Abstract
Stimulation of the β2-adrenergic receptor (β2AR) on a CD40L/interleukin-4-activated B lymphocyte increases the level of immunoglobulin E (IgE) in a protein kinase A (PKA)- and p38 mitogen-activated protein kinase (MAPK)-dependent manner. However, the mechanism by which β2AR stimulation mediates the increase in the level of p38 MAPK activation has remained unclear. Here we show that the β2AR-induced increase in p38 MAPK activation occurred via a hematopoietic protein tyrosine phosphatase (HePTP)-mediated cross talk between PKA and p38 MAPK. β2AR agonists, cAMP-elevating agents, and PKA inhibitors were used to show that β2AR stimulation resulted in a PKA-dependent increase in p38 MAPK phosphorylation. Pharmacological agents and gene-deficient mice revealed that p38 MAPK phosphorylation was regulated by the G-stimulatory (Gs)/cAMP/PKA pathway independently of the G-inhibitory or β-arrestin-2 pathways. Coimmunoprecipitation and Western blot analysis showed that HePTP was phosphorylated in a PKA-dependent manner, which inactivated HePTP and allowed for increased free p38 MAPK to be phosphorylated by the MAPK cascade that was activated by CD40L. HePTP short hairpin RNA confirmed that HePTP played a role in regulating the level of p38 MAPK phosphorylation in a B cell. Thus, β2AR stimulation on a B cell phosphorylates and inactivates HePTP in a Gs/cAMP/PKA-dependent manner to release bound p38 MAPK, making more available for phosphorylation and subsequent IgE regulation.
ACKNOWLEDGMENTS
This research was supported in part by grants NIH-AI-37326 (to V.M.S.) and the Training Program in Integrative Immunobiology, grant T32 AI-55411 (to J.W.M.), from the National Institutes of Health.
We thank Nicholas Kin (University of Alabama at Birmingham) for critical reading of the manuscript.