Involvement Of MAPK Signaling Pathways Research Articles

EVL Promotes Osteo-/Odontogenic Differentiation of Dental Pulp Stem Cells via Activating JNK Signaling Pathway.

Human dental pulp stem cells (hDPSCs) were recognized as a suitable and promising source of stem cells in dental pulp regeneration. However, the mechanism by which hDPSCs differentiation into osteo-/odontogenic lineage remains unclear. Ena/VASP-like protein (EVL) has been found to be involved in diverse biological processes. In this study, we explored the role and underlying mechanism of EVL in osteo-/odontogenic differentiation of hDPSCs. Expression of EVL was detected in hDPSCs by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot (WB) analyses during osteo-/odontogenic differentiation. The function of EVL in osteo-/odontogenic differentiation and involvement of MAPK signaling pathways were evaluated by alkaline phosphatase (ALP) staining and activity, alizarin red staining (ARS), and qRT-PCR and western blot analyses. The expression of EVL was upregulated during osteo-/odontogenic differentiation of hDPSCs. Overexpression of EVL significantly increased osteo-/odontogenic capacity of hDPSCs, which was reflected in increased alkaline phosphatase (ALP) staining, ALP activity, mineralized nodule formation, and the expressions of genes related to osteo-/odontogenic differentiation, while downregulation of EVL inhibited it. In addition, EVL activated the JNK pathway and phosphorylation of p38 MAPK during differentiation procedure of hDPSCs. The EVL-enhanced differentiation of DPSCs was suppressed by blocking the JNK pathway, rather than the p38 MAPK pathway. EVL promotes the osteo-/odontogenic differentiation of hDPSCs by activating the JNK pathway, providing a future target for osteo-/odontogenic differentiation and dental pulp regeneration.

Transcriptomes of Injured Lamprey Axon Tips: Single-Cell RNA-Seq Suggests Differential Involvement of MAPK Signaling Pathways in Axon Retraction and Regeneration after Spinal Cord Injury.

Axotomy in the CNS activates retrograde signals that can trigger regeneration or cell death. Whether these outcomes use different injury signals is not known. Local protein synthesis in axon tips plays an important role in axon retraction and regeneration. Microarray and RNA-seq studies on cultured mammalian embryonic or early postnatal peripheral neurons showed that axon growth cones contain hundreds to thousands of mRNAs. In the lamprey, identified reticulospinal neurons vary in the probability that their axons will regenerate after axotomy. The bad regenerators undergo early severe axon retraction and very delayed apoptosis. We micro-aspirated axoplasms from 10 growing, 9 static and 5 retracting axon tips of spinal cord transected lampreys and performed single-cell RNA-seq, analyzing the results bioinformatically. Genes were identified that were upregulated selectively in growing (n = 38), static (20) or retracting tips (18). Among them, map3k2, csnk1e and gtf2h were expressed in growing tips, mapk8(1) was expressed in static tips and prkcq was expressed in retracting tips. Venn diagrams revealed more than 40 components of MAPK signaling pathways, including jnk and p38 isoforms, which were differentially distributed in growing, static and/or retracting tips. Real-time q-PCR and immunohistochemistry verified the colocalization of map3k2 and csnk1e in growing axon tips. Thus, differentially regulated MAPK and circadian rhythm signaling pathways may be involved in activating either programs for axon regeneration or axon retraction and apoptosis.

Enamel Matrix Derivative Enhances the Odontoblastic Differentiation of Dental Pulp Stem Cells via Activating MAPK Signaling Pathways.

The odontoblastic differentiation of dental pulp stem cells (DPSCs) contributes to pulp-dentin regeneration. Enamel matrix derivative (EMD) is considered to be a critical epithelial signal to induce cell differentiation during odontogenesis and has been widely applied to clinical periodontal tissue regeneration. The purpose of this study was to explore the effect of EMD on DPSCs proliferation and odontoblastic differentiation, as well as the underlying mechanisms. We conducted in vitro and in vivo researches to get a comprehensive understanding of EMD. In vitro phase: cell proliferation was assessed by a cell counting kit-8 (CCK-8) assay; then, alkaline phosphatase (ALP) activity and staining, alizarin red staining, real-time RT-PCR, and western blot analysis were conducted to determine the odontoblastic potential and involvement of MAPK signaling pathways. In vivo phase: after ensuring the biocompatibility of VitroGel 3D-RGD via scanning electron microscopy (SEM), the hydrogel mixture was subcutaneously injected into nude mice followed by histological and immunohistochemical analyses. The results revealed that EMD did not interfere with DPSCs proliferation but promoted the odontoblastic differentiation of DPSCs in vitro and in vivo. Furthermore, blocking the MAPK pathways suppressed the EMD-enhanced differentiation of DPSCs. Finally, VitroGel 3D-RGD could well support the proliferation, differentiation, and regeneration of DPSCs. Overall, this study demonstrates that EMD enhances the odontoblastic differentiation of DPSCs through triggering MAPK signaling pathways. The findings provide a new insight into the mechanism by which EMD affects DPSCs differentiation and proposes EMD as a promising candidate for future stem cell therapy in endodontics.

To Investigate the Pathogenesis and Inflammatory Response of Premature Ventricular Contractions Based on MAPK Signaling Pathway

Objective: To explore the involvement of MAPK signaling pathway in the pathogenesis of premature ventricular contractions (PVCs) and the regulation of inflammatory response. Methods: A total of 40 patients with PVCs admitted to Xi'an Hospital of Traditional Chinese Medicine from June 2021 to December 2021 were randomly selected as the observation group, and 40 healthy subjects during the same period were selected as the control group. Blood samples were collected intravenously, and the levels of MAPK, IL-1β, IL-6 and TNF-αin serum of the subjects were detected by enzyma-linked immunosorbent assay (ELISA). To analyze the relationship between MAPK signaling pathway and PVC and regulation of inflammatory response. Results: Compared with the control group, the levels of serum MAPK and inflammatory factors IL-1β, IL-6 and TNF-αin observation group were significantly increased (P<0.05), and the expression of MAPK signaling pathway was highly positively correlated with the levels of inflammatory factors IL-1β, IL-6 and TNF-αin observation group. Conclusion: The pathogenesis of PVCs may be related to MAPK signaling pathway and inflammatory response. PVCs may promote the release of IL-1β, IL-6 and TNF-α by activating MAPK signaling pathway, up-regulating MAPK expression, and inducing inflammatory response.

P1747GLOBAL MIRNOME PROFILE REVEALS INVOLMENT OF MITOGEN ACTIVATED PROTEIN KINASE (MAPK) PATHWAY IN PATIENTS WITH ANTIBODY MEDIATED REJECTION (CABMR) OF RENAL TRANSPLANT

Abstract Background and Aims MicroRNAs (miRNAs) are non-coding RNA that play pivotal role in modulating expression of multiple target genes at post-transcriptional level and have potential to modulate physiological &amp; pathological processes thus can be used as potential therapeutic targets. The impact of miRNA regulations have been shown in various kidney disorders but its involvement in allograft function and immunity has not been investigated thoroughly thus we studied the miRNAs expression involved in CABMR. The impact of miRNA regulation involved in allograft function and immunity has not been investigated thoroughly thus we studied the miRNAs expression involved in CABMR. Method Patients with CABMR (Banff’s classification- 2017) were included. 25 blood donors (M=18) with a mean age of 52.4Y were served as controls. Samples were processed for RNA isolation. RNA integrity was checked by running over 1% agarose gel and quantity and qualities were checked using nanodrop with 260/230 and 260/280 ≥ 1.8. Massive parallel sequencing was performed by HiSeq 3000 sequencing system (Illumina Inc.,USA). The data obtained from the sequencing run were processed and filtered using the miRNA analysis app (Illumina Inc., USA) and analysis were performed using the BaseSpace Sequence Hub genomics computing environment (Illumina Inc., USA). Dysregulated miRNAs were detected by quantitative miRNA stem loop RT-PCR technology (TaqMan MicroRNA Assays, Applied Biosystems, CA) as per manufactures protocol. Expression was measured by calculating fold change. Targets of dysregulated miRNAs were predicted by computational analysis using bioinformatics tools like miRTarBase and Target Scan Human as well as using databases. Pathway analysis of predicted targets were performed using DIANA - mirPath online analysis tool and Kyoto Encyclopedia Genes and Genomes (KEGG) database. Evaluation of MAPK signaling pathway was done by Immuno histochemistry (IHC). Results Total 46 patients (Male=40 with mean age of 46.82 Y) were enrolled for the study with post- transplant duration of 33.72 months. The demographic details with mean values were: S Creatinine = 1.68 mg/dl, BUN = 28.26 mg/dl, Tac level = 5.98 ng/ml, S Uric Acid = 6.95 mg/dl, S Albumin = 3.46 g/dl, Na+/K+ = 128.9/4.16 mmol/L, S Phosphorus = 3.18 mg/dl, S Alkaline phosphate = 83.22 u/L. Induction regimen (Basiliximab=40, ATG= 6) Baseline Immunosuppression MMF+Pred (Tacrolimus/Cyclosporin) = 43/3. C4d were positive in 23 and DSA+ in 3 patients. Comparative miRnome analysis revealed that a total of 123 miRNAs showed differential level of expression in CABMR patients (n=3) as compared to the control (n=1) out of which 93 were upregulated while 40 were downregulated. Conserved level of differential expression shows upregulation of miR-9 (p≤0.0001), miR-21 (p=0.0024), miR-29a (p=0.0001), miR-126 (p=0.0076), miR-210 (p=0.0001) and miR-223 (p=0.0006) while hsa-miR-221 was downregulated. Pathway analysis shows involvement of MAPK signaling pathways, Transforming growth factor-β (TGF-β) superfamily signaling pathways, Wnt signaling pathways, ErbB signaling pathways. IHC of MAPK signaling shows significantly positive cytoplasmic tubular intensity as well as inflammatory cells intensity. Conclusion Altered miRNA expression profiling was found in CABMR compared to healthy controls. MAPK signaling pathways is involved in the pathogenesis of CABMR MicroRNAs are crucial regulators of cell function. They are easy to detect and represent potentially good targets for novel therapies.

ERCC6L that is up-regulated in high grade of renal cell carcinoma enhances cell viability in vitro and promotes tumor growth in vivo potentially through modulating MAPK signalling pathway.

Renal cell carcinoma (RCC), which is one of the most diagnosed urological malignancies worldwide, is usually associated with abnormality in both genetic and cellular processes. In the present study, through analyzing The Cancer Genome Atlas (TCGA) dataset, we screened out ERCC6L as a candidate gene that is potentially related to the development of RCC based on its increased expression in ccRCC tissues compared with normal kidney tissues as well as its possible relevance to cancer prognosis. Evidence indicates that ERCC6L is an indispensable component of mammalian cell mitosis, while it fails to disclose the role of ERCC6L in tumorigenesis. By using RT-PCR, it was confirmed that the mRNA expression of ERCC6L was upregulated in RCC tissues as compared to normal controls in 28 pared samples. In addition, the immunohistochemistry study in a tissue microarray (TMA) containing 150 ccRCC samples showed that the staining score of ERCC6L was positively correlated with the Fuhrman grade of cancers. Next, when the expression of ERCC6L was lowered by specific shRNA, the cell viability was significantly inhibited in 786-O and Caki-1 cells, while the apoptosis was induced accordingly. At the same time, RCC cells those were transfected with shRNA targeting to ERCC6L grew significantly slower than parental cells in immunodeficient mice. These results consistently suggest that ERCC6L may play a role in regulating the cell viability of RCC both in vitro and in vivo. Further, gene expression microarray analysis followed by the validating western blot after knocking down ERCC6L expression in 786-O cells highlighted the involvement of MAPK signaling pathway in regulation of ERCC6L on cellular process of RCC. In conclusion, the present study suggests a likely promoting role of ERCC6L on the development of RCC. Thus, further study to explore the potential utility of ERCC6L as a novel therapeutic target of RCC is clearly needed.

Involvement of MAPK Signaling Pathways in Tributyltin‐induced Increases of Interleukin 1 beta and Interleukin 6 mRNA in Human Lymphocytes

IL‐1β and IL‐6 are pro‐inflammatory cytokines produced by monocytes, macrophages, and lymphocytes. Both are responsible for immune response regulation and cellular growth. Increased levels of these two cytokines are associated with several pathologies, including rheumatoid arthritis, multiple sclerosis, and specific cancers (such as breast, lung, and pancreatic). Tributyltin (TBT) is an environmental contaminant which is found in human blood and other tissues, and it has been shown to increase incidences of tumors in mammals. Previous ex vivo studies have shown that when TBT is introduced as a stress inducer to the cellular environment, the production (secretion and/or intracellular levels) of IL‐1β and IL‐6 was increased in human lymphocytes, and ERK1/2 and p38 MAPK pathways were shown to be necessary for this TBT effect. The current study examines whether this increased production (protein levels) of IL‐1β and IL‐6 is due to TBT‐induced increases in the transcription of IL‐1β and IL‐6 mRNA. Additionally, this study will examine the roles of MAPKs (ERK1/2 and p38) on any demonstrated TBT‐induced increases in expression of IL‐1β and IL‐6 mRNA in lymphocytes (monocyte‐depleted (MD) peripheral blood mononuclear cells (PBMCs)). MD‐PBMCs were exposed to 0–200 nM TBT followed by isolation of RNA. The IL‐1β and IL‐6 mRNA levels were monitored using semi‐quantitative RT‐PCR. mRNA levels of each cytokine were also monitored in the presence and absence of ERK1/2 (PD98059) and p38 (SB202190) pathway inhibitors. Results indicated that exposure to 50–200 nM TBT caused increased levels of both IL‐1β and IL‐6 mRNA. Initial results suggest that the MAPK pathways, although involved in the TBT‐induced increased in cytokine production, may not have a role in the TBT‐induced increases on mRNA expression. These data suggest that MAPK pathway activation is needed for TBT to cause increased production for both IL‐1β and IL‐6.Support or Funding InformationNIH grant U54CA163066

Quercetin-3-O-β-D-Glucuronide Suppresses Lipopolysaccharide-Induced JNK and ERK Phosphorylation in LPS-Challenged RAW264.7 Cells.

Quercetin, a flavonol, has been reported to exhibit a wide range of biological properties including anti-oxidant and anti-inflammatory activities. However, pharmacological properties of quercetin-3-O-β-D-glucuronide (QG), a glycoside derivative of quercetin, have not been extensively examined. The objective of this study is to elucidate the anti-inflammatory property and underlying mechanism of QG in lipopolysaccharide (LPS)-challenged RAW264.7 macrophage cells in comparison with quercetin. QG significantly suppressed LPS-induced extracellular secretion of pro-inflammatory mediators such as nitric oxide (NO) and PGE2, and pro-inflammatory protein expressions of iNOS and COX-2. To elucidate the underlying mechanism of the anti-inflammatory property of QG, involvement of MAPK signaling pathways was examined. QG significantly attenuated LPS-induced activation of JNK and ERK in concentration-dependent manners with a negligible effect on p38. In conclusion, the present study demonstrates QG exerts anti-inflammatory activity through the suppression of JNK and ERK signaling pathways in LPS-challenged RAW264.7 macrophage cells.

Midazolam induces apoptosis in MA-10 mouse Leydig tumor cells through caspase activation and the involvement of MAPK signaling pathway

PurposeThe present study aims to investigate how midazolam, a sedative drug for clinical use with cytotoxicity on neuronal and peripheral tissues, induced apoptosis in MA-10 mouse Leydig tumor cells.MethodsThe apoptotic effect and underlying mechanism of midazolam to MA-10 cells were investigated by flow cytometry assay and Western blotting methods.ResultsData showed that midazolam induced the accumulation of the MA-10 cell population in the sub-G1 phase and a reduction in the G2/M phase in a time- and dose-dependent manner, suggesting an apoptotic phenomenon. Midazolam could also induce the activation of caspase-8, -9, and -3 and poly (ADP-ribose) polymerase proteins. There were no changes in the levels of Bax and cytochrome-c, whereas Bid was significantly decreased after midazolam treatment. Moreover, midazolam decreased both pAkt and Akt expression. In addition, midazolam stimulated the phosphorylation of p38 and c-Jun NH2-terminal kinase but not extracellular signal-regulated kinase.ConclusionMidazolam could induce MA-10 cell apoptosis through the activation of caspase cascade, the inhibition of pAkt pathway, and the induction of p38 and c-Jun NH2-terminal kinase pathways.

Involvement of MAPK signaling pathway in the osteogenic gene expressions of Cervi Pantotrichum Cornu in MG-63 human osteoblast-like cells

AimsThe purposes of this study were to determine whether Cervi Pantotrichum Cornu (CPC) has osteogenic activities in human osteoblastic MG-63 cells and to investigate the underlying molecular mechanism. Main methodsThe effects of CPC on alkaline phosphatase activity, collagen synthesis, and calcium deposits were measured. The COL1A1, ALPL, BGLAP, and SPP1 expressions were measured by real-time PCR. Phosphorylated MAP kinases (ERK1/2, JNK1/2, p38, ELK1, and cJUN) were studied by western blot analysis. The involvement of MAPK pathway in osteogenic gene expressions was determined by using each selective MAPK inhibitor (PD98059, SP600125, and SB203580). Key findingsCPC increased alkaline phosphatase activity, collagen synthesis, and calcium deposits. CPC activated ERK1/2, JNK1/2, p38, and ELK1 phosphorylation except cJUN. CPC increased the COL1A1, ALPL, BGLAP, and SPP1 gene expressions. The elevated COL1A1 and BGLAP expressions were inhibited by PD98059, SP600125 or SB203580. The elevated ALPL expression was blocked by SB203580. The elevated SPP1 expression was inhibited by SP600125 or SB203580. CPC increased COL1A1 and BGLAP expressions via ERK1/2, JNK1/2, and p38 MAPKs pathways and SPP1 expression via JNK1/2 and p38 pathways. p38 pathway is needed for ALPL expression. SignificanceThese results imply that MAPK signaling pathway is an indispensable factor for bone matrix genes expression of CPC in MG-63 human osteoblast-like cells.

ERK‐1/2 and p38 in the regulation of hypertrophic changes of normal articular cartilage chondrocytes induced by osteoarthritic subchondral osteoblasts

Previous studies have shown the influence of subchondral bone osteoblasts (SBOs) on phenotypical changes of articular cartilage chondrocytes (ACCs) during the development of osteoarthritis (OA). The molecular mechanisms involved during this process remain elusive, in particular, the signal transduction pathways. The aim of this study was to investigate the in vitro effects of OA SBOs on the phenotypical changes in normal ACCs and to unveil the potential involvement of MAPK signaling pathways during this process. Normal and arthritic cartilage and bone samples were collected for isolation of ACCs and SBOs. Direct and indirect coculture models were applied to study chondrocyte hypertrophy under the influence of OA SBOs. MAPKs in the regulation of the cell-cell interactions were monitored by phosphorylated antibodies and relevant inhibitors. OA SBOs led to increased hypertrophic gene expression and matrix calcification in ACCs by means of both direct and indirect cell-cell interactions. In this study, we demonstrated for the first time that OA SBOs suppressed p38 phosphorylation and induced ERK-1/2 signal phosphorylation in cocultured ACCs. The ERK-1/2 pathway inhibitor PD98059 significantly attenuated the hypertrophic changes induced by conditioned medium from OA SBOs, and the p38 inhibitor SB203580 resulted in the up-regulation of hypertrophic genes in ACCs. The findings of this study suggest that the pathologic interaction of OA SBOs and ACCs is mediated via the activation of ERK-1/2 phosphorylation and deactivation of p38 phosphorylation, resulting in hypertrophic differentiation of ACCs.

Lanthanum chloride suppresses hydrogen peroxide-enhanced calcification in rat calcifying vascular cells

Lanthanum chloride (LaCl(3)) has been shown to retard the progression of established atherosclerotic lesions in animal models, and used as a calcium channel blocker in various cellular experiments. In this study, we assessed the role of lanthanum chloride (LaCl(3)) in H(2)O(2)-enhanced calcification in rat calcifying vascular cells (CVCs) and examined the involvement of MAPK signaling pathways. H(2)O(2) induced growth inhibition of CVCs, as well as increases in intracellular levels of calcium and reactive oxygen species, ALP activity, apoptosis and calcium deposition. These effects of H(2)O(2) were suppressed by pretreatment of the cells with 1 muM of LaCl(3) for 2 h. In addition, H(2)O(2) activated the phosphorylation of ERK1/2, JNK and p38 MAPK, but only the last two were associated with the ALP activity. Our findings demonstrate that H(2)O(2)-enhanced osteoblastic differentiation and apoptosis are responsible for the increased calcification in rat CVCs, and LaCl(3) can counteract these effects by suppressing the activation of JNK (JNK2, but not JNK1) and p38 MAPK signaling pathway.

The Immunomodulating Effect of AS101 on Interleukin-10 Production and the Involvement of MAPK Signaling Pathway in Atopic Dermatitis (37.3)

Abstract Atopic dermatitis (AD) is a chronic inflammatory skin disease. Recently it was reported that interleukin 10 (IL-10) is also overexpressed in skin lesions of atopic dermatitis (AD) patients and this ectopic expression is believed to be an important factor in the pathogenesis of the disease. Thus the regulation of IL-10 production is a potential solution for immunotherapeutic intervention in AD. In this study, we determined whether the tellurium immunomodulating compound, ammonium tri-chloro(dioxoethylene-O,O′-) tellurate (AS101) may inhibit IL-10, and thereby affect the profile of cytokines produced by T cells of AD patients. Further, we investigated the possible correlation between changes in IL-10 levels and the expression of mitogen-activated protein (MAP) kinases. We show here that the IL-10 level was higher in AD patients compared to healthy donors, while their IL-2 and IFNγ levels were reduced. The addition of the AS101 inhibited the production of interleukin-10, while increasing the production of IL-2 and IFNγ. These changes correlate with the inhibition of p38 MAP kinase. The immunomodulatory effect of AS101, together with its excellent clinical safety profile in humans, suggests that AS101 has potential as a therapeutic agent for AD.

Differentiation of Mesenchymal Stem Cells Towards a Nucleus Pulposus-like Phenotype In Vitro: Implications for Cell-Based Transplantation Therapy

Because mesenchymal stem cells can differentiate into chondrocyte-like cells, we ask the question, can mesenchymal stem cells commit to the nucleus pulposus phenotype? Back pain, a significant source of morbidity in our society, is linked to degenerative changes of the intervertebral disc. Absence of suitable graft tissue limits therapeutic approaches for repair of disc tissue. For this reason, there is considerable interest in developing "tissue engineering" strategies for the regeneration of the nucleus pulposus. Rat mesenchymal stem cells were immobilized in 3-dimensional alginate hydrogels and cultured in a medium containing transforming growth factor-beta1 under hypoxia (2% O2) and normoxia (20% O2). Mesenchymal stem cells were examined by confocal microscopy to evaluate their viability and metabolic status after labeling with Celltracker green, a thiol sensitive dye, and Mitotracker red, a dye sensitive to the mitochondrial membrane potential. Flow cytometry, semiquantitative reverse transcription polymerase chain reaction and Western blot analysis were carried out to evaluate phenotypic and biosynthetic activities and the signaling pathways involved in the differentiation process. Under hypoxic conditions, mesenchymal stem cells formed large aggregates and exhibited positive Celltracker and Mitotracker signals. Glucose transporter-3, matrix metalloproteinase-2, collagen type II and type XI, and aggrecan mRNA and protein expression was upregulated, whereas there was no change in the levels of decorin, biglycan, fibromodulin, and lumican. Hypoxia maintained the expression of CD44 (hyaluronan receptor), ALCAM (CD166), and endoglin (transforming growth factor-beta receptor). Likewise, expression of beta3 and alpha2 integrin was upregulated. Transforming growth factor-beta treatment increased MAPK activity and Sox-9, aggrecan, and collagen type II gene expression. Basal levels of the phosphorylated MAPK isoform ERK1/2, but not p38, were higher under hypoxic conditions than normoxia, and its activation was further augmented by treatment of cells with transforming growth factor-beta. In hypoxia, transforming growth factor-beta sustained phosphorylated p38 expression for an extended time period. Pharmacological inhibition of ERK1/2 and p38 enzymatic activity resulted in a decrease in Sox-9, aggrecan, and collagen type II mRNA levels. Our results indicate that hypoxia and transforming growth factor-beta drive mesenchymal stem cell differentiation towards a phenotype consistent with that of the nucleus pulposus. Measurement of selected signaling molecules and response to specific inhibitors suggest involvement of MAPK signaling pathways. It is concluded that mesenchymal stem cells could be used to repopulate the damaged or degenerate intervertebral disc.

Activation of MAPK signaling pathway is essential for Id-1 induced serum independent prostate cancer cell growth.

The helix-loop-helix protein Id-1 has been suggested to play a positive role in cell proliferation and tumorigenesis of many types of human cancers. However, little is known about the molecular mechanism involved in the function of Id-1. In this study, using four stable Id-1 transfectant clones, we investigated the involvement of MAPK signaling pathway in the Id-1 induced serum independent prostate cancer cell growth. Our results demonstrated that both transient and stable ectopic Id-1 expression in prostate cancer LNCaP cells led to activation of the Raf/MEK1/2 signaling pathway. In addition, inhibition of MEK1/2 phosphorylation by one of its inhibitors, PD098059, resulted in the decreased cell cycle S phase fraction and cell growth rate, suggesting that activation of MAPK signaling pathway is essential for Id-1 induced prostate cancer cell proliferation. Furthermore, treatment with antisense oligonucleotide complementary to Id-1 mRNA in PC-3 and DU145 cells resulted in a decreased Id-1 expression which was accompanied by decreased Egr-1 protein. Our results suggest for the first time that the function of Id-1 is associated with MAPK signaling pathway activation and indicate a possible novel mechanism in which Id-1 regulates prostate cancer cell growth and tumorigenesis.