TY - JOUR
T1 - Cellular density-dependent down-regulation of EP4 prostanoid receptors via the up-regulation of hypoxia-inducible factor-1α in HCA-7 human colon cancer cells
AU - Otake, Sho
AU - Yoshida, Kenji
AU - Seira, Naofumi
AU - Sanchez, Christopher M.
AU - Regan, John W.
AU - Fujino, Hiromichi
AU - Murayama, Toshihiko
N1 - Funding Information:
This research was supported in part by a Grant-in-Aid for Scientific Research (22590079 and 25460091) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. In addition, we have no conflict of interest to declare.
Publisher Copyright:
© 2014 John Wiley & Sons Ltd, British Pharmacological Society and American Society for Pharmacology and Experimental Therapeutics.
PY - 2015/2/1
Y1 - 2015/2/1
N2 - Increases in prostaglandin E2 (PGE2) and cyclooxygenase-2 (COX-2) levels are features of colon cancer. Among the different E-type prostanoid receptor subtypes, EP4 receptors are considered to play a crucial role in carcinogenesis by, for example, inducing COX-2 when stimulated with PGE2. However, EP4 receptor levels and PGE2-induced cellular responses are inconsistent among the cellular conditions. Therefore, the connections responsible for the expression of EP4 receptors were investigated in the present study by focusing on cell density-induced hypoxia-inducible factor-1α (HIF-1α). The expression of EP4 receptors was examined using immunoblot analysis, quantitative polymerase chain reaction, and reporter gene assays in HCA-7 human colon cancer cells with different cellular densities. The involvement of HIF-1α and its signaling pathways were also examined by immunoblot analysis, reporter gene assays, and with siRNA. We here demonstrated that EP4 receptors as well as EP4 receptor-mediated COX-2 expression levels decreased with an increase in cellular density. In contrast, HIF-1α levels increased in a cellular density-dependent manner. The knockdown of HIF-1α by siRNA restored the expression of EP4 receptors and EP4 receptor-mediated COX-2 in cells at a high density. Thus, the cellular density-dependent increase observed in HIF-1α expression levels reduced the expression of COX-2 by decreasing EP4 receptor levels. This novel regulation mechanism for the expression of EP4 receptors by HIF-1α may provide an explanation for the inconsistent actions of PGE2. The expression levels of EP4 receptors may vary depending on cellular density, which may lead to the differential activation of their signaling pathways by PGE2. Thus, cellular density-dependent PGE2-mediated signaling may determine the fate/stage of cancer cells, i.e., the surrounding environments could define the fate/stage of malignancies associated with colon cancer.
AB - Increases in prostaglandin E2 (PGE2) and cyclooxygenase-2 (COX-2) levels are features of colon cancer. Among the different E-type prostanoid receptor subtypes, EP4 receptors are considered to play a crucial role in carcinogenesis by, for example, inducing COX-2 when stimulated with PGE2. However, EP4 receptor levels and PGE2-induced cellular responses are inconsistent among the cellular conditions. Therefore, the connections responsible for the expression of EP4 receptors were investigated in the present study by focusing on cell density-induced hypoxia-inducible factor-1α (HIF-1α). The expression of EP4 receptors was examined using immunoblot analysis, quantitative polymerase chain reaction, and reporter gene assays in HCA-7 human colon cancer cells with different cellular densities. The involvement of HIF-1α and its signaling pathways were also examined by immunoblot analysis, reporter gene assays, and with siRNA. We here demonstrated that EP4 receptors as well as EP4 receptor-mediated COX-2 expression levels decreased with an increase in cellular density. In contrast, HIF-1α levels increased in a cellular density-dependent manner. The knockdown of HIF-1α by siRNA restored the expression of EP4 receptors and EP4 receptor-mediated COX-2 in cells at a high density. Thus, the cellular density-dependent increase observed in HIF-1α expression levels reduced the expression of COX-2 by decreasing EP4 receptor levels. This novel regulation mechanism for the expression of EP4 receptors by HIF-1α may provide an explanation for the inconsistent actions of PGE2. The expression levels of EP4 receptors may vary depending on cellular density, which may lead to the differential activation of their signaling pathways by PGE2. Thus, cellular density-dependent PGE2-mediated signaling may determine the fate/stage of cancer cells, i.e., the surrounding environments could define the fate/stage of malignancies associated with colon cancer.
KW - COX-2
KW - Cell density
KW - EP4 prostanoid receptor
KW - GPCRs
KW - HCA-7 cells
KW - HIF-1α
KW - Human colon cancer
KW - PGE
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U2 - 10.1002/prp2.83
DO - 10.1002/prp2.83
M3 - Article
AN - SCOPUS:84947603898
SN - 2052-1707
VL - 3
SP - 1
EP - 13
JO - Pharmacology Research and Perspectives
JF - Pharmacology Research and Perspectives
IS - 1
ER -