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.
The prostanoid biosynthetic enzyme cyclooxygenase-2 (Cox-2) is up-regulated in several neuroendocrine tumors. The aim of the current study was to employ a neuroendocrine cell (PC12) model of Cox-2 overexpression to identify gene products that might be implicated in the oncogenic and/or inflammatory actions of this enzyme in the setting of neuroendocrine neoplasia. Expression array and real-time PCR analysis demonstrated that levels of the neuroendocrine marker chromogranin A (CGA) were 2- and 3.2-fold higher, respectively, in Cox-2 overexpressing cells (PCXII) vs. their control (PCMT) counterparts. Immunocytochemical and immunoblotting analyses confirmed that both intracellular and secreted levels of CGA were elevated in response to Cox-2 induction. Moreover, exogenous addition of prostaglandin E(2) (1 microm) mimicked this effect in PCMT cells, whereas treatment of PCXII cells with the Cox-2 selective inhibitor NS-398 (100 nm) reduced CGA expression levels, thereby confirming the biospecificity of this finding. Levels of neuron-specific enolase were similar in the two cell lines, suggesting that the effect of Cox-2 on CGA expression was specific and not due to a global enhancement of neuroendocrine marker expression/differentiation. Cox-2-dependent CGA up-regulation was associated with significantly increased chromaffin granule number and intracellular and secreted levels of dopamine. CGA promoter-driven reporter gene expression studies provided evidence that prostaglandin E(2)-dependent up-regulation required a proximal cAMP-responsive element (-71 to -64 bp). This study is the first to demonstrate that Cox-2 up-regulates both CGA expression and bioactivity in a neuroendocrine cell line and has major implications for the role of this polypeptide in the pathogenesis of neuroendocrine cancers in which Cox-2 is up-regulated.
Connolly
Roisin
R
Department of Medicine, Queen's University Belfast, Royal Group of Hospitals, Belfast, Northern Ireland, UK.
Gates
Damien
D
Loh
Nellie
N
Baban
Dilair
D
Thakker
Rajesh
R
Johnston
Brian
B
McCance
David
D
Ardill
Joy
J
O'Connor
Daniel T
DT
Taupenot
Laurent
L
McGinty
Ann
A
D000818:Animals; D053379:Chromogranin A / Q000235:genetics* / Q000378:metabolism*; D000242:Cyclic AMP; D051546:Cyclooxygenase 2 / Q000235:genetics*; D015232:Dinoprostone / Q000494:pharmacology* / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020411:Oligonucleotide Array Sequence Analysis; D016716:PC12 Cells; D016133:Polymerase Chain Reaction; D012334:RNA, Neoplasm / Q000235:genetics; D051381:Rats; D014162:Transfection
D053379:Chromogranin A; D012334:RNA, Neoplasm; D000242:Cyclic AMP; D051546:Cyclooxygenase 2; D015232:Dinoprostone