丁苯酞对阿尔茨海默病大鼠海马p38丝裂原激活蛋白激酶和细胞外信号调节激酶表达的影响

目的探究丁苯酞对阿尔茨海默病（AD）大鼠海马区中p38丝裂原激活蛋白激酶（MAPK）和细胞外信号调节激酶（ERK）表达的影响。方法雄性成年SD大鼠90只随机分为试验组、对照组和空白组各30只,在试验组和对照组大鼠海马区内注射Aβ1-42建立AD模型,建模后第2天开始给予试验组丁苯酞灌胃,对照组和空白组给予相同剂量的食用麻油,共喂养30 d。之后通过Y型迷宫比较三组学习记忆能力,通过免疫组织化学染色方法比较三组脑组织中p38MAPK和ERK的表达水平。结果三组学习记忆能力由强到弱依次为空白组,试验组和对照组;三组CA1海马区p38MAPK表达阳性的细胞数量由高到低依次为对照组、试验组和空白组;三组大脑皮层中ERK表达水平由高到低依次为空白组,试验组和对照组,差异均有统计学意义（P〈0.05）。结论丁苯酞可明显改善AD大鼠的学习记忆能力,其原因可能与海马区p38MAPK表达下降及大脑皮层中ERD表达提高有关。

p38 MAPK在小鼠睾丸出生后不同发育阶段的表达

目的 :探讨p38MAPK在小鼠睾丸出生后不同发育阶段的表达 .方法 :应用免疫组织化学SABC法检测 1～ 7周龄小鼠睾丸p38MAPK的表达和定位 .结果 :在 2周龄小鼠睾丸生精小管上皮中即可观察到p38MAPK免疫阳性反应 ,免疫反应阳性细胞为精原细胞 ;3,4和 5周龄小鼠睾丸仅有个别生精小管上皮可见p38MAPK免疫阳性反应 ;6 ,7周龄小鼠睾丸中p38MAPK表达较丰富 ,免疫反应阳性细胞为精原细胞和初级精母细胞 ,免疫阳性反应物均主要位于细胞核内 .在 7周龄小鼠睾丸中还可见到部分间质细胞呈p38MAPK阳性 ,免疫阳性反应物主要位于细胞质内 .结论

P38MAPK抑制剂对小鼠急性水肿型胰腺炎的作用

目的:探讨P38MAPK抑制剂对急性水肿型胰腺炎的疗效及其机制。方法:雨蛙素建立小鼠水肿型胰腺炎模型,分成对照组、造模组和SB203580治疗组,分别测定血清淀粉酶、血清TNF-α和IL-6,并作胰腺病理评分。结果:SB203580组水肿型胰腺炎的病理病变减轻,血清淀粉酶水平下降,但血清TNF-α与IL-6水平无变化。结论:抑制P38MAPK传导途径能减轻水肿型胰腺炎,但与TNF-α、IL-6无明显关系。

Involvement of ERK1/2 and p38 MAPK in up-regulation of 14-3-3 protein induced by hydrogen peroxide preconditioning in PC12 cells

Objective To investigate the protective effects of hydrogen peroxide preconditioning （HPP） on the pheochromocytoma （PC12） cells treated with 1-methyl-4-phenylpyridinium （MPP^＋） and to explore the potential mechanisms. Methods The viability and apoptosis of PC 12 cells were determinded by 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide （MTT） assay and 4′,6′-diamidino-2-phenylindole （DAPI） staining, respectively. The expressions of 14-3-3 protein and phospholylated p38 mitogen-activated protein kinase （MAPK） were determined by Western blot. Enzyme-linked immunosorbent assay （ELISA） was used to measure the activity of extracellular signal-regulated protein kinase 1/2 （ERK1/2）. Results The cell viability decreased and the number of apoptotic cells increased dramatically in MPP^＋ group compared with that in Control group. HPP induced a significant increase in cell viability and a marked decrease in population of apoptotic cells of the MPP^＋- treated PC 12 cells, accompanied with up-regulation of 14-3-3 protein and increase of ERK 1/2 and p38 MAPK activities. The 14-3-3 protein expression was positively correlated with the phosphorylation of ERK1/2. Furthermore, inhibition of the ERK1/2 with PD98059 abolished the 14-3-3 protein up-regulation in PC 12 cells induced by HPP. Conclusion HPP protects PC 12 cells against MPP＋ toxicity by up-regulating 14-3-3 protein expression through the ERK1/2 and p38 MAPK signaling pathways.

Involvement of MAPK/ERK kinase-ERK pathway in exogenous bFGF-induced Egr-1 binding activity enhancement in anoxia-reoxygenation injured astrocytes

Objective Intravenous administration of basic fibroblast growth factor （bFGF） is effective to reduce the volume of cerebral infract due to ischemia. This study was designed to investigate the molecular mechanism, especially the signal transduction pathways, involved in this protective role of bFGF. Methods Anoxia-reoxygenation treated atrocytes were used to study the role of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase （MAPK/ERK kinase, MEK）-ERK signaling pathway after exogenous bFGF administration by Western blot. Electrophoretic mobile shift assay was used to detect the binding activity of early growth response factor-1 （Egr-1）, an important transcription factor for endogenous bFGF. Results bFGF could protect some signal transduction proteins from the oxygen-derived free radicals induced degradation. ERK1/2 was activated and involved in Egr-1 binding activity enhancement induced by exogenous bFGF. Conclusion MEK-ERK MAPK cascade may be an important signal transduction pathway contributed to bFGF induced enhancement of Egr-1 binding activity in anoxia-reoxygenation injured astrocytes.

HBx activates FasL and mediates HepG2 cell apoptosis through MLK3-MKK7-JNKs signal module

AIM： To investigate the possible mechanism by which hepatitis B virus X protein （HBx） mediates apoptosis of HepG2 cells. METHODS： HBx expression vector pcDNA3.1-X was transfected into HepG2 cells to establish an HBx high- expression cellular model as pcDNA3.1-X transfected group. The pcDNA3.1-X and pSilencer3.1-shHBX （HBx antagonist） were cotransfected into HepG2 cells to es- tablish an HBx low-expression model as RNAi group. Untransfected HepG2 cells and HepG2 cells transfected with negative control plasmid were used as controls. Apoptosis rate, the expression of Fas/FasL signaling pathway-related proteins and the phosphorylation lev- els of MLK3, MKK7 and JNKs, which are upstream molecules of death receptor pathways and belong to the family of mitogen-activated protein kinases （MAPKs）,were measured in each group RESULTS： Compared with HepG2 cell group and RNAi group, apoptosis rate, the expression of Fas and FasL proteins, and the activation of MLK3, MKK7 and 3NKs were increased in the pcDNA3.1-X transfected group. The activation of JNKs and expression of FasL protein were inhibited in the pcDNA3.1-X transfected group when treated with a known JNK inhibitor, SP600125. When authors treated pcDNA3.1-X transfected group with K252a, a known MLK3 inhibitor, the activation of MLK3, MKK7 and 3NKs as well as expression of FasL protein was inhibited. Furthermore, cell apoptosis rate was also significantly declined in the presence of K252a in the pcDNA3.1-X transfected group. CONCLUSION： HBx can induce HepG2 cell apoptosis via a novel active MLK3-MKK7-JNKs signaling module to upregulate FasL protein expression.

Epithelial-to-mesenchymal and mesenchymal-to-epithelial transitions in the colon

Epithelial-to-mesenchymal and mesenchymal-to-epi- thelial transitions are well established biological events which have an important role in not just normal tissue and organ development, but in the pathogenesis of diseases. Increasing evidence has established their presence in the human colon during colorectal carcinogenesis and cancer invasion, chronic inflammation-related fibrosis and in the course of mucosal healing. A large body of evidence supports the role for transforming growth factor-13 and its downstream Smad signaling, the phosphatidylinositol 3＇-kinase/Akt/mTOR axis, the Ras-mitogen-activated protein kinase/Snail/Slug and FOXC2 pathway, and Hedgehog signaling and microR- NAs in the development of colorectal cancers via epi- thelial-to-mesenchymal transition. C-met and Frizzled-7, among others, seem to be the principle effectors of mesenchymal-to-epithelial transition, hence have a role not just in mucosal regeneration but in the progression of colonic wall fibrosis. Here we discuss a role for these pathways in the initiation and development of the transition events. A better understanding of their induction and regulation may lead to the identification of pathways and factors that could be potent therapeu- tic targets. The inhibition of epithelial-to-mesenchymal transition using mTOR kinase inhibitors targeting theATP binding pocket and which inhibit both mTORC1 and mTORC2, RNA aptamers or peptide mimetics, such as a Wnt5A-mimetic, may all be useful in both cancer treatment and delaying fibrosis, while the induction of mesenchymal-to-epithelial transition in induced pluripotent stem cells may enhance epithelial healing in the case of severe mucosal damage. The preliminary results of the current studies are promising, but more clinical investigations are needed to develop new and safe therapeutic strategies for diseases of the colon.

Effects of lysophosphatidic acid on human colon cancer cells and its mechanisms of action

AIM： To study the effects of lysophosphatidic acid （LPA） on proliferation, adhesion, migration, and apoptosis in the human colon cancer cell line, SW480, and its mechanisms of action. METHODS： Methyl tetrazolium assay was used to assess cell proliferation. Flow cytometry was employed to detect cell apoptosis. Cell migration was measured by using a Boyden transweU migration chamber. Cell adhesion assay was performed in 96-well plates according to protocol. RESULTS： LPA significantly stimulated SW480 cell proliferation in a dose-dependent and timeependent manner compared with the control group （P 〈 0.05） while the mitogen-activated protein kinase （MAPK） inhibitor, PD98059, significantly blocked the LPA stimulation effect on proliferation. LPA also significantly stimulated adhesion and migration of SW480 cells in a dosedependent manner （P 〈 0.05）. Rho kinase inhibitor, Y-27632, significantly inhibited the upegulatory effect of LPA on adhesion and migration （P 〈 0.05）. LPA significantly protected cells from apoptosis induced by the chemotherapeutic drugs, cisplatin and 5-FU （P 〈 0.05）, but the phosphoinositide 3-kinase （PI3K） inhibitor, LY294002, significantly blocked the protective effect of LPA on apoptosis. CONCLUSION： LPA stimulated proliferation, adhesion,migration of 5W480 cells, and protected from apoptosis. The Ras/Raf-MAPK, G12/13-Rho-RhoA and PI3K- AKT/PKB signal pathways may be involved.

The effect of C-terminal fragment of JNK2 on the stability of p53 and cell proliferation

The basal activity of JNK is low in normal growing cells and inactivated JNK targets p53 for ubiquitination. To elucidate if the C-terminal part of JNK is responsible for its binding to p53, the low background tet-off inducible NIH3T3 cell line was selected by luciferase reporter gene and a double stable C-JNK Aa (203-424) cell line was established. After withdrawing tetracycline, the C-JNK fragment expression was induced and cell growth was dramati- cally inhibited 24 h later. However, the expresion of p53 was found to be increased after the induction of C-JNK fragment, evaluated by transfecting p21waf-luciferase reporter genes. Our further studies showed that C-JNK fragment could form complex with p53 both in vivo and in vitro. Induction of C-JNK fragment in vivo can increase p53 stability by inhibiting p53 ubiquitination.

p28^GANK inhibits endoplasmic reticulum stress-induced cell death via enhancement of the endoplasmic reticulum adaptive capacity

It has been shown that oncoprotein p28GANK, which is consistently overexpressed in human hepatocellular carcinoma （HCC）, plays a critical role in tumorigenesis of HCC. However, the underlying mechanism remains unclear. Here, we demonstrated that p28GANK inhibits apoptosis in HCC cells induced by the endoplasmic reticulum （ER） stress. During ER stress, p28GANK enhances the unfolded protein response, promotes ER recovery from translational repression, and thereby facilitates cell＇s ability to cope with the stress conditions. Furthermore, p28GANK upregulates glucose-regulated protein 78 （GRP78）, a key ER chaperone protein, which subsequently enhances the ER folding capacity and promotes recovery from ER stress. We also demonstrated that p28GANK increases p38 mitogen-activated protein kinase and Akt phosphorylation, and inhibits nuclear factor kappa B （NF-κB） activation under ER stress, which in turn contributes to GRP78 upregulation. Taken together, our results indicate that p28GANK inhibits ER stress-induced apoptosis in HCC cells, at least in part, by enhancing the adaptive response and GRP78 expression. We propose that p28GANK has potential implications for HCC progression under the ER stress conditions.

Signal transduction pathways in liver and the influence of hepatitis C virus infection on their activities

In liver,the most intensively studied transmembrane and intracellular signal transduction pathways are the Janus kinase signal transduction pathway,the mitogen-activated protein kinases signal transduction pathway,the transforming growth factor β signal transduction pathway,the tumor necrosis factor α signal transduction pathway and the recently discovered sphingolipid signal transduction pathway.All of them are activated by many different cytokines and growth factors.They regulate specific cell mechanisms such as hepatocytes proliferation,growth,differentiation,adhesion,apoptosis,and synthesis and degradation of the extracellular matrix.The replication cycle of hepatitis C virus(HCV) is intracellular and requires signal transduction to the nucleus to regulate transcription of its genes.Moreover,HCV itself,by its structural and non-structural proteins,could influence the activity of the second signal messengers.Thus,the inhibition of the transmembrane and intracellular signal transduction pathways could be a new therapeutic target in chronic hepatitis C treatment.

Reactive oxygen species: A double-edged sword in oncogenesis

Reactive oxygen species (ROS) are molecules or ions formed by the incomplete one-electron reduction of oxygen. Ofinterest, it seems that ROS manifest dual roles, cancer promoting or cancer suppressing, in tumorigenesis. ROS participate simultaneously in two signaling pathways that have inverse functions in tumorigenesis, Ras-Raf-MEK1/2-ERK1/2 signaling and the p38 mitogen-activated protein kinases (MAPK) pathway. It is well known that Ras-Raf-MEK1/2-ERK1/2 signaling is related to oncogenesis, while the p38 MAPK pathway contributes to cancer suppression, which involves oncogene-induced senescence, inflammationinduced cellular senescence, replicative senescence, contact inhibition and DNA-damage responses. Thus, ROS may not be an absolute carcinogenic factor or cancer suppressor. The purpose of the present review is to discuss the dual roles of ROS in the pathogenesis of cancer, and the signaling pathway mediating their role in tumorigenesis.

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.

Molecular mechanism and functional consequences of lansoprazole-mediated heme oxygenase-1 induction

AIM： To investigate the molecular mechanism and functional consequences of heme oxygenase-1 （HO-1） activation by lansoprazole in endothelial cells and macrophages. METHODS： Expression of HO-1 mRNA was analyzed by Northern blotting. Western blotting was used to determine the HO-1 and ferritin protein levels. NADPH-dependent reactive oxygen species （ROS） formation was measured with lucigenin-enhanced chemiluminescence. HO-1 promoter activity in mouse fibroblasts, stably transfected with a 15-kb HO-1 gene that drives expression of the reporter gene luciferase, was assessed usingin vivo bioluminescence imaging. RESULTS： Lansoprazole levels in endothelial cells increased HO-1 mRNA and HO-1 protein levels in macrophages. In addition, lansoprazole-induced ferritin protein levels in both cell systems. Moreover, induction of the antioxidant proteins HO-1 and ferritin by lansoprazole was followed by a decrease in NADPH- mediated ROS formation. The radical scavenging properties of lansoprazole were diminished in the presence of the HO inhibitor, chromium mesoporphyrin IX. Induction of HO-1 gene expression by lansoprazole was not related to oxidative stress or to the activation of the mitogen-activated protein kinase pathway. However, the phosphatidylinositol 3-kinase inhibitor LY294002 showed a concentration-dependent inhibition of HO-1 mRNA and promoter activity.CONCLUSION： Activation of HO-1 and ferritin may account for the gastric protection of lansoprazole and is dependent on a pathway blocked by LY294002.

Effect of Yiguanjian decoction on cell differentiation and proliferation in CCl_4-treated mice

AIM： To investigate the cellular mechanisms of action of Yiguanjian （YGJ） decoction in treatment of chronic hepatic injury. METHODS： One group of mice was irradiated, and received enhanced green fluorescent protein （EGFP）- positive bone marrow transplants followed by 13 wk of CCh injection and 6 wk of oral YGJ administration. A second group of Institute for Cancer Research mice was treated with 13 wk of CCI4 injection and 6 wk of oral YGJadministration. Liver function, histological changes in the liver, and Hyp content were analyzed. The expres- sion of m-smooth muscle actin （α-SMA）, F4/80, albumin （AIb）, EGFP, mitogen-activated protein kinase-2 （PKM2）, Ki-67, fetoprotein （AFP）, monocyte chemotaxis pro- tein-1 and CC chemokine receptor 2 were assayed. RESULTS： As hepatic damage progressed, EGFP-po- sitive marrow cells migrated into the liver and were mainly distributed along the fibrous septa. They showed a conspicuous coexpression of EGFP with ^-SMA and F4/80 but no coexpression with AIb. Moreover, the expression of PKM2, AFP and Ki-67 was enhanced dy- namically and steadily over the course of liver injury. YGJ abrogated the increases in the number of bone marrow-derived fibrogenic cells in the liver, inhibited expression of both progenitor and mature hepatocyte markers, and reduced fibrogenesis. CONCLUSION： YGJ decoction improves liver fibrosis by inhibiting the migration of bone marrow cells into the liver as well as inhibiting their differentiation and suppressing the proliferation of both progenitors and hepatocytes in the injured liver.

Lentiviral vector-mediated down-regulation of IL-17A receptor in hepatic stellate cells results in decreased secretion of IL-6

AIM: To investigate the mechanism of interleukin (IL)-6 secretion through blocking the IL-17A/IL-17A recepto (IL-17RA) signaling pathway with a short hairpin RNA (shRNA) in hepatic stellate cells (HSCs) in vitro . METHODS: HSCs were derived from the livers of adul male Sprague-Dawley rats. IL-6 expression was evalu ated using real-time quantitative polymerase chain reaction and enzyme linked immunosorbent assay. The phosphorylation activity of p38 mitogen activated pro tein kinases (MAPK) and extracellular regulated pro tein kinases (ERK) 1/2 upon induction by IL-17A and suppression by IL-17RA shRNA were examined using Western blotting.RESULTS: IL-6 expression induced by IL-17A was significantly increased compared to control in HSCs (P < 0.01 in a dose-dependent manner). Suppression of IL17RA using lentiviral-mediated shRNA inhibited IL-6 expression induced by IL-17A compared to group with only IL-17A treatment (1.44 ± 0.17 vs 4.07 ± 0.43, P < 0.01). IL-17A induced rapid phosphorylation of p38 MAPK and ERK1/2 after 5 min exposure, and showed the strongest levels of phosphorylation of p38 MAPK and ERK1/2 at 15 min in IL-17A-treated HSCs. IL-6 mRNA expression induced by IL-17A (100 ng/mL) for 3 h exposure was inhibited by preincubation with specific inhibitors of p38 MAPK (SB-203580) and ERK1/2 (PD-98059) compared to groups without inhibitors preincubation (1.67 ± 0.24, 2.01 ± 0.10 vs 4.08 ± 0.59, P < 0.01). Moreover, lentiviral-mediated IL-17RA shRNA 1 inhibited IL-17A-induced IL-6 mRNA expression compared to random shRNA in HSCs (1.44 ± 0.17 vs 3.98 ± 0.68, P < 0.01). Lentiviral-mediated IL17RA shRNA 1 inhibited phosphorylation of p38 MAPK and ERK1/2 induced by 15 min IL-17A (100 ng/mL) exposure. CONCLUSION: Down-regulation of the IL-17RA receptor by shRNA decreased IL-6 expression induced by IL-17A via p38 MAPK and ERK1/2 phosphorylation in HSCs. Suppression of IL-17RA expression may be a strategy to reduce the inflammatory response induced by IL-17A in the liver.

Down-regulation of HIV-1 Infection by Inhibition of the MAPK Signaling Pathway

The human immunodeficiency virus type 1 （HIV-1） can interact with and exploit the host cellular machinery to replicate and propagate itself. Numerous studies have shown that the Mitogen-activated protein kinase （MAPK） signal pathway can positively regulate the replication of HIV-1, but exactly how each MAPK pathway affects HIV-1 infection and replication is not understood. In this study, we used the Extracellular signal-regulated kinase （ERK） pathway inhibitor, PD98059, the Jun N-terminal kinase （JNK） pathway inhibitor, SP600125, and the p38 pathway inhibitor, SB203580, to investigate the roles of these pathways in HIV-1 replication. We found that application of PD98059 results in a strong VSV-G pseudotyped HIV-1NL4-3 luciferase reporter virus and HIV-1NL4-3 virus inhibition activity. In addition, SB203580 and SP600125 also elicited marked VSV-G pseudotyped HIV-INL4-3 luciferase reporter virus inhibition activity but no HIV-1NL4-3 virus inhibition activity. We also found that SB203580 and SP600125 can enhance the HIV-1 inhibition activity of PD98059 when cells were treated with all three MAPK pathway inhibitors in combination. Finally, we show that HIV-1 virus inhibition activity of the MAPK pathway inhibitors was the result of the negative regulation of HIV-1 LTR promoter activity.

FGF-receptor substrate 2 functions as a molecular sensor ntegrating external regulatory signals into the FGF pathway

Fibroblast growth factor （FGF） receptor substrate 2a （FRS2α） is the main mediator of signaling in the FGF pathway. Recent studies have shown that mitogen-activated protein kinase （MAPK） phosphorylates serine and threonine residues in FRS2, negatively affecting FGF-induced tyrosine phosphorylation （PY） of FRS2. Several kinds of stimuli can induce serine/threonine phosphorylation （PS/T） of FRS2, indicating that FRS2 may be useful for studying crosstalk between growth factor signaling pathways. Here, we report that FGF-induced PY of FRS2 can be attenuated by EGF co-stimulation in PC12cells; this inhibitory effect could be completely reversed by U0126, an inhibitor of MEK. We further identified the ERK1/2-binding motif in FRS2 and generated FRS2-3KL, a mutant lacking MAPK binding and PT upon FGF and/or EGF stimulation. Unlike wild-type （WT） FRS2, FGF-induced PY of FRS2-3KL could not be inhibited by EGF co-stimulation, and FRS2-3KL-expressing PC12 cells exhibited more differentiating potential than FRS2-WT-expressing cells in response to FGF treatment. These results suggest that PS/T of FRS2 mediated by the FRS2-MAPK negative regulatory loop may function as a molecular switch integrating negative regulatory signals from other pathways into FGFR-generated signal transduction.

Insights into erlotinib action in pancreatic cancer cells using a combined experimental and mathematical approach

AIM:To gain insights into the molecular action of erlotinib in pancreatic cancer (PC) cells. METHODS:Two PC cell lines, BxPC-3 and Capan-1, were treated with various concentrations of erlotinib, the specific mitogen-activated protein kinase kinase (MEK) inhibitor U0126, and protein kinase B (AKT) inhibitor XIV. DNA synthesis was measured by 5-bromo-2'-deoxyuridine (BrdU) assays. Expression and phosphorylation of the epidermal growth factor receptor (EGFR) and downstream signaling molecules were quantified by Western blot analysis. The data were processed to calibrate a mathematical model, based on ordinary differential equations, describing the EGFRmediated signal transduction. RESULTS:Erlotinib significantly inhibited BrdU incorporation in BxPC-3 cells at a concentration of 1 mol/L, whereas Capan-1 cells were much more resistant. In both cell lines, MEK inhibitor U0126 and erlotinib attenuated DNA synthesis in a cumulative manner, whereas the AKT pathway-specific inhibitor did not enhance the effects of erlotinib. While basal phosphorylation of EGFR and extracellular signal-regulated kinase (ERK) did not differ much between the two cell lines, BxPC-3 cells displayed a more than five-times higher basal phospho-AKT level than Capan-1 cells. Epidermal growth factor (EGF) at 10 ng/mL induced the phosphorylation of EGFR, AKT and ERK in both cell lines with similar kinetics. In BxPC-3 cells, higher levels of phospho-AKT and phospho-ERK (normalized to the total protein levels) were observed. Independent of the cell line, erlotinib efficiently inhibited phosphorylation of EGFR, AKT and ERK. The mathematical model successfully simulated the experimental findings and provided predictions regarding phosphoprotein levels that could be verified experimentally. CONCLUSION:Our data suggest basal AKT phosphorylation and the degree of EGF-induced activation of AKT and ERK as molecular determinants of erlotinib efficiency in PC cells.