The PC12 rat pheochromocytoma cell line expresses the prodynorphin gene and secretes the 8 kDa dynorphin product

Involvement of the Opioid Peptide Family in Cancer Progression

Peptides mediate cancer progression favoring the mitogenesis, migration, and invasion of tumor cells, promoting metastasis and anti-apoptotic mechanisms, and facilitating angiogenesis/lymphangiogenesis. Tumor cells overexpress peptide receptors, crucial targets for developing specific treatments against cancer cells using peptide receptor antagonists and promoting apoptosis in tumor cells. Opioids exert an antitumoral effect, whereas others promote tumor growth and metastasis. This review updates the findings regarding the involvement of opioid peptides (enkephalins, endorphins, and dynorphins) in cancer development. Anticancer therapeutic strategies targeting the opioid peptidergic system and the main research lines to be developed regarding the topic reviewed are suggested. There is much to investigate about opioid peptides and cancer: basic information is scarce, incomplete, or absent in many tumors. This knowledge is crucial since promising anticancer strategies could be developed alone or in combination therapies with chemotherapy/radiotherapy.

Effect of Ghrelin on catecholamine secretion in rat pheochromocytoma PC12 cells

A novel peptide Ghrelin, found to be a ligand to growth hormone (GH) secretagogue receptor (GHS-R), exeterts to stimulates GH release from pituitary gland. Recently, it has been shown that ghrelin and its receptor are existed in a adrenal ground. At concentrations of 10 nM and over (10 nM, 100 nM, and 1 microM), ghrelin significantly inhibited basal dopamine release by 30, 32 and 34%, respectively (P < 0.05) in PC12 cells, suggesting that ghrelin may be involved in the mechanism of catecholamine regulation in chromaffin cells.

kappa-Opioid inhibits catecholamine biosynthesis in PC12 rat pheochromocytoma cell

It was reported that nicotine-induced dopamine release in the rat pheochromocytoma cell line, PC12 cells, was inhibited by kappa-opioid. However, it is not known whether inhibition of catecholamine biosynthesis is involved in the inhibitory mechanisms of kappa-opioids in PC12 cells. U-69593 (a kappa-opioid agonist: >/=100 nM) significantly inhibited the nicotine-induced increase of tyrosine hydroxylase (TH, a rate-limiting enzyme in biosynthesis of catecholamine) enzyme activity and TH mRNA levels. These inhibitory effects were completely reversed by naloxone and nor-binaltorphimine dihydrochloride (nor-BNI), a specific kappa-antagonist, whereas pertussis toxin (PTX) only partially reversed this inhibitory effect. Also, U-69593 (>/=100 nM) significantly inhibited the nicotine-induced increase of cAMP production. This inhibitory effect was completely reversed by naloxone and nor-BNI, whilst only partially reversed by PTX. Moreover, U-69593 (>/=100 nM) significantly inhibited the nicotine-induced increase of both the TH protein level and intracellular catecholamine levels. These results indicate that the anti-cholinergic actions of kappa-opioid can be explained partially by its inhibition of both TH enzyme activity and TH synthesis, through suppression of the cAMP/protein kinase A pathway. It would also appear that the PTX-sensitive G-protein mediates the inhibitory effect of this pathway, at least in part.

Opioids transiently prevent activation of apoptotic mechanisms following short periods of serum withdrawal

Opioids exert a proapoptotic effect on several normal and tumoral cells. The aim of the present article was to examine the effect of opioids on the PC12 rat pheochromocytoma cell line, a model for the study of chromaffin cell apoptosis. These cells produce delta- and kappa-opioid agonists and their receptors. Our results were as follows: The kappa- and delta2-opioid receptor agonists had a rapid but transient effect on apoptosis at 3 h, whereas mu opioids did not. The effect of opioids was reversible by the opioid antagonists naloxone and nor-binaltorphimine. The effect of opioids was protective, suppressing serum deprivation-induced apoptosis to approximately 50% of controls. The protective effect of opioids on PC12 apoptosis was measurable only under serum deprivation. The effect of opioids was remarkably reproducible and highly constant in timing, which did not appear to depend on the duration of the preceding serum deprivation. Finally, opioids prevented the elevation of the Bcl-2 and Bak proteins following serum deprivation to the levels attained by serum supplementation. Our combined data suggest that opioids protect PC12 cells from entering a state of induced apoptosis following serum deprivation.

Kappa1-opioid binding sites are the dominant opioid binding sites in surgical specimens of human pheochromocytomas and in a human pheochromocytoma (KAT45) cell line

The adrenal medulla produces opioids which exert paracrine effects on adrenal cortical and chromaffin cells and on adrenal splanchnic nerves, via specific binding sites. The opioid binding sites in the adrenals are detectable mainly in the medullary part of it and differ in type between species. Thus, the bovine adrenal medulla contains mostly kappa-opioid binding sites and fewer delta- and mu-opioid binding sites while primate adrenals contain mainly delta sites and few kappa-opioid binding sites. Most chromaffin cell tumors, the pheochromocytomas, produce opioids which suppress catecholamine production by the tumor. The aim of the present work was to identify the types of opioid binding sites in human pheochromocytomas. For this purpose, we characterized the opioid binding sites on crude membrane fractions prepared from 14 surgically excised pheohromocytomas and on whole KAT45 cells, a recently characterized human pheochromocytoma cell line. Our data showed that human pheohromocytomas are heterogeneous, as expected, with regard to the production of catecholamines and the distribution and profile of their opioid binding sites. Indeed, only one out of the 14 pheochromocytomas expressed exclusively delta and mu opioid sites, while in the remaining 13 tumors kappa-type binding sites were dominant. The KAT45 cell line possessed a significant number of kappa1 binding sites, fewer kappa2-opioid binding sites and kappa3-opioid binding sites, and minimal binding capacity for delta- and mu-opioid receptor agonists sites. More specifically, the kappa1 sites/cell were approximately 18,000, the kappa2 4500/cell and the kappa3 sites 2000/cell. Our findings for the surgical specimens and the cell line combined with previously published pharmacological data obtained from KAT45 cells suggest that kappa sites appear to be the most prevalent opioid binding sites in pheochromocytomas. Finally, in normal bovine adrenals the profile of opioid binding sites differs in adrenaline and noradrenaline producing chromaffin cells. To test the hypothesis that the type of catecholamine produced by a pheochromocytoma depends on its cell of origin, we compared our binding data with the catecholamine content of each pheochromocytoma examined. We found no correlation between the type of the predominant catecholamine produced and the opioid binding profile of each tumor suggesting that this hypothesis may not be valid.

Simulated microgravity conditions enhance differentiation of cultured PC12 cells towards the neuroendocrine phenotype

We are studying microenvironmental cues which contribute to neuroendocrine organ assembly and tissue-specific differentiation. As our in vitro model, we cultured rat adrenal medullary PC12 pheochromocytoma cells in a novel cell culture system, the NASA rotating wall vessel (RWV) bioreactors. This "simulated microgravity" environment in RWV bioreactors, characterized by randomizing gravitational vectors and minimizing shear stress, has been shown to favor macroscopic tissue assembly and to induce tissue-specific differentiation. We hypothesized that the unique culture conditions in the RWV bioreactors might enhance the in vitro formation of neuroendocrine organoids. To test our hypothesis, we evaluated the expression of several markers of neuroendocrine differentiation in cultures of PC12 cells maintained for up to 20 d in the slow turning lateral vessel (STLV) type RWV. PC12 cell differentiation was assessed by morphological, immunological, biochemical and molecular techniques. PC12 cells, cultured under "simulated microgravity" conditions, formed macroscopic, tissue-like organoids several millimeters in diameter. Concomitantly, the expression of phenylethanolamine-N-methyl transferase (PNMT), but not of other catecholamine synthesizing enzymes, was enhanced. Increased PNMT expression, as verified on both the gene and protein level, was accompanied by an increase in the specific activity of the enzyme. Furthermore, after 20 d in culture in the STLV, we observed altered patterns of protein tyrosine phosphorylation and prolonged activation of c-fos, a member of the AP-1 nuclear transcription factor complex. We conclude that culture conditions in the RWV appear to selectively activate signal transduction pathways leading to enhanced neuroendocrine differentiation of PC12 cells.

Kappa opioids exert a strong antiproliferative effect on PC12 rat pheochromocytoma cells

Pheochromocytomas synthesize several types of opioids and their receptors. Opioids affect the proliferation rate of normal and tumoral cells. We have previously shown that the PC12 rat pheochromocytoma cells synthesize multiple opioids. The aim of the present work was to study the effect of opioids on the proliferation of these pheochromocytoma cells. Thus, the effect of several opioid agonists and antagonists was examined on basal and EGF-induced PC12 cell proliferation. The kappa opioid agonists dynorphin A, U-69593, and U-50488 suppressed basal proliferation in a dose-dependent manner. The effect of kappa opioids was blocked by the general opioid antagonist naloxone and the selective kappa antagonist nor-binaltorphimine. Furthermore, both opioid antagonists given alone had a strong stimulatory effect, a findings suggesting that the proliferation of PC12 cells is under tonic inhibition by locally produced kappa opioids. Finally, the mu-opioid agonist DAGO and the delta and mu agonists DADLE and DSLET were ineffective.