Dual role for RhoA in suppression and induction of cytokines in the human neutrophil

Production of tumor necrosis factor-alpha (TNF alpha) by the neutrophil (PMN) is a pivotal event in innate immunity, but the signals regulating TNFa induction in this primary cell are poorly understood. Herein, we use protein transduction to identify novel, opposing anti- and procytokine-inducing roles for RhoA in the resting and lipopolysaccharide (LPS)-stimulated human PMN, respectively. In the resting cell, RhoA suppresses Cdc42 activation, I kappa B alpha degradation, nuclear factor-kappa B (NF-kappa B) activation, and induction of TNF alpha and NF-kappa B-dependent chemokines. Suppression of TNF alpha induction by RhoA is Rho kinase alpha (ROCK alpha) independent, but Cdc42 dependent, because TNF alpha-induction by C3 transferase is attenuated by inhibition of Cdc42, and constitutively active Cdc42 suffices to activate NF-kappa B and induce TNF alpha. By contrast, we also place RhoA downstream of p38 mitogen-activated protein kinase and Cdc42 in a novel LPS-activated pathway in which p38, Cdc42, and ROCK alpha all promote TNF alpha protein expression. The p65 subunit of NF-kappa B coprecipitates with RhoA in a manner sensitive to the RhoA activation state. Our findings suggest a new, 2-faced role for RhoA as a checkpoint in innate immunity.