DJ-1 is a redox-sensitive protein with multiple roles in cell homeostasis whose levels are altered in mast cell (MC)-related disorders. However, whether DJ-1 can regulate human MC function is unknown.
We sought to investigate the potential role of DJ-1 in the responses of human MCs to antigen stimulation.
DJ-1 was silenced in human CD34+-derived and LAD2 MCs using lentiviral sh-RNA constructs. Release of β-hexosaminidase, PGD2 and GM-CSF and changes in reactive oxygen species (ROS) levels were measured after FcεRI engagement. Enzymatic assays, sucrose density gradient centrifugation, immunoprecipitations, dot and Western blots, and confocal imaging were performed for signaling, cellular localization and co-association studies.
DJ-1 knockdown substantially reduced mediator release as well as Lyn and Syk kinase activation and signaling by mechanisms which appeared largely unrelated to DJ-1 antioxidant activity. Upon FcεRI activation, non-oxidized rather than oxidized DJ-1 translocated to lipid rafts where it associated with Lyn, an interaction that appeared critical for maximal Lyn activation and initiation of signaling. Using purified recombinant proteins, we demonstrated that DJ-1 bound to Lyn directly but no other Src kinases, and this interaction was specific for human but not mouse proteins. In addition, DJ-1 reduced SHP-2 phosphatase activity by scavenging ROS thus preventing Syk dephosphoryation and perpetuating MC signaling.
We demonstrate a novel role for DJ-1 in the early activation of Lyn by FcεRI that is essential for human MC responses and which provides the basis for an alternative target in allergic diseases therapy.
KEY WORDS : Human mast cells, IgE receptor, Lyn activation, DJ-1, signaling, reactive oxygen species, Syk