The molecular pathways mediating the role of cyclooxygenase enzymes and prostaglandins in cervical neoplasias

Includes bibliographical references (leaves 146-170).Cervical Carcinoma is one of the leading causes of cancer-related death in women. The prevalence of this disease is particularly high in South Africa, occurring on average, in 60 out of every 100 000 women. Previous studies have demonstrated over-expression of cyclooxygenase-2 enzyme and enhanced synthesis of prostanoids, such as prostaglandin E2, in cervical carcinomas. Prostaglandin E2 mediates its effects by interacting with one of four receptors termed EPI-4. Expression and signalling of EP receptors, including EP4, are elevated in cervical carcinomas. The initial aim of this study was to localise the site of expression of EP4 receptors in cervical squamous cell- and adenocarcinomas. Immunohistochemical analysis performed on paraffm wax-embedded cervical tissue sections localised the site of EP4 receptor expression to the neoplastic epithelial cells of all squamous cell carcinomas and adenocarcinomas studied. Minimal EP4 receptor immunoreactivity was detected in normal cervix. The site of localisation of the EP4 receptor within the epithelial compartment suggested that prostaglandin E2 may act in an autocrine/paracrine manner to modulate epithelial cell function and promote tumourigenesis. In addition to endogenous prostaglandin E2, EP receptors in cervical carcinomas can be activated by seminal plasma prostaglandins. Prostaglandin concentration in seminal plasma is 10,000 times higher than that found at a site of inflammation, and prostaglandin E2 is the predominant type of prostaglandin detected in semen. In order to investigate the potential activation of the EP4 receptor by prostaglandin E2 or seminal plasma prostaglandins, we developed an EP4-overexpressing adenocarcinoma cell model system using HeLa (cervical carcinoma) cells.Using this model system the signal transduction pathways activated by prostaglandin E2-or seminal plasma-EP4 receptor interaction in HeLa wild type and EP4 receptor overexpressing(EP4S) He La cells were investigated. Treatment of EP4S cells with seminal plasma or prostaglandin E2 resulted in a rapid accumulation of cAMP (p<;0.001) and phosphorylation of ERK1I2 (p<;O.OOI) in EP4S compared with wild-type cells. This elevated phosphorylation of ERK1I2 is inhibited by co-treatment of cells with chemical inhibitors of MEK (PD98059), epidermal growth factor receptor tyrosine kinase (AGI478) or EP4-selective receptor antagonist (ONO-AE2-227). We next investigated the target genes activated by seminal plasma or prostaglandin E2-EP4 ligand-receptor interaction. Treatment of EP4S cells with seminal plasma or prostaglandin E2 also resulted in elevated expression of the twnourigenic gene, cyclooxygenase-2 (p<;O.OOI), and two genes associated with angiogenesis, vascular endothelial growth factor (p<;O.OOI) and basic fibroblast growth factor (p<;O.05). Expression of these genes was inhibited by co-treatment of cells with seminal plasma or prostaglandin E2 and the MEK inhibitor, the epidermal growth factor receptor tyrosine kinase inhibitor or the EP4-selective receptor antagonist