Induction Of Group Ivc Phospholipase A(2) In Allergic Asthma: Transcriptional Regulation By Tnf Alpha In Bronchoepithelial Cells

Airway inflammation in allergen-induced asthma is associated with eicosanoid release. These bioactive lipids exhibit anti-and pro-inflammatory activities with relevance to pulmonary pathophysiology. We hypothesized that sensitization/challenge using an extract from the ubiquitous fungus Aspergillus fumigatus in a mouse model of allergic asthma would result in altered phospholipase gene expression, thus modulating the downstream eicosanoid pathway. We observed the most significant induction in the group IVC PLA(2) (phospholipase A(2)) [also known as cPLA(2)gamma (cytosolic PLA(2)gamma) or PLA2G4C]. Our results infer that A. fumigatus extract can induce cPLA(2)gamma levels directly in eosinophils, whereas induction in lung epithelial cells is most likely to be a consequence of TNF alpha (tumour necrosis factor alpha) secretion by A.fumigatus-activated macrophages. The mechanism of TNF alpha-dependent induction of cPLA(2)gamma gene expression was elucidated through a combination of promoter deletions, ChIP (chromatin immunoprecipitation) and overexpression studies in human bronchoepithelial cells, leading to the identification of functionally relevant CRE (cAMP-response element), NF-kappa B (nuclear factor kappa B) and E-box promoter elements. ChIP analysis demonstrated that RNA polymerase II, ATF-2 (activating transcription factor 2)-c-Jun, p65-p65 and USF (upstream stimulating factor) 1-USF2 complexes are recruited to the cPLA(2)gamma enhancer/promoter in response to TNF alpha, with overexpression and dominant-negative studies implying a strong level of co-operation and interplay between these factors. Overall, our results link cytokine-mediated alterations in cPLA(2)gamma gene expression with allergic asthma and outline a complex regulatory mechanism.