Theoretical analysis of a morphine withdrawal phenotype in a cultured cell line

Differential effects of opioid and adrenergic agonists on proliferation in a cultured cell line

A novel clonal cell line transfected with the delta-opioid receptor (delta-OR) encoding gene was used to study agonist-activated regulation of cell proliferation. In this cell line, endogenous beta2-adrenergic receptors (beta2-ARs) are coexpressed with the exogenous delta-ORs. Upon individual acute treatments with morphine and procaterol (a selective beta2-AR agonist), both the delta-OR and beta2-AR are coupled to differential modulation of cyclic AMP (cAMP) levels in accord with the classical second messenger response patterns to these agonists in the normal cellular settings of the receptors. But chronic morphine activation of the delta-OR inhibits cellular proliferation, while chronic procaterol activation of the beta2-AR stimulates it. Chronic treatment with the individual agonists is accompanied by differential activation of the mitogen-activated protein kinase (MAPK) isozymes, extracellular-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). The findings suggest that chronic beta2-AR activation stimulates proliferation by interacting with the ERK signalling cascade independent of a cAMP-mediated pathway. In contrast to treatment with individual agonists, chronic dual agonist treatment suppresses procaterol-induced stimulation of ERK activity and stimulation of proliferation indicating that a cross-regulatory interaction occurs between the delta-OR and beta2-AR signalling systems in the cells under these conditions.

The effects of morphine on cell proliferation

There is increasing evidence that endogenous opioid peptides ("enkephalins") and other neurotransmitters have widespread, receptor-mediated roles as growth regulators in non-neuronal cells and tissues. For example, it is now believed that enkephalins produced in placental trophoblast giant cells have multiple roles in supporting embryo growth, and in maternal adaptation to pregnancy. Since plant and synthetic narcotics (e.g., morphine) bind to the same receptors, the questions immediately arise: Do narcotics also have actions as growth regulators? If so, do these actions have physiological significance in addicts? Recent work on the first of these questions is covered in this review. While the greatest volume of research has been focused on the proliferative effects of narcotics for cells of the immune system, the roles of opioid peptides and narcotics on the growth of a variety of other cells has come under study recently.

Opioid agonists modify breast cancer cell proliferation by blocking cells to the G2/M phase of the cycle: involvement of cytoskeletal elements

Opioids decrease cell proliferation in different systems including breast, prostate, lung, kidney, and intestine, through an interaction with opioid as well as other membrane-receptor systems (somatostatin, cholinergic), through an unidentified mechanism. Recently, we have reported an interaction of taxol with opioid membrane sites (BBRC 235, 201-204, 1997), and an involvement of opioids to the modification of actin cytoskeleton in renal OK cells (J Cell Biochem. [19981 70:60-69), indicating a possible action of the opioid effect. In the present work, we have examined the effect of two general opioid agonists (ethylketocyclazocine and etorphine) on the cell cycle, in human breast cancer T47D cells, as well as a possible modification of the cellular cytoskeleton under their action, in order to explain the antiproliferative effect of these agents. These two opioids produce a dose-dependent and reversible decrease of the proliferation of T47D cells, with a maximum attained at 10(-8) M. The addition of 10(-8) M of either opioid produced a significant increase of the number of cells arrested in the G2/M phase. Confocal laser microscopy revealed a modification of the actin and tubulin microfilaments, with a clear redistribution at the periphery of the cell, reversed by the addition of the general opioid antagonist diprenorphine. Furthermore, differences between the two opioids were obvious, attributed to the different receptor affinity of each agent. The observed redistribution of actin and tubulin cytoskeletal elements gives therefore a possible answer of the antiproliferative action of opioids. The modification of the cytoskeleton, directly involved to cell division, might provoke a "mechanical" obstacle, which could be the reason of the antiproliferative effect of these agonists. Furthermore, the observed tubulin-opioid interaction by opioids provides a possible explanation of the arrest at the G2/M phase of T47D cells under opioid treatment. Nevertheless, although the observed interaction of opioids with cytoskeletal elements gives a plausible answer of the antiproliferative effects of the agents, this might not be the only action of these agents in cell proliferation. Other, direct or indirect, genomic actions, which which remains to be elucidated, might be taken into consideration.

Endogenous opiates: 1997

This paper is the twentieth installment of our annual review of research concerning the opiate system. It summarizes papers published during 1997 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.