Raf kinase inhibitor protein inhibits cell proliferation but promotes cell migration in rat hepatic stellate cells

Aim: Hepatic stellate cells (HSCs) play an important role in the pathogenesis of liver fibrosis and cirrhosis. Raf kinase inhibitor protein (RKIP), an inhibitor of extracellular signal‐regulated kinases (ERK)/mitogen‐activated protein kinase (MAPK) signalling pathway, has been proved to suppress tumor metastasis. Interestingly, RKIP promotes cell migration in Madin–Darby canine kidney epithelial cells. However, the effects of RKIP on HSC behaviours are unknown. The purpose of the present study is to investigate the role of RKIP in HSC proliferation, apoptosis and migration. Methods: Two types of cells, freshly isolated HSC and HSC‐T6 cell line, were used in this study. The amount of RKIP, the phosphorylation of RKIP, Raf and ERK (pRKIP, pRaf and pERK) were analysed in quiescent and activated HSCs by Western blots. HSC‐T6 cells were transfected with RKIP‐expressing plasmid or treated with locostatin, a RKIP inhibitor. HSC proliferation, apoptosis and migration were evaluated with 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay, terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick‐end labelling (TUNEL) staining and Transwell cell migration assay respectively. Results: In activated HSCs, RKIP protein expression was downregulated whereas pRKIP, pRaf and pERK were upregulated. RKIP overexpression significantly mitigated the phosphorylation of RKIP, Raf and ERK. This in turn inhibited HSC proliferation. Locostatin not only inhibited RKIP protein expression but also, to some extent, reversed the RKIP‐inhibited phosphorylation of RKIP, Raf and ERK. RKIP augmented HSC migration and enhanced wound closure. Locostatin reversed the effects of RKIP. Conclusion: Raf kinase inhibitor protein inhibits ERK/MAPK signalling and this inhibition impedes HSC proliferation. RKIP promotes HSC migration and wound closure.     

Bidirectional signals transduced by TOPK-ERK interaction increase tumorigenesis of HCT116 colorectal cancer cells

BACKGROUND & AIMS: Aberrant activation of Ras and Raf in mitogen-activated protein kinase (MAPK) signaling has been linked with cancer. However, the role of MAPK kinases (MAPKKs or MEKs) in cancer is unclear, although constitutively activated MEK1, which does not exist in nature, is "oncogenic." Herein, we found that T-cell-originated protein kinase (TOPK), a member of the MAPKK protein family, is highly expressed in human colorectal cancer tissues and cell lines and plays an important role in the transformation of colorectal cancer. METHODS: The biologic consequences of overexpression or knockdown of TOPK in JB6 Cl41 and HCT116 colorectal cancer cells were studied in vitro and in vivo, respectively. Kinase assay or transient transfection experiments were performed to study the bidirectional signaling pathway between TOPK and extracellular signal-regulated kinase (ERK). RESULTS: TOPK was shown to promote transformation in vitro and in vivo, and knockdown of TOPK in HCT116 colorectal cancer cells reduced this cell lines' tumorigenic properties in vitro and in vivo. Furthermore, a positive feedback loop between TOPK and ERK2 was identified. With epidermal growth factor treatment, knockdown of either TOPK or ERK2 in HCT116 cells resulted in a decreased phosphorylation of ERK2 or TOPK, respectively, and knockdown of TOPK in HCT116 colorectal cancer cells blocked the phosphorylation of downstream substrates of ERK2. CONCLUSIONS: The positive feedback loop between TOPK and ERK2 increases tumorigenesis properties of HCT116 colorectal cancer cells, and TOPK-regulated signaling may serve as a potential therapeutic target in colorectal cancer.     

The chemotactic and mitogenic responses of vascular smooth muscle cells to insulin-like growth factor-I require the activation of ERK1/2

Insulin-like growth factors (IGFs) play an important role in regulating vascular smooth muscle cell (VSMC) proliferation and directed migration. IGFs exert these biological actions through the activation of the IGF-I receptor and its downstream signaling network. While the involvement of the IRS-PI3 kinase-Akt pathway in mediating the chemotactic and mitogenic actions of IGFs is clear, the role of the mitogen-activated protein kinase (MAPK) signaling pathway is still under debate. In this study, the role of ERK1 and 2 in mediating the chemotactic and mitogenic actions of IGF-I in cultured porcine VSMCs was investigated. IGF-I treatment caused a significant increase in the phosphorylation state, as well as the kinase activity, of ERK1 and 2. Compared to the strong and sustained MAPK activation induced by platelet-derived growth factor-BB, the IGF-I-induced MAPK activation was weaker and more transient. Specific inhibition of the MAPK activation by PD98059 or U0126, two selective MEK inhibitors, significantly inhibited IGF-I-stimulated cell proliferation, and reduced the number of cells that migrated towards IGF-I. The p38 MAPK inhibitor SB203580 had no such effect. Likewise, depletion of ERK1/2 using antisense oligonucleotides abolished the IGF-I-induced VSMC migration and proliferation. These results suggest that the chemotactic and mitogenic responses of VSMCs to IGF-I require the activation of ERK1 and 2.     

Silencing profilin-1 inhibits gastric cancer progression via integrin β1/focal adhesion kinase pathway modulation

AIM:To investigate the role of profilin-1(PFN1)in gastric cancer and the underlying mechanisms.METHODS:Immunohistochemical analysis,quan-titative real-time polymerase chain reaction(q RTPCR)and Western blot were performed to detect PFN1expression in clinical gastric carcinoma and adjacent tissues,and the association of PFN1 expression with patient clinicopathological characteristics was analyzed.PFN1 was knocked down to investigate the role of this protein in cell proliferation and metastasis in the SGC-7901 cell line.To explore the underlying mechanisms,the expression of integrinβ1 and the activity of focal adhesion kinase(FAK)and the downstream proteins extracellular-regulated kinase(ERK)1/2,P38 mitogen-activated protein kinase(MAPK),phosphatidylinositol 3-kinase(PI3K),AKT and mammalian target of rapamycin(m TOR)were measured through Western blot or q RT-PCR analysis.Fibronectin(FN),a ligand of integrinβ1,was used to verify the correlation between alterations in the integrinβ1/FAK pathway and changes in tumor cell aggressiveness upon PFN1 perturbation.RESULTS:Immunohistochemical,Western blot and q RT-PCR analyses revealed that PFN1 expression was higher at both the protein and m RNA levels in gastric carcinoma tissues compared with the adjacent tissues.In addition,high PFN1 expression(53/75,70.4%)was correlated with tumor infiltration,lymph node metastasis and TNM stage in gastric cancer,but not with gender,age,location,tumor size,or histological differentiation.In vitro experiments showed that PFN1knockdown inhibited the proliferation of SGC-7901cells through the induction G0/G1 arrest.Silencing PFN1 inhibited cell migration and invasion and downregulated the expression of matrix metalloproteinase(MMP)-2 and MMP9.Moreover,silencing PFN1 reduced the expression of integrinβ1 at the protein level and inhibited the activity of FAK,and the downstream effectors ERK1/2,P38MAPK,PI3K,AKT and m TOR.FN-promoted cell proliferation and metastasis via the integrinβ1/FAK pathway was ameliorated by PFN1silencing.CONCLUSION:These findings suggest that PFN1 plays a critical role in gastric carcinoma progression,and these effects are likely mediated through the integrinβ1/FAK pathway.     

RKIP and 14-3-3ε Exert an Opposite Effect on Human Gastric Cancer Cells SGC7901 by Regulating the ERK/MAPK Pathway Differently

Background

Raf-1 kinase inhibitor protein (RKIP) inhibits Raf (a key element in the ERK/MAPK pathway) and is regarded as anti-tumoral. In contrast, 14-3-3 is considered protumoral. However, the pathogenetic role of RKIP and 14-3-3ε in gastric cancer is unclear.

Aim

The purpose of this study was to examine the influence of 14-3-3ε and RKIP on SGC7901, the regulation of the ERK/MAKP pathway by both, and the interaction between the two proteins.

Methods

RKIP and 14-3-3ε genes were introduced into SGC7901 cells using gene cloning technique, then, the bioactivities including the proliferation, migration and invasion of the cells were assessed by MTT and migration assays. ERK/MAKP pathway’s activity was examined using real-time quantitative RT–PCR, western blot, immunoprecipitation and 3D-immunolocalization techniques.

Results

Our results showed that RKIP inhibited SGC7901 cells’ bioactivities whereas 14-3-3ε upregulated them through the involvement of the ERK/MAPK pathway. RKIP inactivated this pathway, but 14-3-3ε activated it. RKIP and 14-3-3ε were co-localized in the cells and interacted with each other; this attributed to their opposite influence on the ERK/MAPK pathway and the cells bioactivities.

Conclusions

The ERK/MAPK pathway is involved in the pathogenesis of gastric cancer; RKIP and 14-3-3ε exert an opposite effect on this pathway and the cells possibly via both direct and indirect reactions with the elements in this pathway. The interaction between RKIP and 14-3-3ε may also contribute to their pathogenetic roles in gastric cancer.     

Low levels of raf kinase inhibitory protein in growth hormone-secreting pituitary adenomas correlate with poor response to octreotide treatment

CONTEXT: Excessive GH production by pituitary tumors causes acromegaly. Medical treatment of acromegaly with somatostatin analogs (SMSs), like octreotide, is well established, but the clinical effect is variable. One mechanism for octreotide effect is inhibition of the MAPK signaling pathway after binding to the G protein-coupled somatostatin receptor. Nonphosphorylated Raf kinase inhibitory protein (RKIP) binds to and inhibits Raf1 kinase, and thereby attenuates MAPK signaling, whereas phosphorylated RKIP inhibits G protein receptor internalization and degradation due to inhibition of G protein receptor kinase 2. Objective: Our objective was to study RKIP levels in pituitary somatotroph adenomas, and relate them to clinical characteristics and response to octreotide treatment in patients with acromegaly. PATIENTS AND METHODS: RKIP level was analyzed by Western blot of proteins extracted from somatotroph tumors frozen a short time after surgery in 51 patients with active acromegaly. An acute somatostatin test was performed in 46 of the patients, and in 21 the IGF-I level before and 6 months after SMS treatment was available. RESULTS: The adenoma RKIP level correlated significantly to both the acute and the long-term octreotide responses on serum levels of GH and IGF-I, respectively. In multiple regression analyses, the RKIP level was a significant determinant for both the GH reduction in the acute test and the IGF-I reduction after approximately 6 months. CONCLUSION: The RKIP level in somatotroph adenomas seems to be important for the clinical effect of SMS treatment, in which low levels of RKIP correlate to poor clinical response to SMSs.     

RN181 suppresses hepatocellular carcinoma growth by inhibition of the ERK/MAPK pathway

The activation of oncogenes and the inactivation of tumor suppressor genes by mutations or chronic hepatitis virus infections play key roles in the pathogenesis of hepatocellular carcinoma (HCC). Here we report that RN181, a really interesting new gene finger domain-containing protein, was down-regulated in highly malignant cell lines and in tumor cells of 139 HCC clinical samples in comparison with adjacent normal liver tissues. The expression of RN181 was strongly associated with the pathological grade of HCC. Alterations of the expression of RN181 by retrovirus-transduced up-regulation and short hairpin RNA-mediated down-regulation demonstrated the function of RN181 as a tumor suppressor because it decreased the proliferation and colony formation of HCC cells in vitro and inhibited tumor growth in vivo by suppressing cell proliferation and enhancing cell apoptosis in xenografted tumors. Proteomic analyses showed that RN181 regulates the expression of many proteins that are important in many cellular processes. Statistical analyses identified 33 proteins with consistent changes (≥2-fold) in RN181-transformed cells. Ten of these proteins were up-regulated by RN181, and 23 were down-regulated. Representative proteins were validated by western blotting. Interaction network investigations revealed that 20 RN181-regulated proteins could integrate several key biological processes such as survival, metabolism, and mitogen-activated protein kinase (MAPK) pathways. Remarkably, 11 of the 33 proteins are associated with MAPK signaling in one or more ways. RN181 suppressed the tyrosine phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in cell lines and in tumor cells of xenografts and HCC clinical samples, and removing the suppression increased tumor growth. CONCLUSION: We have shown that RN181 suppresses the tumorigenesis of HCC through the inhibition of ERK/MAPK signaling in the liver. Our results provide new insights into the pathogenesis of HCC and may help with the development of novel therapeutic strategies.     

Stimulation of insulin-like growth factor (IGF) binding protein-3 synthesis by IGF-I and transforming growth factor-alpha is mediated by both phosphatidylinositol-3 kinase and mitogen-activated protein kinase pathways in mammary epithelial cells

IGF binding protein (IGFBP)-3 is an important regulator of mammary epithelial cell (MEC) growth and can enhance the ability of both IGF-I and epidermal growth factor ligands such as TGFalpha to stimulate MEC proliferation. Here we investigate the role of the phosphatidylinositol-3 kinase (PI3K) and MAPK pathways in the regulation of IGFBP-3 expression by IGF-I and TGFalpha in bovine MECs. Both growth factors stimulated DNA synthesis, although IGF-I was the stronger mitogen. IGF-I and TGFalpha also stimulated IGFBP-3 mRNA and protein levels. TGFalpha stimulated rapid, transient activation of Akt that was maximal at 5 min and diminished by 15 min. In contrast, IGF-I-induced Akt activation was maximal between 15 and 90 min and was sustained for 6 h. Although ERK 1/2 was maximally stimulated by TGFalpha between 5 and 15 min, IGF-I did not stimulate discernible activation of ERK 1/2. In addition, TGFalpha but not IGF-I induced rapid phosphorylation of Shc, whereas only IGF-I activated insulin receptor substrate-1. Pretreatment with the PI3K inhibitor LY294002 or knockdown of p85 with small interfering RNA inhibited IGF-I or TGFalpha-stimulated IGFBP-3 expression. Similarly, MAPK kinase-1 inhibitors PD98059 and U0126 each abolished TGFalpha-stimulated increases in IGFBP-3 mRNA levels. In contrast to TGFalpha, IGF-I retained the ability to partially increase IGFBP-3 mRNA levels in the presence of MAPK kinase-1 inhibitors, indicating that IGF-I may activate alternative substrates of the PI3K pathway that are involved in IGFBP-3 regulation. In conclusion, stimulation of IGFBP-3 mRNA levels by mitogens is regulated through both the PI3K and MAPK pathways in bovine MECs.     

Acid exposure activates the mitogen-activated protein kinase pathways in Barrett's esophagus

BACKGROUND & AIMS: To explore mechanisms whereby acid reflux might contribute to carcinogenesis in Barrett's esophagus (BE) we studied: (1) the effects of acid on the mitogen-activated protein kinase (MAPK) pathways, cell proliferation, and apoptosis in a Barrett's adenocarcinoma cell line (SEG-1); and (2) the ability of acid to activate the MAPK pathways in vivo in patients with BE. METHODS: SEG-1 cells were exposed to acidic media for 3 minutes, and the activities of 3 MAPKs (ERK, p38, and JNK) were determined. Proliferation was assessed using flow cytometry; cell growth and apoptosis were assessed using cell counts and an apoptosis ELISA assay. MAPK activation was studied in biopsy specimens taken from patients with BE before and after esophageal perfusion for 3 minutes with 0.1N HCl. RESULTS: Acid-exposed SEG-1 cells exhibited a significant increase in proliferation and total cell numbers, and a significant decrease in apoptosis. These effects were preceded by a rapid increase in the activities of ERK and p38, and a delayed increase in JNK activity. PD 98059 abolished the acid-induced increase in G0/G1 and decrease in subG0 phases of the cell cycle. Both SB 203580 and DN-JNK 1/2 inhibited the acid-induced progression from G0/G1 to G2/M. The acid-induced decrease in apoptosis was abolished by inhibition of either ERK or p38. In the patients, acid exposure significantly increased the activity of p38 in the metaplastic epithelium. CONCLUSIONS: Acid increases proliferation and survival, and decreases apoptosis in SEG-1 cells by activating the MAPK pathways. Acid also activates the MAPK pathways in BE in vivo. These findings suggest that acid might contribute to carcinogenesis in BE through activation of MAPK pathways.     

Long-Term Ethanol Exposure Impairs Neuronal Differentiation of Human Neuroblastoma Cells Involving Neurotrophin-Mediated Intracellular Signaling and in Particular Protein Kinase C

Background: Revealing the molecular changes in chronic ethanol‐impaired neuronal differentiation may be of great importance for understanding ethanol‐related pathology in embryonic development but also in the adult brain. In this study, both acute and long‐term effects of ethanol on neuronal differentiation of human neuroblastoma cells were investigated. We focused on several aspects of brain‐derived neurotrophic factor (BDNF) signaling because BDNF activates the extracellular signal‐regulated kinase (ERK) cascade, promoting neuronal differentiation including neurite outgrowth. Methods: The effects of ethanol exposure on morphological differentiation, cellular density, neuronal marker proteins, basal ERK activity, and ERK responsiveness to BDNF were measured over 2 to 4 weeks. qRT‐PCR and Western blotting were performed to investigate the expression of neurotrophin receptor tyrosin kinase B (TrkB), members of the ERK‐cascade, protein kinase C (PKC) isoforms and Raf‐Kinase‐Inhibitor‐Protein (RKIP). Results: Chronic ethanol interfered with the development of a neuronal network consisting of cell clusters and neuritic bundles. Furthermore, neuronal and synaptic markers were reduced, indicating impaired neuronal differentiation. BDNF‐mediated activation of the ERK cascade was found to be continuously impaired by ethanol. This could not be explained by expressional changes monitored for TrkB, Raf‐1, MEK, and ERK. However, BDNF also activates PKC signaling which involves RKIP, which finally leads to ERK activation as well. Therefore, we hypothesized that ethanol impairs this branch of BDNF signaling. Indeed, both PKC and RKIP were significantly down‐regulated. Conclusions: Chronic ethanol exposure impaired neuronal differentiation of neuroblastoma cells and BDNF signaling, particularly the PKC‐dependent branch. RKIP, acting as a signaling switch at the merge of the PKC cascade and the Raf/MEK/ERK cascade, was associated with neuronal differentiation and significantly reduced in ethanol treatment. Moreover, PKC expression itself was even more strongly reduced. In contrast, members of the Raf‐1/MEK/ERK cascade were less affected and the observed changes were not associated with impaired differentiation. Thus, reduced RKIP and PKC levels and subsequently reduced positive feedback on ERK activation provide an explanation for the striking effects of long‐term ethanol exposure on BDNF signal transduction and neuronal differentiation, respectively.     

Signaling mechanisms leading to regulation of proliferation and differentiation of the mesenchymal chondrogenic cell line RCJ3.1C5.18 in response to IGF-I

Since IGF-I is an important chondrocyte growth factor, we sought to examine the intracellular mechanisms by which it exerts two of its pivotal effects, stimulation of proliferation and differentiation. We used the mesenchymal chondrogenic cell line RCJ3.1C5.18, which progresses spontaneously to differentiated growth plate chondrocytes. This differentiation process could be enhanced by exogenous IGF-I. Pharmacological inhibition of the phosphatidylinositol-3 (PI-3) kinase by LY294002, mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK)1/2 by U0126, the protein kinase (PK) A pathway by H-89 or KT5720, and the PKC pathway by bisindolylmaleimide suppressed IGF-I-stimulated cell proliferation. In contrast, IGF-I-enhanced early cell differentiation, as assessed by collagen type II and aggrecan gene expression, was not affected by MAPK/ERK1/2 pathway inhibition, but significantly diminished by inhibition of the PI-3 kinase, the PKC and the PKA pathway. Moreover, terminal differentiation of chondrocytes in response to IGF-I, as assessed by gene expression of alkaline phosphatase, Indian hedgehog, and collagen type X, were only interrupted by PI-3 kinase pathway inhibition. In conclusion, IGF-I exerts its differential effect on chondrocyte proliferation vs differentiation through the use of at least four partially interacting intracellular signaling pathways, whose activity is temporarily regulated. When chondrocytes progress from proliferating cells to early and terminal differentiating cells, they progressively inactivate IGF-I-related intracellular signaling pathways. This mechanism might be essential for the complex and cell stage-specific anabolic action of IGF-I in the growth plate.     

胃癌组织中Raf激酶抑制蛋白的表达临床意义

目的 探讨Raf激酶抑制蛋白(RKIP)在胃癌中的差异表达及临床意义.方法 采用激光捕获显微切割技术(LCM)获得12例纯化的胃腺癌细胞(GAC)及其癌旁(＞5 cm)胃黏膜上皮细胞(NGEC),应用18O/16O分别标记两种细胞样本酶切后的多肽混合物.结合纳升级液相色谱定量鉴定GAC和NGEC的差异表达蛋白质.免疫印迹法验证差异蛋白RKIP在胃癌中的表达.免疫组化检测RKIP蛋白在胃癌组织(118例)、癌旁胃黏膜组织(70例)、转移的淋巴结组织(35例)的表达.结果 共筛选出78个差异表达蛋白质,其中RKIP蛋白表达水平在GAC中较NGEC明显下调(1:4.37).免疫组化结果显示,RKIP蛋白表达与胃癌的浸润深度、TNM分期及淋巴结转移呈负相关,与分化程度呈正相关(P＜0.05).结论 胃癌组织中RKIP蛋白低表达可能影响胃癌的生物学行为.     

Raf激酶抑制蛋白在乳腺癌组织中的表达及意义

目的探讨Raf激酶抑制蛋白（RKIP）在浸润性乳腺癌进展中的意义。方法应用免疫组化SP法检测RKIP在16例乳腺非典型增生性病变和48例浸润性乳腺癌原发灶及其淋巴结转移灶中的表达情况,并对RKIP表达与临床病理特征的关系行Spearman等级相关分析。结果由非典型增生性病变至乳腺癌原发灶、转移灶RKIP表达水平逐渐下降,乳腺癌淋巴结转移灶与原发灶及非典型增生性病变相比RKIP表达水平明显下降（P均〈0．05）;RKIP在乳腺癌组织中的表达与患者年龄、肿瘤大小及组织学分级均无明显相关性（P均〉0．05）。结论RKIP表达异常在浸润性乳腺癌转移过程中具有重要作用,可作为判断乳腺癌进展和预后的独立指标。     

H pylori stimulates proliferation of gastric cancer cells through activating mitogen-activated protein kinase cascade

INTRODUCTION H pylori is an important pathogen associated with gastritis and peptic ulcers[1]. It has also been defined as a carcinogen[2]. The mechanisms of pathogenic and carcinogenic effects of H pylori infection are under intensive investigation. Rese…     

Components of the mitogen-activated protein kinase cascade are activated in hepatic cells by Echinococcus multilocularis metacestode

AIM： To explore the effect of Echinococcusmultilocularis on the activation of mitogen-activated protein kinase （MAPK） signaling pathways and on livercell proliferation.METHODS： Changes in the phosphorylation of MAPKs and proliferating cell nuclear antigen （PCNA）expression were measured in the liver of patients withalveolar echinococcosis （AE）. MAPKs, MEK1/2 [MAPK/extracellular signal-regulated protein kinase （ERK）kinase] and ribosomal S6 kinase （RSK） phosphorylationwere detected in primary cultures of rat hepatocytesin contact in vitro with （1） E. multilocu/aris vesicle fluid（EmF）, （2）E. multilocularis-conditioned medium （EmCM）.RESULTS： In the liver of AE patients, ERK 1/2 andp38 MAPK were activated and PCNA expression wasincreased, especially in the vicinity of the metacestode.Upon exposure to EmF, p38, c-Jun N-terminal kinase（JNK） and ERK1/2 were also activated in hepatocytesin vitro, as well as MEK1/2 and RSK, in the absenceof any toxic effect. Upon exposure to EmCM, only JNKwas up-regulated.CONCLUSION： Previous studies have demonstratedan influence of the host on the MAPK cascade inE. multilocularis. Our data suggest that the reverse,i.e. parasite-derived signals efficiently acting onMAPK signaling pathways in host liver ceils, is actuallyoperating.     

Down-regulation of the dual-specificity phosphatase MKP-1 suppresses tumorigenicity of pancreatic cancer cells

BACKGROUND & AIMS: In both pancreatic cancer and chronic pancreatitis, there is enhanced expression of mitogenic growth factors and their tyrosine kinase receptors, which have the capacity to activate mitogen-activated protein kinase (MAPK). In view of the important role of MAPK kinase phosphatase (MKP)-1 in the regulation of MAPK activation, the expression and functional role of MKP-1 was analyzed. METHODS: Pancreatic tissues were analyzed by Northern blotting, Western blotting, and immunohistochemistry. Pancreatic cancer cells were transfected with a full-length MKP-1 antisense construct. Growth characteristics and tumorigenicity in vivo and the effects of mitogenic growth factors on cell growth and MAPK activation were determined in transfected and control cells. RESULTS: MKP-1 messenger RNA (mRNA) levels were increased in pancreatic cancer and chronic pancreatitis (CP) tissues. Moderate to strong MKP-1 immunoreactivity was present in the cancer cells, ductal cells of pancreatic intraepithelial neoplasia, and in tubular complexes in CP. Down-regulation of MKP-1 resulted in decreased anchorage-dependent and -independent growth of pancreatic cancer cells, and decreased tumorigenicity in a nude mouse tumor model. MKP-1 down-regulation led to decreased proliferation and sustained MAPK activation in response to mitogens. CONCLUSIONS: Suppression of MKP-1 expression reduces the tumorigenicity of pancreatic cancer cells in vivo, suggesting that MKP-1 contributes to enhanced mitogenic signaling in pancreatic cancer cells.     

Mixed-lineage kinase 3 regulates B-Raf through maintenance of the B-Raf/Raf-1 complex and inhibition by the NF2 tumor suppressor protein

The Ras --> Raf --> MEK1/2 --> extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway couples mitogenic signals to cell proliferation. B-Raf and Raf-1 function within an oligomer wherein they are regulated in part by mutual transactivation. The MAPK kinase kinase (MAP3K) mixed-lineage kinase 3 (MLK3) is required for mitogen activation of B-Raf and cell proliferation. Here we show that the kinase activity of MLK3 is not required for support of B-Raf activation. Instead, MLK3 is a component of the B-Raf/Raf-1 complex and is required for maintenance of the integrity of this complex. We show that the activation of ERK and the proliferation of human schwannoma cells bearing a loss-of-function mutation in the neurofibromatosis 2 (NF2) gene require MLK3. We find that merlin, the product of NF2, blunts the activation of both ERK and c-Jun N-terminal kinase (JNK). Finally, we demonstrate that merlin and MLK3 can interact in situ and that merlin can disrupt the interactions between B-Raf and Raf-1 or those between MLK3 and either B-Raf or Raf-1. Thus, MLK3 is part of a multiprotein complex and is required for ERK activation. The levels of this complex may be negatively regulated by merlin.     

贲门腺癌组织中RKIP、E-cadherin的表达变化及相关性

目的 观察Raf激酶抑制蛋白（RKIP）、上皮型钙黏蛋白（E-cadherin）在贲门腺癌组织中的表达变化,并探讨其相关性.方法 应用免疫组化SP法检测160例贲门腺癌组织及癌旁非肿瘤组织中RKIP、E-cadherin的蛋白表达情况,分析其表达与临床病理参数的关系以及两者表达的相关性.结果 RKIP和E-cadherin在贲门腺癌组织中表达明显低于癌旁组织（P均＜0.05）.RKIP和E-cadherin在高分化、中分化和低分化的贲门腺癌组织中的表达差异有统计学意义（P均＜0.01）,在有淋巴结转移的贲门腺癌组织中表达低于无淋巴结转移的组织（P均＜0.05）.RKIP和E-cadherin在贲门腺癌组织中的表达呈正相关（r=0.388,P＜0.05）.结论 RKIP和E-cadherin 在贲门腺癌组织中表达降低,且两者表达呈正相关.