A Rit GTPase-p38 mitogen-activated protein kinase survival pathway confers resistance to cellular stress

Cells mobilize diverse signaling cascades to protect against stress-mediated injury. Ras family GTPases play a pivotal role in cell fate determination, serving as molecular switches to control the integration of multiple signaling pathways. p38 mitogen-activated protein kinase (MAPK) signaling serves as a critical fulcrum in this process, regulating networks that stimulate cellular apoptosis but also have the capacity to promote cell survival. However, relatively little is known concerning this functional dichotomy, particularly the regulation of p38-dependent survival pathways. Here, we demonstrate that the Rit GTPase promotes cell survival by directing an unexpected p38 MAPK-dependent AKT survival pathway. Following stress exposure, Rit small hairpin RNA interference (shRNAi)-treated cells display increased apoptosis and selective disruption of p38 MAPK signaling, while expression of constitutively activated Rit promotes p38-AKT-dependent cell survival. Rit, but not Ras or Rap GTPases, can associate with, and is critical for, stress-mediated activation of the scaffolded p38-MK2-HSP27-AKT prosurvival signaling complex. Together, our studies establish Rit as a central regulator of a p38 MAPK-dependent signaling cascade that functions as a critical cellular survival mechanism in response to stress.