Insulin stimulation of high frequency phosphorylation dynamics in murine erythroleukemia cells

An appreciation of the prescience of Don Gilbert (1930-2011): master of the theory and experimental unravelling of biochemical and cellular oscillatory dynamics

We review Don Gilbert's pioneering seminal contributions that both detailed the mathematical principles and the experimental demonstration of several of the key dynamic characteristics of life. Long before it became evident to the wider biochemical community, Gilbert proposed that cellular growth and replication necessitate autodynamic occurrence of cycles of oscillations that initiate, coordinate and terminate the processes of growth, during which all components are duplicated and become spatially re-organised in the progeny. Initiation and suppression of replication exhibit switch-like characteristics, that is, bifurcations in the values of parameters that separate static and autodynamic behaviour. His limit cycle solutions present models developed in a series of papers reported between 1974 and 1984, and these showed that most or even all of the major facets of the cell division cycle could be accommodated. That the cell division cycle may be timed by a multiple of shorter period (ultradian) rhythms, gave further credence to the central importance of oscillatory phenomena and homeodynamics as evident on multiple time scales (seconds to hours). Further application of the concepts inherent in limit cycle operation as hypothesised by Gilbert more than 50 years ago are now validated as being applicable to oscillatory transcript, metabolite and enzyme levels, cellular differentiation, senescence, cancerous states and cell death. Now, we reiterate especially for students and young colleagues, that these early achievements were even more exceptional, as his own lifetime's work on modelling was continued with experimental work in parallel with his predictions of the major current enterprises of biological research.

Temporal variation in the expression of the p53 protein in proliferating and differentiating murine erythroleukaemia cells

Temporal changes in the expression of p53 were investigated during hexamethylene bisacetamide (HMBA)-induced differentiation of murine erythroleukaemic (MEL) cells. Cell preparations were analysed by SDS-PAGE and western immunoblotting, which detected an immunospecific band of molecular mass 53 kDa. This analysis provided semi-quantitative information. Cell extracts were analysed further by means of ELISA techniques, using a p53-specific antibody, to provide quantitative data. In time series experiments in which cells were isolated at 15, 30 and 60 min intervals, dynamic variations in the expression of the p53 protein were detected in both the untreated and the HMBA-treated MEL cells. In all cases, the effects were complex with variations in amplitude, frequency and phasing of the rhythms. The available evidence suggests that the observed patterns, like periodic variations in other systems, are modified in rhythmic fashion with respect to period and amplitude. The results add further support for our view that it is essential to consider the dynamics when interpreting the role of p53 and cellular processes in general.

Direct cell-cell communication: a new approach derived from recent data on the nature and self-organisation of ultradian (circahoralian) intracellular rhythms

Recent data concerning ultradian (circahoralian) intracellular rhythms are used to assess the biochemical mechanisms of direct cell-cell communication. New results and theoretical considerations suggest a fractal nature of ultradian rhythms and their self-organisation. The fundamental and innate nature of these rhythms relates to their self-similarity at different levels of cell and tissue organisation. They can be detected in cell-free systems as well as in cells and organs in vivo. Such rhythms are a means of finding an optimal state of cell function rather than achieving a state of absolute stability. As a consequence, oscillations, being irregular and numerous by the set of periods, are resilient to functional overload and injury. Recent data on the maintenance of their fractal structure and, especially on the selection of optimal periods are discussed. The positive role of chaotic dynamics is stressed. The ultradian rhythm of protein synthesis in hepatocytes in vitro was used as a marker of direct cell-cell communication. The system demonstrates cell cooperation and synchronisation throughout the cell population, and suggests that the ultradian rhythms are self-organised. These observations also led to the detection of mechanisms of direct cell-cell communication in which extracellular factors have an essential role. Experimental evidence indicated the involvement of gangliosides and/or catecholamines in this large-scale synchronisation of protein synthesis. The response of all, or a major part, of the cell population is important; after the initial trigger effect, a periodic pattern is retained for some time. The influence of Ca2+-dependent protein kinases on protein phosphorylation can be a final step in the phase modulation of rhythms during cell-cell synchronisation. The intercellular medium plays an important role in self-synchronisation of ultradian rhythms between individual cells. Low cooperative activity of hepatocytes of old rats resulted from altered composition of the intercellular medium rather than direct effects of animal and cellular ageing. Similarly, in the whole body, changes in levels of gangliosides and catecholamines in the blood serum, a natural intercellular medium, can be critical events in age-dependent changes of the serum and accordingly cell-cell synchronisation. Hepatocytes of old rats exhibit some of the properties of young cells following an increase in blood serum ganglioside level, as well as, in in vitro conditions, after the addition of gangliosides to the culture medium. Together with data on ultradian functional and metabolic rhythms, all the material reviewed here allows us to propose a mechanism of direct cell-cell cooperation via the medium in which the cells exist, that supplements the nervous and hormonal central regulation of organ functions. Ultradian intracellular rhythms may thus provide a finer framework within which the integrated dynamics of respiration, heart rate, brain activity, and even behavioural patterns, are brought to an optimal functional pattern. Innate and direct cell-cell cooperation may have been employed as a means of intercellular regulation during the course of metazoan evolution, that preceded nervous regulation and is presently retained in mammals.

Temporal variations in protein tyrosine kinase activity in leukaemic cells: response to all-trans retinoic acid

Protein tyrosine kinases (PTKs) play a critical role in the modulation of a wide variety of cellular events such as cell division, differentiation and metabolism. Regulation of PTK activity must be tightly controlled as over-stimulation is known to impair normal cell growth, resulting in oncogenic transformation. Since evidence suggests that dynamic oscillatory behaviour occurs in metabolic control processes, we investigated the patterns of oscillatory behaviour in the total protein content and enzyme activity of PTK exhibited by proliferating and differentiating human acute promyelocytic cells. Distinct rhythmic patterns of oscillatory behaviour were observed in both the amount of extractable protein and PTK enzyme activity. Rhythmic characteristics such as period and amplitude were significantly modulated following treatment with all-trans retinoic acid, an inducing agent. These results support the view that dynamic oscillatory control processes may play an important role in regulating cellular behaviour.

Ageing, oscillations and efficiency

The phenomenon of ageing still defies understanding. Theoretical studies have indicated that glycolysis is more efficient at maintaining a high ATP/ADP ratio when oscillating at its resonant frequency. Earlier, it was proposed that the differentiated state results from the establishment of a stable pattern of temporal organisation. It is now suggested that ageing involves a decrease in efficiency due to the detuning of oscillating glycolysis as a result of frequency locking with other cellular oscillations in the differentiated state.

Oscillatory variations in the amount of protein extractable from murine erythroleukemia cells: stimulation by insulin

The amount of protein extractable from murine erythroleukemia (MEL) cells varies in an oscillatory manner at high frequency and high amplitude as it does for several other cell lines. Moreover, the rhythm appears to be modulated in periodic fashion with respect to the mean, period and amplitude. The phenomenon thus seems to be universal and fundamental. Time series analyses support the view that several periodicities contribute to the observed protein rhythm. Insulin affects the dynamics as it does for both morphological and phosphorylation oscillations. Caution is necessary in the interpretation of 'specific activities' of cellular components and in electrophoretic studies wherein equal amounts of protein are applied to the wells in an effort to correct for random errors.