Protein kinase C (PKC)θ is an established component of the immunological synapse and has been implicated in the control of AP-1 and NF-κB. To study the physiological function of PKCθ, we used gene targeting to generate a PKCθ null allele in mice. Consistently, interleukin 2 production and T cell proliferative responses were strongly reduced in PKCθ-deficient T cells. Surprisingly, however, we demonstrate that after CD3/CD28 engagement, deficiency of PKCθ primarily abrogates NFAT transactivation. In contrast, NF-κB activation was only partially reduced. This NFAT transactivation defect appears to be secondary to reduced inositol 1,4,5-trisphosphate generation and intracellular Ca2+ mobilization. Our finding suggests that PKCθ plays a critical and nonredundant role in T cell receptor–induced NFAT activation.

Compared to free breathing treatments, the primary benefit of the DIBH technique was the separation of the heart from the target rather than more accurate targeting. Despite a small gating window, occasional large errors in the chest wall position were observed for some patients, illustrating limitations of the external marker block as surrogate in a broad patient population.

Lipoprotein receptors, such as LRP, have been shown to assemble multiprotein complexes containing intracellular signaling molecules; however, in vivo, their signaling function is poorly understood. Using a novel LRP receptor fusion construct, a type I transmembrane protein chimera, termed sIgG-LRP (bearing the intracellular COOH-terminal tail of human LRP as recombinant fusion to a transmembrane region plus the extracellular IgG-F c domain), we here investigated LRP signal transduction specificity in intact cells. First and similar to activated ␣2-macroglobulin as agonist of endogenous LRP, expression of sIgG-LRP demonstrated significant apoptosis protection. Second and similar to ␣2-macroglobulin-induced endogenous LRP, sIgG-LRP is sufficient to negatively modulate mitogen-induced Elk-1 and cJun (but not NF-B) transcriptional activity. Third, expression of sIgG-LRP also impaired cJun transactivation mediated by constitutive active mutants of Rac-1 and MEKK-1. Fourth and unexpectedly, sIgG-LRP expression was found to be associated with a marked enhancement of mitogen-induced cJun amino-terminal kinase (JNK) activation. Fifth, confocal microscopic examination and subcellular fractionation demonstrated that sIgG-LRP and JNK co-localize in transfected cells. Therefore, sIgG-LRP expression was found to significantly impair activation-induced translocation of JNK into the nucleus. Taken together, we here demonstrate that sIgG-LRP protein sequesters activated JNK into the plasma membrane compartment in intact cells, inhibiting nuclear activation of the JNK-dependent transcription factors Elk-1 and cJun. Low density lipoprotein receptor-related protein (LRP)1 is one member of the LDL receptor family that also includes the LDL receptor, the very low density lipoprotein receptor, megalin, LRP5, LRP6, and apoER2 receptor (see Ref. 1 LRP is expressed abundantly in neurons and microglia of the central nervous system (3, 4). Disruption of the LRP gene in mice blocks development of LRP Ϫ/Ϫ embryos around the implantation (5). However, the complex phenotype of the few malformed LRP-deficient embryos that survive until E10 (6), similar to the very low density lipoprotein ApoER2 receptor double knockout phenotype (7), postulated some LRP receptor signaling function(s). Consistently, LRP and several of its ligands, including ␣2-macroglobulin, tissue plasminogen activator (tPA), apoE-containing lipoproteins, and the amyloid precursor protein (APP) (8, 9), have been implicated in various cellular functions including the neuropathogenesis of Alzheimer's disease (see Ref. 10 for review).Based on yeast two-hybrid and co-immunoprecipitation analysis, lipoprotein receptors assemble intracellular multiprotein complexes containing the adapter and scaffold proteins Dab-1 (7), FE65 (11) and Shc (12, 13), the non receptor tyrosine kinases Src and Fyn (14), and the JNK-interacting proteins (JIP-1 & 2) (15, 16), which act as molecular scaffolds for the JNK signaling pathway (see Ref. 17 for review). Quite similarly, such intracellular signali...

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