PT  - JOURNAL ARTICLE
AU  - Y. Dai
AU  - N. L. Dudek
AU  - T. B. Patel
AU  - N. A. Muma
TI  - Transglutaminase-Catalyzed Transamidation: A Novel Mechanism for Rac1 Activation by 5-Hydroxytryptamine<sub>2A</sub> Receptor Stimulation
AID  - 10.1124/jpet.107.135046
DP  - 2008 Jul 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 153--162
VI  - 326
IP  - 1
4099  - http://jpet.aspetjournals.org/content/326/1/153.short
4100  - http://jpet.aspetjournals.org/content/326/1/153.full
SO  - J Pharmacol Exp Ther2008 Jul 01; 326
AB  - Transglutaminase (TGase)-induced activation of small G proteins via 5-hydroxytryptamine (HT)2A receptor signaling leads to platelet aggregation (Cell115:851–862, 2003). We hypothesize that stimulation of 5-HT2A receptors in neurons activates TGase, resulting in transamidation of serotonin to a small G protein, Rac1, thereby constitutively activating Rac1. Using immunoprecipitation and immunoblotting, we show that, in rat cortical cell line A1A1v, serotonin increases TGase-catalyzed transamidation of Rac1. This transamidation occurs in both undifferentiated and differentiated cells. Treatment with a 5-HT2A/2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine, but not the 5-HT1A receptor agonist 5-hydroxy-2-dipropylamino tetralin, increases transamidation of Rac1 by TGase. In A1A1v cells, 5-HT2A receptors mediate the transamidation reaction because expression of 5-HT2C receptors was not detectable and the selective 5-HT2A receptor antagonist blocked transamidation. Time course studies demonstrate that transamidation of Rac1 is significantly elevated after 5 and 15 min of serotonin treatment, but returns it to control levels after 30 min. The activity of Rac1 is also transiently increased following serotonin stimulation. Inhibition of TGase by cystamine or small interfering RNA reduces TGase modification of Rac1, and cystamine also prevents Rac1 activation. Serotonin itself is bound to Rac1 by TGase following 5-HT2A receptor stimulation as demonstrated by coimmunoprecipitation experiments and a dose-dependent decrease of serotonin-associated Rac1 by cystamine. These data support the hypothesis that Rac1 activity is transiently increased due to TGase-catalyzed transamidation of serotonin to Rac1 via stimulation of 5-HT2A receptors. Activation of Rac1 via TGase is a novel effector and second messenger of the 5-HT2A receptor-signaling cascade in neurons. The American Society for Pharmacology and Experimental Therapeutics