Involvement Of c-Jun Research Articles

Neuroprotective effects of curcumin on endothelin-1 mediated cell death in hippocampal neurons

Objectives: Alzheimer's disease is a progressive neurodegenerative disease characterized by loss of hippocampal neurons leading to memory deficits and cognitive decline. Studies suggest that levels of the vasoactive peptide endothelin-1 (ET-1) are increased in the brain tissue of Alzheimer's patients. Curcumin, the main ingredient of the spice turmeric, has been shown to have anti-inflammatory, anti-cancer, and neuroprotective effects. However, the mechanisms underlying some of these beneficial effects are not completely understood. The objective of this study was to determine if curcumin could protect hippocampal neurons from ET-1 mediated cell death and examine the involvement of c-Jun in this pathway.Methods: Primary hippocampal neurons from rat pups were isolated using a previously published protocol. Viability of the cells was measured by the live/dead assay. Immunoblot and immunohistochemical analyses were performed to analyze c-Jun levels in hippocampal neurons treated with either ET-1 or a combination of ET-1 and curcumin. Apoptotic changes were evaluated by immunoblot detection of cleaved caspase-3, cleaved fodrin, and a caspase 3/7 activation assay.Results: ET-1 treatment produced a 2-fold increase in the levels of c-Jun as determined by an immunoblot analysis in hippocampal neurons. Co-treatment with curcumin significantly attenuated the ET-1 mediated increase in c-Jun levels. ET-1 caused increased neuronal cell death of hippocampal neurons indicated by elevation of cleaved caspase-3, cleaved fodrin and an increased activity of caspases 3 and 7 which was attenuated by co-treatment with curcumin. Blockade of JNK, an upstream effector of c-Jun by specific inhibitor SP600125 did not fully protect from ET-1 mediated activation of pro-apoptotic enzymes in primary hippocampal cells.Discussion: Our data suggests that one mechanism by which curcumin protects against ET-1-mediated cell death is through blocking an increase in c-Jun levels. Other possible mechanisms include decreasing pro-apoptotic signaling activated by ET-1 in primary hippocampal neurons.

Involvement of c-jun in human liposarcoma growth: supporting data from clinical immunohistochemistry and DNAzyme efficacy

c-jun has been found to be upregulated in a variety of cancers. Recently, this oncogene has also been implicated in liposarcoma (LS) progression. c-jun knockdown mediated by a deoxyribozyme induced apoptosis in LS cells via evoking caspase-10, but not the Fas/FasL pathway. A novel orthotopic model for LS was established in the hindlimb of mice using human cells to extend the evaluation of effects of c-jun knockdown in vivo. Tumor take in vivo was 100%, with growths resembling high grade aggressive LS. The c-jun deoxyribozyme inhibited the growth of LS in this model. Clinically, downregulation of c-jun may proffer an improved treatment outcome for liposarcoma. The new model for LS described here will enable better testing of agents with therapeutic potential against LS.

Endoplasmic Reticulum Stress Increases the Expression of Methylenetetrahydrofolate Reductase through the IRE1 Transducer

Methylenetetrahydrofolate reductase (MTHFR), an enzyme in folate and homocysteine metabolism, influences many cellular processes including methionine and nucleotide synthesis, methylation reactions, and maintenance of homocysteine at nontoxic levels. Mild deficiency of MTHFR is common in many populations and modifies risk for several complex traits including vascular disease, birth defects, and cancer. We recently demonstrated that MTHFR can be up-regulated by NF-kappaB, an important mediator of cell survival that is activated by endoplasmic reticulum (ER) stress. This observation, coupled with the reports that homocysteine can induce ER stress, prompted us to examine the possible regulation of MTHFR by ER stress. We found that several well characterized stress inducers (tunicamycin, thapsigargin, and A23187) as well as homocysteine could increase Mthfr mRNA and protein in Neuro-2a cells. The induction of MTHFR was also observed after overexpression of inositol-requiring enzyme-1 (IRE1) and was inhibited by a dominant-negative mutant of IRE1. Because IRE1 triggers c-Jun signaling, we examined the possible involvement of c-Jun in up-regulation of MTHFR. Transfection of c-Jun and two activators of c-Jun (LiCl and sodium valproate) increased MTHFR expression, whereas a reported inhibitor of c-Jun (SP600125) and a dominant-negative derivative of c-Jun N-terminal kinase-1 reduced MTHFR activation. We conclude that ER stress increases MTHFR expression and that IRE1 and c-Jun mediate this activation. These findings provide a novel mechanism by which the ER can regulate homeostasis and allude to an important role for MTHFR in cell survival.

C-Jun, a crucial molecule in metastasis of breast cancer and potential target for biotherapy

Human breast cancer cell line SKBR3 expresses high level of the ErbB2 molecule, which has been associated with poor prognosis of breast cancer. Elevated ErbB2 functions as a transactivating co-receptor and promotes the formation of ErbB2 containing heterodimers, which are more mitogenic and transforming, and have a higher ligand affinity and signaling potency by virtue of the potent latent kinase activity of ErbB2. Interestingly, SKBR3 cells are non-tumorigenic in nude mice. By ectopic overexpression of c-Jun in SKBR3 cells, involvement of c-Jun in invasiveness and metastasis in vivo was investigated in this study. The critical role of c-Jun in the tumorigenesis and metastasis is demonstrated in nude mice.

Identification of c‐Jun as a critical mediator for the intracrine 24 kDa FGF‐2 isoform‐induced cell proliferation

Tumor cells frequently synthesize an N-terminally extended the FGF-2 isoform of 24 kDa devoid of signal peptide but that contains a functional nuclear localization sequence (NLS). Although the signaling pathways elicited by secreted FGF-2 are well described, the molecular mechanisms involved in the growth promoting action of nuclearized 24 kDa FGF-2 remain unknown. The cancer cell line AR4-2J was engineered to stably express only the 24 kDa FGF-2 isoform and cDNA microarrays were used to identify targets implicated in the intracrine-induced cell proliferation. Levels of 27 transcripts were found either upregulated or downregulated compared to control cells. Among the 18 upregulated genes was c-jun, which is often involved in cell proliferation. Real-time PCR and Western blot analyses confirmed c-jun induction at both mRNA and protein levels. The c-jun antisense oligonucleotide strategy pointed out the involvement of c-Jun in the 24 kDa FGF-2-induced cell proliferation. The mitogenic effect was found to depend on ERK pathway and not on phosphoinositide 3-kinase, p38 MAPK, c-Jun NH2-terminal kinase signal transducers. In addition, the MEK inhibitor PD98059 reduced the 24 kDa FGF-2-dependent c-Jun level. These data show that intracrine FGF-2-mediated regulation of cell growth involves ERK activation and consequent c-Jun expression. Thus, despite its incapacity to be secreted, the intracellular-localized 24 kDa FGF-2 can activate a growth-related signaling pathway normally elicited by cell surface receptors.

P38 and Activating Transcription Factor-2 Involvement in Osteoblast Osmotic Response to Elevated Extracellular Glucose

Poorly controlled or untreated type I diabetes mellitus is characterized by hyperglycemia and is associated with decreased bone mass and osteoporosis. We have demonstrated that osteoblasts are sensitive to hyperglycemia-associated osmotic stress and respond to elevated extracellular glucose or mannitol by increasing c-jun and collagen I expression. To determine whether MAPKs are involved in this response, MC3T3-E1 osteoblasts were treated with 16.5 mm glucose, mannitol, or contrast dye for 1 h. Immunoblotting of phosphorylated p38 demonstrated activation of p38 MAPK by hyperosmotic stress in vitro and in vivo. Activation peaked at 20 min, remained detectable after 24 h, and was protein kinase C-independent. Activating transcription factor-2 (ATF-2) activation followed the same pattern as phospho-p38. Transactivation of cAMP response element (CRE)- and c-jun promoter (containing a CRE-like element)-reporter constructs increased following hyperosmotic treatment. SB 203580 (a p38 MAPK inhibitor) blocked ATF-2 phosphorylation, CRE transactivation, and c-jun promoter activation. Hyperosmotic activation of collagen I promoter activity was also inhibited by SB 203580, consistent with the involvement of c-jun in collagen I up-regulation. Therefore, we propose that hyperglycemia-induced increases in p38 MAPK activity and ATF-2 phosphorylation contribute to CRE activation and modulation of c-jun and collagen I expression in osteoblasts.

Involvement of c-JUN in the regulation of terminal differentiation genes in normal and malignant keratinocytes.

In stratifying cultures of human keratinocytes, expression of the proto-oncoprotein c-JUN and the small proline rich 2 (SPRR2) protein, a precursor of the cornified cell envelope, are inversely related. Whereas c-JUN is typically found in basal proliferating cells, SPRR2 is restricted to suprabasal differentiating layers. Malignant keratinocytes (derived from squamous cell carcinoma, SCC) have reduced sprr2 expression, consistent with their low potential to differentiate, and express c-jun at higher levels than normal keratinocytes. A direct relation between c-jun and sprr2 expression was shown in several ways: transient ectopic expression of c-jun inhibits sprr2a promoter activity in normal differentiating cells, whereas in malignant keratinocytes a dominant negative c-jun mutant restored at least partially both the low promoter activity and the expression of endogenous sprr2. These effects are mediated via a 134 bp promoter fragment which does not include the sprr2a AP-1 binding site. Interestingly, in an SCC cell line, constitutively expressing the dominant c-jun mutant, expression of the terminal differentiation marker involucrin is also strongly increased, suggesting that c-JUN is a general modulator of keratinocyte terminal differentiation rather than only affecting the expression of sprr2.

Enhancement of interleukin-3-dependent mast cell proliferation by suppression of c-jun expression.

We have previously shown that protein kinase C (PKC) depletion is associated with an increase in the proliferation of interleukin 3 (IL-3)-induced mast cells. Here we show that the AP-1 components c-Jun and c-Fos are induced by IL-3. While c-Jun's induction by IL-3 is totally dependent on PKC, c-Fos induction by IL-3 is only attenuated by PKC depletion. AP-1 binding activity was also induced by IL-3 but this induction was PKC independent. These results indicated a possible involvement of c-Jun in the inhibition of IL-3-induced growth regulation. A support for this assumption came from experiments in which an increase in thymidine incorporation into mast cells was noted when c-jun antisense oligomers were administered to IL-3-treated cells. Since the only known effect of direct inhibition of c-Jun on proliferation rates in several cellular systems was a reduction of proliferation, we verified that our c-jun antisense oligomer could also inhibit proliferation rates in fibroblasts where such a repression was previously reported. Thus c-Jun has an inhibitory effect on IL-3 induction of mast cells proliferation that is distinct from its role in several other cellular environments. These observations reveal the involvement of AP-1 and its components in IL-3-induced signal transduction and the importance of the mast cell environment in determining their specific cellular function.

Involvement of c-Jun in the control of glucocorticoid receptor transcriptional activity during development of chicken retinal tissue.

The ability of the glucocorticoid receptor (GR) to induce gene expression in embryonic chicken retinal tissue increases dramatically during development, although the quantity of the receptor molecules does not change greatly with age. This study examines the possible involvement of c-Jun in the developmental control of GR activity. Expression of c-Jun in retinal tissue was high at early embryonic ages and declined during development. Elevation of c-Jun expression in retina of mid-developmental ages by treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), or by introduction of a c-Jun expression vector, caused a pronounced decline in the inducibility of the endogenous glutamine synthetase gene and the transiently transfected CAT constructs p delta G46TCO and pGS2.1CAT, that are controlled by a minimal consensus glucocorticoid response element (GRE) promoter and the glutamine synthetase promoter, respectively. The effect of c-Jun was dose dependent and could be reversed by overexpression of GR. C-Jun-evoked repression of GR activity could be relieved by overexpression of Jun D. Overexpression of Jun D could also elevate the responsiveness of early embryonic retina to glucocorticoids and cause a 5-fold increase in p delta G46TCO induction. The effect of Jun D could be reversed by overexpression of c-Jun. Expression of c-Jun might therefore be important for repression of GR activity at early embryonic ages.