Dickkopf-related protein 1/cytoskeleton-associated protein 4 signaling activation by Helicobacter pylori-induced activator protein-1 promotes gastric tumorigenesis via the PI3K/AKT/mTOR pathway

BACKGROUND Gastric cancer(GC)is a common malignant tumor with high incidence and mortality rates globally,especially in East Asian countries.Helicobacter pylori(H.pylori)infection is a significant and independent risk factor for GC.However,its underlying mechanism of action is not fully understood.Dickkopf-related protein(DKK)1 is a Wnt signaling antagonist,and cytoskeleton-associated protein(CKAP)4 is a newly identified DKK1 receptor.Recent studies found that the binding of DKK1 to CAKP4 mediated the procancer signaling of DKK1 independent of Wnt signaling.We hypothesize that H.pylori-induced activation of DKK1/CKAP4 signaling contributes to the initiation and progression of GC.AIM To investigate the interaction of H.pylori infection,DKK1 and CAKP4 in GC,as well as the underlying molecular mechanisms.METHODS RNA sequencing was used to identify differentially expressed genes(DEGs)between H.pylori-infected and uninfected primary GC cells.Gain-and loss-offunction experiments were performed to verify the H.pylori-induced upregulation of activator protein-1(AP-1)in GC cells.A dual-luciferase reporter assay and co-immunoprecipitation were used to determine the binding of AP-1 to the DKK1 promoter and DKK1 to CKAP4.Western blotting and immunohistochemistry detected the expression of DKK1,CKAP4,and phosphatidylinositol 3-kinase(PI3K)pathway-related proteins in GC cells and tissues.Functional experiments and tumorigenicity in nude mice detected malignant behavior of GC cells in vitro and in vivo.RESULTS We identified 32 DEGs between primary GC cells with and without H.pylori infection,including JUN,fos-like antigen-1(FOSL1),and DKK1,and confirmed that the three proteins and CKAP4 were highly expressed in H.pylori-infected GC cells,H.pylori-infected gerbil gastric tissues,and human GC tissues.JUN and FOSL1 form AP-1 to transcriptionally activate DKK1 expression by binding to the DKK1 promoter.Activated DKK1 bound to CKAP4,but not the most common Wnt coreceptor low-density lipoprotein receptor-related protein 5/6,to promote GC cell growth,colony formation,migration,invasion,and xenograft tumor growth in nude mice.All these effects were driven by activation of the PI3K/AKT/mammalian target of rapamycin(mTOR)pathway.Targeting the PI3K signaling pathway by LY294002 inhibited DKK1-mediated CKAP4/PI3K signaling activity and the malignant behavior of GC cells.CONCLUSION H.pylori induces JUN and FOSL1 expression to form AP-1,which transcriptionally activates DKK1.Binding of DKK1 to KAKP4 contributes to gastric tumorigenesis via the PI3K/AKT/mTOR pathway.

Regulation of cytoskeleton-associated protein activities: Linking cellular signals to plant cytoskeletal function

The plant cytoskeleton undergoes dynamic remodeling in response to diverse developmental and environmental cues. Remodeling of the cytoskeleton coordinates growth in plant cells, including trafficking and exocytosis of membrane and wall components during cell expansion, and regulation of hypocotyl elongation in response to light. Cytoskeletal remodeling also has key functions in disease resistance and abiotic stress responses. Many stimuli result in altered activity of cytoskeleton-associatedproteins,microtubuleassociated proteins(MAPs) and actin-binding proteins(ABPs). MAPs and ABPs are the main players determining the spatiotemporally dynamic nature of the cytoskeleton, functioning in a sensory hub that decodes signals to modulate plant cytoskeletal behavior. Moreover, MAP and ABP activities and levels are precisely regulated during development and environmental responses, but our understanding of this process remains limited. In this review, we summarize the evidence linking multiple signaling pathways, MAP and ABP activities and levels, and cytoskeletal rearrangements in plant cells. We highlight advances in elucidating the multiple mechanisms that regulate MAP and ABP activities and levels, including calcium and calmodulin signaling, ROP GTPase activity, phospholipid signaling, and post-translational modifications.

Cytoskeleton-associated protein tyrosine phosphorylation involved in induction of differentiation in mouse melanoma cells

The malignancy of a cancer is due partly to its poor differentiation. Genistein, a protein tyrosine kinase inhibitor, is found to induce the highly malignant B16-BL6 mouse melanoma cells to differentiate to mature phenotypes. When Triton X-100 insoluble fraction of the differentiated cells is prepared and analyzed, tyrosine phosphorylation levels of three cytoskeleton-associated proteins (65, 60 and 53 ku respectively) are found to decrease dramatically. But no any change is found when phosphotyrosine contents of the cytosol fraction or the total cellular protein preparations are evaluated. It is concluded that cytoskeleton-associated protein tyrosine phosphorylation may be involved in the control of differentiation of cancer cells. The decrease of phosphotyrosine contents of cytoskeleton-associated proteins may be one of the important mechanisms underlying the differentiation induction of cancer cells by anticancer agents.

Changes in structural plasticity of hippocampal neurons in an animal model of multiple sclerosis

Structural plasticity is critical for the functional diversity of neurons in the brain.Experimental autoimmune encephalomyelitis(EAE)is the most commonly used model for multiple sclerosis(MS),successfully mimicking its key pathological features(inflammation,demyelination,axonal loss,and gliosis)and clinical symptoms(motor and non-motordysfunctions).Recentstudieshave demonstrated the importance of synaptic plasticity in EAE pathogenesis.In the present study,we investigated the features of behavioral alteration and hippocampal structural plasticity in EAE-affected mice in the early phase(11 days post-immunization,DPI)and chronic phase(28DPI).EAE-affected mice exhibited hippocampus-related behavioral dysfunction in the open field test during both early and chronic phases.Dendritic complexity was largely affected in the cornu ammonis 1(CA1)and CA3 apical and dentate gyrus(DG)subregions of the hippocampus during the chronic phase,while this effect was only noted in the CA1 apical subregion in the early phase.Moreover,dendritic spine density was reduced in the hippocampal CA1 and CA3 apical/basal and DG subregions in the early phase of EAE,but only reduced in the DG subregion during the chronic phase.Furthermore,mRNA levels of proinflammatory cytokines(Il1β,Tnfα,and Ifnγ)and glial cell markers(Gfap and Cd68)were significantly increased,whereas the expression of activity-regulated cytoskeletonassociated protein(ARC)was reduced during the chronic phase.Similarly,exposure to the aforementioned cytokines in primary cultures of hippocampal neurons reduced dendritic complexity and ARC expression.Primary cultures of hippocampal neurons also showed significantly reduced extracellular signal-regulated kinase(ERK)phosphorylation upon treatment with proinflammatory cytokines.Collectively,these results suggest that autoimmune neuroinflammation alters structural plasticity in the hippocampus,possibly through the ERK-ARC pathway,indicating that this alteration may be associated with hippocampal dysfunctions in EAE.

Analyses of fear memory in Arc/Arg3.1-deficient mice: intact short-term memory and impaired long-term and remote memory

Activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) was originally identified in patients with seizures. It is densely distributed in the hip-pocampus and amygdala in particular. Because the expression of Arc/Arg3.1 is regulated by nerve in-puts, it is thought to be an immediate early gene. As shown both in vitro and in vivo, Arc/Arg3.1 is in-volved in synaptic consolidation and regulates some forms of learning and memory in rats and mice [1,2]. Furthermore, a recent study suggests that Arc/Arg3.1 may play a significant role in signal transmission via AMPA-type glutamate receptors [3-5]. Therefore, we conducted a detailed analysis of fear memory in Arc/Arg3.1-deficient mice. As previously reported, the knockout animals exhib-ited impaired fear memory in both contextual and cued test situations. Although Arc/Arg3.1-deficient mice showed almost the same performance as wild-type littermates 4 hr after a conditioning trial, their performance was impaired in the retention test after 24 hr or longer, either with or without reconsolidation. Immunohistochemical analyses showed an abnormal density of GluR1 in the hip-pocampus of Arc/Arg3.1-deficient mice;however, an application of AMPA potentiator did not improve memory performance in the mutant mice. Memory impairment in Arc/Arg3.1-deficient mice is so ro-bust that the mice provide a useful tool for devel-oping treatments for memory impairment.