Abstract 432: Post-translational Regulation of Group X Secretory Phospholipase A2
Group X secretory phospholipase A2 (GX sPLA2) hydrolyzes phospholipids within membrane bilayers, liberating free fatty acids and lysophospholipids. We reported previously that C57BL/6 mice deficient in GX sPLA2 (GX KO) have increased plasma corticosterone levels under both basal and adrenocorticotropic hormone (ACTH) stimulated conditions (Shridas et al. 2010, J. Biol. Chem. 285:20031-9). Conversely, overexpression of GX sPLA2 but not a catalytically inactive mutant, suppresses steroid production in mouse Y1 adrenal cells. GX sPLA2 is produced as a proenzyme that contains an N-terminal 11 amino acid propeptide ending in a dibasic motif, suggesting cleavage by a furin-like proprotein convertase. While propeptide cleavage is clearly required for enzymatic activity, the protease(s) responsible for GX sPLA2 activation have not been identified. In this study we report that ACTH treatment increases the phospholipase activity secreted by Y1 adrenal cells stably expressing GX sPLA2 (Y1-GX cells). Western blot analysis showed an increase in the ratio of mature/total GX sPLA2 in the media of ACTH-treated Y1-GX cells. Use of broad specificity proprotein convertase inhibitors confirmed the involvement of furin-like proteases in the processing and subsequent activation of GX sPLA2. Results from qRT-PCR analysis indicated that furin and PACE4, but not other members of the convertase family, are upregulated by ACTH in Y1 cells. siRNA-mediated gene targeting indicated that both furin and PACE4 mediate GX sPLA2 activation under both basal and ACTH-induced conditions. These results clearly demonstrate a role for furin and PACE4 in the proteolytic activation of GX sPLA2 in Y1 adrenal cells.
- © 2013 by American Heart Association, Inc.