PHILIP STORK

..We demonstrate that CTLA-4 activates Rap1, and we propose that intracellular signals from CTLA-4 antagonize CD28, at least in part, at the level of Rap1...

..Recent studies implicating Rap1 in the maturation of megakaryocytes, the pathogenesis of chronic myelogenous leukemia (CML), and activation of peripheral T cells will receive particular attention...

..Emerging new data suggest that one of these mechanisms might involve the activation of the GTPase Rap1, which can activate or inhibit ERK signaling in a cell-specific manner...

..These diverse functions of Rap1 underscore that the activation and action of Rap1 are regulated by complex factors that are cell-type specific...

..Contrary to our hypothesis, elevated levels of T(3) powerfully inhibit proliferation of midgestation fetal cardiomyocytes. Thus, midgestation maternal hyperthyroidism might lead to an underendowed fetal myocardium...

..Furthermore, Rap1, but not Ras, activation by PKA appears to require the action of Src family kinases...

..We propose a model that specific GEFs activate distinct pools of Rap1 that are differentially coupled to downstream effectors...

..This study identifies an antiproliferative role for Src in the physiological regulation of cell growth by cAMP...

..PKA phosphorylation of Src may therefore be required for Rap1 activation in PC12 cells...

..However, studies using anti-TCR antibody-induced anergy showed that the ability of ERKs to reverse T cell anergy is dependent on the anergic model utilized...

..We propose that the beta(2)-adrenergic receptor activates Src via two independent mechanisms to mediate distinct signaling pathways, one through Galpha(s) to Rap1 and ERKs and the other through Gbetagamma to Ras and AKT...

..Coincident detection of both cAMP and Ras signals is essential for Epac2 to activate Rap1 in a temporally and spatially controlled manner...

..Because these ERK-dependent phosphorylations are required for proper c-fos function, and occur sequentially, we propose that c-fos is a sensor for ERK signaling duration in the neuronal-like cell line PC12...

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..However, PKA activity was also not necessary for the early translocation of Erk into the nucleus by NGF or Ras, but it was able to induce a small influx of Erk that could be measured with GFP-Erk2...

..We propose that Ran and RanBP2 anchor Epac1 to the nuclear pore, permitting cAMP signals to activate Rap1 at the nuclear envelope...

..Thyroidectomized fetuses had reduced cell cycle activity and binucleation. These findings support the hypothesis that T(3) is a prime driver of prenatal cardiomyocyte maturation...

..These studies provide the first direct genetic evidence of Rap1-mediated activation of the MAP kinase cascade in eukaryotic organisms...

..Finally, Specific Aim 4 explores a novel mechanism of ERK regulation by Galpha-i and Galpha-o through their interaction with Rap 1 GAP, a selective inhibitor or Rap 1. ..

..In addition, we will test the hypothesis that CD28 co-stimulation achieves increased ERK activation, IL-2 production and proliferation by blocking Rap1 activation. ..

..We will determine the biochemical basis for this specificity of Rap1 for B-Raf in Specific Aim 3. In this aim, we will also establish novel mouse models to test the hypothesis that B-Raf has irreplaceable functions in vivo. ..

..The applicant believes that the experiments outlined in this proposal may ultimately impact more general research on synaptic plasticity, long-term potentiation (LTP) and neuronal survival. ..

..Lastly, we will determine whether other physiological signals can activate this novel pathway (Specific Aim 3). ..

..We will determine the biochemical basis for this specificity of Rap1 for B-Raf in Specific Aim 3. In this aim, we will also establish novel mouse models to test the hypothesis that B-Raf has irreplaceable functions in vivo. ..