Molecular cloning and biochemical studies identified protein kinase C (PKC) enzymes as members of a distinct family of serine/threonine protein kinases, playing critical roles in the regulation of cellular differentiation and proliferation of diverse cell types (reviewed in reference 36). In an attempt to find PKC isoforms that are involved in growth control and/or activation of T lymphocytes, we have identified PKC-(5), whose human gene locus was recently mapped to chromosome 10p15 (15). PKC-is characterized by a unique tissue distribution, i.e., in skeletal muscle, lymphoid organs, and hematopoietic cell lines, particularly T cells (4,5,10,34,39,53), and by isoenzyme-specific activation requirements and substrate preferences in vitro (4). PKC-undergoes cytosol-to-membrane translocation in T cells stimulated with phorbol esters (4), implying that this isoform is likely to be involved in T-cell activation pathways. The unique expression and functional properties of PKC-suggest that it may play a specialized role in T-cell signaling pathways.T-cell activation results in the expression of interleukin-2 (IL-2), an autocrine growth factor that is a critical stimulus for the growth and differentiation of B and T lymphocytes. Pharmacological and biochemical studies indicate that activation of two major signaling pathways, one of which can be triggered by phorbol esters (such as phorbol 12-myristate 13-acetate [PMA]) and the other of which can be triggered by Ca 2ϩ ionophores, is required for induction of IL-2 (reviewed in reference 51). A substantial amount of work over the past several years has shown the requirement of cooperative interactions of several transcription factors, including AP-1, NF-B, NF-AT, and NF-IL2A (Oct-1), with the minimal inducible promoter/enhancer region of the IL-2 gene (11). Several lines of evidence point to AP-1 as a critical transcription factor for IL-2 regulation. AP-1 is a dimer of different members of the Fos (c-Fos, FosB, Fra-1, Fra-2, and FosB2) and Jun (c-Jun, JunB, and JunD) family of proteins (1). AP-1 thereby interacts with the IL-2 regulatory region directly (25,26,33,47) and also indirectly as a component of NF-AT and NF-IL2 (37, 50). AP-1 activity is regulated by de novo synthesis of Jun and Fos proteins, as well as by posttranslational modifications such as phosphorylation and dephosphorylation (1,8,9,30,43,48). Two potential AP-1-binding sites have been identified in the mouse and human IL-2 enhancer region at Ϫ150 bp (proximal AP-1) and Ϫ180 bp (distal AP-1). These elements show sequence similarity to the consensus AP-1 enhancer sequence and have been studied by deletional, mutational, and gel shift analyses (14,18,25,40). Most of these data support an important role for AP-1 in IL-2 transcription, especially as a result of the interaction with the proximal enhancer site (25).PKC has been implicated in the activation of AP-1 in T lymphocytes, as demonstrated by studies involving PKC-specific pharmacological inhibitors (24, 28) or PKC down-regulation by chronic phorbol este...

Soluble tumour necrosis factor receptors (sTNF‐Rs) play a role as modulators of the biological function of tumour necrosis factor‐α (TNF‐α) in an agonist/antagonist pattern. In various pathologic states the production and release of sTNF‐Rs may mediate host response and determine the course and outcome of disease by interacting with TNF‐α and competing with cell surface receptors. The determination of sTNF‐Rs in body fluids such as plasma or serum is a new tool to gain information about immune processes and provides valuable insight into a variety of pathological conditions. Regarding its immediate clinical use, sTNF‐Rs levels show high accuracy in the follow‐up and prognosis of various diseases. In HIV infection and sepsis, sTNF‐Rs concentrations strongly correlate with the clinical stage and the progression of disease and can be of predictive value. Determination of sTNF‐Rs also gives useful information for monitoring cancer and autoimmune diseases. The information provided is often even superior to that obtained with classical disease markers, probably due to the direct involvement of the “TNF system” in the pathogenetic mechanisms in these patients. The available data imply that the measurement of sTNF‐Rs, especially of the sTNF‐R 75kD type, is a useful adjunct for quantification of the Th1‐type immune response, similar to other immune activation markers such as neopterin and β2‐microglobulin. Endogenous sTNF‐Rs concentrations appear to reflect the activation state of the TNF‐α/TNF receptor system.

Expression of transforming Ha-Ras L61 in NIH3T3 cells causes profound morphological alterations which include a disassembly of actin stress fibers. The Ras-induced dissolution of actin stress fibers is blocked by the specific PKC inhibitor GF109203X at concentrations which inhibit the activity of the atypical aPKC isotypes λ and ζ, whereas lower concentrations of the inhibitor which block conventional and novel PKC isotypes are ineffective. Coexpression of transforming Ha-Ras L61 with kinase-defective, dominant-negative (DN) mutants of aPKC-λ and aPKC-ζ, as well as antisense constructs encoding RNA-directed against isotype-specific 5′ sequences of the corresponding mRNA, abrogates the Ha-Ras–induced reorganization of the actin cytoskeleton. Expression of a kinase-defective, DN mutant of cPKC-α was unable to counteract Ras with regard to the dissolution of actin stress fibers. Transfection of cells with constructs encoding constitutively active (CA) mutants of atypical aPKC-λ and aPKC-ζ lead to a disassembly of stress fibers independent of oncogenic Ha-Ras. Coexpression of (DN) Rac-1 N17 and addition of the phosphatidylinositol 3′-kinase (PI3K) inhibitors wortmannin and LY294002 are in agreement with a tentative model suggesting that, in the signaling pathway from Ha-Ras to the cytoskeleton aPKC-λ acts upstream of PI3K and Rac-1, whereas aPKC-ζ functions downstream of PI3K and Rac-1.This model is supported by studies demonstrating that cotransfection with plasmids encoding L61Ras and either aPKC-λ or aPKC-ζ results in a stimulation of the kinase activity of both enzymes. Furthermore, the Ras-mediated activation of PKC-ζ was abrogated by coexpression of DN Rac-1 N17.