Dynamics of MAP kinase cascade in immune response

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The MAP kinase cascade is essential for signaling of various extracellular stimuli to the nucleus. Stimulation of T cells, B cells, and mast cells through aggregation of antigen receptors and other stimulants results in activation of MAP kinase. In this study, we focused on the dynamics of MAP kinase (MAPK) cascade protein in mast cells using yellow fluorescent protein (YFP)-tagged MAPK (ERK2) and YFP-tagged MAPKKK (Raf-1). Here, we have shown many aspects of MAP kinase signaling in immune response.1.In wild type mast cells, the membrane translocation of MAPKKK (Raf-1) reached 〜3 min after antigen stimulation, and thereafter the nuclear import of MAPK (ERK2) reached the maximum at 5〜7 min Raf-1 did not co-localize with lipid microdomain.2.In the presence of leptomycin B (inhibitor of nuclear export), the export of ERK2 became more slowly though ERK2 was imported to the nucleus as like as in non-treated cells.3.We have studied the effects of FcγRIIB on the FcεRI-mediated nuclear shuttling of MAP kinase in immune cells. The co-clustering of FcεRI and FcγRIIB increased the [Ca-<2+>]_i and induced the nuclear import of ERK2. However, the calcium increase was transient and ERK2 was rapidly exported to the cytoplasm.4.We have studied the effects of two tyrosine phosphatases, HePTP (a tyrosine-specific phosphatase) and VHR (a dual specificity protein-tyrosine phosphatase), on the FcεRI-mediated nuclear shuttling of ERK2 in the mast cells. In HePTP-overexpressing cells, the maximal amount of ERK2 accumulated in the nucleus was much less than that in wild type cells though the nuclear import of ERK2 reached the maximum in the similar time-course. In VHR-overexpressing cells, the amount of imported ERK2 decreased more rapidly though ERK2 was imported to the nucleus as like as in wild type cells.Thus we succeeded to show the molecular mechanism of MAP kinase cascade protein in immune response.