Increased ecto-metallopeptidase activity in cells undergoing apoptosis

Abstract

Release from the cell surface of a variety of growth factors, cytokines, and proteases follows exposure to genetically stressful agents capable of inducing apoptosis and necrosis. Increased ectoprotease activity is responsible for their release. We show that increased activity of several metalloproteases on the HeLa cell surface occurs after stresses due to UVC, actinomycin D, cycloheximide, and cisplatinum, which induce the release of transforming growth factor-alpha (TGFalpha) and other bioactive molecules. The ectoprotease activities increase preferentially on apoptotic cells, while little change occurs in viable cells. Gross decreases, except for the putative TGFalphaase activity, accompany necrosis. These changes may contribute to tissue repair and the absence of an inflammatory reaction to apoptotic cell death. They appear to be due to preferential enzyme activation or to retention by cells undergoing significant categorical decreases in protein content.

Increased cell surface protease activity in UV-irradiated cells undergoing apoptosis

“…4 Cells were trypsinized, washed and irradiated under UVB (FS-20 fluorescent tubes) in a similar procedure to that previously described for UVCirradiated HeLa cells, 4 prior to being plated out in tissue culture flasks containing either no inhibitor (control cells) or DEVD (1 µM) for 20 h before being harvested for FACS analysis.…”

“…4 The reduced level of CSP activity in the necrotic cells could result from the shedding of these proteases from the cell membrane as the cell dies by necrosis. Other eP activities (dipeptidase, tripeptidase and TGFα-ase) 6 were also elevated in cells undergoing apoptosis but was only observed when AP activity was inhibited by bestatin.…”

“…2,3 Recently, it has been shown that cell surface metallopeptidase activity was increased on cells undergoing apoptosis. 4,5 The mechanism by which cell surface metallopeptidases are activated on apoptotic cells is unknown. This activation may be due to actions of caspases, but not caspase 1.…”

“…This activation may be due to actions of caspases, but not caspase 1. 4 Another caspase found in the cell, caspase 3, cleaves a wide range of proteins including PARP, α-fodrin and gelsolin, 2,3 which may affect the activity of CSP found on the plasma membrane.…”

Increased Activity of Cell Surface Peptidases in HeLa Cells Undergoing UV-Induced Apoptosis Is Not Mediated by Caspase 3

“…ICE cleaves IL-1β from its precursor form, which in vivo attracts macrophages to engulf these cells as they undergo apoptosis. The mechanisms by which cell surface peptidases (CSP) in HeLa cells [17] are activated during apoptosis still remain to be elucidated. This activation could be a result of phosphatidylserine inversion in the cell membrane [8,9].…”