Adenovirus-directed expression of Q227L-G alpha(s) inhibits growth of established tumors of later-stage human breast cancer cells in athymic mice

Multidrug resistance in cancer or inefficacy of neuroactive agents: innovative strategies to inhibit or circumvent the active efflux transporters selectively

Multidrug resistance (MDR) is a crucial issue in the treatment of cancer cells that protect themselves by overexpression of active efflux transporters (AETs). AET expression maintains the homeostasis in healthy tissues and in the blood-brain barrier it often prevents drugs from reaching the brain. Inhibition of AETs could therefore be a valuable solution for preventing MDR; but nonselective long-term AET blocking can be harmful toward healthy tissues and, in particular, the brain. This review looks at the development of innovative formulations suitable for selectively blocking or avoiding AETs as promising ways to overcome the challenges of MDR and inefficacy of neuroactive agents.

The role of high cell density in the promotion of neuroendocrine transdifferentiation of prostate cancer cells

Background

Tumor heterogeneity and the plasticity of cancer cells present challenges for effective clinical diagnosis and therapy. Such challenges are epitomized by neuroendocrine transdifferentiation (NED) and the emergence of neuroendocrine-like cancer cells in prostate tumors. This phenomenon frequently arises from androgen-depleted prostate adenocarcinoma and is associated with the development of castration-resistant prostate cancer and poor prognosis.

Results

In this study, we showed that NED was evoked in both androgen receptor (AR)-positive and AR-negative prostate epithelial cell lines by growing the cells to a high density. Androgen depletion and high-density cultivation were both associated with cell cycle arrest and deregulated expression of several cell cycle regulators, such as p27^Kip1, members of the cyclin D protein family, and Cdk2. Dual inhibition of Cdk1 and Cdk2 using pharmacological inhibitor or RNAi led to modulation of the cell cycle and promotion of NED. We further demonstrated that the cyclic adenosine 3′, 5′-monophosphate (cAMP)-mediated pathway is activated in the high-density conditions. Importantly, inhibition of cAMP signaling using a specific inhibitor of adenylate cyclase, MDL-12330A, abolished the promotion of NED by high cell density.

Conclusions

Taken together, our results imply a new relationship between cell cycle attenuation and promotion of NED and suggest high cell density as a trigger for cAMP signaling that can mediate reversible NED in prostate cancer cells.

Leptin potentiates antiproliferative action of cAMP elevation via protein kinase A down-regulation in breast cancer cells

Previously, we have shown that leptin potentiates the antiproliferative action of cAMP elevating agents in breast cancer cells and that the protein kinase A (PKA) inhibitor KT-5720 prevented the antiproliferative effects induced by the leptin plus cAMP elevation. The present experiments were designed to gain a better understanding about the PKA role in the antitumor interaction between leptin and cAMP elevating agents and on the underlying signaling pathways. Here we show that exposure of MDA-MB-231 breast cancer cells to leptin resulted in a strong phosphorylation of both ERK1/2 and STAT3. Interestingly, intracellular cAMP elevation upon forskolin pretreatment completely abrogated both ERK1/2 and STAT3 phosphorylation in response to leptin and was accompanied by a consistent CREB phosphorylation. Notably, leptin plus forskolin cotreatments resulted in a strong decrease of both PKA regulatory RIα and catalytic subunits protein levels. Importantly, pretreatment with the PKA inhibitor KT-5720 blocked the forskolin-induced CREB phosphorylation and prevented both the inhibition by forskolin of leptin-induced ERK1/2 and STAT3 phosphorylation and the PKA subunits down-regulation induced by the combination of leptin and forskolin. Altogether, our results indicate that leptin-dependent signaling pathways are influenced by cAMP elevation and identify PKA as relevantly involved in the pharmacological antitumor interaction between leptin and cAMP elevating drugs in MDA-MB-231 cells. We propose a molecular model by which PKA confers its effects. Potential therapeutic applications by our data will be discussed.

Signalling pathway alterations in pituitary adenomas: involvement of Gsalpha, cAMP and mitogen-activated protein kinases

Despite extensive research on sporadic pituitary adenomas, it is not yet possible to assign one protein alteration to one specific type of pituitary adenomas. Nevertheless, alterations of the cAMP pathway appear to be molecular hallmarks of most growth hormone (GH)-secreting adenomas. However, these alterations do not confer specific phenotypes to patients carrying these alterations. In this review, we summarise the literature regarding signalling alterations observed in GH-secreting adenomas. We focus on Gsalpha alterations and their possible cross-talk with the extracellular signal-related kinase (ERK)1/2 pathway. In the light of results obtained on human somatotroph adenoma cells in primary culture and on models of murine somatotroph cell lines, we postulate a crucial role for ERK1/2 in GH-secreting adenomas downstream of cAMP pathway alterations that might impact the tumoural phenotype.

G protein-coupled receptor 30 down-regulates cofactor expression and interferes with the transcriptional activity of glucocorticoid

G protein-coupled receptor 30 (GPR30) has previously been described to be important in steroid-mediated growth and to inhibit cell proliferation. Here we investigated whether the effect of GPR30 on cell growth is dependent on steroid hormone receptors. We stably introduced GPR30 in immortalized normal mammary epithelial (HME) cells using retroviruses for gene delivery. GPR30 inhibited the growth and proliferation of the cells. They expressed glucocorticoid receptor, but not estrogen or progesterone receptor. GPR30 down-regulated the expression of cofactor transcription intermediary factor 2 (TIF2) analyzed using quantitative RT-PCR analysis, and also diminished the expression of TIF2 at protein level analyzed by Western blotting using nuclear extracts from mammary epithelial cells. When HME cells were transiently transfected with the glucocorticoid response element MMTV-luc reporter plasmid, stable expression of GPR30 resulted in the abolition of ligand-induced transactivation of the promoter. In COS cells, transient transfection of GPR30 with glucocorticoid receptor alpha resulted in an abrogation of the MMTV-luc and GRE-luc reporter activities induced by dexamethasone. The results suggest a novel mechanism by which membrane-initiated signaling interferes with steroid signaling.

Synergy between LRH-1 and beta-catenin induces G1 cyclin-mediated cell proliferation

LRH-1 is an orphan nuclear receptor predominantly expressed in tissues of endodermal origin, where it controls development and cholesterol homeostasis. We show here that LRH-1 induces cell proliferation through the concomitant induction of cyclin D1 and E1, an effect that is potentiated by its interaction with beta-catenin. Whereas beta-catenin coactivates LRH-1 on the cyclin E1 promoter, LRH-1 acts as a potent tissue-restricted coactivator of beta-catenin on the cyclin D1 promoter. The implication of LRH-1 in cell proliferation highlights an unanticipated crosstalk between LRH-1 and the beta-catenin/Tcf4 signaling pathway, which is relevant for the renewal of intestinal crypt cells.

Progestin and G protein-coupled receptor 30 inhibit mitogen-activated protein kinase activity in MCF-7 breast cancer cells

We have previously shown that the G protein-coupled receptor (GPR)30 is critical for progestin-induced growth inhibition. In this study, we addressed signal transduction pathways involved in progestin-mediated signaling. Progestin could not provide any additional growth inhibitory effect to MCF-7 cells treated with specific MAPK kinase inhibitors, PD98059 and U0126. Medroxyprogesteroneacetate (MPA) induced a late (22-23 h) decrease in ERK-1 and -2 activities verified by immunoblotting and kinase assay. The inactivation was abrogated by antiprogestin. Transient expression of GPR30 decreased ERK-1 and -2 activity; and in the cells in which GPR30 expression was decreased by the antisense, ERK activities were increased. The antisense-expressing cells were able to significantly resist the growth-inhibitory effect of the MAPK kinase inhibitors PD98059 and U0126 but not that of other factors tested. Interestingly, the decrease of ERK activity induced by MPA was abrogated by GPR30 antisense. Collectively, these results show that MAPK activity is inhibited by progestin and GPR30 and suggest that progestin-induced ERK inactivation is mediated through GPR30. Coupled with our previous findings, the data imply that up-regulation of GPR30 by progestin leads to ERK-1 and -2 inactivation associated with MPA-induced growth inhibition.