Key role of 12-lipoxygenase and biphasic mitogen activated protein kinase activity. Wen, Yeshao, Jerry L. Nadler, Noe Gonzales, Stephen Scott, Eric Clauser, and Rama Natarajan. Department Of Diabetes, Endocrinology and Metabolism, City Of Hope Medical Center, 1500 East Duarte Road, Shapiro 106, Duarte, CA 91010, Laboratoire de Medicine Experimentale, College de France, 3, rue d, Ulm 75005, Paris France
APStracts 3:0156C, 1996.
The potential mechanisms of angiotensin II (AII)-induced mitogenesis were studied in a Chinese hamster ovary fibroblast cell line overexpressing the rat vascular type 1a AII receptor (CHO-AT1a). AII had potent mitogenic effects in these CHO-AT1a cells leading to a sustained increase in cell number as well as a dose-dependent increase in DNA synthesis. AII treatment also induced a biphasic elevation of mitogen activated protein (MAP) kinase activity of both P42MAPK and P44MAPK with a rapid early peak at 5 min (2-6 fold) followed by a second sustained increase that reached a peak at 3 hr (1.5-3 fold). We have previously shown that the 12-lipoxygenase (12 -LO) pathway of arachidonate metabolism plays a key role in AII -induced growth of vascular smooth muscle and adrenal cells. In the present study, AII (10-7 M) increased the formation of the 12 -lipoxygenase product, 12-hydroxyeicosatetraenoic acid (12-HETE). AII -induced DNA synthesis was inhibited by a specific LO inhibitor, cinnamyl-3,4-dihydroxy-[alpha]-cyanocinnamate (CDC, 10 [mu]M). In contrast, a cyclooxygenase blocker of arachidonate metabolism such as ibuprofen had no effect on AII-induced DNA synthesis. AII-induced DNA synthesis was also partially (32%) blocked by pertussis toxin (PTX). CDC and PTX also selectively blocked only the late (3 hr) peak of AII-induced MAP kinase activity suggesting that the late sustained peak of MAP kinase activity may be linked to the mitogenic effect of AII. Direct addition of 12-HETE (10-7 M) led to a sustained increase in cell number similar to the effect of AII. 12-HETE also caused an increase in MAP kinase activity and 12-HETE effects were blocked by PTX. These results suggest that AII-induced mitogenic response is associated with sustained MAP kinase activation and that LO activation may play a key role in this process. 

Received 16 October 1995; accepted in final form 22 April 1996.
APS Manuscript Number C630-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 May 96