Cox-2 promotes chromogranin A expression and bioactivity: evidence for a prostaglandin E2-dependent mechanism and the involvement of a proximal cyclic adenosine 5'-monophosphate-responsive element

Mice overexpressing chromogranin A display hypergranulogenic adrenal glands with attenuated ATP levels contributing to the hypertensive phenotype

OBJECTIVE

Elevated circulating chromogranin A (CHGA) is observed in human hypertension. CHGA is critical for granulogenesis and exocytosis of catecholamine stores from secretory large dense core vesicles (LDCV). This study aims to understand the morphological, molecular and phenotypic changes because of excess CHGA and the mechanistic link eventuating in hyper-adrenergic hypertension.

METHODS

Blood pressure and heart rate was monitored in mouse models expressing normal and elevated level of CHGA by telemetry. Catecholamine and oxidative stress radicals were measured. Adrenal ultrastructure, LDCV content and mitochondrial abundance were compared and respiration analyzed by Seahorse assay. Effect of CHGA dosage on adrenal ATP content, electron transport chain components and uncoupling protein 2 (UCP-2) were compared in vivo and in vitro.

RESULTS

Mice with excess-CHGA displayed hypertensive phenotype, higher heart rate and increased sympathetic tone. They had elevated plasma catecholamine and adrenal ROS levels. Excess-CHGA caused an increase in size and abundance of LDCV and adrenal mitochondria. Nonetheless, they had attenuated levels of ATP. Isolated adrenal mitochondria from mice with elevated CHGA showed higher maximal respiration rates in the presence of protonophore, which uncouples oxidative phosphorylation. Elevated CHGA resulted in overexpression of UCP2 and diminished ATP. In vitro in chromaffin cells overexpressing CHGA, concomitant increase in UCP2 protein and decreased ATP was detected.

CONCLUSION

Elevated CHGA expression resulted in underlying bioenergetic dysfunction in ATP production despite higher mitochondrial mass. The outcome was unregulated negative feedback of LDCV exocytosis and secretion, resulting in elevated levels of circulating catecholamine and consequently the hypertensive phenotype.

Pasireotide in the treatment of neuroendocrine tumors: a review of the literature

Somatostatin analogs have an important role in the medical therapy of neuroendocrine tumors (NETs). Octreotide and lanreotide, both somatostatin analogs binding with high affinity for the somatostatin receptor (SSTR)2, can control symptoms in functional NETs. In addition, these compounds, because of their antiproliferative effects, can stabilize growth of well-differentiated NETs. Pasireotide is a novel multireceptor-targeted somatostatin analog with high affinity for SSTR1, 2, 3, and 5. This review provides an overview of the state of the art of pasireotide in the treatment of NETs, with the aim of addressing clinical relevance and future perspectives for this molecule in the management of NETs.

The role of cell lines in the study of neuroendocrine tumors

Cell lines originating from neuroendocrine tumors (NETs) represent useful experimental models to assess the control of synthesis and release of different hormones and hormone-like peptides, to evaluate the mechanisms of action of these agents in target tissues at the cellular and subcellular levels, and to study cell proliferation and tumor development, as well as the effect of different drugs on these complex processes. To date, the understanding of NET biology (with regard to their mechanisms of hormone secretion, cell proliferation and metastatic spread) has been hampered by the lack of appropriate animal models or cell lines for their study. In the present review, we aim to summarize the recent in vitro/in vivo data regarding cell lines derived from NETs which are most frequently employed in experimental neuroendocrinology.

Apo J/clusterin expression and secretion: evidence for 15-deoxy-Δ(12,14)-PGJ(2)-dependent mechanism

Cyclooxygenase-2 (Cox-2) and Apo J/clusterin are involved in inflammatory resolution and have each been reported to inhibit NF-κB signalling. Using a well-validated rat pheochromocytoma (PC12) cell culture model of Cox-2 over-expression the current study investigated inter-dependence between Cox-2 and clusterin with respect to induction of expression and impact on NF-κB signalling. Both gene expression and immunoblot analysis confirmed that intracellular and secreted levels of clusterin were elevated in Cox-2 over-expressing cells (PCXII). Clusterin expression was increased in control (PCMT) cells in a time- and dose-dependent manner by 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), but not PGE(2), and inhibited in PCXII cells by pharmacological Cox inhibition. In PCXII cells, inhibition of two transcription factors known to be activated by 15d-PGJ(2), heat shock factor 1 (HSF-1) and peroxisome proliferator activated receptor (PPAR)γ, by transcription factor oligonucleotide decoy and antagonist (GW9662) treatment, respectively, reduced clusterin expression. While PCXII cells exhibited reduced TNF-α-induced cell surface ICAM-1 expression, IkB phosphorylation and degradation were similar to control cells. With respect to the impact of Cox-2-dependent clusterin upregulation on NF-κB signalling, basal levels of IκB were similar in control and PCXII cells, and no evidence for a physical association between clusterin and phospho-IκB was obtained. Moreover, while PCXII cells exhibited reduced NF-κB transcriptional activity, this was not restored by clusterin knock-down. These results indicate that Cox-2 induces clusterin in a 15d-PGJ(2)-dependent manner, and via activation of HSF-1 and PPARγ. However, the results do not support a model whereby Cox-2/15d-PGJ(2)-dependent inhibition of NF-κB signalling involves clusterin.