Search PubMed⌕ Search

Biomedical subjects

W R Loewenstein

Publications and source records attributed to W R Loewenstein.

At least 19 recordsLinked to original sources
PubMed1992

The cell-cell channel in the control of growth.

Several lines of evidence indicate that the cell-cell channels in gap junction are conduits for growth-regulating signals. Experimental upregulation of the channels by retinoids causes inhibition of cellular growth and, conversely, their downregulation by oncogenes, e.g. activated src, stimulates growth. In either direction, the extent of growth correlates tightly with the degree of communication. Cogent evidence of the channel's function in growth regulation is now on hand: incorporation of a channel-protein gene into the genome of a transformed communication-deficient cell line normalizes communication and growth. The current data conform to a model of growth control with discrete regulatory centers.

Animals↗
PubMed1991

Incorporation of the gene for a cell-cell channel protein into transformed cells leads to normalization of growth.

Incorporation of the gene for connexin43, a cell-cell channel protein of gap junction, into the genome of communication-deficient transformed mouse 10T1/2 cells restored junctional communication and inhibited growth. Growth was slowed, saturation density reduced and focus formation suppressed, and these effects were contingent on overexpression of the exogenous gene and the consequent enhancement of communication. In coculture with normal cells the growth of the connexin overexpressors was completely arrested, as these cells established strong communication with the normal ones. Thus, in culture by themselves or in coculture, the connexin overexpressor cells grew like normal cells. These results demonstrate that the cell-cell channel is instrumental in growth control; they are the expected behavior if the channel transmits cytoplasmic growth-regulatory signals.

Animals↗
PubMed1991

Differential regulation of communication by retinoic acid in homologous and heterologous junctions between normal and transformed cells.

The permeability of junctions between cells of the same type (homologous junctions) is greatly increased by retinoic acid (10(-9)-10(-8) M), a probable morphogen, and this responsiveness is shared by a variety of normal and transformed cell types (Mehta, P.P., J.S. Bertram, and W.R. Loewenstein. 1989. J. Cell Biol. 108:1053-1065). Here we report that the heterologous junctions between the normal and transformed cells respond in the opposite direction; their permeability is reduced by retinoic acid (greater than or equal to 10(-9) M) and its benzoic acid derivative tetrahydrotetramethylnaphthalenylpropenylbenzoic acid (greater than or equal to 10(-11) M). The opposite responses of the two classes of junction are shown to be concurrent; in cocultures of normal 10T1/2 cells and their methylcholanthrene-transformed counterparts, the permeability of the heterologous junctions, which is lower than that of the homologous junctions to start with, falls (within 20 h of retinoid application), at the same time that the permeability of the homologous junctions rises in both cell types. Such a counter-regulation requires a minimum of three degrees of cellular differentiation. A model is proposed in which the differentiations reside in a trio of junctional channel protein. The principle of the model may have wide applications in the regulation of intercellular communication at tissue boundaries, including embryonic ones.

Animals↗
PubMed1990

Cell-to-cell communication and the control of growth.

Growth of transformed cells is inhibited by cell-to-cell communication with normal cells. This communication is regulated by certain oncogenes that alone or in cooperation can block the communication.

Cell Communication↗
PubMed1990

Tyrosine phosphorylation of a gap junction protein correlates with inhibition of cell-to-cell communication.

Cell-to-cell communication is achieved by passage of small molecules through gap junction membrane channels. The expression of the transforming gene from Rous sarcoma virus, v-src, induces a rapid and dramatic reduction in cell-to-cell communication in cultured cells. To determine whether connexin43, a major gap junction protein expressed in fibroblasts, is a target for the v-src protein tyrosine kinase activity, we examined the phosphorylation state of connexin43 in cells expressing variants of src. Using an antipeptide serum that recognizes connexin43, we demonstrate that this protein is phosphorylated on serine and tyrosine residues in avian and mammalian cells expressing activated src proteins. Connexin43 from control cells and cells expressing nonactivated variants of the src protein was phosphorylated solely on serine residues. In lysates from v-src-transformed cells, all phosphorylated connexin43 molecules were cleared from the lysate by sequential immunoprecipitations using the phosphotyrosine antibodies, suggesting that each molecule of phosphorylated connexin43 contains both phosphoserine and phosphotyrosine. We have also examined junctional permeability in cells expressing src variants and find that loss of cell-to-cell communication correlates with tyrosine phosphorylation of connexin43.

Animals↗
PubMed1989

The actions of retinoids on cellular growth correlate with their actions on gap junctional communication.

Retinoic acid (a possible morphogen), its biological precursor retinol, and certain synthetic derivatives of retinol profoundly change junctional intercellular communication and growth (saturation density) in 10T 1/2 and 3T3 cells and in their transformed counterparts. The changes correlate: growth decreases as the steady-state junctional permeability rises, and growth increases as that permeability falls. Retinoic acid and retinol exert quite different steady-state actions on communication at noncytotoxic concentrations in the normal cells: retinoic acid inhibits communication at 10(-10)-10(-9) M and enhances at 10(-9)-10(-7) M, whereas retinol only enhances (10(-8)-10(-6) M). In v-mos-transformed cells the enhancement is altogether lacking. But regardless of the retinoid or cell type, all growth responses show essentially the same dependence on junctional permeability. This is the expected behavior if the cell-to-cell channels of gap junctions disseminate growth-regulating signals through cell populations.

Animals↗
PubMed1989

Junctional intercellular communication is cooperatively inhibited by oncogenes in transformation.

We examined the actions of the cellular src (c-src) and adenovirus E1A genes on junctional cell-to-cell communication. Neither gene causes complete transformation of NIH3T3 cells on its own, but the two do so in conjunction with one another. This cooperation goes hand in hand with summation of the actions of the two genes on junctional communication: junctional permeability is reduced when the cells are transfected with either gene; it is reduced significantly more when they are transfected with both. This cooperative loss of communication approaches the noncooperative loss induced by the viral src gene (v-src), chimeric c-src/v-src, or Tyr527-mutant c-src--genes that cause transformation on their own. This provides a rationale for the hitherto unexplained complementation of the two oncogenes in carcinogenesis; it is the expected behavior if the loss of communication is causal in the decontrol of growth in transformation.

Adenovirus Early Proteins↗
PubMed1988

The cellular src gene product regulates junctional cell-to-cell communication.

Overexpression of the cellular src gene in NIH 3T3 cells causes reduction of cell-to-cell transmission of molecules in the 400- to 700-dalton range. This down-regulation of gap junctional communication correlates with the activity of the gene product, the protein tyrosine kinase pp60c-src. The down-regulation was enhanced by point mutation of Tyr527 (a site that is phosphorylated in pp60c-src and that inhibits kinase activity) or by substitution of the viral-src for the cellular-src carboxyl-terminal coding region. Mutation of Tyr416 (a site phosphorylated upon Tyr527 mutation) suppresses both the down-regulation of communication by Tyr527 mutation and that by gene overexpression. The regulation of communication by src may be important in the control of embryonic development and cellular growth.

Animals↗
PubMed1988

Growth factors modulate junctional cell-to-cell communication.

The epidermal growth factor (EGF) and the platelet-derived growth factor (PDGF) inhibit gap junctional communication in the mammalian cell lines NRK and BalbC 3T3: cell-to-cell transfer of a 400-dalton tracer molecule is reduced and junctional conductance is reduced. The inhibition of cell-to-cell transfer is reversible and dose dependent; half-maximal effects are obtained at 10(-9) and 10(-11) M concentrations of EGF and PDGF, respectively. The response of junctional conductance is detectable within 2 min of EGF application and reaches a maximum within 10 min. It is among the earliest cellular responses to this growth factor and may be significant in the regulation of growth. The response is lacking in EGF receptor-deficient NIH 3T3 cells. The transforming factor beta (TGF beta) enhances junctional communication in BalbC 3T3: cell-to-cell transfer is increased over a period of 8 hr. But in NRK cells, where it upregulates EGF receptors, TGF beta reduces junctional communication synergistically with EGF.

Animals↗
PubMed1988

Neural differentiation, NCAM-mediated adhesion, and gap junctional communication in neuroectoderm. A study in vitro.

We studied the development of NCAM and gap junctional communication, and their mutual relationship in chick neuroectoderm in vitro. Expression of NCAM, as detected by monoclonal and polyclonal antibodies, and development of junctional communication, as detected by extensive cell-to-cell transfer of 400-500-D fluorescent tracers, occurred in cultures from stage-2 embryos onward. Both expressions presumably required primary induction. The differentiating cells formed discrete fields of expression on the second to third day in culture, with the NCAM fields coinciding with the junctional communication fields delineated by the tracers. Other neural differentiations developed in the following order: tetanus toxin receptors, neurofilament protein, and neurite outgrowth. Chronic treatment with antibody Fab fragments against NCAM interfered with the development of communication, suggesting that NCAM-mediated adhesion promotes formation of cell-to-cell channels. Temperature-sensitive mutant Rous sarcoma virus blocked (reversibly) communication and the subsequent development of neurofilament protein and neurites, but expression of NCAM continued.

Animals↗
PubMed1988

Genetic regulation of cell-to-cell communication.

Overexpression of the cellular src gene in NIH-3T3 cells causes reduction of cell-to-cell transmission of molecules in the 400-700 dalton range. This down-regulation of gap junctional communication correlates with the activity of the gene product, the protein tyrosine kinase pp60c-src. The down-regulation is enhanced by point mutation of Tyr527 (a site phosphorylated in pp60c-src and which inhibits kinase activity) or by substitution of the viral- for the cellular-src carboxyl terminal coding region. Mutation of Tyr416 (a site phosphorylated upon Tyr527 mutation) suppresses both the down-regulation by Tyr527 mutation and that by gene overexpression. The regulation of communication by src may be important in the control of embryonic development and cellular growth.

Cell Communication↗
PubMed1987

Polyomavirus middle T antigen downregulates junctional cell-to-cell communication.

We examined the effect of polyomavirus middle T antigen on cell-to-cell communication in rat F cells transfected with an inducible middle T recombinant DNA or infected with a conditional mutant virus. Junctional permeability fell (reversibly) when middle T transcription was induced or when middle T was switched to the transformation+ form. The effect correlates with the rise of protein tyrosine kinase activity.

Animals↗
PubMed1986

Growth inhibition of transformed cells correlates with their junctional communication with normal cells.

The growth of various chemically and virally transformed cell types in culture is inhibited when they are in contact with normal cell types. We show that this growth inhibition is contingent on the presence of junctional communication between the normal and transformed cells (heterologous communication), as probed with a 443 dalton microinjected fluorescent tracer. In cell combinations where heterologous communication is weak or absent there is no detectable growth inhibition; the inhibition appears when communication is induced by cyclic AMP-dependent phosphorylation, and only then. In cell combinations where heterologous communication is spontaneously strong, the growth inhibition is present, but it is abolished when the communication is blocked by retinol or retinoic acid. The cell-to-cell membrane channels of gap junctions are the likely conduits of the signals for this growth control.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1986

Downregulation of cell-to-cell communication by the viral src gene is blocked by TMB-8 and recovery of communication is blocked by vanadate.

The viral src gene downregulates junctional communication, closing cell-to-cell membrane channels presumably by way of the phosphoinositide signal route. We show that TMB-8 [8-N, N-(diethylamino) octyl-3,4,5-trimethoxybenzoate] counteracts this downregulation in cells transformed by temperature-sensitive mutant Rous sarcoma virus: TMB-8 (36-72 microM) raises junctional permeability when applied during activity of src protein kinase, i.e., at steady permissive temperature; and TMB-8 inhibits the fall of junctional permeability, when the activity of src protein kinase gets turned on. TMB-8 also (reversibly) inhibits the growth of the cells at permissive temperature and reverses the morphological changes associated with transformation. The morphological reversal lags several hours behind the junctional-permeability reversal. Communication recovers within a few minutes when the activity of the src protein kinase is turned off (in absence of TMB-8). Sodium orthovanadate (20 microM) prevents this recovery, but it has no major effect on junctional permeability on its own. We discuss possible modes of action of these agents on critical stages of the signal route, related to intracellular Ca2+ and protein kinase C.

Animals↗
PubMed1985

Diacylglycerol downregulates junctional membrane permeability. TMB-8 blocks this effect.

We tested the question whether junctional cell-to-cell communication is regulated by the diacylglycerol branch of the phosphoinositide transmembrane signal pathway. Cultured epithelial rat liver cells were treated with the synthetic diacylglycerol 1-oleoyl-2-acetyl glycerol, while their junctional permeability was probed with the microinjected 443-dalton fluorescent tracer Lucifer Yellow. The treatment reduced junctional permeability (without affecting Lucifer permeability of nonjunctional cell membrane). The effect was dose dependent, with a threshold of about 25 micrograms diacylglycerol/ml in sparse cultures and about 50 micrograms/ml in confluent cultures. The reduction of junctional permeability began within 3 min of diacylglycerol application, peaked within 20 min, and reversed spontaneously within 90 min. The phorbol ester TPA mimicked the diacylglycerol effect, but the (spontaneous) reversal was slower. We propose that cell-to-cell communication is under dual physiological control: an up-regulatory one, as exerted by the cyclic AMP signal route (Loewenstein, W.R., 1985, Biochem. Soc. Symp. London, 50: 43-58), and a downregulatory one, by the diacylglycerol signal route. TMB-8 (54-70 microM)--a blocker of intracellular Ca2+ mobilization--impeded the diacylglycerol action on junctional permeability. It prevented the effect of low diacylglycerol doses completely and it markedly reduced the effect of high doses. (It also counteracted the effect of TPA.) Ca2+ thus emerges as a possible candidate for a role in the junctional downregulation by the diacylglycerol signal route. We tentatively advance two models. In one, leaning closely on the Calcium Hypothesis of cell-to-cell channel regulation (Loewenstein, W.R., 1966, Ann. N.Y. Acad. Sci. 137:441-472), Ca2+ mediates the action of the route on the channel. In the other, Ca2+ acts farther removed from the channel, on protein kinase C. Calmidazolium (5-10 microM)--an inhibitor of calmodulinactivated proteins--did not prevent the diacylglycerol-induced reduction of junctional permeability. Nor did sodium orthovanadate (25 or 50 microM)--an inhibitor of tyrosyl phosphatase--prevent the reversal of diacylglycerol-induced (or TPA-induced) reduction of junctional permeability.

Animals↗
PubMed1979

Experimental depression of junctional membrane permeability in mammalian cell culture. A study with tracer molecules in the 300 to 800 Dalton range.

Cell-to-cell junctional permeability in mammalian cell cultures was probed with a series of fluorescent tracers ranging 300 to 800 in molecular weight, during treatment with metabolic inhibitors, Ca-transporting ionophore, and carbon dioxide. Treatment with the combination of cyanide and iodoacetic acid (1--2 mM each), but not with either one alone, caused reversible junctional blockade to all tracer molecular species, large and small. (Electrical coupling, however, persisted in a proportion of the junctions tested.) Treatment with the ionophore A23187 (2--10 micrometers) or with CO2 (an atmosphere of 100% CO2 equilibrated with the medium) produced selective junctional blockade: transmission of a 688 and an 817-dalton tracer was generally blocked, while that of a 376-dalton traced and, in certain conditions, that of a 559-dalton one, persisted. The junctional effect of the ionophore required the presence of Ca in the external medium; and effective junctional blockade by CO2 required pretreatment in medium with high Ca concentration or, interchangeably, pretreatment in medium with high CO2 concentration. In one cell type, prolonged exposure to medium with high Ca concentration alone sufficed to block transmission of the 688-dalton tracer. These effects are discussed in terms of the Ca hypothesis of junctional permeability regulation. In comparison with mammalian (or other vertebrate and invertebrate) organized tissues or with insect cell cultures, the mammalian cell cultures are more resistant to junctional blockade. This difference in transmission stability is discussed in terms of the electron-microscopic finding in the mammalian cultures of fine, bilateral cell processes connected by gap junctions.

Animals↗