SAV. Submerged plant beds in tidal freshwater marsh creeks not only afford protection from predators, but also provide a rich foraging habitat. By foraging in SAV, fish consume larger prey and may have higher growth rates, lower mortality, and higher fecundity.

Time with children: the impact of couples work-time commitments.

Abstract: Using detailed time diaries of a 1981 national sample of 226 married couples with children, we analyze the extent of the trade-off between their time commitments to work and time with their children. Parents in single-earner families spend substantially more time with children than their dual-earner counterparts; the overall difference is largely accounted for by the lesser time of employed mothers in activities that involve children only peripherally, not in directly child-oriented activities. Dual-earner couples have lesser parental time with children for the simple fact that they work more as a unit than single-earner couples. Although the widespread employment of women has not led to a more directly participative male parental role, work time affects fathers' time with children more than mothers'.

Astrocytes synthesize angiotensinogen in brain

Abstract: Cell types associated with angiotensinogen mRNA in rat brain were identified in individual brain sections by in situ hybridization with tritiated RNA probes or with a sulfur-35--labeled oligonucleotide combined with immunocytochemical detection of either glial fibrillary acidic protein (GFAP) for astrocytes or microtubule-associated protein (MAP-2) for neurons. Autoradiography revealed silver grains clustered primarily over GFAP-reactive soma and processes; most grain clusters were not associated with MAP-2--reactive cells. These results demonstrate that, in contrast to other known neuropeptide precursors, angiotensinogen is synthesized by glia.

Calf Deep Venous Thrombosis: A Wolf in Sheep's Clothing?

Abstract: • To determine the natural history of calf deep venous thrombosis (C-DVT), an analytic review of the 20 relevant English-language papers published since 1942 was performed. Remarkably little methodologically sound research on this subject was found. However, available evidence suggests that C-DVT propagates to the thigh in up to 20% of cases and that propagation invariably occurs before embolization. No fatal emboli were reported in patients presenting with isolated C-DVT. Traditional anticoagulation treatment with heparin sodium and warfarin sodium of symptomatic patients with C-DVT appears to prevent extension, embolization, and early recurrence. There is no convincing evidence that C-DVT leads to chronic venous insufficiency or whether the risks of anticoagulation exceed the risks of no treatment. As an option to anticoagulation, physicians may choose to follow patients with C-DVT with serial impedance plethysmography, treating only if there is evidence of proximal extension. (Arch Intern Med1988;148:2131-2138)

Transforming growth factor-beta-induced growth inhibition and cellular hypertrophy in cultured vascular smooth muscle cells.

Abstract: We have explored the hypothesis that hypertrophy of vascular smooth muscle cells may be regulated, in part, by growth inhibitory factors that alter the pattern of the growth response to serum mitogens by characterizing the effects of the potent growth inhibitor, transforming growth factor-beta (TGF-beta), on both hyperplastic and hypertrophic growth of cultured rat aortic smooth muscle cells. TGF-beta inhibited serum-induced proliferation of rat aortic smooth muscle cells (ED50 = 2 pM); this is consistent with previously reported observations in bovine aortic smooth muscle cells (Assoian et al. 1982. J. Biol. Chem. 258:7155-7160). Growth inhibition was due in part to a greater than twofold increase in the cell cycle transit time in cells that continued to proliferate in the presence of TGF-beta. TGF-beta concurrently induced cellular hypertrophy as assessed by flow cytometric analysis of cellular protein content (47% increase) and forward angle light scatter (32-50% increase), an index of cell size. In addition to being time and concentration dependent, this hypertrophy was reversible. Simultaneous flow cytometric evaluation of forward angle light scatter and cellular DNA content demonstrated that TGF-beta-induced hypertrophy was not dependent on withdrawal of cells from the cell cycle nor was it dependent on growth arrest of cells at a particular point in the cell cycle in that both cycling cells in the G2 phase of the cell cycle and those in G1 were hypertrophied with respect to the corresponding cells in vehicle-treated controls. Chronic treatment with TGF-beta (100 pM, 9 d) was associated with accumulation of cells in the G2 phase of the cell cycle in the virtual absence of cells in S phase, whereas subsequent removal of TGF-beta from these cultures was associated with the appearance of a significant fraction of cycling cells with greater than 4c DNA content, consistent with development of tetraploidy. Results of these studies support a role for TGF-beta in the control of smooth muscle cell growth and suggest that at least one mechanism whereby hypertrophy and hyperploidy may occur in this, as well as other cell types, is by alterations in the response to serum mitogens by potent growth inhibitors such as TGF-beta.