Prostaglandins induce proliferation of rat hepatocytes through a prostaglandin E2 receptor EP3 subtype

Abstract

We characterized the proliferative action of prostaglandins (PGs) in relation to their membrane receptors on rat hepatocytes in primary culture. PGs in the order 16,16-dimethyl PGE2 > PGE2 > PGF2alpha >> PGD2 augmented epidermal growth factor (EGF)/insulin-induced DNA synthesis, assessed by [(3)H]thymidine incorporation, in a concentration-dependent manner, whereas PGs alone did not stimulate basal DNA synthesis without EGF and insulin. The cells exhibited [(3)H]PGE2 binding sites that were displaced by unlabeled PGs in the order PGE1 = PGE2 > PGF2alpha > PGD2. PGE2 inhibited glucagon-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation concentration dependently. The mean effective concentration for DNA synthesis, median inhibitory concentration for cAMP accumulation, and dissociation constant for [(3)H]PGE2 binding at 25 degrees C were almost identical (approximately 70 nM). Treatment of the cells with pertussis toxin (100 ng/ml), which ADP-ribosylated most of the 41-kDa substrate, abolished the proliferative effects of PGs. We detected the expression of mRNA of the EP3 subtype PGE2 receptor using reverse transcription-polymerase chain reaction. Moreover, an EP3 agonist, enprostil, but not the EP1 agonist 17-phenyl-trinor-PGE2 or the EP2/EP4 agonist 11-deoxy-PGE1, stimulated EGF/insulin-induced DNA synthesis. These results indicate that PGs act as comitogenic growth factors through the EP3 subtype PGE2 receptor coupled with G(i) protein in cultured rat hepatocytes.

Prostaglandins Enhance Epidermal Growth Factor-Induced DNA Synthesis in Hepatocytes by Stimulation of E Prostanoid 3 and F Prostanoid Receptors

“…Taken together, our results suggest that, although a minor effect is exerted by FP receptors, EP3 receptors mediate most of the growth stimulatory effects of prostaglandins in hepatocytes. Thus, we have confirmed the involvement of EP3 receptors as described by Hashimoto et al (1997); however, we could not detect a significant contribution from EP1 receptors (Kimura et al, 2001). …”

“…Subsequent studies have suggested that G i may exert an effect on hepatocyte DNA synthesis downstream of receptor coupling . In other studies, growth enhancement induced by prostaglandins in hepatocytes has been attributed to EP3 (Hashimoto et al, 1997) and EP1 receptors (Kimura et al, 2001), respectively. The aim of the present study was to further elucidate the role of the different prostaglandin receptors in growth enhancement, using receptor-selective agonists and antagonists.…”

“…Prostaglandins stimulate proliferation in a number of different cell types (Watanabe et al, 1994;Sheng et al, 2001;Yau and Zahradka, 2003;Chang et al, 2005;Krysan et al, 2005), including neonatal and adult rat hepatocytes (Andreis et al, 1981;Skouteris et al, 1988;Refsnes et al, 1994;Hashimoto et al, 1997;Kimura et al, 2001). In primary cultures of rat hepatocytes, prostaglandins exert a small stimulatory effect on DNA synthesis on their own compared with the strong stimulation of DNA synthesis induced by mitogens, such as epidermal growth factor (EGF), and they act mainly by enhancing the growth stimulatory effect of mitogens .…”

Cyclooxygenases in hepatocellular carcinoma

“…Indeed, evidence indicates that PGs promote cell proliferation, and conversely the growth-inhibitory effects of COX inhibitors can be reversed by exogenous addition of PGs. It has been demonstrated that prostaglandins increase DNA synthesis and cell proliferation of rat hepatocytes [68,69] , and of human HCC cells [45] . On the other hand, it has been demonstrated that COX-2 inhibitors are able to suppress HCC cell growth [44,45,58,[70][71][72][73][74] .…”

Role of EP1 and EP4 PGE2subtype receptors in serum-induced 3T6 fibroblast cycle progression and proliferation

“…Several studies have suggested the role of PGE 2 receptors in cellular proliferation and tumor development. The EP 3 subtype PGE 2 receptor is responsible for the proliferative effect of PGs on rat hepatocytes (16). Experiments on EP 1 -deficient mice show that this subtype receptor is required for the development of preneoplastic lesions induced in colon epithelium by the carcinogen azoxymethane (56).…”