Presenting Author:
Principal Investigator:
Department:
Pathology
Keywords:
Inflammation, vascular biology, signaling, endothelial cells, transendothelial migration, protein kinase A, Rac
Location:
Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital
B138 - Basic Science
CD99 Regulates Leukocyte Transendothelial Migration via a PKA-Rac1-dependent signaling pathway
CD99, a 32 kD highly O-glycosylated protein expressed on leukocytes and at the borders of endothelial cells, plays a central role in inflammation through its regulation of transendothelial migration (TEM). Recently, our laboratory reported that CD99 regulates TEM via a process that involves activation of cAMP dependent protein kinase A (PKA) via soluble adenylyl cyclase. Specifically, we showed that activation of PKA is required for the trafficking of the lateral border recycling compartment (LBRC) to the site of transmigration; a step that is required for the passage of leukocytes across the endothelium. The goal of the present study was to identify cellular targets downstream of PKA that are involved in the CD99 signaling pathway for trafficking of the LBRC and TEM. Preliminary data turned our focus to Rac 1. Using a pharmacologic and genetic approach to inhibit Rac1 activity in endothelial cells, we found that leukocyte transendothelial migration was inhibited in endothelial cells that expressed dominant negative Rac1 (N17Rac) but not wild type Rac1. Specifically, the leukocytes interacting with endothelial cells expressing N17Rac were arrested partway through the junction—identical to the phenotype obtained when CD99 is blocked or knocked down—and trafficking of the lateral border recycling compartment was inhibited. We obtained similar results using pharmacologic inhibitors of Rac1 (NSC-23766 and ET-1864). Furthermore, an activator of Rac 1 (CNO2) rescued trafficking of the LBRC under conditions where PKA was inhibited and thus restored leukocyte transendothelial migration. In summary, our studies show that CD99 regulates transendothelial migration via a signaling pathway that involves activation of soluble adenylyl cyclase, PKA and Rac1. We hypothesize that CD99 signaling must be spatially and temporally regulated during TEM. This work was funded by RO1 HL046849 and R37HL064774
