Role of superoxide in apoptosis induced by growth factor withdrawal. Lieberthal, Wilfred, Veronica Triaca, Jason S. Koh, Patrick J. Pagano and Jerrold S. Levine. Renal Section, Department of Medicine, Boston University Medical Center, MA 02118 and Division of Hypertension and Vascular Research*, Henry Ford Hospital, Detroit, MI 48202.
APStracts 5:0136F, 1998.
We have examined the role of reactive oxygen species in apoptosis induced by growth factor deprivation in primary cultures of mouse proximal tubular (MPT) cells. When confluent monolayers of MPT cells are deprived of all growth factors, the cells die by apoptosis over a 10-14 day period. Both epidermal growth factor (EGF) and high-dose insulin directly inhibit apoptosis of MPT cells deprived of growth factors. Growth factor deprivation results in an increase in the cellular levels of superoxide anion while apoptosis of MPT cells induced by growth factor withdrawal is inhibited by a number of antioxidants and scavengers of reactive oxygen species (ROS). Growth factor deprivation also results in activation of caspase activity which is inhibited by EGF and high-dose insulin as well as by the ROS scavengers and anti-oxidants that inhibit apoptosis. The cell permeant caspase inhibitor, z-Val-Ala-Asp-CH2F (zVAD-fmk), prevents the increase in caspase activity and markedly inhibits apoptosis induced by growth factor deprivation. However, z-Val-Ala-Asp-CH2F (zVAD-fmk) had no effect on the increased levels of superoxide associated with growth factor deprivation. Thus, we provide novel evidence that reactive oxygen species play an important role in mediating apoptosis associated with growth factor deprivation. ROS appear to act upstream of caspases in the apoptotic pathway. We hypothesize that oxidant stress, induced by growth factor withdrawal, represent a signaling mechanism for the default pathway of apoptosis. 

Received 12 May 1998; accepted in final form 6 August 1998.
APS Manuscript Number F160-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 21 September 1998