Activation of the de novo biosynthesis of sphingolipids mediates angiotensin II type 2 receptor-induced apoptosis

This study examines the role of sphingolipids in mediating the apoptosis of PC12W cells induced by the angiotensin II type 2 (AT(2)) receptor. PC12W cells express abundant AT(2) receptor but not angiotensin II type 1 receptor and undergo apoptosis when stimulated by angiotensin II. AT(2) receptor-induced ceramide accumulation preceded the onset of caspase 3 activation and DNA fragmentation. AT(2) receptor-induced ceramide accumulation did not result from the degradation of complex sphingolipids (SL) such as sphingomyelin or glycosphingolipids, as no changes in neutral or acidic sphingomyelinase activities, sphingomyelin level, nor in cellular glycolipid composition were observed. AT(2) receptor activated serine palmitoyltransferase with a maximum time of 24 h after angiotensin II stimulation. The AT(2) receptor-induced accumulation of ceramide was blocked by inhibitors of the de novo pathway of SL synthesis, beta-chloro-L-alanine and fumonisin B-1. Inhibition of the de novo biosynthesis of SLs by fumonisin B-1 and beta-chloro-L-alanine completely abrogated the AT(2) receptor-mediated apoptosis, Pertussis toxin and orthovanadate blocked AT(2) receptor-mediated ceramide production. Taken together our data demonstrate that in PC12W cells the stimulation of AT(2) receptor induces the activation of de novo pathway, and a metabolite of this pathway, possibly ceramide, mediates AT(2) receptor-induced apoptosis.