Mitogen-activated protein kinases (MAPKs) are implicated in regulating plant growth, development, and response to the environment. However, the underlying mechanisms are unknown because of the lack of information about their substrates. Using a conditional gain-of-function transgenic system, we demonstrated that the activation of SIPK, a tobacco (Nicotiana tabacum) stress-responsive MAPK, induces the biosynthesis of ethylene. Here, we report that MPK6, the Arabidopsis thaliana ortholog of tobacco SIPK, is required for ethylene induction in this transgenic system. Furthermore, we found that selected isoforms of 1-aminocyclopropane-1-carboxylic acid synthase (ACS), the rate-limiting enzyme of ethylene biosynthesis, are substrates of MPK6. Phosphorylation of ACS2 and ACS6 by MPK6 leads to the accumulation of ACS protein and, thus, elevated levels of cellular ACS activity and ethylene production. Expression of ACS6 DDD , a gain-of-function ACS6 mutant that mimics the phosphorylated form of ACS6, confers constitutive ethylene production and ethylene-induced phenotypes. Increasing numbers of stress stimuli have been shown to activate Arabidopsis MPK6 or its orthologs in other plant species. The identification of the first plant MAPK substrate in this report reveals one mechanism by which MPK6/ SIPK regulates plant stress responses. Equally important, this study uncovers a signaling pathway that modulates the biosynthesis of ethylene, an important plant hormone, in plants under stress.

Hypersensitive response (HR), a form of programmed cell death, is frequently associated with plant disease resistance. It has been proposed that mitogen-activated protein kinase (MAPK) cascades regulate HR cell death based on pharmacological studies by using kinase inhibitors. However, direct evidence is lacking. Here, we demonstrate that NtMEK2, a MAPK kinase, is upstream of salicylic acid-induced protein kinase (SIPK) and wounding-induced protein kinase (WIPK), two tobacco MAPKs that are activated by various pathogens or pathogen-derived elicitors. Expression of a constitutively active mutant of NtMEK2 induces HR-like cell death in tobacco, which is preceded by the activation of endogenous SIPK and WIPK. In addition, NtMEK2-SIPK͞WIPK cascade appears to control the expression of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and L-phenylalanine ammonia lyase (PAL), two defense genes encoding key enzymes in the phytoalexin and salicylic acid biosynthesis pathways. These results demonstrate that a plant MAPK cascade controls multiple defense responses against pathogen invasion.

Many proteins have been proposed to act as surrogate markers of organ damage, yet for many candidates the essential characteristics which link the protein to the injured organ have not yet been described. We generated an NGAL-reporter mouse by inserting a di-fusion reporter gene, Luciferase2(Luc2)/mCherry(mC) into the Ngal locus. The Ngal-Luc2/mC reporter accurately recapitulated the endogenous message and illuminated injuries in vivo in real-time. In the kidney, Ngal-Luc2/mC imaging showed a sensitive, rapid, dose-dependent, reversible, and organ and cellular specific relationship with tubular stress, which quantitatively paralleled urinary Ngal (uNgal). Unexpectedly, specific cells of the distal nephron were the source of uNgal. Cells isolated from Ngal-Luc2/mC mice could also track both the onset and the resolution of the injury, and monitor the actions of NF-κB inhibitors and antibiotics in the case of infection. Accordingly, the imaging of Ngal-Luc2/mC mice and cells identified injurious and reparative agents which effect kidney damage.

In Arabidopsis, NPR1 mediates the salicylic acid (SA)-induced expression of pathogenesis-related (PR) genes and systemic acquired resistance (SAR). Here, we report the identification of another component, CPR6, that may function with NPR1 in regulating PR gene expression. The dominant CPR6-1 mutant expresses the SA/NPR1-regulated PR genes ( PR-1 , BGL2 , and PR-5 ) and displays enhanced resistance to Pseudomonas syringae pv maculicola ES4326 and Peronospora parasitica Noco2 in the absence of SAR induction. cpr6-1 -induced PR gene expression is not suppressed in the cpr6-1 npr1-1 double mutant but is suppressed when SA is removed by salicylate hydroxylase. Thus, constitutive PR gene expression in cpr6-1 requires SA but not NPR1. In addition, resistance to P. s. maculicola ES4326 is suppressed in the cpr6-1 npr1-1 double mutant, despite expression of PR-1 , BGL2 , and PR-5 . Resistance to P. s. maculicola ES4326 must therefore be accomplished through unidentified antibacterial gene products that are regulated through NPR1 . These results show that CPR6 is an important regulator of multiple signal transduction pathways involved in plant defense. INTRODUCTIONPathogens annually cause billions of dollars in damage to crops worldwide (Baker et al., 1997). Consequently, an increasing amount of research has been dedicated to developing novel methods for controlling plant diseases. Such studies have centered on the plant's innate ability to resist pathogen invasion in an effort to buttress the plant's own defenses to counter pathogen attacks (Staskawicz et al., 1995; Baker et al., 1997). One such defense mechanism under study is known as systemic acquired resistance (SAR; reviewed in Ryals et al., 1996). SAR is defined as a generalized defense response, which is often induced by avirulent pathogens and provides enhanced resistance to a broad spectrum of virulent pathogens (Chester, 1933;Ross, 1961;Kuc, 1982;Ryals et al., 1994). Avirulent pathogens carry an avirulence ( avr ) gene whose product can be recognized by the product of a corresponding resistance ( R ) gene carried by plants. Such recognition triggers both a programmed cell death response, known as the hypersensitive response (HR), around the point of pathogen infection and release of a systemic SAR-inducing signal (Hammond-Kosack and Jones, 1996). After a rapid, localized HR, the elevated state of resistance associated with SAR is effective throughout the plant for a period of time ranging from several days to a few weeks (Van Loon and Van Kammen, 1970;Malamy et al., 1990;Ward et al., 1991; Yalpani et al., 1991;Uknes et al., 1992).Salicylic acid (SA) is an integral signaling component of SAR (Gaffney et al., 1993). During an SAR response, endogenous levels of SA increase dramatically throughout the plant (Malamy et al., 1990(Malamy et al., , 1992Métraux et al., 1990;Rasmussen et al., 1991; Yalpani et al., 1991; Enyedi et al., 1992;Uknes et al., 1993). Exogenous application of SA (White, 1979) or the SA analogs 2,6-dichloroisonicotinic acid (INA;Métraux et al....

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Annexin A2 (AnxA2) was originally identified as a substrate of the pp60v-src oncoprotein in transformed chicken embryonic fibroblasts. It is an abundant protein that associates with biological membranes as well as the actin cytoskeleton, and has been implicated in intracellular vesicle fusion, the organization of membrane domains, lipid rafts and membrane-cytoskeleton contacts. In addition to an intracellular role, AnxA2 has been reported to participate in processes localized to the cell surface including extracellular protease regulation and cell-cell interactions. There are many reports showing that AnxA2 is differentially expressed between normal and malignant tissue and potentially involved in tumour progression. An important aspect of AnxA2 function relates to its interaction with small Ca2+-dependent adaptor proteins called S100 proteins, which is the topic of this review. The interaction between AnxA2 and S100A10 has been very well characterized historically; more recently, other S100 proteins have been shown to interact with AnxA2 as well. The biochemical evidence for the occurrence of these protein interactions will be discussed, as well as their function. Recent studies aiming to generate inhibitors of S100 protein interactions will be described and the potential of these inhibitors to further our understanding of AnxA2 S100 protein interactions will be discussed.Linked ArticlesThis article is part of a themed section on Pharmacology of the Gasotransmitters. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-7

The CXC chemokine receptor 4 (CXCR4) exerts a variety of functions at different steps of hepatocellular carcinoma (HCC) progression. The molecular mechanisms and therapeutic value of CXCR4 in the development of HCC remain undefined. Here we show that aberrant CXCR4 overexpression is associated with poor prognosis and aggressive characteristics of HCC. Suppression of CXCR4 activity via CXCR4 knockdown, AMD3100 or neutralizing antibody administration inhibits hepatoma cell tumorigenesis in vitro and in vivo. CXCR4 overexpression displays the opposite effects. Using Mir library screening we identify miR-622 as a regulator of CXCR4. Further studies show that miR-622 directly target the 3′ untranslated region of CXCR4 and is transcriptionally repressed by EZH2-induced H3K27 trimethylation and promoter methylation. EZH2/miR-622 promotes tumorigenesis through CXCR4. EZH2-mediated loss of miR-622 is found to correlate with CXCR4 overexpression and unfavourable prognosis in HCC patients. This study establishes EZH2/miR-622/CXCR4 as a potential adverse prognostic factor and therapeutic target for HCC patients.

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