Pleiotypic Control by Adenosine 3′:5′-Cyclic Monophosphate: A Model for Growth Control in Animal Cells

Abstract

The effects of serum deprivation on several general cellular biochemical processes ("pleiotypic response") related to the growth of normal fibroblasts can be mimicked by treatment of these cells with prostaglandin El in the presence of serum. N8,02'-Dibutyryl adenosine 3': 5'-cyclic monophosphate and theophylline inhibit the membrane transport processes without much effect on other pleiotypic reactions such as overall protein and RNA synthesis and protein degradation. The amount of intracellular cyclic AMP increases during serum starvation and returns to the initial concentration in unstarved cells when growth is initiated again upon addition of serum. Fibroblasts transformed by simian virus 40 have a lower cyclic AMP content than their untransformed parents. Serum deprivation neither increases cyclic AMP content nor significantly affects the pleiotypic reactions in transformed cells. Cycloheximide causes a decrease in cyclic AMP content of normal fibroblasts coincidentally with the ability of this inhibitor to stimulate uridine transport and slow protein degradation in cells deprived of serum.In normal cells, several biochemical parameters, including membrane transport, overall rates of protein and RNA synthesis, and protein degradation, fluctuate coordinately with changes in cell-growth rate. These mechanistically unrelated processes and their coordinated response to environmental changes comprise what we have defined as the "pleiotypic program" and "pleiotypic control," respectively. In malignant cells, the pleiotypic program and the rate of growth are relatively insensitive to changes in cultural conditions; we thus picture transformed cells as having a defect in the pleiotypic control mechanism (1).In cultured fibroblasts, insulin as well as serum activates the pleiotypic program (1, 2). Moreover, the same set of reactions is regulated in many other cell types by specific hormones or growth factors. Thus, certain general features of hormonal regulation may also be exerted through the pleiotypic mechanism (1).We have postulated that a "mediator", probably formed at the cell membrane, coordinates the responses of the different reactions under pleiotypic control. Because of the resemblance of this regulatory program to "stringent control" in bacteria, we inquired whether guanosine 5'-diphosphate, 2'-or 3'-diphosphate (ppGpp) (a possible mediator of stringent control) (3, 4) could be involved in control in animal cells. However, this nucleotide was not detected in cultured 3T3 cells under conditions that should have elicited its appearance (5).In the meantime, numerous reports have implicated cAMP as a regulator of growth, morphology, and contact inhibition in cultured cells (6-11). We report here that altering the inAbbreviations: Bu2cAMP, N6,02'-dibutyryl adenosine 3':5'-cyclic monophosphate; PGE,, prostaglandin El; SV40, simian virus 40. tracellular cAMP content by various means can affect all the reactions under pleiotypic control in a way, suggesting that cAMP is very likely the pleiotypic mediator...

The role of cyclic nucleotides in the development and function of rat mammary tissue

“…In studies with rat mammary gland explants in culture [2] cyclic AMP inhibited the increase of enzyme activities normally associated with lactogenesis, in particular the activities of those enzymes involved in lipogenesis, and also markedly depressed the synthesis of DNA, RNA and fatty acids. This analogy with the pleiotypic response observed for other cells grown in culture [3], and the reversal by cyclic GMP of the pleiotypic inhibition of 3T3 cells treated with dibutyryl cyclic AMP [4] , led us to investigate the simultaneous fluctuations of both cyclic nucleotides throughout the lactation cycle. differentiation of the mammary gland during pregnancy, its response to hormones and the promotion of specific cell programmes for the synthesis of the characteristic components of milk may all be mediated by modification of the ratio between the two nucleotides.…”

“…Some of these activities may be highly relevant to the mammary gland a) the role of cyclic AMP as promoter of differentiation could be of special significance to the development of the gland during pregnancy, a stage at which the level of this nucleotide is high; b) the rise of cyclic GMP after the onset of lactation may explain the wave of mitosis which follows shortly after parturition in the rat [23], a process which is also significant (in addition to increasing the number of secretory cells present) in that it may, as suggested by Stockdale and Topper [24] , make these cells specially susceptible to environmental factors capable of modifying the metabolic pattern; c) the complex endocrine control of the mammary gland and the tissue response to hormones may be expressed through the dualistic system of opposing cyclic AMP and cyclic GMP levels which could, as has already been shown for other cells grown in culture [3,4] , also modulate the pleiotypic control of mammary cells [2] .…”

Adenylate cyclase from synchronized neuroblastoma cells: responsiveness to prostaglandin E1, adenosine, and dopamine during the cell cycle.

“…It was suggested that the changes of cyclic nucleotides regulate the cell cycle and more generally that cyclic nucleotides are involved in the "pleiotypic" control of cell growth (5,6 The aim of the present work was to analyze the evolution pattern of adenylate cyclase during the cell cycle in neuroblastoma cells and the evolution patterns of the responses to three different regulatory agents: adenosine, dopamine, and prostaglandin (PG) El. The latter seems to be a candidate for intracellular regulation because several cell lines, including neuroblastoma, are able to synthesize prostaglandins (7).…”

Polyamines and cellular adenosine 3′ :5′-cyclic monophosphate

“…We are tempted to suggest that this phenomenon might be related to a different availability of free and more active polycations inside the cell. However, considering the inverse correlation between growth rate and cyclic AMP concentrations (Otten et al, 1972;Kram et al, 1973;Bombik & Burger, 1973), the opposite effects elicited by low or high exogenous polyamine concentrations are consistent with their observed ability to act as promoters (Ham, 1964;Clo et al, 1976) or inhibitors (Halevy et al, 1962;Gahl et al, 1976) of cell growth, respectively.…”