The effects of corticotrophin (ACTH1-24), cyclic AMP and TPA (12-O-tetradecanoyl phorbol-13-acetate) on DNA replication and proliferation of primary rabbit adrenocortical cells in a synthetic medium

Pioglitazone, an anti-diabetic drug requires sustained MAPK activation for its anti-tumor activity in MCF7 breast cancer cells, independent of PPAR-γ pathway

BACKGROUND

The thiazolidinedione (TZD) class of peroxisome proliferator-activated receptor gamma (PPAR-γ) ligands are known for their ability to induce adipocyte differentiation, to increase insulin sensitivity including anticancer properties. But, whether or not upstream events like MAPK activation or PPAR-γ signaling are involved or associated with this anticancer activity is not well understood in breast cancer cells. The role of MAPK and PPAR pathways during the pioglitazone (Pio) induced PPAR-γ independent anticancer activity in MCF7 cells has been focused here.

METHODS

The anticancer activity of Pio has been investigated in breast cancer cells in vitro. Anti-tumor effects were assessed by alamar blue assay, Western blot analysis, cell cycle analysis, and annexin V-FITC/PI binding assay by flow cytometry, Hoechst staining and luciferase assay.

RESULTS

The anticancer activity of Pio is found to be correlating with the up regulation of CDKIs (p21/p27) and down regulation of CDK-4. This study demonstrates that the induction of CDKIs by Pio is due to the sustained activation of MAPK. The Pio-mediated activation of MAPK is transmitted to activate ELK-1 and the related anti-proliferation is blocked by MEK inhibitor (PD-184352).

CONCLUSIONS

Pio suppresses the proliferation of MCF7 cells, at least partly by a PPAR-γ-independent mechanism involving the induction of p21 which in turn requires sustained activation of MAPK. These findings implicate the utility of Pio in the treatment of PPAR positive or negative human cancers and the development of a new class of compounds to enhance the effectiveness of Pio.

ACTH 1-24 inhibits proliferation of adrenocortical tumors in vivo

OBJECTIVES

Although several lines of evidence suggest that the overall effects of the ACTH receptor, melanocortin 2 receptor (MC2-R), mediated signal transduction on adrenocortical growth and tumorigenesis are anti-proliferative, activation of MC2-R induces mitogens like jun, fos, and myc and activates the MAPK pathway. In vivo, potential effects of endogenous ACTH on adrenal tumori-genesis can not be separated from effects of other POMC derived peptides.

METHODS

Murine adrenocortical tumor cells that lack MC2-R expression (Y6(pcDNA)) and Y6 cells stablely transfected with MC2-R (Y6(MC2-R)) were generated. Presence of functional MC2-R was demonstrated by RT-PCR and Western blot using an antibody for phosphorylated CREB. As a syngenic tumor model, LaHeF1/J mice simultaneously received 10(7) Y6(MC2-R) and Y6(pcDNA) subcutaneously, giving rise to MC2-R positive and negative tumors within the same animal. Animals were treated for 3 weeks in groups of 12 according to the following schedule: group A, control animals receiving saline injection; group B, animals receiving 5.7 ng/injection of a slow release formula of ACTH 1-24 administered i.p. three times a week (aiming at a low physiologic dose); and group C, animals receiving 57 ng/injection of ACTH 1-24 (high physiological dose).

RESULTS

Twenty days of ACTH 1-24 treatment did not significantly affect corticosterone levels, endogenous ACTH levels or adrenal and thymus weight compared with saline injection. However, ACTH 1-24 treatment of group B and C mice significantly reduced tumor weight in MC2-R positive tumors in a dose dependent manner (P = 0.03), while no significant difference in tumor mass was observed in MC2-R negative tumors. PCNA and TUNEL staining, together with morphological characterization, demonstrated that these in vivo effects were due to reduced proliferation, while apoptosis and cellular hypertrophy within the tumor remained unchanged.

CONCLUSION

MC2-R expression is associated with a less aggressive adrenal tumor phenotype and anti-proliferative effects can be amplified through stimulation with physiological doses of ACTH.

Adrenocortical zonation and ACTH

The clear morphological distinction between the cells of the different adrenocortical zones has attracted speculation and experiment to interpret their functions and the ways in which they are regulated. Considerable data have been produced in recent years that has benefited a fuller understanding of the processes of steroidogenesis and of cell proliferation at the molecular level. This now enables the reexamination of earlier concepts. It is evident that there is considerable species variation, and this article, dealing mainly with the rat, reaches conclusions that do not necessarily apply to other mammals. In the rat adrenal, however, the evidence suggests that the greatest differences between the functions of the zones are between the glomerulosa and the fasciculata. Here the sometimes all-or-nothing demarcation in their complement of components associated with steroidogenesis or with cell proliferation suggests a stark division of labor. In this model the fasciculata is the main engine of steroid hormone output and the glomerulosa is the site of cell proliferation, recruitment, and differentiation. Regulating these functions are angiotensin II and other paracrine components that modulate and maintain the glomerulosa, and ACTH, that maintains the fasciculata, and recruits new fasciculata cells by transformation of proliferating glomerulosa cells. Grafted onto this mostly vegetative function of the glomerulosa is CYP11B2, limited to just a fraction of the outer glomerulosa in rats on a normal laboratory diet and generating aldosterone (and 18-hydroxycorticosterone) from precursors whose origin is not, from the evidence summarized here, very clear, but may include the fasciculata, directly or indirectly. The biosynthesis of aldosterone in the rat certainly requires reinterpretation.

Rat glomerulosa cells in primary culture and E. coli lipopolysaccharide action

During endotoxic shock there is a dysfunction of the adrenal gland; both corticosterone and aldosterone secretion are altered. The aim of the present study is to use glomerulosa cells in primary culture as a target of lipopolysaccharide (LPS) action. Glomerulosa cells cultured in basal conditions are able to proliferate; bFGF and ACTH have antagonic effects, bFGF increases proliferation whereas ACTH is antimitogenic. LPS has a biphasic effect, in the short term it is antimitogenic and in the long term increases the proliferation rate. LPS inhibits ACTH-induced corticosterone secretion in a dose-dependent manner in glomerulosa cells in culture similar to that in fasciculata cells, but it does not exert an important direct effect on aldosterone secretion. These results show that LPS exerts different effects in ACTH and ANG II signal transduction pathways and in the two enzymes which catalyze the late step in the steroidogenesis, 11beta-hydroxylase and aldosterone synthase, which could be in agreement with the existence of both enzymes, regulated independently, in rat zona glomerulosa cells.

Proliferation of capsular stem cells induced by ACTH in the rat adrenal cortex

Despite great efforts devoted to clarifying the localization of proliferative activity in the adrenal cortex, the agents that stimulate proliferation remain controversial, and the nature of the stem cells from which cortical cells differentiate is incompletely understood. We studied proliferative activity in the rat adrenal cortex using an immunohistochemical method to detect the presence of the Proliferating Cell Nuclear Antigen (PCNA) (an intranuclear enzyme whose synthesis reaches the maximum intensity during the S-phase of the cell cycle). Groups of six rats were subjected to daily intraperitoneal injection of either corticotropin (ACTH1-24--0.2 mg/kg), dexamethasone (Dexa--4 mg/kg) or 0.9% saline for three consecutive days and killed 24 h after the last injection. Adrenal weight was significantly increased by ACTH treatment and reduced by Dexa. Concentrations of endogenous ACTH in plasma were lower in the Dexa group than in controls, and curiously, this was true in the ACTH1-24 treated group as well, probably in consequence of the increased corticosterone levels providing negative feedback at the hypothalamic-pituitary level. Corticosterone levels, as expected, were increased by the ACTH stimulus and reduced by the use of Dexa. Proliferating cell nuclear antigen immunostaining was close to zero in Dexa treated animals and low in controls. In ACTH treated rats, a significantly increased number of cells were positively stained. Positive cells were identified in both in zona glomerulosa (ZG) and zona intermedia (ZI) but many were located in the capsule. Zona fasciculata (ZF) and zona reticularis (ZR) were devoid of staining in all of these cases. We conclude that pharmacological doses of ACTH induce proliferation of capsular fibroblasts. Following descriptions by early 20th century researchers it is possible that these cells may also be stem cells and differentiate into adrenal cortex cells.

Annexin V inhibits the 12-O-tetradecanoylphorbol-13-acetate-induced activation of Ras/extracellular signal-regulated kinase (ERK) signaling pathway upstream of Shc in MCF-7 cells

Annexin V is a Ca2+-dependent phospholipid binding protein. Although it has been shown to inhibit protein kinase C (PKC) in cell-free systems, its role in the intact cell is unclear. A stable MCF-7 human breast cancer cell overexpression system was established to investigate the function of annexin V. In these cells, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced phosphorylation and kinase activity of ERK1/2 were suppressed. Morphological changes induced by TPA were reduced by annexin V overexpression as well as by the pan-PKC inhibitor, bisindolylmaleimide I, and by the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor, PD98059. TPA-induced MEK1/2 and Raf-1 phosphorylation were reduced in these cells. The TPA-enhanced active Ras, and its association with Raf-1, were reduced. TPA treatment of MCF-7 cells caused an increased association of Shc with Grb2. However, this increased association was prevented in the annexin V-overexpressors. p21WAF/CIP1 is responsible for inhibition of cell cycle progression in MCF-7 cells. TPA induced the expression of p21WAF/CIP1 to a greater extent in MCF-7 parent and control plasmid cells than in annexin V overexpressors. PD98059 inhibited this increase, suggesting that TPA upregulation of p21WAF/CIP1 occurs via the MEK pathway, and that annexin V overexpression blunts it. This work shows that annexin V overexpression suppresses the TPA-induced Ras/ERK signaling by inhibiting at/or upstream of Shc, possibly through the inhibition of PKCs. Oncogene (2000).

Mitogenic signaling of insulin-like growth factor I in MCF-7 human breast cancer cells requires phosphatidylinositol 3-kinase and is independent of mitogen-activated protein kinase

Addition of insulin-like growth factor I (IGF-I) to quiescent breast tumor-derived MCF-7 cells causes stimulation of cyclin D1 synthesis, hyperphosphorylation of the retinoblastoma protein pRb, DNA synthesis, and cell division. All of these effects are independent of the mitogen-activated protein kinase (MAPK) pathway since none of them is blocked by PD098059, the specific inhibitor of the MAPK activating kinase MEK1. This observation is consistent with the finding that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a strong inducer of MAPK activity in MCF-7 cells, effectively inhibits proliferation. The anti-proliferative effect of TPA in these cells may be accounted for, at least in part, by the MAPK-dependent stimulation of the synthesis of p21(WAF1/CIP1), an inhibitor of cyclin/cyclin-dependent kinase complexes. In contrast, all of the observed stimulatory effects of IGF-I on cell cycle progression, cyclin D1 synthesis, and pRb hyperphosphorylation were blocked by the specific phosphatidylinositol 3-kinase inhibitor LY294002, suggesting that phosphatidylinositol 3-kinase activity but not MAPK activity is required for transduction of the mitogenic IGF-I signal in MCF-7 cells.

Peptide growth factors and the adrenal cortex

Increasing evidence suggests that the actions of classical stimulants of adrenocortical growth and function, such as ACTH or dietary sodium restriction, may partially be mediated via locally produced regulators. Several peptide growth factors, such as basic fibroblast growth factor, insulin-like growth factors, and transforming growth factor-beta 1, have emerged in recent years as multifunctional molecules that typically play such regulatory roles. Adrenocortical cells are highly responsive to these growth factors, in particular in the regulation of cell growth and differentiated functions, such as steroidogenesis. In addition, growth factor expression in the adrenal cortex has been shown to be regulated by physiological stimulants. The spatial expression, release, and activation of these growth factors may, therefore, locally mediate or amplify the actions of the hypothalamo-pituitary axis and the renin-angiotensin system on adrenocortical proliferation, differentiation, and steroidogenesis.

Mitochondrial-genome-encoded RNAs: differential regulation by corticotropin in bovine adrenocortical cells

Differential screening of an adrenal cortex cDNA library for corticotropin (ACTH)-inducible genes led to the isolation of a group of cDNAs representing mitochondrial genes that encode subunits of cytochrome oxidase, ATPase, and NADH dehydrogenase. Northern blot analysis of RNA from cells stimulated by ACTH confirmed the induction of these genes by ACTH yet revealed major differences in the relative responses of the respective mRNAs. The levels of mRNAs for cytochrome oxidase subunit I and ATPase increased 2- to 4-fold and for NADH dehydrogenase subunit 3 increased 20-fold, whereas the levels of the mitochondrial 16S rRNA showed no change within 6 h of ACTH stimulation. These effects of ACTH on mitochondrial mRNA levels probably result from both activation of the H2 transcription unit that encodes mitochondrial mRNAs and alteration of mRNA stability. ACTH also increased the activity of cytochrome oxidase after 12 h of stimulation. Examination of the tissue specificity of expression of five mitochondrial genes showed a wide range of RNA levels among 11 tissues but high correlations between individual RNA levels, consistent with a coordinated expression of the mitochondrial genes, although at different levels in each cell type. Proportionately high levels of mitochondrial mRNAs were found in adrenal cortex, probably reflecting a stimulatory effect of ACTH in vivo. Overall, the results indicate that ACTH enhances the energy-producing capacity of adrenocortical cells.

Basic fibroblast growth factor expression is regulated by corticotropin in the human fetal adrenal: a model for adrenal growth regulation

Human fetal adrenal growth after midgestation is very rapid and appears to be dependent upon pituitary adrenocorticotropin (ACTH) in vivo. We hypothesized that the regulation of fetal adrenal growth by ACTH is mediated by ACTH-stimulated local growth factor production. As we have found basic fibroblast growth factor (bFGF) to be a potent mitogen for human fetal adrenal cells in culture, we conducted studies to determine whether bFGF is synthesized by the human fetal adrenal gland and whether bFGF gene expression in primary cultures of human fetal adrenal cells is regulated by ACTH. Bioassayable bFGF-like activity was detected in extracts of whole human fetal adrenal glands and primary cultures of human fetal adrenal cells. Northern blot analysis of total RNA from whole human fetal adrenal glands revealed a characteristic 7-kilobase bFGF mRNA, indicating that the fetal adrenal bFGF bioactivity was most likely due to local synthesis. Slot blot and ribonuclease protection analysis showed that bFGF mRNA was present in very low amounts in total RNA from primary cultures of unstimulated human fetal adrenal cells but was increased 2- to 3-fold in cells exposed to 10 nM ACTH-(1-24) or 1 mM 8-bromoadenosine 3',5'-cyclic monophosphate for 24 hr. bFGF mRNA was localized to adrenocortical cells and not fibroblasts by in situ hybridization. bFGF mRNA was barely detectable in unstimulated cells, whereas it was markedly increased in cells exposed to either ACTH or 8-bromoadenosine 3',5'-cyclic monophosphate. These data support our hypothesis that the regulation of human fetal adrenal growth by ACTH at midgestation may be mediated by the stimulation of local growth factor production, and we suggest that bFGF may play a major role in this process.

Role of cyclic AMP in proliferation of lung tissue in organ culture

The role of cyclic AMP in cell proliferation and division has been the subject of study by a number of investigators in the past 30 years, but the argument of whether cyclic AMP is a negative or a positive regulator has not been settled. We studied the effect of cyclic AMP on proliferation of normal and postpneumonectomized lung tissues in young adult rats by measuring the incorporation of tritiated thymidine into lung DNA in organ culture. In normal lung tissues the incorporation of [3H]thymidine was increased by exogenous dibutyryl cyclic AMP, or by isoproterenol or forskolin to stimulate adenylate cyclase, or by caffeine, which inhibits cAMP phosphodiesterase. The effect of isoproterenol, but not forskolin, was abolished by the beta-adrenergic blocking agent propranolol. The effect of caffeine on [3H]thymidine incorporation was further enhanced in normal lung tissues in the presence of dibutyryl cyclic AMP and in postpneumonectomized lung tissues. Imidazole, a cAMP phosphodiesterase stimulator, also increased [3H]thymidine incorporation in culture, but the effect was not magnified in the presence of exogenous dibutyryl cyclic AMP, nor in postpneumonectomized lung tissues. The data suggest that cyclic AMP acts as a positive regulator in proliferation of lung tissues.

Adrenocorticotropin is a specific mitogen for mammalian myogenic cells

Peptides derived from proopiomelanocortin (POMC) have been found to stimulate the proliferation of murine myogenic cells. Among these peptides, adrenocorticotropin (ACTH) and alpha-, beta-, and gamma-melanocyte-stimulating hormones (MSH) were found to be active, whereas the opioid peptides were not. At clonal density, both ACTH and MSH caused a three- to fourfold increase in the average number of cells per clone in myogenic but not in fibroblast colonies. At high cell density, ACTH and MSH caused a three- to fourfold increase in proliferation of myogenic cells, reflected by an increased accumulation of skeletal myosin. On the other hand mouse embryo skin or muscle fibroblasts or vertebral chondroblasts did not increase proliferation in response to POMC-derived peptides. The half-maximal dose at which ACTH stimulated myoblast proliferation was around 5 nM, and the mitogenic effect was doubled by suboptimal doses of fibroblast growth factor. The possible physiological significance of the mitogenic effect of ACTH on myogenic cells is discussed.