Functional interactions of protein kinase A and C in signalling networks: a recapitulation

On the basis of evidence collected from the literature, we propose a general model by which protein kinase (PK) A and the different PKC isoforms can inversely affect cell growth. Molecular switches, which are able to direct the signal towards antiproliferative or mitogenic pathways, are the different isoforms of Raf and PKC. Conflicting data are also reported and discussed in an attempt to reconcile them. Received 10 November 2005; received after revision 28 December 2005; accepted 3 January 2006     

T-cell signal transduction and the role of protein kinase C

The T lymphocyte has a vital part to play in maintaining the host response to bacterial and viral infection and also appears to play a key pathological role in autoimmune diseases such as rheumatoid arthritis. In this review, we summarize the signalling pathways which trigger antigen-driven T-cell proliferation and examine the evidence which suggests that protein kinase C (PKC) is fundamental to this process. Finally, we discuss the therapeutic potential that PKC inhibitors may have in the treatment of autoimmune disease. Received 31 March 1998; received after revision 19 May 1998; accepted 19 May 1998     

Arachidonic acid mobilization in platelets: the possible role of protein kinase C and G-proteins

A major route for the release of arachidonic acid from platelet phospholipids appears to be catalyzed by a phospholipase A2 that can be stimulated by a rise of cytosolic Ca2+. This paper discusses certain other mechanisms for regulation of this process. Release of arachidonic acid by calcium ionophores is potentiated by pretreatment with stimulators of protein kinase C; e.g. diglyceride, phorbol esters and the terpene diester mezerein. This effect appears to be coincident with phosphorylation of a certain group of proteins (not 47 KDa protein), and is sensitive to depletion of ATP, activation of Ca2+ dependent phosphatase, and the kinase C inhibitor H-7, but is unaffected by Na+/H+ exchange inhibitors. Recent results in other cell types strongly indicate that phospholipase A2 is also directly under control of certain GTP-binding proteins.     

Action of juvenile hormone on the follicle cells ofRhodnius prolixus: Evidence for a novel regulatory mechanism involving protein kinase C

Summary Juvenile hormone (JH) is known to act on the membranes of the follicle cells ofRhodnius, activating a specific Na⁺, K⁺-ATPase. This leads to a decrease in volume of the cells and the appearance of spaces between them (patency). The addition of an inhibitor of protein kinase C, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), to the medium in vitro inhibits the action of JH on the follicle cells. PDBU (phorbol-12,13-dibutyrate) mimics the action of JH in vitro and the response of the follicle cells to, PDBU is blocked by ouabain. It is concluded that the activation of protein kinase C is a required step in the chain of events leading to activation of the JH-dependent ATPase and set in train by the binding of JH to the membrane.     

Regulation of caldesmon activity by Cdc2 kinase plays an important role in maintaining membrane cortex integrity during cell division

To study the mitosis-specific phosphorylation of caldesmon (CaD), we generated a mutant of the C-terminal fragment (amino acids 244–538) of human fibroblast CaD (CaD39-6F), as well as a mutant of the full-length CaD (CaD-6F), in which all six potential phosphorylation sites for Cdc2 kinase were abolished. The mitotic CaD39-6F-overexpressing cells required more time to progress from anaphase start to 50% cytokinesis, exhibited larger size, and abnormally formed numerous small blebs. In contrast, overexpression of the wild-type C-terminal fragment of CaD (CaD39) did not result in abnormal bleb formation, but led to larger size and prolonged the time requirement between anaphase start and 50% cytokinesis. Similar abnormal blebs were also observed in the CaD-6F-overexpressing cells. CaD-6F-overexpressing cells did not show larger size but required more time to progress from anaphase start to 50% cytokinesis. These results suggest that mitosis-specific phosphorylation of CaD plays a role in inhibiting bleb formation and that the N-terminal fragment of CaD is required for cell size determination. Received 4 September 2002; received after revision 25 November 2002; accepted 4 December 2002     

Opposite roles of protein kinase C isoforms in proliferation, differentiation, apoptosis, and tumorigenicity of human HaCaT keratinocytes

We have previously shown that the protein kinase C (PKC) system plays a pivotal role in regulation of proliferation and differentiation of the human keratinocyte line HaCaT which is often used to assess processes of immortalization, transformation, and tumorigenesis in human skin. In this paper, using pharmacological and molecular biology approaches, we investigated the isoform-specific roles of certain PKC isoenzymes (conventional cPKC and ; novel nPKC and ) in the regulation of various keratinocyte functions. cPKC and nPKC stimulated cellular differentiation and increased susceptibility of cells to actions of inducers of apoptosis, and they markedly inhibited cellular proliferation and tumor growth in immunodeficient mice. In marked contrast, cPKC and nPKC increased both in vitro and in vivo growth of cells and inhibited differentiation and apoptosis. Our data present clear evidence for the specific, antagonistic roles of certain cPKC and nPKC isoforms in regulating the above processes in human HaCaT keratinocytes.Received 13 January 2004; received after revision 18 February 2004; accepted 25 February 2004     

AMP-activated protein kinase in skeletal muscle: From structure and localization to its role as a master regulator of cellular metabolism

The AMP-activated protein kinase (AMPK) is a metabolite sensing serine/threonine kinase that has been termed the master regulator of cellular energy metabolism due to its numerous roles in the regulation of glucose, lipid, and protein metabolism. In this review, we first summarize the current literature on a number of important aspects of AMPK in skeletal muscle. These include the following: (1) the structural components of the three AMPK subunits (i.e. AMPKα, β, and γ), and their differential localization in response to stimulation in muscle; (2) the biochemical regulation of AMPK by AMP, protein phosphatases, and its three known upstream kinases, LKB1, Ca²⁺/calmodulin-dependent protein kinase kinase (CaMKK), and transforming growth factor-β-activated kinase 1 (TAK1); (3) the pharmacological agents that are currently available for the activation and inhibition of AMPK; (4) the physiological stimuli that activate AMPK in muscle; and (5) the metabolic processes that AMPK regulates in skeletal muscle. Received 04 May 2008; received after revision 14 June 2008; accepted 14 July 2008     

Regulation of the H<Superscript>+</Superscript>-ATP synthase by IF1: a role in mitohormesis

The mitochondrial H⁺-ATP synthase is a primary hub of cellular homeostasis by providing the energy required to sustain cellular activity and regulating the production of signaling molecules that reprogram nuclear activity needed for adaption to changing cues. Herein, we summarize findings regarding the regulation of the activity of the H⁺-ATP synthase by its physiological inhibitor, the ATPase inhibitory factor 1 (IF1) and their functional role in cellular homeostasis. First, we outline the structure and the main molecular mechanisms that regulate the activity of the enzyme. Next, we describe the molecular biology of IF1 and summarize the regulation of IF1 expression and activity as an inhibitor of the H⁺-ATP synthase emphasizing the role of IF1 as a main driver of energy rewiring and cellular signaling in cancer. Findings in transgenic mice in vivo indicate that the overexpression of IF1 is sufficient to reprogram energy metabolism to an enhanced glycolysis and activate reactive oxygen species (ROS)-dependent signaling pathways that promote cell survival. These findings are placed in the context of mitohormesis, a program in which a mild mitochondrial stress triggers adaptive cytoprotective mechanisms that improve lifespan. In this regard, we emphasize the role played by the H⁺-ATP synthase in modulating signaling pathways that activate the mitohormetic response, namely ATP, ROS and target of rapamycin (TOR). Overall, we aim to highlight the relevant role of the H⁺-ATP synthase and of IF1 in cellular physiology and the need of additional studies to decipher their contributions to aging and age-related diseases.     

Possible involvement of protein kinase C in the stimulation of amino acid transport by phorbol ester,platelet-derived growth factor and A23187 in Swiss 3T3 cells

Summary Stimulation of amino acid transport induced by phorbol-12, 13-dibutyrate, platelet-derived growth factor or A23187 was not observed in cells lacking protein kinase C. On the other hand, stimulation of transport by epidermal growth factor or insulin was not affected. These results suggested that the stimulation of amino acid transport is mediated by at least two separate pathways.This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, and the Ministry of Health and Welfare of Japan.     

Possible involvement of protein kinase C in the stimulation of amino acid transport by phorbol ester, platelet-derived growth factor and A23187 in Swiss 3T3 cells

Stimulation of amino acid transport induced by phorbol-12,13-dibutyrate, platelet-derived growth factor or A23187 was not observed in cells lacking protein kinase C. On the other hand, stimulation of transport by epidermal growth factor or insulin was not affected. These results suggested that the stimulation of amino acid transport is mediated by at least two separate pathways.     

Receptor communication within the lymphocyte plasma membrane: a role for the thrombospondin family of matricellular proteins

Lymphocytes, the principal cells of the immune system, carry out immune surveillance throughout the body by their unique capacity to constantly reposition themselves between a free-floating vascular state and a tissue state characterized by migration and frequent adhesive interactions with endothelial cells and components of the extracellular matrix. Therefore, mechanisms co-ordinating adhesion and migration with signals delivered through antigen recognition probably play a pivotal role for the regulation of lymphocyte behaviour and function. Endogenous thrombospondin-1 (TSP-1) seems to be the hub in such a mechanism for autocrine regulation of T cell adhesion and migration. TSP-1 functions as a mediator of cis interaction of vital receptors within the T lymphocyte plasma membrane, including integrins, low density lipoprotein receptor-related protein, calreticulin and integrin-associated protein. Received 1 June 2006; received after revision 28 June 2006; accepted 11 October 2006     

The Penicillium chrysogenum antifungal protein PAF, a promising tool for the development of new antifungal therapies and fungal cell biology studies

In recent years the interest in antimicrobial proteins and peptides and their mode of action has been rapidly increasing due to their potential to prevent and combat microbial infections in all areas of life. A detailed knowledge about the function of such proteins is the most important requirement to consider them for future application. Our research in recent years has been focused on the low molecular weight, cysteine-rich and cationic antifungal protein PAF from Penicillium chrysogenum, which inhibits the growth of opportunistic zoo-pathogens including Aspergillus fumigatus, numerous plant-pathogenic fungi and the model organism Aspergillus nidulans. So far, the experimental results indicate that PAF elicits hyperpolarization of the plasma membrane and the activation of ion channels, followed by an increase in reactive oxygen species in the cell and the induction of an apoptosis-like phenotype. Detailed knowledge about the molecular mechanism of action of antifungal proteins such as PAF contributes to the development of new antimicrobial strategies that are urgently needed. Received 09 August 2007; received after revision 17 September 2007; accepted 19 September 2007     

Procaine, a local anesthetic, interacting with the cell membrane and inhibiting the processing of exported protein precursors in Escherichia coli]

In E. coli cells grown in the presence of procaine (0.55% w/v), precursor forms of alkaline phosphatase and of glutamine binding protein accumulate besides mature forms synthesized prior to procaine addition. An experimental technique, of general application, for isolation and purification of mature and precursor forms obtained under these conditions, is described.     

Meiosis: role of a histone kinase in the condensation of ovarian oocyte chromosomes of Xenopus laevis and Ambystoma mexicanum]

By injecting heterologous histone-kinase preparations into ovarian Axolotl oocytes, it has been possible to speed up the progesterone-induced process of chromosome condensation. Moreover, in some instances, this condensation and even complete maturation have been obtained after injection of protein kinase alone, thus in the absence of hormone stimulation. Two different histone kinase preparations have been used: one was prepared from ascites cell chromatin and the other from in vitro ovulated Xenopus oocytes.     

Changes in glycosaminoglycan sulfation and protein kinase C subcellular distribution during differentiation of the human colon tumor cell line Caco-2

Summary During the spontaneous differentiation (day 5 to day 15 of the culture) of Caco-2 cells, the sulfation of cell layer glycosaminoglycans increased, whereas protein kinase C activity was concomitantly redistributed from the membrane to the cytosol. The protein kinase C activators, 4-phorbol 12-myristate, 13-acetate and 1,2-dioctanoyl-glycerol inhibited glycosaminoglycan sulfation. By contrast, 4-phorbol 12, 13 didecanoate was ineffective.These results suggest that membrane-bound PKC may exert a modulatory effect on glycosaminoglycan sulfation, and this effect is gradually attenuated as Caco-2 cell differentiation progresses.