Su1887 Mechanism of Inhibition of Na-Glutamine Co-Transport by Prostaglandin E2 in Intestinal Epithelial Cells

Abstract

generate PCTV to transport the chylomicron from ER to Golgi. The chylomicron output into lymph is correlated to intestinal luminal phosphatidylcholine (PC). Luminal PC is absorbed as lyso-phosphatidylcholine (lyso-PC). We previously showed that the dietary lipids are absorbed from the apical membrane by Caveolin-1 containing Cytosolic Endocytic Vesicles (CEV). We tested the hypothesis that lyso-PC activates the PKCζ; detach it from CEV, enabling PKCζ to phosphorylate Sar1b. Methods: Cytosol was isolated from rats whose intestinal PC was altered by (A) bile diversion, no PC (B) saline infusion, low PC (C) chow fed, normal PC (D) fat fed, high PC and (E) PC infusion, very high PC. PKCζ activity was measured by phosphorylation of PKCζ pseudo substrate. Lyso-PC was measured by HPLC. Results: PKCζ was activated by lyso-PC, non-linear regression curve for PKCζ vs. lyso-PC, calculated as Km=1.49 ± 0.244 nM and Vmax = 1.12 ± 1.058 nM. The amount of cytosolic lyso-PC in A to E ranges from 0 to 0.45 nM, suggesting that the amount of cytosolic lysoPC is always within a range to control PKCζ activation. PKCζ activity ranges from 0 to 0.7 Arbitrary Unit in A to E. Post absorptive CEV contain PKCζ by western blot but PKCζ detachment from the CEV is proportional to cytosolic lyso-PC as estimated by western blot of CEV. Biotinylation of r-PKCζ showed a conformational change on activation by lyso-PC. We conclude that PKCζ on CEV was activated by lyso-PC, changes its conformation and eluted from vesicles, enter into the cytosol and phosphorylate Sar1b, split the heteroquatramer protein complex to release FABP1. Now free FABP1 can bind to ER membrane for PCTV formation, which transports chylomicrons from ER to Golgi. Fig. 1 illustrated the scheme for control of dietary lipid transport.